Saloman 1991 - Resonance Ionization Techniques

S ectrochimica Am. Vol. 46B. No. 3. pp.319-37% 1991 Pfinted in Great Britain.

TOPICS IN LASER SPECTROSCOPY

n%44547/91 g3.00 + .Ml Pergamon Press pk.

A Resonance Ionization Spectroscopy/Resonance Ionization Mass Spectrometry data service. II-Data sheets for Al, Ca, Cs, Cr, Co, Cu,

Kr, Mg, Hg and Ni

E. B. SALOMAN

Electron and Optical Physics Division, National Institute of Standards and T,echnology, Gaithersburg, MD 20899, U.S.A.

(Received 21 September 1990; accepted 27 October 1990)

Abstract-A data service has been established at the National Institute of Standards and Technology to provide the necessary information to apply the techniques of Resonance Ionization Spectroscopy (RIS) and Resonance Ionization Mass Spectrometry (RIMS) to routine use in analytical chemistry. This service collects and calculates the relevant atomic data, chooses appropriate resonance ionization schemes, and indicates pertinent operating details of successful RIMS studies. The first group of data sheets was published previously covering the elements As, B, Cd, C, Ge, Au, Fe, Pb, Si and Zn. The second group of data sheets is presented here. It covers the elements Al, Ca, Cs, Cr, Co, Cu. Kr, Mg, Hg and Ni. Othen will be published periodically. Reprints of RIYRIMS work are solicited so that those efforts may be included in future data sheets.

1. IN-rRoouCno~

THE TECHNIQUES of Resonance Ionization Spectroscopy (RIS) and Resonance Ionization Spectroscopy followed by Mass Spectrometry (RIMS) have been demonstrated in several state-of-the-art laser laboratories to be analytical techniques of extremely high sensitivity and selectivity which are applicable, in principle, to nearly all atoms [l]. They are applicable to important problems in nondestructive testing, monitoring environmental pollutants, performing trace impurity analysis, measuring radioactive contamination and many other areas.

To meet their potential, these techniques have to be made available to analytical chemists and other scientists who do not have the most comprehensive knowledge of atomic structure and laser physics. The task is made more difficult for these scientists because much of the information needed to apply RIS/RIMS exists in scattered data bases. Many key data are not currently available at all (especially excited state photo- ionization cross sections). The chemists require the RIS schemes and atomic data which will allow the techniques to be applied without sophisticated calculations and a major literature search in advance for each element to be measured. It is the objective of this data service to organize the available information, supplement it with calculations (where gaps exist), and provide formatted data and application sheets to permit the routine use of RIYRIMS in elemental analysis.

The first group of data sheets [2] was published previously covering the elements As, B, Cd, C, Ge, Au, Fe, Pb, Si and Zn. The second group of data sheets is included here. It covers the elements Al, Ca, Cs, Cr, Co, Cu, Kr, Mg, Hg and Ni. Others will be published periodically. These sheets list the element, its stable isotopes, isotope shifts and hyperfine structure, RIS schemes, atomic energy levels, lifetimes, oscillator strengths, laser-excitation schemes, atom sources, estimates of laser power requirements and references. Also included are the results of calculations of excited state photo-ionization cross sections by Hartree-Fock techniques involving several atomic configurations. Reprints, preprints and other forms of information about successful RIWRIMS work are solicited for inclusion in future new data sheets and in updates of the sheets presented here.

319

320 E. B. SALOMAN

2. EXPLANATION OF DATA SHEETS

The data sheets begin with the name, symbol and atomic number, 2, of the element. Then the ground state atomic configuration is specified, followed by the energy of the first ionization potential with respect to the ground state. A conversion factor [3] of 1 eV = 8~5.5410(24) cm”’ is used. Next comes an introducto~ paragraph which includes RIS schemes that have been experimentally observed and additional schemes when needed for this element. Schemes which involve either one- or two-photon excitations may be cited. Two-photon excitation schemes need relatively high laser powers for saturation and often require a mass-selective detection system to avoid interferences from unwanted non-resonant or near-resonant ionization of concomitant species in the sample. A number of two-photon excitation schemes are included where the most obvious one-photon resonance transition wavelength is very difficult to generate with present day commercial technology or where a single-color scheme may be employed instead of a two- or three-color scheme for convenience and/or economy. Two-photon schemes are valuable when high-resolution Doppler-free techniques are required for additional isotopic selectivity 141.

Information about the sensitivity of demonstrated schemes is provided when that information is available. Other pertinent information and possible applications are included.

A Grotrian diagram is included, illustrating the energy levels and transitions used in the RIS schemes. Standard atomic notation is used. In some cases so many levels are utilized in RIS schemes that groups of levels must be shown thematically. In these cases their energy is indicated as a range rather than providing the individual energies of each level.

Next we include information specific to each type of RIS scheme covered by the data sheet. The laser wavelengths in air are listed for the transitions in the RIS scheme (except for wavelengths less than 200 nm for which vacuum wavelengths are given), as well as the energies and abbreviated spectroscopic notation for the states involved. “Low. Level” stands for the lower level of a transition, B, is its energy, “Res. Level” stands for the upper or resonance level of a transition, E, is its energy, h is the air wavelength (or vacuum wavelength if A < 200 nm) of the transition, and fabs is its absorption oscillator strength. Then we provide some parameters important to the energetics of the RIS process. Where possible, existing atomic data are used. However, in many cases these parameters must be calculated. These calculations are made using the Hartree-Fock codes of COWAN [5] with approximate relativistic corrections. In most cases the calculations involve several configurations for each state. Lifetimes, T, of the excited states involved in the schemes are given. Also provided, when a single photon transition is involved, is an estimate of the power required to saturate the first step of the RIS process. This estimate is for an idealized situation where all power is delivered within the spectral range of the absorption line for free, thermal atoms. It is obtained using the formalism of LETOKHOV et al. [6] where the cross section of the absorption is given by:

X2 A,i D=2nQw (1)

where h is the wavelength of the transition, A,; is the Einstein transition coefficient between the initial state and the resonant state (calculated with the Hartree-Fock code if necessary), and Ao is the transition linewidth. For purposes of this estimate, in the case of solid samples, this linewidth is taken to be the Doppler width for a free atom at the boiling point. The saturation power is given by:

hc p=-..- 2hUT ’ (2)

where h is Planck’s constant, c is the speed of light, and T is the excited level’s relaxation time (which is taken to be the excited state lifetime for this estimate). This

RIhURIS Data Service 321

estimate must be adjusted by the user to fit the actual experimental parameters used. For discrete transitions other than the first step, the cross section is estimated with Eqn 1 while for photo-ionization, in most cases, the cross section is calculated with Cowan’s code. Then an estimate of the laser energy needed to saturate the transition or the photo-ionization is obtained by using the condition Nu B 1, where N is the number of photons in the laser pulse per unit area within the absorption bandwidth delivered within the lifetime of the excited state which absorbs the photon. This leads to a saturation energy (in mJ/cm2):

Esat = 1 / (5.03 x lo+ OX)

if u is in units of lo-l8 cm2 and h is in nm. Actual bandwidth (for discrete transitions) and laser pulse length must be considered as well as geometric factors to obtain a value of the needed laser energy for a specific experimental arrangement. Also to be noted is that in the calculation of the photo-ionization cross sections, no account is taken of continuum resonances which may be present unless specifically stated. If present, these resonances can greatly increase the photo-ionization cross section, thereby reducing the required laser energy. We estimate an uncertainty of a factor of two or three in the calculation of the photo-ionization cross sections even in the absence of resonances.

We follow this with some data on the isotopes of the element. For the stable isotopes we list the isotope, the natural abundance (in parentheses), and the nuclear spin, I. For some radioactive isotopes of interest we list the isotope, its nuclear spin, and its lifetime, T. Where known for the transitions used in the RIS schemes, we provide the isotope shift and the hyperfine structure (hfs) interaction constants A (dipole interaction constant) and B (quadrupole interaction constant). The hfs shift, E, may be calculated from the center of gravity of the level of the isotope by [7]

where

E=ACi2+ BDl4

c = F(F+ 1) - 1(2+ 1) - J(J+ 1)

and

D _ (3/2)C(C+ 1) - 21(Z+ l)J(J+ 1)

1(21- lM2.!- 1)

where F is the total angular momentum, both electronic and nuclear, I is the nuclear spin, and J is the total electronic angular momentum. There is no hfs for an isotope if I=O. The quadrupole term is non zero only if Z=l. No state will show hfs splitting if J=O and the quadrupole term of the hfs will not be observable unless J>l.

The laser scheme section suggests possible means of generating the laser wavelengths required by the RIS schemes. In most cases where an experimental scheme is known, the laser used is cited. For proposed schemes, Nd:YAG is often proposed as the pump laser because of the availability of its harmonics for photo-ionization from excited states. Pumping with other lasers or flashlamps may often be equivalent to the given source (but note that the pump affects the wavelength range over which a given dye will operate). High repetition rate pump sources or cw lasers can improve sample utilization efficiency when used with continuous atomization sources. The atom source section suggests how a sample may be atomized for measurement. RIS and atomic data references are given.

Acknowledgements-I wish to thank G. S. HURST, J. E. PARKS, J. C. TWVIS and T. B. LUCATORTO for their assistance in the design of the data sheets. The NIST Atomic Energy Level and Atomic Transition Probability Data Centers and especially A. MUSGROVE and J. FUHR provided much assistance to this work. This project is supported in part by the U. S. Department of Energy Office of Health and Environmental Research under contract DE-AI0586ER-60447.

322 E. B. SA~MAN

REFERENCES

[l] See for example G. S. Hurst and M. G. Payne, Specfrochim. Acta 43B, 715 (1988) and the references contained therein.

[2] E. B. Saloman, Spectrochim. Acta 45B, 37 (1990). [3J E. R. Cohen and B. N. Taylar, Rev. Mod. P!zys. 59, 1121 (1987). [4] C. W. Clark, J. D. Fassett, T. B. Lucatorto and L. J. Moore, Enhan~ment of the isotopic abundance

sensitivity of mass spectrometry by Doppler-free resonance ionization, in Resoaence fonizution Spectroscopy 1984, Eds, G. S. Hurst and M. G. Payne, p. 107. Institute of Physics, Bristol (1984).

[S] t9gj Cowan, The Theory of Atomic Strucfure and Spectra. University of California Press, Berkeley

[6] V. S. Letokhov, V. I. Mishin and A. A. Puretzky, Prog. Quantum Electron. 5, 139 (1977). [7] G. H. Fuher, f. Phys. Chem. Re& Dara 5, 835 (1976).

RIM/RN Data Service 323

Data sheet for RIWRIMS schemes Aluminum

Al Z = 13

Ground state [l] ls22s22p63s23p 2P1,2o

First ionization potential [2] 48278.480 cm-’ = 5.985771 eV

A number of groups have applied RIS to the analysis of aluminum. Several types of RIS schemes have been used. BEKOV et al. [A-C] excited the Al atoms from the *P ;,* level of the ground state configuration to the 4s 2S1n resonant level. They then excited the atoms from this level to one of the 15p *P ’ Rydberg states. The Rydberg states were then ionized with 100% efficiency by electric field pulse ionization (a so- called o, + 05 process). Using this scheme they demonstrated detection limits of 2 ppt (trillion) for an aqueous solution of AlC&, 20 ppt for Al in a germanium crystal, 2 ppb for Al in sea water, and 6 ppb for Al in human blood. A simpler variant of this scheme, which uses only one laser, was demonstrated by NOGAR et al. [D]. They studied mixtures of Al and Fe. For Al the atoms were excited from their ground state to the 4s 2S1,2 resonant level and then photo-ionized from this level by a second photon from the same laser (a so-called wi + wi process). This scheme is less efficient and less selective than the previous one. A more efficient one-color two-photon scheme was demonstrated by BETEROV et al. [El. They excited Al atoms from the ground state to the 3d 2D3,2 resonant level and then photo-ionized from this level by a second photon from the same laser. A more efficient variant of this scheme was employed by KIMOCK et al. [F, G] for the analysis of solid samples. They excited the atom from its ground state configuration to the 3d *D 3,2,5/2 levels using doubled dye laser radiation. They then photo-ionized the atom from these levels using non-doubled radiation from the same dye laser (a so-called w1 + w2 process). Calculations indicate that photo- ionization at this frequency requires far less power than at the doubled frequency. A highly selective scheme was proposed by KUDRIAVTSEV and LETOKHOV [HI. In this scheme the Al atoms are excited from the ground state to the 4s 2S1,2 resonant level by the first photon. The second photon excites the atoms from this resonant level to the 5p 2P1,2o level from which it is excited by a third photon to the 3s3p2 2P1,2,3,2 auto- ionizing levels (a so-called w1 + w2 + w *J process). A variant of this would be a scheme where the final step (excitation to the auto-ionizing levels) is replaced by photo-ionization using IR radiation from a Nd:YAG laser (a so-called w1 + w2 + w3 process). PARKS et al. [I, J] used sputter initiated RIS (SIRIS) to measure the amount of Al in steel, demonstrating linearity from 7 ppm to 10“ ppm. They also studied layered GaAslAlGaAdGaAs and demonstrated 150 A depth resolution. They did not specify which RIS schemes were used. Analysis of trace quantities of aluminum is important in determining the purity of semiconductor materials, in determining the amount of Al in ocean waters as an indicator of terrigenous run-off and in relation to certain biological processes [K], its presence in blood [L], and in characterizing Al containing layered materials [J]. A Grotrian diagram of the RIS schemes in aluminum is shown in Fig. 1 [l, 21.

RIS schemes of type (w,+ wI) or (w, + w2) One- or two-color two-photon process consisting of a resonance step followed by

photo-ionization. A, = 308-310 nm [E-G] or 394397 nm [D], and A,=616419 nm [F,

Gl.

Lifetimes and photo-ionization cross section from excited states The table below gives the laser wavelength, hi, to the resonant level, the wavelength

of the second laser beam, h2, for the wi + w2 schemes, the lifetime, 7, of the resonant

324 E. B. SALOMAN

3925p

3s23d

Fig. 1. Grotrian diagram of resonance ionization spectroscopy schemes in aluminum.

Data for RIS schemes of type (w,+o,) or (w1+02) [l-3]

396.1525 3P 2P,,,” 112.561 4s 2%,2 25347.756 5.115

level [4, 51, an estimate of the laser power, P,,,, required to saturate the resonant transition, the photo-ionization cross section of the resonant level, o, for an o1 + o1 scheme in the case of the 4s *S1,* resonant level and for both o1 + o1 and w1 + wz schemes for the *D levels, calculated by means of a Hartree-Fock code [6], and an estimate of the energy, ES,,, delivered during the lifetime of the resonant state required to saturate the photo-ionization.

* Reference [E] measured a cross section of 5.6 2 1.1 x 1O-1x cm2 which corresponds to an E,,, of 120 mJ/cm2.

RIIWRIS Data Service 325

RZS schemes of type ( wI + 4) : [A-C] Two-color two-photon process consisting of a resonance step followed by excitation

to a high-lying Rydberg state. The Rydberg state is ionized with 100% efficiency by a suitably timed electric field pulse. AI between 394 and 397 nm. hr$ = 447.3 nm.

Data for RIS schemes of type (o,+&) [l-3, 6, 71

Lifetimes and photo-ionization cross section from excited levels [4, 6, 81 T(4S *&,*) = 6.85 ns; 7(15p *&&)=4600 ns. The power in AI required to saturate the excitation to the 4s *S1,* level is estimated

to be 100 W/cm* for 394.4 nm and 51 W/cm* for 396.2 nm radiation. An estimate of’ the energy in A2 needed to saturate the excitation to the 15p *F’ levels within the absorption bandwidth delivered while the first step is being pumped is 6.1 mJ/cm*. The Rydberg levels are ionized by an electric field pulse. The combination of the excitation with A2 and the electric field pulse corresponds to an ionization cross section of 73 X lo-l8 cm*.

RIS schemes of type (q + w2+ 03) and (q + wz+ o”.:,, Three-color process consisting of two resonance steps followed by either photo-

ionization by an IR photon or excitation to an auto-ionizing state. A,=394-397 nm, A2=669-670nm, A,=iO64 nm, AA$=607-612 nm [HI.

Data for RI.5 scheme of type (o,+o,+o,) or (co,+wz+w~!) [l-3, 61

E. B. SALOMAN 326

396.1520 669.6023 607.8413

396.1520 669.6023 61'1.1130

396.1520 669.8673 607.6231

396.1520 669.8673 610.8924

0.115 0.0227 1.4E-4

0.115 0.0227 3.OE-5

0.115 0.0114 7.23-5

0.115 0.0114 1.2E-4

Lifetimes and photo-ionization cross sections and auto-ionization rates from excited states [4-6, 91 ~(4s *S&=6.85 ns, ~(5p *Pln,~,2’)=275 ns, T&J* *P&=2.4 X lo-‘i S, 7(3p2

*P&=9.4 x lo-” s. The power in A, required to saturate the excitation to the 4s 2S1,2 level is estimated

to be 100 W/cm* for 394.4 nm and 51 W/cm* for 396.2 nm radiation. An estimate of the energy in A2 needed to saturate the second step from this level to the 5p 2P,,2,3,20 levels, within the absorption bandwidth delivered while the first step is being pumped is 5.0 X 10m3 mJ/cm2. The photo-ionization cross section of the 5p *P1,2,3,2’ levels by 1064 nm radiation is calculated to be 30 X lo-l8 cm*. This corresponds to a laser energy requirement of 6.2 mJ/cm* for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state. An estimate of the laser energy, E,,,, needed in A3 to saturate the excitation from the 5p *P” levels to the 3p2 *P1,2,3/2 auto-ionizing levels within the absorption bandwidth while the first and second steps are pumped is given in the following table.

610.8924 0.62 II

Measurements indicate an auto-ionization rate for the 3p2 *P3/2 level of 4.0 x 10’” s-l and for the 3p2 2P 1l2 level of 0.87 x 10” s-i. They also show that auto-ionization dominates radiative decay for these levels. The auto-ionization rate should not limit the RIS process.

Isotope data [lo, 111 Stable isotope: *‘Al (100%) 1=5/2.

Isotope shiftslhfs [2, 7, 81 Aluminium has only one stable isotope and no long-lived unstable isotopes. There

is no isotope shift data to report. The hfs interaction constants for the indicated levels of *‘Al are given in the following

table.

Laser schemes For 308.2 nm, tunable XeCl laser [El; for 30&310 nm, Nd:YAG pumped frequency

doubled Rhodamine 640 dye laser; for 394-397 nm, Nd:YAG pumped LDS 390 dye laser; for 447.3 nm, XeCl or Nd:YAG pumped Coumarin 440 dye laser; for 607419 nm,

RIM/RIS Data Service 327

hfs Interaction constants (IO-” cm-‘)

Nd:YAG pumped Rhodamine 640 dye laser; for 669-670 nm, Nd:YAG pumpe dye laser; for 1064 nm, Nd:YAG direct IR.

DCM

Atom reservoirs and sources Several methods have been used to produce atomic aluminum atoms for RIS studies.

These include thermal vaporization of solid samples [A, E], evaporation of liquid samples followed by thermal vaporization of the dry residuum [B, C], sputtering solid samples with an argon ion beam [F, G, I, J], and laser ablation of solid samples [D,

Ml-

RIS References

[A] R. Akilov, G. I. Bekov, V. S. Letokhov, G. A. Maksimov, V. I. Mishin, V. N. Radaev and V. N. Shishov, Sov. J. Quanfum Electron. 12, 1201 (1982).

[B] G. I. Bekov and V. S. Letokhov, Trends Anal. Chem. 2, 252 (1983). [C] G. I. Bekov and V. S. Letokhov, Appl. Phys. B 30, 161 (1983). [D] N. S. Nogar, R. C. Estler, M. W. Rowe, B. L. Fearey and C. M. Miller, Laser desorption/ablation

studies by resonance ionization mass spectroscopy, in Resonance Ionization Spectroscopy 1988, Eds, T. B. Lucatorto and J. E. Parks, p.147. Institute of Physics, Bristol (1989).

[E] I. M. Beterov, V. N. Ishchenko, S. A. Kochubei and V. L. Kurochkin, Opt. Commun. 54, 100 (1985). [F] F. M. Kimock, J. P. Baxter, D. L. Pappas, P. H. Kobrin and N. Winograd, Examination of excited

state populations in sputtering using multiphoton resonance ionization, in Analytical Spectroscopy, Ed. W. S. Lyon, p.179. Elsevier, Amsterdam (1984).

[G] F. M. Kimock, J. P. Baxter, D. L. Pappas, P. H. Kobrin and N. Winograd, Anal. Chem. 56, 2782 (1984).

[H] Yu. A. Kudriavtsev and V. S. Letokhov, Appl. Phys. B 29, 219 (1982). [I] J. E. Parks, H. W. Schmitt, G. S. Hurst and W. M. Fairbank, Jr., Sputter initiated RIS (SIRIS) for

analysis of semiconductor impurities, in Resonance Ionization Spectroscopy 1984, Eds, G. S. Hurst and M. G. Payne, p.167. Institute of Physics, Bristol (1984).

[J] J. E. Parks, M. T. Spaar and P. J. Cressman, J. Cryst. Growth 89, 4 (1988). [K] G. I. Bekov, A. S. Yegorov, V. S. Letokhov and V. N. Radayev, Nature (Lond.) 301. 410 (1983). [L] G. I. Bekov, V. S. Letokhov and V. N. Radayev, Laser Chem. 5, 11 (1984). [M] D. W. Beekman and N. Thonnard, Laser ablation as an atomization source for ultratrace element

analysis using resonance ionization time-of-flight mass spectrometry, in Resonance Ionization Spectroscopy 1988, Eds, T. 8. Lucatorto and J. E. Parks, p.163. Institute of Physics, Bristol (1989).

Data references

[l] W. C. Martin and R. Zalubas, J. Phys. Chem. Ref. Data 8, 817 (1979). [2] E. S. Chang, J. Phys. Chem. Refi Data 19, 119 (1990). [3] W. L. Wiese and G. A. Martin, Atomic transition probabilities, in CRC Handbook of Chemistry and

Physics 70th Edn, Eds R. C. Weast and D. R. Lide, p.E-338. CRC Press, Boca Raton, Florida (1989).

328 E. B. SALOMAN

[4] E. P. Buurman, A. Dbnszelmann, J. E. Hansen and C. Snoek, Astron. Astrophys. 164, 224 (1986). [5] J. Z. Klose, Phys. Rev. A 19, 678 (1979). [6] Calculated using the HartreeFock code with relativistic corrections of R. D. Cowan, The Theory of

Atomic Structure nnd Spectra. University of California Press, Berkeley (1981). [7) Extrapolated from the data in Refs [1,2]. [8] Extrapolated from the data in G. JBnsson, S. KrW, H. Lundberg and S. Svanberg, Z. Phys. A 316,

259 (1984). [9] G. G. Lombardi, B. L. Cardon and R. L. Kurucz, Astrophys. J. 248, 1202 (1981).

[lo] N. E. Holden, R. L. Martin and I. L. Barnes, Pure Appl. Chem. 55, 1119 (1983). [l l] G. H. Fuller, J. Phys. Gem. Ref. Data 5, 835 (1976).


Data sheet for RWRIMS schemes Calcium

Ca z = 20

Ground state [l] ls22s22p63s23p6 4s2 ‘S,

First ionization potential [l] 49305.95 cm-’ = 6.113161 eV

A number of groups have applied RIS to the analysis of calcium. Two schemes using step-wise excitations involving only single-photon transitions will be discussed. In addition three schemes involving two-photon transitions will also be covered since they can be used with Doppler-free techniques to enhance the isotopic selectivity of the analysis. LETOKHOV [A] has proposed a scheme in which a photon from the first laser excites the atom from its ground state to the 4s4p lPlo level followed by a photon from a second laser which further excites the atom from this level to the 4p2 ‘Dz level. Photo-ionization can then take place by means of another photon from either of the first two lasers or by an IR photon from a Nd:YAG laser (so called 01-to2+01, w,+02+w2, or 01+02+w3 processes). Another scheme is to excite the atom from the ground state to the 4s4p 3P,o level with the first laser, then to the 4~5s 3S1 level with the second laser. Next, as done by BRINKMANN et al. [B], a third laser is used to excite the atom to the 3&p jP10 auto-ionizing level (a so called 01+02+~3 process). The absorption wings of this level can be reached by the 488 nm line of the cw argon ion laser. The use of cw lasers for all three steps can greatly increase sample utilization efficiency and their narrow lines are well suited for isotopically selective schemes. Isotopic selectivity can be enhanced by combining isotope-sensitive RIS excitation with mass spectrometric detection. BEIGANG and TIMMERMANN [C] demonstrated isotopic selectivity in the Dopper-free two-photon excitation from the ground state to the 4~10s ‘So level. This excitation is strongly enhanced by having the 4s4p iPro level located almost exactly midway between these levels. The 4~10s ‘S,, level may be photo-ionized by a third photon from the exciting laser (a so called 2w,+wi process) or by an IR photon from a Nd:YAG laser (a so called 20,+02 process). Unfortunately both of these are relatively inefficient due to a small photo-ionization cross section. However, calculations show that one can somewhat more efficiently excite the 4~6s ‘Pi’ auto- ionizing level either at its center or near its center using the second harmonic of a Nd:YAG laser (a so called 201+wA: p recess). Other 201+01 processes have been demonstrated by APEL et al.[D] (involving the 4s4d ‘II2 level) and by BLAZEWICZ et al. [E] (involving the 4~5s ‘S,, level). BLAZEWICZ et al. report a detection limit of 7 ppb. Other studies of calcium excited levels have been made using thermionic diode detectors [F] and ionization in buffer gas [G] where sensitivities of 160 fg were reported. Detection of trace quantities of calcium is important in many areas. Of special interest is the monitoring of calcium loss due to old age or to low gravity conditions by means of enriched isotope mixtures. A Grotrian diagram of the RIS schemes in calcium is shown in Fig. 2 [l].

RIS schemes of type (w, +wz+ CO,), (0, +oz+oz), or (w,+wz+ 03) involving the 4s4p ‘Pi ’ level

Two- or three-color process consisting of two resonance steps followed by photo- ionization with a photon of the same wavelength as one of the first two photons or by an infrared photon. hi=422.7 nm, AZ=5857 nm, A,=1064 nm [A].

Lifetimes and photo-ionization cross section from excited state ~(4s4p ‘P,“)=4.49 ns [2]; 7(4p2 *D2)=14.6 ns [3]. The power in hi required to saturate the excitation to the 4s4p ‘P,’ is 17 W/cm2.

An estimate of the energy required in X2 to saturate the second step from this level

330 E. B. SALOMAN

1 OP 3d5p P,

L

4s4d ‘D,

4858 ‘so

536.1 nm

421.: nm

k

421.5 nm

\ 600.1 P nm

4se ‘SO

23652 cm-’ I 4s4p 3Pp

-I,

15210 cm-’

422.7 nm

657.3 nm

- 0 cm-’

Fig. 2. Grotrian diagram of resonance ionization spectroscopy schemes in calcium.

Data for RIS schemes of type (o,+w~+w,) or (o,+o,+w,) or (w,+o~+oJ involving the 4s4p ‘PI’ level:

[I, 2, 31

x (nm) Low. Level E, (cm-‘) Res. Level E, (cm-‘) f&S

Xl 422.6728 492 ‘s 0 0.000 4s4p lP,O 23652.304 1.79

585.7451 4s4p 1P,” 23652.304 4p2 ‘D , 40719.847 0.58

to the 4p2 lD2 level, within the absorption bandwidth delivered while the first step is being pumped, is 1.4 x 10e4 mJ/cm*. For the photo-ionization cross section of the 4p2 ‘II2 level to the continuum by radiation of the indicated wavelengths a calculation by means of a Hartree-Fock code [4] gives estimates (units lo-l8 cm*) of: 1064 nm: 1.1; 585.7 nm: 0.93; 422.7 nm: 25. This corresponds to a laser energy requirement for photo-ionization by radiation of these wavelengths of 170, 370 and 19 mJ/cm*, respectively, for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state.

RIS schemes of type (w,+c++&$) involving the 4s4p 3P10 level Three-color process consisting of two resonance steps followed by excitation to an

auto-ionizing level. X,=657.3 nm. h2=612.2 nm. h,=490.8 nm or 488.0 nm.

Data for RIS schemes of type (w,+w,+o”\) involving the 4s4p ‘PI0 level [I, 5, 6, 71

Low. Level El (cm-l) Bes. Level E, (cm-‘) f,

Xl 657.2779 482 1s SPO,’

0.00 4s4p spl* 15210,063 4.83-5 x2 612.2217 4s4p 15210.063 4s5s 31539.495 0.157

490.82 4858 ss. ss,

31539.495 3d5a sP.v 51908 _ 0.026

Lifetimes and auto-ionization rates $4~4~ “P,“)=4.1E-4 s [6]; ~(4s5s 3S1)=11.6 ns [3]. The power in A, required to saturate the excitation to the 4s4p 3PIo is 3.0 W/cm*

provided that the very large radiative lifetime can be a realistic estimate of the lifetime

RIM&IS Data Service 331

of the state (that is, the lifetime is not affected by collisions). If the lifetime is shortened by collisions, the power required is increased by the factor the lifetime is shortened from its radiative lifetime value. An estimate of the energy required in h2 to saturate the second step from this level to the 4~5s jS1 level, within the absorption bandwidth delivered while the first step is being pumped, is 2.9 X 10e4 mJ/cm2. The calculated auto-ionization rate [5] for the 3d5p 3P10 level is 4.7 X loll s-l. As a result the auto-ionization rate is not expected to be a limiting factor on the efficiency of these RIS schemes. The energy required to saturate the transitions from the excited state to the center of the auto-ionizing state if the pulse length is shorter than the lifetime of the excited state is about 6.8 x 1O-2 mJlcm2. Reference [B] reports a cross section for ionization with the 488 nm line of an argon ion laser through the wings of the 3d5p 3P10 auto-ionizing level of the order of 11 x lo-‘* cm2. The corresponding energy required to saturate the transitions from the excited state to the wing of the auto-ionizing state reached by 488 nm radiation if the pulse length is shorter than the lifetime of the excited state is about 37 mJ/cm2.

RIS schemes of type (2~0, +wI) and (20,+ oA$ One- or two-color excitation involving a two-photon transition to the resonant level

followed either by photo-ionization by a third photon of the same color or excitation to an auto-ionizing state by a third photon of another color. X1 = 421.5 or 536.1 or 600.1 nm, A2~555.2 nm [C, D, E].

Data for RIS schemes of type (2qfoJ and (2q+w*i) [I, 51

Lov. Lavel E, (CaP) Res. I&v01 E, (cm-l)

Al 421.4889 482 ‘s 1s;

0.00 4slOs ‘s, 47437.471 x2 555.17 4slOs 47437.471 4~6s ‘PI0 65445. 1.6E-3

Al 536.0686 482 1s 0 0.00 4s4d ‘D2 37298.287

600.1232 4sa ‘s. 0.00 4858 Is, 33317.264

Lifetimes, photo-ionization cross sections and auto-ionization rates ~(4~10s l&)=294 ns [8]; T(4s4d lD2)=65.0 ns [3]; ~(4~5s l&)=33 ns [3]. For photo-ionization to the continuum from the 4~10s IS0 excited level a calculation

by means of a Hartree-Fock code [4] indicates quite small photo-ionization cross sections. For 1064 nm radiation the calculated cross section is 0.02 x lo-l8 cm2 and for 421.5 nm radiation it is 0.04 x lo-l8 cm2. This corresponds to a laser energy requirement for photo-ionization from this level of 10 000 and 13 000 mJ/cm2, respectively, for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state. One can, however, ionize by means of the 4~6s ‘P,“auto-ionizing level. A calculation indicates an auto-ionizing rate of 4.2 x lOI s-l, so the auto-ionization rate will not limit the process. The energy required to saturate the transitions from the excited state to the center of the auto- ionizing state if the pulse length is shorter than the lifetime of the excited state is about 2600 mJ/cmZ. The calculation indicates the auto-ionizing level is quite broad. If second harmonic radiation from a Nd:YAG laser (532 nm) is used the energy required for saturation is estimated to be 4000 mJ/cm2.

For photo-ionization to the continuum from the 4s4d ID2 excited level a calculation by means of a Hartree-Fock code [4] indicates a cross section of 8.5 x 10-lR cm2 for 536.1 nm radiation. This corresponds to a laser energy requirement for photo-ionization from this level of about 44 mJ/cm2 for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state. There are also several nearby auto-ionizing levels which may contribute to the ionization and significantly lower the required laser energy. An estimate indicates that it could be lowered to 5 mJ/cm2. However in Ref. [D] the results are interpreted as indicating that even at 800 mJ/cm2 they do not saturate the photo-ionization step. 8Ai(tl, ,6:3-A

332 E. B. SALOMAN

For photo-ionization to the continuum from the 45s l&, excited level a calculation by means of a Hartree-Fock code [4] indicates a relatively small photo-ionization cross section, perhaps 0.2 x 1O-18 cm2 for 600.1 nm radiation. This corresponds to a laser energy requirement for photo-ionization from this level of the order of 1600 ml/cm2 for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state. In Ref. [E] energies of W-105 mJ/cm2 were used and it was reported that this was roughly enough to saturate the two-photon step as well as the photo-ionization step.

Isotope data [9, lo] Stable isotopes: ‘Wa (96.941%) Z=O; 42Ca (0.647%) Z=O; 43Ca (0.135%)

1=7/2; Wa (2.086%) Z=O; ‘Wa (0.004%) Z=O; @Ca (0.187%) Z=O. Unstable isotopes: 41Ca Z=7/2 ~=l.l X lo5 y; 45Ca 1=7/2 r=163.8 d; 47Ca

I=712 7=4.54 d.

Isotope shiftslhfs [ll-15, F] Isotope shift relative to Wa (units 10e3 cm-r). For two photon transitions the shifts

are for the total transition (twice as large as for each of the two photons). For odd isotopes the center of gravity of the hyperfine splittings is used.

Transition from 482 Is,

Isotope Mass Number to' . 40 41 42 43 44 45 46 47 48

4S4D 'P,O 0 7.45 13.05 20.38 25.71 32.82 38.66 44.99 SO.39

4s4p SP," 0 9.37 17.00 26.09 33.23 42.02 49.40 64.13

4s4d 'Dz 0 42.3 81.8 153.6

4sss 's, 0 20.22 30.23 39.03 56.85 73.17

28.0 41.8 53.9 78.4 100.7

The even isotopes have no hyperfine structure. For the old isotopes the hypetline interaction constants for levels of the 4s4p configuration are (units 10e3 cm-l): 41Ca: 3P10: A= -8.029, B= +0.133; lP,O: A=-0.628, B=-0.31; 43Ca: 3P10: A= -6.63426, B= +0.07672; lPlo: A= -0.516, B= -0.32; 45Ca: 3P10: A= -6.685, B= -0.09; lPlO: A= -0.515, B= +0.06; 47Ca: lPlO: A= -0.540, B= +0.14.

Laser schemes For 421.5 or 422.7 nm, Nd:YAG pumped Stilbene 420 dye laser; for 488.0 nm,

argon ion laser; for 490.8 or 536.1 nm, Nd:YAG pumped Coumarin 500 dye laser; for 532 nm, Second harmonic of Nd:YAG; for 555.2 nm, Nd:YAG pumped Rhodamine 575 dye laser; for 585.7 nm, Nd:YAG pumped Rhodamine 610 dye laser; for 600.1 nm, Nd:YAG pumped Rhodamine 610 or 640 dye laser; for 612.2 nm, Nd:YAG pumped Rhodamine 640 dye laser or, for cw, argon-ion pumped Rhodamine 590 dye laser; for 657.3 nm, Nd:YAG pumped DCM dye laser or, for cw, argon-ion pumped DCM dye laser; for 1064 nm, Nd:YAG direct IR.

Atom reservoirs and sources A variety of methods have been used to produce calcium for RIS analysis: evaporation

from a hot rhenium filament [D, G]; heating in a stainless steel heat pipe [C, F]; a calcium atomic beam [B]; and passing an aqueous calcium salt solution through an air/acetylene analytical burner into a sampling cell [El.


RIS references

[A] V. S. Letokhov, Later Photoionization Spectroscopy. Academic Press, Orlando (1987). [B] U. Brinkmann, W. Hartig, H. Telle and H. Walther, Appf. Phys. 5, 109 (1974). [C] R. Beigang and A. Timmermann, Phys. Rev. US, 14% (1982). [D] E. C. Apel, J. E. Anderson, R. C. Estler, N. S. Nogar and C. M. Miller, Appl. Opt. 26, 1045 (1987). [E] P. R. Blazewicz, W. B. Whitten and J. M. Ramsey, Anal. Chem. 61, 1010 (1989). [Fj C-J. Lorenzen, K. Niemax and L. R. Pendrill, Phys. Rev. A28, 2051 (1983). [G] G. K. Gerke, B. A. Bushaw and T. J. Whitaker, Low-levels of radionuclide analysis using resonantly

enhanced collisional ionization, in Resonance Ionization Spectroscopy 1988, Eds, T. B. Lucatorto and J. E. Parks, p.311. Institute of Physics, Bristol (1989).

Data references

[l] J. Sugar and C. Co&s, J. Phys. Chem. Re$ Data 14, Suppl. 2 (1985). [2] F. M. Kelly and M. S. Mathur, Can. J. Phys. Ss, 1004 (1980). [3] G. Smith, J. Phys. B 21, 2827 (1988). [4] R. D. Cowan, The Theory of Atomic Strucmre and Specfra. University of California Press, Berkeley

(1981). [5] Calculation using Hartree-Fock code of Ref. [4]. [6] W. H. Parkinson, E. M. Reeves and F. S. Tomkins, 1. Phys. B 9, ,157 (1976). [7] K. Ueda, Y. Hamaguchi and K. Fukuda, J. Phys. Sot. Jpn. 51, 2973 (1982). [8] W. Hansen, J. Phys. B 16, 2309 (1983). [9] N. E. Holden, R. L. Martin and I. L. Barnes, Pure Appl. Chem 55, 1119 (1983).

(lo] G. H. Fuller, J. Phys. Chem. Re& Data 5, 835 (1976). [ll] C. W. P. Palmer et al., J. Phys. B 17, 2197 (1984). [12] A. Andl et al., Phys. Rev. C 26, 2194 (1982). [13] E. Bergmann, P. Bopp, Ch. Dorsch, J. Kowalski, F. Trtiger and G. zu Putlitz, 2. Phys. A 294, 319

(1980). [14] K.-H. Weber, J. Lawrenz and K. Niemax, Phys. Scripta 34, 14 (19%). [15] M. Arnold et al., Hyperfine Interacrions 9, 159 (1981).

RIM/RN Data Service 335

Data sheet for RWRIMS schemes Cesium

cs z = 55

Ground state [l] ls22s22p63s23p6 3d10~24p64d’~5s25p66s 2S1,2


Several different types of RIS schemes are available for the analysis of cesium. One- color two-photon schemes were reported by ZEMAN [A]. In his schemes, the cesium atoms are excited from their ground state to one of the 7p 2P“ levels by the first photon and then the resonant state is photo-ionized by a second photon from the same laser (a so called ol+ol process). HURST and his co-workers [B-D] utilized these schemes to demonstrate the detection of a single Cs atom which was in the same laser beam as 1019 Ar atoms and 10ls CH, molecules in a proportional counter. The use of a proportional counter provides the ultimate in sensitivity, however, collisions with the counter gas broaden the resonance line of the Cs atom and may limit the isotopic selectivity of the scheme. Also, as is typical for one-color schemes, the laser power required for photo-ionization exceeds the optimum power for exciting the resonant state which may lead to reduced elemental selectivity. If more elemental selectivity is required, three-color schemes based on transitions used in the laser-enhanced ionization schemes of CHEKALIN et al. [E] are proposed. The cesium atom is excited from its ground state to one of the 6p 2P levels by the first photon (which can be provided by a laser diode). It is excited from this level to one of the 8d 2D levels by the second photon and subsequently photo-ionized by IR radiation from a Nd:YAG laser (so called w1+02+03 process). Should more isotopic selectivity be required to detect radioactive Cs isotopes (cesium has only one stable isotope) a scheme which can utilize Doppler-free two-photon excitation is proposed. The atom is excited from its ground state to the 8s 2S level by a two-photon transition. Normally, a third photon of the same color would be used for photo-ionization. However, in Cs, the photo-ionization cross section of the 8s 2S level is very low for this wavelength, so photo-ionization by IR radiation from a Nd:YAG laser is proposed instead (so called 20,+wz process). Other 201+02 schemes have been demonstrated [F]. Also reported are other wi+wi and 2o,+wr schemes [G]. Much spectroscopy of cesium has been carried out by excitation of high lying states which are detected by thermionic detectors and related devices [2, H-J]. The high lying Rydberg states can also be detected by means of electric field pulse ionization [K]. The detection of small quantities of cesium is important in monitoring fission products in the environment. The extreme sensitivity of the RIS technique for cesium allows its use to detect single atoms produced by fission [L] and to detect the photodissociation of single molecules of CsI [Ml. A Grotrian diagram of the RIS schemes in cesium is shown in Fig. 3 [2-51.

RIS schemes of type (q+w,): [A-D] One-color two-photon process consisting of a resonance step followed by photo-

ionization with a photon of the same color as the initial step. X,=455.5 or 459.3 nm.

Data for RIS schemes of type (CO,+@,) [2, 3, 61

334 E. 3. SALOMAN

4DD.D n -1064 nm

83

24317 -1

*%I,* cm

m 2lQ

6p “%2 .

%P “p;,z

-_(

Fig. 3 Grotrian diagram of resonance ionization spectroscopy schemes in cesium.

Lifetimes and photo-ionization cross section from excited state In tabular form are listed the laser wavelength, Al, to the resonant level, the resonant

level, the lifetime, T, of the resonant level [7, 81, an estimate of the laser power, P,,, required to saturate the resonant transition, the photo-ionization cross section, o, of the resonant level for radiation of wavelength X1 [A], and an estimate of the energy, E,,, delivered during the lifetime of the resonant state required to saturate the photo- ionization.

RZS schemes of type ( wl + 02+ w3) Three-color process consisting of two resonance steps followed by photo-ionization

by an IR photon. hi=852-895 nm. X2=601-622 nm. X3=1064 nrni

Data for RIS scheme of type (o,+o~+w~ [2, 4-6, 91

Lifetimes and photo-ionization cross section from excited states [7, IO-123 $6~ 2P1,20)=34.0 ns, ~(6p 2P,,20)=30.9 ns, $8d 2D3,,)=141 ns, T(8d 2D5~)=145 ns. The power in A1 required to saturate the excitation to the 6p 2P1,20 is 0.40 W/cm2

and that required for the 6p 2P3/2” level is 0.41 W/cm2. An estimate of the energy

RIMiRIS Data Service 337

required in Az to saturate the second step from these levels to the 6d *D levels, within the absorption bandwidth delivered while the Iirst step is being pumped is: for 601.0 mn, 9.0 X 10m4 mJ/cmz; for 621.3 nm, 6.0 x 10e4 mJ/cmz; and for 621.8 nm, 3.1 x 10m3 m.I/cm2. The photo-ionization cross section of the 8d 2D levels by 1064 nm radiation have been calculated to be 4.0 x 1O-18 cm2 [ll] and 9.7 x 10-l* cm* [12]. An average of these corresponds to a laser energy requirement of 27 mJ/cm2 for photo- ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of- the excited state.

RIS schemes of type (20,+4 Two-color process consisting of a two-photon transition to the resonant level followed

by photo-ionization with a photon of a different color than that used for the initial step. hr=822.2 nm, h2=1064 nm.

Data for RIS schemes of type (2w,+g) [2]

Lifetimes and photo-ionization cross section from excited state [7, 10-121 ~(8s 2S1,)=91 ns. For photo-ionization by 822 nm radiation, an extremely low photo-ionization cross

section (0.034 x 10-i* cm2) has been calculated [ll]. If 1064 nm radiation is used, a cross section of 0.22 x lo-‘* cm* is reported [ll] while another calculation results in 0.48 x 10-r* cm* [12]. An average of these two values corresponds to a laser energy requirement of 530 mJ/cm* for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state.

Isotope data [13-151 Stable isotopes: i=cs (100%) 1=7/2. Unstable isotopes: 131Cs Z=5/2 r=9.688 d; 13*Cs I=2 ~=6.47 d; 134Cs I=4

7=2.062 y; ljsCs Z=7/2 ~=3 x 106 y; i3Ts I=5 ~=13.16 d; 13’Cs 1=7/2 7=30.17 y.

Isotope shiftslhfs [M-21] The isotope shift of the indicated lines of the Cs isotopes are given in the following

table relative to the line in 133Cs,

Isotope shift (10e3 cm-l)

The hfs interaction constants for the indicated levels of the listed Cs isotopes are given in the following table:

For 133Cs for the 6p 2P1/29 level A=9.7 x 10e3 cm-l and for the 8.r 2S1,2 level A=5.7 X 1O-3 cm-‘.

338 E. B. SALOMAN

hfs Interaction constants (lo-” cm- I)

Isotope ldass

Number

6s =%,z 6~ %,a’

I

7P %,a’

A AlB AIB I

7P %,a’

A

146.56111 3.222 -3.05 1.058 - .955 6.10

115.58 2.524 2.48 .835 .79 4.80

Laser schemes For 455-460 nm, Nh:YAG pumped Coumarin 460 dye laser; for 601-622 nm,

Nd:YAG pumped Rhodamine 640 dye laser; for 822.2 nm, Nd:YAG pumped LDS 821 dye laser; for 852-895 nm, laser diode [21] or Nd:YAG pumped LDS 867 dye laser; for 1064 nm, Nd:YAG direct IR.

Atom reservoirs and sources Several methods have been used to produce atomic cesium. These include heated

samples [B, F, I], atomic beams [A], evaporation from bulk cesium at room temperature [G], fission of 252Cf [L], and laser photodissociation of CsI [Ml.

RIS references

[A] H. D. Z&man, Electron spin polarization from multiple photo-ionization processes, in Electron und Photon Interactions wifh Atoms, Eds, H. Kleinpoppen and M. R. C. McDowell, p.581. Plenum, New York (1976).

[B] G. S. Hurst, M. H. Nayfeh and J. P. Young, Appl. Phys. Lert. 30, 229 (1977). [C] G. S. Hurst, M. H. Hayfeh and J. P. Young, Phys. Rev. A 15, 2283 (1977). (D] G. S. Hurst and M. G. Payne, Principles and Applications of Resdnance Ionisation Spectroscopy. Adam

Hilger, Bristol (1988). [E] N. Chekalin, M. Marunkov and I. Vlasov, Analytical applications of RIS in flames, in Resonance

Ionization Specfroscopy 1988, Eds, T. B. Lucatorto and J. ,E. Parks, p.175. ,Iostitute of Physics, Bristol (1989).

[F] K. D. Bonin, M. Gatzke, C. L. Collins and M. A. Kadar-Kallen, Phys. Rev. A 39, 5624 (1989). [G] C. M. Houston et al., 1. Phys. D 21, S59 (1988). [H] D. Popescu, C. B. Collins, D. W. Johnson and I. Popescu, Phys. Rev. A 9, 1182 (1974). [I] S. M. Curry, C. B. Collins, M. Y. Mirza, D. Popescu and I. Popescu, Opt. Commun. 16, 251 (1976). [J] K. Niemax and K.-H. Weber, J. Phys. B 11, L267 (1978). [K] V. S. Letokhov, Laser Phofoionization Specrroscopy. Academic Press, Orlando (1987). [L] S. D. Kramer, C. E. Bemis, Jr., J. P. Young and G. S. Hurst, Opt. Lett. 3, 16 (1978). [M] L. W. Grossman, G. S. Hurst, M. G. Payne and S. L. Allman, Chem. Phys. Lert. 50. 70 (1977).

Data references

[l] C. E. Moore, Atomic Energy Levels, National Standards Reference Data Service (US. National Bureau Standards) NSRDS-NBS 35, Vol. 3 (1971).

[2] K.-H. Weber and C. J. Sansonetti, Phys. Rev. A 35, 4650 (1987). [3] C. J. Sansonetti and C.-J. Lorenzen, Phys. Rev. A 30, 1805 (1984). [4] G. Avila, P. Gain, E. de Clercq and P. Cerez, Merrologia 22, 111 (1986). [5] C.-J. Lorenzen and K. Niemax, 2. Phys. A 315, 127 (1984). [6] R. J. Extort, J. Quant. Specrrosc. Radial. Transfer 16, 309 (1976). [7] C. E. Theodosiou, Phys. Rev. A 30, 2881 (1984).


[8] M. Ortiz and J. Campos, J. &rnt. Spectrosc. Rudiat. Transfer 26, 107 (1981). [9] L. Agnew and C. Summers, Quantitative spectroscopy of cesium plasmas, in Proceedings of the Seventh

International Conference on Phenomena in Ionized Gases, Eds, B. Perovic and D. Tasic, Vol. II, ~574. Gradjevinska Knjinska, Belgrade (1966).

(10) W. S. Neil and J. B. Atkinson, 1. Phys. B 17, 693 (1984). [ll] J. Lahiri and S. T. Manson, Phys. Rev. A 33, 3151 (1986). (121 Calculated using the Hartree-Fock code with relativistic corrections of R. D. Cowan, The Theory of

Atomic Structure and Spectra. University of California Press, Berkeley (1981). [13] G. H. Fuller, J. Phys. Chem. Ref. Data 5, 835 (1976). (141 N. E. Holden, R. L. Martin and I. L. Barnes, Pure Appl. Chem. 55, 1119 (1983). [15] P. Raghavan, Atomic Data Nucl. Data Tables 42, 189 (1989). [16] G. Huber et al., Phys. Rev. Lett. 41, 459 (1978). [17] H. Gerhardt, E. Matthias, F. Schneider and A. Timmermann, 2. Phys. A 2.38, 327 (1978). [18] C. Thibault et al., Nucl. Phys. A367, 1 (1981). [19] H. Hiihnermann and H. Wagner, Z. Phys. 199, 239 (1967); Z. Phys. 216, 28 (1968). [20] F. Ackermann, E. W. Otten, G. zu Puthtz, A. Schenck and S. Ullrich, Nucl. Phys. A248, 157 (1975). (211 C. E. Tanner and C. Wieman, Phys. Rev. A 38, 1616 (1988).

RIMIRIS Data Service 341

Data sheet for RIWRIMS Chromium

Cr

Ground state [l]

First ionization potential [l]

schemes

Z = 24

ls22,s22p63s23p6 3d54s 7S,

54575.6 cm-’ = 6.76651 eV

RIMS has been applied to the analysis of chromium by several groups. All used two-photon schemes involving excitation to a resonant state by the first photon followed by photo-ionization by a second photon of either the same color (a so called o1 + o1 process) or of another color (a so called o1 + o2 process). WILLIAMS et al. [A] excited the Cr atom from its 7S, ground state to a level of the z 7P2,3,40 multiplet. The resonant state was then photo-ionized by 308 nm radiation from a XeCl excimer laser. This allows separate optimization of resonant and photo-ionizing steps. A laser microprobe was used as the atomization source to study Cr in stainless steel. They report an isotopic sensitivity of 1 ppm and a sensitivity to airborne Cr atoms of about 0.05 mg/m3 or 6 x 108 atoms/mm3. HE,SS and HARRISON [B] excited the Cr atom from its ground state to a level of the y 7P 2,3,4’ multiplet. The resonant state was then photo-ionized by a second photon of the same color. A glow discharge sputtering high chromium steel served as the atomization source. GELIN et al. [C] excited the Cr atom from its ground state to the z 5D40 level. The resonant state was then photo-ionized by a second photon of the same color. Their atomization source used l-5 keV argon ions to sputter neutral atoms from the sample. They claim a 2 ppm real time sensitivity and a 7 ppb sensitivity in a 18 000 laser shot counting mode [D] for their measurements. In addition, we propose alternate schemes which calculations indicate may be more efficient. These involve excitation first to z 5D40, 7P30, or 7P20 resonant levels as above followed by excitation from these levels to auto-ionizing states such as g ‘D1,2,3,4 or e 3D3 (so called w + w*J processes). Analysis of trace quantities of Cr should be of importance in the study of alloys, semiconductors, and biological systems (e.g. to investigate diabetes mellitus or cardiovascular disease [El). A Grotrian diagram of the RIS schemes in chromium is shown in Fig. 4 [l].

RIS schemes of type ( o1 + WI) or (0,s w2) One- or two-color two-photon process consisting of a resonance step followed by

photo-ionization. hi between 295 and 429 nm [A-D], X,=308 nm [A].

Data for RIS schemes of type (ol+o,) or (q +02) [l-3]

342 E. B. SALOMAN

357-361 nm

Fig. 4. Grotrian diagram of resonance ionization spectroscopy schemes in chromium.

Lifetimes and photo-ionization cross section from excited state In tabular form are listed the laser wavelength, Xi, to the resonant level, the lower

level, the resonant level, the lifetime, T, of the resonant level calculated from Ref. [2], an estimate of the laser power, P,,, required to saturate the resonant transition, the photo-ionization cross section of the resonant level, u, for an o1 + o1 scheme in the case of the z 5D4o and y ‘PO levels and for photo-ionization by 308 nm radiation for the z ‘P” levels calculated by means of a Hartree-Fock code [4], and an estimate of the energy, E,,,, delivered during the lifetime of the resonant state required to saturate the photo-ionization.

Low. Lavel Res. Level CL

P sat 0 E W/cm2) (lo-l8 cn?)

sat W/cm')

295.63 a 7S, 2 SD," 88 7.334 10 66 *

357.87 a 7S Y rP,O 6.8 37 2.6 210 .________,________,___,________________________-__-________________~~_~___________________.

359.35 a 7S, Y 7P*0 6.7 37 2.5 220

360.53 a 7S3 Y 7Ps0 6.2 36 2.4 230

425.43 a 7S3 2 7PbO 32 19 15 44 .___________________~~~~~~~~~-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-~~~~~~~~~~_~~__~_____~___________

427.48 a 7S1 33 ia 15 44

* Reference [C] reports a higher value for u, but improved measurements by the same group [F] lower that value by a factor of about five in agreement with the result calculated here.

RIS schemes of type (w,+ w”$) Two-color excitation involving a transition to a resonance level followed by excitation

to an auto-ionizing state. X, = 295 nm or between 427 and 429 nm. XAi between 467 and 473 nm or 314 and 319 nm.

Calculations [3] indicate that other lines from these resonant levels to the g 5Dq,3,2.1 and e 3D3,2,1 auto-ionizing levels are weaker than those included here.


Data for RIS schemes of type (w,+dJ) (l-31

A mo X1 295.6311 X, 467.3129

X, 295.6311 A, 467.4051

X, 295.6311 A, 472.2175

A, 427.4796 A, 314.1505

A, 427.4796 A, 316.3595

A, 428.9716 As 315.5472

A, 428.9716 A, 317.2321

A, 428.9716 A, 318.7153

Low. Level E, (cm-‘) Ra8. Lwel I& (cm-l) f,

a 7S, 0.00 z 5D,* 33816.06 2.1E-5 z SD,’ 33816.06 g % 55209.01 0.067

a 7S, 0.00 z ‘D4* 33816.06 2.1E-5 z $0 33816.06 e ‘D3 55204.79 1.3&3

a 7S3 0.00 2 SD,’ 33816.06 2.1E-5 2 %,” 33816.06 g ‘D3 54986.82 0.011

a 7S3 0.00 z 7P30 23386.35 0.0840 z 7P,’ 23386.35 B sD, 55209.01 3.73-4

a 7S3 0.00 z 23386.35 0.0840 z 7P30

7Ps0 23386.35 g ‘L’s 54986.82 1.2&4

a 7S3 0.00 z 23305.01 0.0622 2 7P20

7PsO 23305.01 g 9)s 54986.82 4.OE-4

a 7S3 0.00 z %s* 23305.01 0.0622 z 7P,O 23305.01 g ‘Dz 54818.55 2.83-4

a 7S3 0.00 z 7P20 23305.01 0.0622 z 7P20 23305.01 g ‘DI 54671.90 7.83-5

m

Lifetimes and auto-ionization rates The lifetimes of the resonant levels and the laser powers required to saturate their

excitation are as given above for the (o,+ol) or (w1+02) schemes. The calculated auto-ionization rates [3] for the indicated levels are (units loll s-i): g 5Dq: 2.0; g 5D3: 2.0; g 5D2: 1.9; g 5D,: 1.9; e 3D3: 4.4; e 3D2: 4.4; e 3D1: 4.3. As a result the auto- ionization rates are not expected to be a limiting factor on the efficiency of these RIS schemes. The energy (in mJ/cm*) required to saturate the transitions from the excited state to the auto-ionizing state if the pulse length is shorter than the lifetime of the excited state [3] is given below:

AZ (nm) 467.31 467.41 472.22 314.15 316.36 315.55 317.23 318.72

L W/cm? 1.2E-2 1.1 5.7E-2 4.1 10 4.2 4.1 5.5

Thus the auto-ionizing schemes require orders of magnitude less laser energy for the ionizing step than do the photo-ionization schemes while providing the added selectivity of the second excitation step.

Isotope data [5, 61 Stable isotopes: Yr (4.35%) Z=O; 52Cr (83.79%) Z=O; 53Cr (9.50%) 1=3/2; 54Cr

(2.36%) Z=O. Unstable isotopes: 49Cr Z=5/2 r=41.9 min; 51Cr Z=7/2 r=27.70 d.

Isotope shiftsfhfs [&9]

Isotope shift relative to Wr (units lo-” cm-‘)

The even isotopes have no hyperfine structure. For the odd isotopes the hyperfine interaction constants for the ground state are (units lo-” cm-‘):

344 E. B. SALOMAN

4Tr: ‘S3: \~l=i.6596, \~(=6~-4* B/A > 0 Wr: ‘S3: -]A]=2.3250, (BI=5E-4* B/A < 0 53Cr: ‘S3: A = -2.75522, B= +3E-4*

For s3Cr the hyperfine interaction constants for the indicated levels are (units 10e3 cm-l): .? 7P4”: A= -0.394, B= -0.02* 2 7P3O: A= -0.05,* B=-0.07* f ‘P2O: A= 0.89, B= 0.09* y 7P30: A=-2.27, B= 0.2 y ‘P2”: A=-2.1, B= O.l* * Uncertainty of quoted value is equal to or larger than the value.

Laser schemes For 295.6 nm, Nd:YAG pumped frequency doubled Rhodamine 610 dye laser [Cl;

for 308 nm, XeCl excimer laser; for 314-319 nm, Nd:YAG pumped frequency doubled DCM dye laser; for 357-361 nm, Nd:YAG pumped frequency doubled LDS 750 dye laser; for 425-429 nm, XeCl excimer pumped bis-MSB dye laser [A] or Nd:YAG pumped Stilbene 420 dye laser; and for 467-473 nm, Nd:YAG pumped Coumarin 460 dye laser.

Atom reservoirs and sources Several different methods have been used to atomize Cr for RIS studies: laser

desorption [A]; glow discharge [B]; and sputtering by an argon ion beam [Cl.

RIS references

[A] M. W. Williams, D. W. Beekman, J. B. Swan and E. T. Arakawa, Anal. Ckem. 56, 1348 (1984). [B] K. R. Hess and W. W. Harrison, Anal. Ckem. 58, 1696 (1986). [C] P. Gelin, 0. Gobert, B. Dubreuil, J. L. Debrun and R. L. Inglebert, Studies on the analysis of trace

metallic elements in semiconductors using RIMS, in Resohnce Ionization Spectroscopy 1988, Eds, T. B. Lucatorto and J. E. Parks, p.201. Institute of Physics, Bristol (1989).

[D] P. Gelin, J. L. Debrun, 0. Gobert, R. L. Inglebert and B. Dubreuil, Nucl. Insfrum. Methods B 40/41, 290 (1989).

[E] L. J., Moore, J. E. Parks, E. H. Taylor, D. W. Beekman and M. T. Spaar, Medical and biological applications of resonance ionization spectroscopy, in Resonance Ionization Spectroscopy 1986, Eds, G. S. Hurst and C. G. Morgan, p-239. Institute of Physics, Bristol (1987).

[F] B. Dubreuil, Private commun. (1990).

Data references

[l] J. Sugar and C. Corliss, J. Phys. Ckem. Ref. Data 14, Suppl. 2 (1985). [2] G. A. Martin, J. R. Fuhr and W. L. Wiese, J. Phys. Ckem. Ref. Data 17, Suppl. 3 (1988). [3] Calculated using the Hartree-Fock code with relativistic corrections of Ref. [4]. [4] R. D. Cowan, The Theory of Atomic Structure and Spectra. University of California Press, Berkeley

(1981). [5] N. E. Holden, R. L. Martin and I. L. Barnes, Pure Appl. Ckem. 55, 1119 (1983). [6] G. H. Fuller, J. Pkys. Ckem. Ref. Data 5, 835 (1976). [7] K. Heilig and D. Wendlandt, Pkys. Lea. 25A, 277 (1967). [8] R. Bruch, K. Heilig, D. Kaletta, A. Steudel and D. Wendlandt, J. Pkys. (Paris), Suppl. 30, Cl-51

(1969). [9] U. Becker, U. Teppner and U. Wiisthof, J. Pkys. B 11, 2435 (1978).


Data sheet for RWRIMS schemes Cobalt

co Z = 27

Ground state [l] ls22r22p63s23p6 3dr4r2 4Fgn

First ionization potential [2] 635646 cm-’ = 7.88101 eV

A number of groups have applied RIS to the analysis of cobalt. All used one-color two-photon schemes involving excitation of the cobalt atoms from either their ground state or another low-lying level to an excited state by the first photon followed by photo-ionization of the excited state by a second photon of the same color (a so called wl + o1 process). MOORE et al. [A, B] used thermal vaporization of a sample containing many elements to analyze cobalt (and the others). They used a number of ground state originating (GSO) and excited state originating (ESO) schemes. KIMOCK et al. [C, D] used sputter initiated RIS (SIRIS) to analyze solids for the presence of cobalt. They also used several GSO and ES0 schemes. GOBERT et al. [E-H] also applied SIRIS to trace analysis of cobalt in high purity materials. Using GSO schemes, they report detection limits as low as 10 ppm for real-time measurements and 25 ppb for counting the ions produced by 18 000 laser shots. A more selective and efficient scheme would involve two resonant steps followed by photo-ionization (a so called w1 + o2 + w3 process). Such a scheme allows for individual optimization of the laser intensity driving each of the resonant steps and the choice of a photo-ionization laser which can easily provide the power required to saturate the photo-ionization. TURK et al. [I] demonstrated a laser enhanced ionization scheme in flames using 252.1 nm and 591.7 nm radiation (the ionization being completed by collisions, etc. in the flame). Since 1064 nm IR from a Nd:YAG laser would provide enough energy to ionize the atoms after the first two photons (from the g 4P5,2 level) this scheme was considered. However, calculations [3] show the photo-ionization cross section from this level to be very small. An alternate scheme with more efficiency is proposed. The cobalt atoms are excited from their ground state to the y 4D 7/2o resonant level by the first photon, then from this level to

or 252.1 nm

or 262.1 nm

A

/////////////////c 63564 cni’

165-313 nm 532 nm

31871- 36676 or_,

=39649 cm

y %,z

165-313 nm

= 3462- _, = 5076 cm

525.5 nm

L 32026 crii’

312.1 nm

-, - 0 cm

Fig. 5. Grotrian diagram of resonance ionization spectroscopy schemes in cobalt.

346 E. B. SALOMAN

the e 4D7a level by the second photon. The e 4D 7/Z level is then photo-ionized by second harmonic radiation from a Nd:YAG laser. Analysis of trace quantities of Co is important in a number of areas: Co can be an impurity in semiconductor materials, it is an important constituent of many alloys, and in biological systems it is a part of vitamin B-12 and interacts with iron [J]. A Grotrian diagram of the RIS schemes in cobalt is shown in Fig. 5 [l, 21.

RIS schemes of type (w, + w,) One-color two-photon process consisting of a resonance step followed by photo-

mization. Xi between 252 and 315 nm [A-H].

Data for RIS schemes of type (o,+o,): [l, 3, 41

* The L-S-coupling designation of this odd-parity term was not provided in Ref. [l] or Ref. [2] and following the notation of those works, is not used here.


Lifetimes and photo-ionization cross section from excited states In tabular form are listed the laser wavelength, Ai, to the resonant level, the lower

level, the resonant level, the lifetime, T, of the resonant level [3-71, an estimate of the laser power, P sBt, required to saturate the resonant transition, the photo-ionization cross section of the resonant level, IY, for an o1 + o1 scheme [3], and an estimate of the energy, ES,,, delivered during the lifetime of the resonant state required to saturate the photo-ionization.

348 E. B. SALOMAN

RIS schemes of type ( OJ, + o2 + CO?) Three-color process consisting of two resonance steps followed by photo-ionization

by a photon of a third color. A i=312.1 nm, X,=525.5 nm, X3=532 nm.

Data for RIS scheme of type (0, +o,+o,) [l, 3, 41

Lifetimes and photo-ionization cross section from excited states [3, 7) ~0, 4D,,Zo)=11 ns, r(e 4D,,)=7.6 ns. The power in A, required to saturate the excitation to the y 4D,,20 level is estimated

to be 2700 W/cm2. An estimate of the energy required in AZ to saturate the second step from this level to the e 4D 7,2 level, within the absorption bandwidth delivered while the first step is being pumped is 3.2 x 10e4 mJ/cm2. The photo-ionization cross section of the e 4D,,2 level by 532 nm radiation is calculated to be 3.9 x lo-l8 cm2. This corresponds to a laser energy requirement of 97 mJ/cm* for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state.

Isotope data [8, 91 Stable isotope: “‘Co (100%) I= 7/2. Unstable isotopes: ‘hCo I=4 ~=78.8 d; “‘Co I=712 ~=271 d; s8Co I=2 ~=70.8 d;

MCo 1=5 ~=5.271 y.

Isotope shiftslhfs [lo] Cobalt has only one stable isotope. There is no isotope shift data to report. The hfs

interaction constants for the indicated ground and low-lying levels of 59Co are given in the following table.

hfs Interaction constants ( 10m3 cm-‘)

Laser schemes For 252.1 nm, Nd:YAG pumped frequency doubled Coumarin 500 dye laser; for

283-287 nm, Nd:YAG pumped frequency doubled Rhodamine 590 dye laser; for 292-305 nm, Nd:YAG pumped frequency doubled Rhodamine 610 dye laser; for 305-315 nm, Nd:YAG pumped frequency doubled Rhodamine 640 dye laser; for 525.5 nm, Nd:YAG pumped Coumarin 500 dye laser; for 532 nm, second harmonic of Nd:YAG.

Atom reservoirs and sources Atoms of cobalt have been produced for RIS studies by thermal vaporization of a

sample deposited on a filament [A, B] and by argon ion sputtering of a solid sample [C-H].

RIM/RI!3 Data Service 349

RIS references

[A] L. J. Moore, J. D. Fassett and J. C. Travis, Anal. Gem. 56, 2770 (1984). [B] J. C. Travis, J. D. Fassett and L. J. Moore, A survey of elements detected using resonance ionization

mass spectrometry with thermal vaporization, in Resonance Ionization Spectroscopy 1984, Eds, G. S. Hurst and M. G. Payne, p.97. Institute of Physics, Bristol (1984).

[C] F. M. Kimock, J. P. Baxter, D. L. Pappas, P. H. Kobrin and N. Winograd, Examination of excited state populations in sputtering using multiphoton resonance ionization, in Analyfical Spectroscopy. Ed. W. S. Lyon, p.179. Elsevier, Amsterdam (1984).

[D] F. M. Kimock, J. P. Baxter, D. L. Pappas, P. H. Kobrin and N. Winograd, Anal. Chem. 56, 2782 (1984).

[E] P. Gelin, 0. Gobert, B. Dubreuil, J. L. Debrun and R. L. Inglebert, Studies on the analysis of trace metallic elements in semiconductors using RIMS, in Resonance Ionization Spectroscopy 1988, Eds, T. B. Lucatorto and J. E. Parks, p.201. Institute of Physics, Bristol (1989).

[F] P. Gelin, J. L. Debrun, 0. Gobert, R. L. Inglebert and B. Dubreuil, Nucl. lnsfrutn. Methods B 40141, 290 (1989).

[G] 0. Gobert, B. Dubreuil, P. Gelin, J. L. Debrun and R. L. Inglebert, Trace analysis using laser postionisation of sputtered neutral atoms--Preliminary results obtained with a Nd-YAG pumped dye laser and a quadrupole mass spectrometer, in Secondary Ion Mass Spectrometry SIMS VI, Eds, A. Benninghoven, A. M. Huber, and H. W. Werner, p.845. Wiley, Chichester (1988).

[H] 0. Gobert, Spectromttrie de masse par ionisation laser r6sonnante. Etude des processus multiphotoniques et applications a l’analyse des mat&iaux solides, These, I’Universitt d’Orltans, unpublished (1989).

[I] G. C. Turk, J. R. DeVoe and J. C. Travis, Stepwise excitation laser enhanced ionization spectrometry, Anal. Chem. 54, 643 (1982).

[J] L. J. Moore, J. E. Parks, E. H. Taylor, D. W. Beekman and M. T. Spaar, Medical and biological applications of resonance ionization spectroscopy, in Resonance Ionization Spectroscopy 1986, Eds, G. S. Hurst and C. G. Morgan, p.239. Institute of Physics, Bristol (1987).

Data references

[1] J. Sugar and C. Corliss, J. Phys. C/rem. Ref. Data 14, Suppl. 2 (1985). [2] R. H. Page and C. S. Gudeman, J. Opt. Sot. Am. Bl, 1761 (1990). [3] Calculated using the Hartree-Fock code with relativistic corrections of R. D. Cowan, The Theory of

Atomic Structure and Spectra. University of California Press, Berkeley (1981). [4] J. R. Fuhr, G. A. Martin and W. L. Wiese, J. Phys. C/tern. Ref. Data 17, Suppl. 4 (1988). [5] H. Figger, J. Heldt, K. Siomos and H. Walther, Astron. Astrophys. 43, 389 (1975). [6] J. Marek and K. Vogt, Z. Phys. A 280, 235 (1977). [7] B. L. Cardon, P. L. Smith, J. M. Scala, L. Testerman and W. Whaling, Asrrophys. J. 260, 395 (1982). [8] N. E. Holden, R. L. Martin and I. L. Barnes, Pure Appl. &em. 55, 1119 (1983). [9] P. Raghavan, Atom. Data Nucl. Data Tables 42, 189 (1989).

[lo] G. H. Fuller, J. Phys. Chem. Ref. Data 5, 835 (1976).


Data sheet for RIS/RIMS schemes

Copper cu Z = 29

Ground state [l] ls22s22p63s23p6 3d1°4s 2Sln


A number of groups have applied RIS to the analysis of copper. In addition, several schemes for ionizing copper have been used where two photons with the wavelength of one of the resonance transitions from the ground state to the 3d1°4p 2P1,2,3no levels are utilized [A, B]. The two photons in these schemes do not by themselves provide the atom with enough energy to ionize. The schemes depend on energy from an ionized plasma to complete the process. These laser enhanced ionization schemes will not be discussed here. A related RIS scheme was demonstrated by GELIN et al. [C, D] and GOBERT [El. Here the atom is excited by a photon from the ground state to the 3d1°4p 2P3no level from which it is photo-ionized by a second photon of wavelength shorter than 317 nm (a so called o1 + o2 process). They also demonstrated a more efficient scheme where the excitation was from the ground state to the 384~4~ 4D3no level which was then photo-ionized by a second photon of the same color (a so called wI + w1 process). The most efficient scheme they reported had this excitation to the 384~4~ 4D3no level as its first step which was followed by a second photon exciting the atom from this level to the 3d%6d 2D5n auto-ionizing level (a so called o1 + w*s process). They report a detection limit of 10 ppm for real time measurements and 30 ppb for ion counting over 18 000 laser shots. By having two resonant steps, this scheme should have greater selectivity. Alternate schemes of type w1 + o*i are proposed. Here the first photon excites one of the 3d104p 2P,n,3no or 3d%4p4 PIn, 3n0 levels. Then a second photon excites the atom from this level to one of the 384~5s 4D5,2,3,2 auto-ionizing levels. These schemes should have the increased selectivity of the previous one while utilizing photons of easier to produce wavelengths, APEL et al. [F], MILLER et al. [G], and BLAZE~ICZ et al. [H] report on a scheme in which a two-photon transition is used to excite the atom from its ground state to the 3d1°5s 2SI,z level which is then photo-ionized by a third photon of the same color (a so called 20, + w1 process). BLAZE~ICZ et al. report a detection limit of 25 ppt (trillion). This scheme is amenable to Doppler-free excitation making it suitable for isotopically selective measurements. PARKS et al. [I-K] and MOORE et al. [L] report copper measurements using sputter initiated resonance ionization spectroscopy (SIRIS) but do not specify any RIS schemes. They have measured Cu in steel at 60-10 000 ppm and Cu in 0.25 ml of blood at the 0.76 kg/g level by combining SIRIS with isotope dilution techniques. Detection of trace quantities of copper is important in the analysis of impurities in semiconductor materials and in metabolic disorders such as Wilson’s disease, Menkes disease, and anemia [L]. A Grotrian diagram of the RIS schemes in copper is shown in Fig. 6 [l, E].

RIS schemes of type (w,+o,) or (o,+02) One- or two-color two-photon process consisting of a resonance step followed by

photo-ionization. A, = 222.6 or 224.4 nm for (w,+w,) [Cl, A, = 324.8 or 327.4 and X2=308 nm for (w,+w2).

Lifetimes and photo-ionization cross sections from excited states In tabular form are listed the laser wavelength, X,, to the resonant level, the resonant

level, its energy, E,, the lifetime, T, of the resonant level [2-4], an estimate of the

352 E. B. SALOMAN

3da4sf3d %,,, 79603 cm'

3ds4s5s

-;liit;ll cm

224.1 nrr

244.2 nm

I 222.6 or 224.4 nm

463.5

a nm

222.6 nm

Fig. 6. Grotrian diagram of resonance ionization spectroscopy schemes in copper.

Data for RIS schemes of type (o,+o,) or (w,+o*) [l, 21

laser power, P,,,, required to saturate the resonant transition, the photo-ionization cross section of the resonant level, o, for an o1 + o1 scheme in the case ,of the 4D” levels and for photo-ionization by 308 nm radiation for the 2P” levels calculated by means of a Hartree-Fock code [5], and an estimate of the energy, E,,,, delivered during the lifetime of the resonant state required to saturate the photo-ionization.

II 4 Res. Level E, E (cm-') cd, Cla.zcm2~

222.5705 4p' 'DI12" 44915.61 522 2230 19 l 47

224.4267 4p' 4D,,20 44544.153 376 500 21 l 42

324.7537 4Q 2Pw.0 30783.686 7.17 51 6.6 93

II 327.3954 49 2P,,.0 30535.302 7.27 49 7.5 ai

* GOBERT [E] obtains cross sections of 6.2 x lo-lx cm2 for these levels by the quantum defect method. However, some important channels, made available by the mixed character of the JDO levels, are not included in this calculation.

RIS schemes of type (w, + gA$ Two-color excitation involving a transition to a resonance level followed by excitation

of an auto-ionizing level [Cl. A, Between 224 and 327 nm. AA: Between 285 and 442 nm.


Data for RIS schemes of type (o,+oA3 [l, 2, 6, E]

x (ma0 LQw.til El (cm-') Rq8. Lwral q (cm-') f,

X, 224.4267 4s z%,a 0.000 4p' )Ds,a* 44544.153 1.80E-3 A, 285.15 4P ' 'D 2/2* 44544.153 6d' 2D 512 79603 2.7 E-3

A, 244.1636 4s '%,2 0.000

’ 'P 4P ’ 'P l/2* 40943.73 1.8 E-3

A, 441.5557 4P 1,2n 40943.73 Se' 'D 512 63584.57 0.14

A, 249.2144 4s 2s,,2 0.000 4P t 'P 3,2O 40113.99 5.793-3 A, 425.9454 4p' 'Ps12' 40113.99 5s' 'Ds12 63584.57 0.052

A, 249.2144 4s 2%,2 0.000

'Ps12e 4p' 'PslzO 40113.99 5.793-3

A, 437.8146 4p' 40113.99 5s' 'Ds12 62948.29 0.18

X, 324.7537 4s 2%,2 0.000 4P 2p,,2’ 30783.686 0.440 A, 304.7812 4P 2%,2’ 30783.686 58' 'D 312 63584.57 1.4 E-3

A, 324.7537 4s 2%,2 0.000 4p aP,,," 30783.686 0.440 A, 310.8106 4P 2%,2’ 30783.686 5s' 'D,,2 62948.29 2.8 E-3

Lifetimes and auto-ionization rates from excited levels [l-4, 6, 7, E] Listed in tabular form for the first step of these schemes are the laser wavelength,

Al, to the resonant level, the resonant level, the energy of the resonant level, E,, the lifetime, T, of the resonant level, and an estimate of the laser power, I’,,,, required to saturate the resonant transition.

4 Bes. Level =, P (nm) (cm-') Cn's, (W/Z2)

224.4267 4D' 'D*r.,O 44544 376 so0

244.1636 4p' 4P1,20 40944 ~500 8160

249.2144 4P' 4Pl,,o 40114 329 140

324.7537 4p 2P,,20 30784 7.17 51

737.395& 30535 7.27 49

For the second step of these schemes are listed in tabular form the laser wavelength, AZ, to the auto-ionizing level, the auto-ionizing level, its energy EA1, the lifetime of the auto-ionizing level, T (the reciprocal of the auto-ionization rate), and an estimate of the laser energy, E,,,, required to saturate the second step of the process within the absorption bandwidth delivered while the first step is being pumped.

A.I. Level EN (cm-') tps) ~aFi,Zrn2~

285.15 6d' 2D s/2 79603 10 0.34

302.490s 5s 'D,,, 63585 1.28 1.3

304.7812 5s' 'Ds/2 63585 1.28 3.2

310.8106 5s 'D 512 62948 1.59 1.4

425.9454 5s' 'D,,, 63585 1.28 0.061

437.8146 5s' kDs/2 62948 1.59 0.015

441.5557 5s' 'D,,, 63585 1.28 0.043

3.54 E. B. SALOMAN

RZS schemes of type (2w,+ol): [F-H] One-color process consisting of a two-photon transition to the resonant level followed

by photo-ionization with a photon of the same color as for the initial step. X1=463.5 nm.

Data for RIS schemes of type (2o,+w,) [l, M]

The two photon absorption cross section has been estimated to be 5 x 1O-42 cm4s [MI*

Lifetimes and photo-ionization cross section from excited state ~(5s 2Sl,2) = 22 ns [8]. The energy in X1 required to produce a 10% excitation of the 5s 2S1,2 level for a

pulse length of IO ns has been estimated to be 6 mJ/cm2 [Ml. For photo-ionization to the continuum by 463.5 nm radiation a calculation by means of a Hartree-Fock code [5] for the 5s 2S iI2 level gives an estimate for the cross section of 1.8 X lo-l8 cm*. This corresponds to a laser energy requirement of 230 ml/cm2 for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state.

Zsotope data [P-11] Stable isotopes: 63Cu (69.17%) 1=3/2; “sCu (30.83%) 1=3/2. Unstable isotopes: ti’Cu I=2 ~=23.4 min, + 61Cu I=312 7=3.41 h; “*Cu I=1 7=9.73 min;

‘“lCu i=l 7=12.70 h; 66Cu I=1 ~=5.10 min.

isotope sk~ts/kfs [lo, 12-15, M] The isotope shift of 65Cu levels with respect to those of 63Cu are given in the

following table which lists the atomic configuration, the energy level, its energy, and the isotope shift, IS.

The hyperfine interaction constants for “3Cu and Wu levels are given in the following table which lists the atomic configuration, the level, its energy, the dipole and quadrupole interaction constants, A and B, for ““Cu and h5C~ respectively.

In units of lo-” cm-‘, the 3d”‘4s 2SI,2 ground state has values for the dipole interaction constant A for the indicated isotopes of: M’C~: 80.49, “*Cu: -50.195, 64Cu: -28.65, Mtcu: 37.10984, while for h4Cu in the 3d1(‘4p configuration A(2P~,zo)=-0.95, and A(2P,,z0)= -0.045.


s3cu %u Config. Level Energy A B A B

(cm-‘) (10-j cm-l) ( low3 cm-‘)

3d1’4s %,z 0 195.70 -- 209.64 --

3d1’4p zP 1/2O 30535 16.8 -- 18.2 --

2p3,2' 30784 6.512 -0.959. 6.957 -0.864

3ds4s4p ‘P 3/2O 40114 71.38 -1.26 76.46 -1.17

‘P 1/2O 40944 76 __ 81.5 --

4D3,2a 44544 0 0

3d1’5s 2s l/2

43137 29.4 -- 31.2 -- w

Laser schemes For 222-225 nm, doubling and mixing Nd:YAG pumped Rhodamine 610 and 590

dye laser [C] or Nd:YAG pumped frequency doubled (using BBO) Coumarin 440 dye laser; for 244-250 nm, Nd:YAG pumped frequency doubled Courmarin 500 dye laser; for 285.2 nm, Nd:YAG pumped frequency doubled Rhodamine 590 dye laser [Cl; for 302-305 nm, Nd:YAG pumped frequency doubled Rhodamine 610 dye laser; for 308 nm, XeCl excimer laser; for 310-328 nm, Nd:YAG pumped frequency doubled DCM dye laser; for 425.9 nm, Nd:YAG pumped Stilbene 420 dye laser; for 437-442 nm, Nd:YAG pumped Coumarin 440 dye laser; for 463.5 nm, Nd:YAG pumped Coumarin 460 dye laser.

Atom reservoirs and sources The methods used to atomize Cu for RIS and related studies have been: evaporation

of the sample by a hot rhenium filament [F]; sputtering by a pulsed argon ion beam [C, I-M]; evaporation by a focused laser beam [B]; by passing an aqueous salt solution through an air/acetylene analytical burner into a sample cell [HI; and by means of a glow discharge [A].

RIS references

[A] P. J. Savickas, K. R. Hess, R. K. Marcus and W. W. Harrison, Anal. Chem. 56, 817 (1984); K. R. Hess and W. W. Harrison, Anal. C/tern. 58, 1696 (1986).

[B] F. R. Verdun, G. Krier and J. F. Muller, Anal. Gem. 59, 1383 (1987). [C] P. Gelin, 0. Gobert, B. Dubreuil, J. L. Debrun and R. L. Inglebert, Studies on the analysis of trace

metallic elements in semiconductors using RIMS, in Resonance Ionization Spectroscopy 1988, Eds, T. B. Lucatorto and J. E. Parks, p.201. Institute of Physics, Bristol (1989).

[D] P. Gelin, J. L. Debrun, 0. Gobert, R. L. Ingelbert and B. Dubreuil, Nucl. Instrum. Methods B40/41, 290 (1989).

[E] 0. Gobert, Spectrometrie de masse par ionisation laser resonnante. Etude des processus multiphotoniques et applications a I’analyse des mattriaux solides, These, I’Universite d’OrlCans, unpublished (1989).

[F] E. C. Apel, J. E. Anderson, R. C. Estler, N. S. Nogar and C. M. Miller, Appl. Opt. 26, 1045 (1987). [G] C. M. Miller, N. S. Nogar, E. C. Apel and S. W. Downey, Resonance ionization mass spectrometry

at Los Alamos National Laboratory, in Resonance Ionization Spectroscopy 1986, Eds, G. S. Hurst and C. G. Morgan, p.109. Institute of Physics, Bristol (1987).

[H] P. R. Blazewicz, W. B. Whitten and J. M. Ramsey, Anal. Chem. 61. 1010 (1989). [I] J. E. Parks, D. W. Beekman, H. W. Schmitt and E. H. Taylor, Nucl. Instrum. Methods B lO/ll, 280

(1985). [J] J. E. Parks, Opt. News 12 (lo), 22 (1986). [K] J. E. Parks, D. W. Beekman, L. J. Moore, H. W. Schmitt, M. T. Spaar, E. H. Taylor, J. M. R.

Hutchinson and W. M. Fairbank Jr., Progress in analysis by sputter initiated resonance ionization spectroscopy, in Resonance Ionization Spectroscopy 1986, Eds, G. S. Hurst and C. G. Morgan, p.157. Institute of Physics, Bristol (1987).

[L] L. J. Moore, J. E. Parks, E. H. Taylor, D. W. Beekman and M. T. Spaar, Medical and biological applications of resonance ionization spectroscopy, in Resonnnce Ionization Spectroscopy 1986, Eds, G. S. Hurst and C. G. Morgan, p.239. Institute of Physics, Bristol (1987).

81,s) ,6:,-D

[M] R. Engleman, Jr., R. A. Keller, C. M. Miller, N. S. Nogar and J. A. Paisner, Nucl. htrum. Methods B ui, 448 (1987).

[l] J. Sugar and A. Musgrove, I, Phys. Chem. Refi Dtrta 19, 527 (1990). [2] W. L. Wiese and G. A, Martin, Atomic transition probabilities, in CRC Handbook of Chemirrry and

Physics 70th Edn. Eds, R. C. Weast and D. Lide, p.E-338. CRC Press, Boca Raton (1989). [3] A. L. Osherovich, G. L. Plekhotkina and V. R. Obidin, Opt. Spectrosc. (USSR) 90, 576 (1981). [4] J. Car&on, L. Sturesson and S. Svanberg, 2, Phys. I) 11, 287 (1989). {5] R. D. Cowan, T&e Theory of Atcmdc Stmsttm md Specs. U~~ve~it~ of Caiifornia Press, Berkeley

(1981). [6] Cal&a&d using the Hartree-Fock code with refativistic corrections of Ref. [S]. [7] H. Kerkhoff, G. Micali, K. Werner, A. Wolf and P. Zimmermann, 2. Phys. A 300, 115 (1981). [S] Yu. I. Malakhov, Opt. Spectrosc. (USSR) 44, 125 (1978). [9] N. E. Nalden, R. L. Martin and I. L. Barnes, Pure Appl. Chem. 55, 1119 (1983).

IlO] G. H. Fuller, 3. Phys. Chem. Re$ Dota 5, 835 (1976). fll] P. Raghavan, Atom. Da&t Nuci. Datu Tables 42, I89 (1989). [L2f S. Wagner, Z. Pkyx Ml, 122 (t95S). [13] M, Elbet and W. Fischer, Amt. Phys. jteipzig) f4, 78 (1964). [14] M. Elbel and W. Fischer, 2. Phys. 165, 151 (1961). [15] P. Brix, 2. Phys. 126, 725 (1949).


Data sheet for RIS/RIMS schemes Krypton

Kr Z = 36

Ground state [l] ls22s22p63s23p6 3d’%s24p6 ‘SO

First ionization potential [l] 112914.40 cm-l = 13.999606 eV

A considerable amount of effort has been put into developing RIS techniques for the measurement of krypton and its isotopes. The noble gas atoms are difficult to excite from their ground states with a single photon due to the large energy difference between their ground states and their first excited levels. HURST and his co-workers [A, B] developed a technique which employed four-wave mixing [C] to generate the vacuum UV radiation required for the first step of a scheme where the krypton atom is excited from its ground level to the 5s’[1/2]y,level. From this level it is excited to the 6p[1/2], level from which it is photo-ionized by IR from a Nd:YAG pump laser (a so-called o1 + o2 + o3 process). This is a highly selective scheme, with two resonant steps whose power level may be adjusted individually independent of the power in the photo-ionizing step. They were able to count 1000 atoms of 81Kr which was mixed with 2 x lo5 other krypton atoms and 1 x 10’” helium atoms through the use of an atom buncher and other elegant techniques. Commercial application of this method for geological dating purposes [D] (including pre-enrichment techniques) indicates a sensitivity for 81Kr in ground water of about 500 atoms per liter. TRICKL et al. [E] have used four-wave mixing to generate vacuum UV radiation to excite the krypton atom from the ground state to one of several of the odd parity levels which is then photo- ionized by a second more easily generated photon. These two-color two-photon schemes are called o1 + o2 processes. The availability of BBO doubling crystals has simplified various schemes involving the excitation of krypton from its ground state by a two- photon transition to an even parity excited state followed by photo-ionization by a third photon of the same wavelength (a so-called 2wi + o, process). Such schemes allow for the possibility of Doppler-free excitation. BUSHAW and WH~TAKER [F] used such a scheme to carry out Doppler-free RIS in 83Kr using the 6p[5/2], as the resonant level. GEOHAGAN et al. [G] used the overlap of the ArF laser output at 193 nm with the two-photon transition to the 6p[3/2], level to carry out this type of scheme while MILLER [H] used doubling in BBO to carry out a 2wi + o1 scheme for the 5p[5/2],, 5p[3/2],, and 5p[1/2],, levels. Schemes involving radiationless excitation to various metastable excited states are not included here because they are relatively inefficient. Also schemes involving N-photon transitions with N > 2 are not included because the high energy levels they require are likely to produce interferences from other elements and molecules. The measurement of small quantities of krypton isotopes are important as tracers in hydrological, oceanographic and atmospheric studies [I]. They could also be used to detect Pu in soil by means of 86Kr produced by neutron induced fission [J]. Note that for wavelengths below 200 nm vacuum wavelengths will be used while air wavelengths will be used for wavelengths above 200 nm in these data sheets. A Grotrian diagram of the RIS schemes in krypton is shown in Fig. 7 [l].

RIS schemes of type (w,+02) Two-photon two-color process consisting of a resonance step followed by photo-

ionization. A, = 94-124 nm, A2 = 266-560 nm [El.

Lifetimes and photo-ionization cross section from excited states In tabular form are listed the laser wavelength, A,, to the resonant level, the resonant

level, the lifetime, T, of the resonant level [3, E], an estimate of the laser power, P,,,,

358 E. B. SALOMAN

266 nm

t

560

355 212.5~1~.7

I

Fig. 7. Grotrian diagram of resonance ionization spectroscopy schemes in krypton.

Data for RIS schemes of type (o,+o,) [l-4, E]

required to saturate the resonant transition, the wavelength used [E] to photo-ionize the resonant state, X2, the photo-ionization cross section of the resonant level ES, 61, o, and an estimate of the energy, EWt, delivered during the lifetime of the resonant state required to saturate the photo-ionization.

RIS schemes of type (~~-t-u~+to~): [A, B, C] Three-color process consisting of two resonance steps followed by photo-ionization

by an IR photon. X,=116.5 nm. A2=558.0 nm. X3=1064 nm.


Data for RIS schemes of type (W,+(IEL+WJ) [I, 3, 4, 61

Lifetimes and photo-ionization cross section from excited states 7(5s’[1/2];)=3.11 ns [3], ~(6p[1/2],,)=72 ns [7]. The power in Al required to saturate the excitation to the 5s’[1/2]7 is 860 W/cm2. An

estimate of the energy required in A2 to saturate the second step from this level to the 6p[1/210 level, within the absorption bandwidth delivered while the first step is being pumped, is 1.7 X 10V3 mJ/cm2. The photo-ionization cross section of the 6p[1/2]e level by 1064 nm radiation is 14 x lo-r8 cm2 [8]. This corresponds to a laser energy requirement of 13 mJ/cm2 for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state.

RIS schemes of type (201+01): [F-H] One-color process consisting of a two-photon transition to the resonant level followed

by photo-ionization with a photon of the same color as those used for the initial step. X,=193-217 nm.

Data for RIS schemes of type (2o,+w,) [l]

Lifetimes and photo-ionization cross section from excited states [5, 7-111 Estimates have been made of the two-photon excitation cross sections for the 6p[3/212

level. A value of 2.4 X 1O-4y cm2s for a 25 cm-r laser line width was obtained [9] and values of 2.1 x lo-“” cm2s for a broad ArF laser line (140 cm-’ FWHM) and 5 x 1O-46 cm2s for a 300 Mhz line were estimated [G]. The table below lists the excited level, its lifetime, T, the wavelength used for photo-ionization (and two-photon excitation), X1, the photo-ionization cross section of the level for this wavelength, u, and an estimate of the energy required, E,,,, to obtain a photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state.

Isotope data [12-141 Stable isotopes: 7XKr (0.35%) I=O; “‘Kr (2.25%) I=O; X2Kr (11.6%) Z=O; H3Kr

(11.5%) 1=9/2; n4Kr (57.0%) I=O; n6Kr (17.3%) Z=O. Unstable isotopes: “Kr 1=1/2 7=35.04 h; X’Kr 1=7/2 ~=2.13 x 10” y; nsKr 1=9/2

~=10.72 y; X7Kr 1=5/2 ~=76 min.

360 E. B. SALOMAN

Isotope sh#s/hfs [15, 16, 17, E, F] The isotope shift of the indicated levels of the stable isotopes of Kr are given in the

following table relative to those of 86Kr.

Isotope shift (lo-” cm-l)

The %[3/2]; level is reported to have slightly smaller isotope shifts than the %‘[1/2]: level. For the 437.6 nm transition between the 5s[3/2]; and the 6p[1/2]0 levels the isotope shift (units 10e3 cm-‘) with respect to MKr are: 78Kr:-20.83; 80Kr:-15.24; 8zKr:-9.63; 84Kr: -4.90.

The Kr isotopes with even isotope mass number have no hyperfhre structure (I=O). The hfs interaction constants for the indicated levels in 83Kr are given in the following table.

Laser schemes For 94-124 nm, four-wave mixing techniques [C, E]; for 193.5 nm, ArF excimer

laser [G]; for 212-217 nm, Nd:YAG pumped frequency doubled (using BBO) Stilbene 420 dye laser [HI; for 266 nm, fourth harmonic of Nd:YAG; for 355 nm, third harmonic of Nd:YAG; for 558-560 nm, Nd:YAG pumped Rhodamine 590 dye laser.

Atom reservoirs and sources Krypton is an atomic gas at room temperature. Atomic bunching techniques [A, B]

are required to efficiently measure very small quantities of rare isotopes.

RIS references

[A] C. H. Chen, S. D. Kramer, S. L. Allman and G. S. Hurst, Appl. Phys. Lerr. 44, 640 (1984). [B] G. S. Hurst, et al., Rep. Prog. Phys. 48, 1333 (1985). [C] S. D. Kramer, C. H. Chen, M. G. Payne, G. S. Hurst and B. E. Lehmann, Appl. Opt. 22,327l (1983). [D] R. D. Willis, N. Thonnard, M. C. Wright, B. E. Lehmann and D. Rauber, Counting *‘Kr atoms in

groundwater using RIS-TOF, in Resonance Ionization Spectroscopy 1988, Eds, T. B. Lucatorto and J. E. Parks, p.213. Institute of Physics, Bristol (1989).

[E] T. Trick& M. J. J. Vrakking, E. Cromwell, Y. T. Lee and A. H. Kung, Phys. Rev. A 39, 2948 (1989).

RIM&US Data Service 361

[F] B. S. Bushaw and T. J. Whitaker, Doppler-free RIS of noble gases, in Resonance Ionization Spectroscopy 1984, Eds, G. S. Hurst and M. G. Payne, p. 330. Institute of Physics, Bristol (1984).

[G] D. B. Geohegan, A. W. McCown and J. G. Eden, Phys. Rev. A 33, 269 (1986). [H] J. C. Miller, Phys. Rev. A 40, 6969 (1989). [I] B. E. Lehmann and H. H. Loosli, Use of noble gas radioisotopes for environmental research, in

Resonance Ionization Spectroscopy 1984, Eds, G. S. Hurst and M. G. Payne, p. 219. Institute of Physics, Bristol (1984).

[J] C. H. Chen, G. S. Hurst and M. G. Payne, Resonance ionization spectroscopy: inert atom detection, in Progress in Atomic Spectroscopy Part C, Eds, H. J. Beyer and H. Kleinpoppen, p.115. Plenum, New York (1984).

Data references

[l] J. Sugar and A. Musgrove, J. Phys. Chem. Re$ Data (to be published). [2] J. Geiger, Z. Phys. A 282, 129 (1977). [3] E. Matthias, R. A. Rosenberg, E. D. Poliakoff, M. G. White, S.-T. Lee and D. A. Shirley, Chem.

Phys. Lett. 52, 239 (1977). [4] M. Aymar and M. Coulombe, Atom. Data Nucl. Data Tables 21, 537 (1978). [6] Calculated using the Hartree-Fock code with relativistic corrections of R. D. Cowan, The Theory of

Atomic Structure and Spectra. University of California Press, Berkeley (1981). [7] M. V. Fonseca and J. Campos, Phys. Rev. A 17, 1080 (1978). [8] T. N. Chang and Y. S. Kim, Phys. Rev. A 26, 2728 (1982). [9] J. Bokor, J. Zavelovich and C. K. Rhodes, Phys. Rev. A 21, 1453 (1980).

[lo] R. S. F. Chang, H. Horiguchi and D. W. Setser, J. Gem. Phys. 73, 778 (1980). [ll] B. D. Cannon, G. R. Janik, R. Ogorzalek-Loo, W. L. Glab and B. A. Bushaw, Photophysics of

metastable noble gas atoms, in Abstracts of the Workshop on Advanced Laser Technology for Chemical Measurements 911 May 1989, p.15, unpublished.

[12] N. E. Holden, R. L. Martin and I. L. Barnes, Pure Appf. Gem. 55, 1119 (1983). [13] P. Raghavan, Atom. Data Nucf. Data Tables 42, 189 (1989). [14] J. Miiller, Nucl. Data Sheets 46, 487 (1985); B. Singh and D. A. Viggars, Nucl. Data Sheets 37, 393

(1982); J. W. Tepel, Nucl. Data Sheets 30, 501 (1980). [15] D. A. Jackson, J. Opt. Sot. Am. 70, 1139 (1980). [16] D. A. Jackson, J. Opt. Sot. Am. 67, 1638 (1977). (171 B. D. Cannon and G. R. Janik, Phys. Rev. A 42, 397 (1990).


Data sheet for RIS/RIMS schemes Magnesium

Mg z = 12

Ground state [l] ls22,r22p63s2 ‘S,

First ionization potential [2] 61671.05 cm-i = 7.646238 eV

Several different types of RIS schemes are available for the analysis of magnesium. The simplest was applied by GELIN et al. [A, B]. They used a one-color two-photon scheme in which the first photon excited the Mg atom from its ground state to the 3s3p ‘Plo resonant level. The atom was then photo-ionized from this level by a second photon from the same laser (a so called wl+ol process). They report detection limits for Mg of 0.3 ppm for a one-shot analog mode and 1 ppb for an 18 000 shot counting mode of data collection. A related scheme which makes use of the increased ionization efficiency obtained by exciting an auto-ionizing state was used by BRADLEY et al. [Cl, BONNANO et al. [D], and GOBERT [El. In this scheme the Mg atom is again excited to the 3s3p iP10 resonant level by the first photon. The atom is then ionized by exciting from this level to the 3p2 ‘5, auto-ionizing level with a photon of a second color (a so called u~+w~’ 2 process). In addition to its larger ionization efficiency, this scheme allows separate optimization of the powers of the lasers driving each step and provides enhanced selectivity due to having two resonance steps (even though one step is to an auto-ionizing level which is broad compared to the line width of transitions between discrete levels). If even more selectivity is required, together with the ability to optimize the laser power for each step, a three-color three-photon scheme is proposed. As before, the atom is excited from its ground state to the 3s3p lpi“ level by the first photon, then it is excited from this level to the 3s4d ‘D2 level by the second photon, and then photo-ionized from that level by IR radiation from a Nd:YAG laser (so called oI+w2+wj process). APEL et al. [F] have demonstrated schemes which could be used for Doppler-free excitation. The atom is excited from its ground state to either the 3~6s ‘SC, or 3s5d ID2 levels by a two-photon transition and the resonant level is then photo-ionized by a third photon from the same laser (so called 2wifwi process). These schemes have the simplicity of using a single laser, but the high powers they require will likely limit the selectivity which can be obtained. Analysis of magnesium is important in the characterization of alloys and in the determination of impurities in semiconductor materials. A Grotrian diagram of the RIS schemes in magnesium is shown in Fig. 8 [l, D].

RZS schemes of type (w,+o,): [A, B] One-color two-photon process consisting of a resonance step followed by photo-

ionization with a photon of the same color as for the initial step. X,=285.2 nm.

Data for RIS schemes of type (qfo,) [l, 31

Lifetimes and photo-ionization cross section from excited state [3-5, E, G] 43~3~ lPIo)=2.01 ns. The power in X1 required to saturate the excitation to the 3s3p ‘Pi” resonant level

is 96 W/cm*. The photo-ionization cross section from this level for 285.2 nm radiation has been calculated to be 62 x 1O-‘x cm* and measured to be

364 E. B. SALOMAN

1 nm 1 3fG&+L51 cm-’

11 285.2 nm

nm 355.1 nm

I I 0 cm-’

Fig. 8. Grotrian diagram of resonance ionization spectroscopy schemes in magnesium.

45 (- 50% +lOO%) x 10-18 cm

2. These values correspond to a laser energy requirement of

11 mJ/cm2 for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state.

RIS schemes of type (q+oA:): [C, D, E] Two-photon two-color process consisting of a transition to the resonant level followed

by excitation of an auto-ionizing level. X1=285.2 nm, A*:=301 nm.

Data for RIS schemes of type (q+oA~\:) [I, 3, 5, D]

Lifetimes, photo-ionization cross section, and auto-ionization rate from excited states [4, 5, C, E]

~(3s3p ‘P1”)=2.01 ns. The power in AI required to saturate the excitation to the 3s3p rPlo resonant level

is 96 W/cm2. The photo-ionization cross section from this level for 301 nm radiation has been calculated to be 419 X lo-In cm2 [5] in agreement with experimental

determinations of 800 + 400 x 10-r” cm2 [C] and 300 (_ 5oo/ +laoYI) x 10-rx cm2 [El. This

corresponds to a laser energy requirement of 1.6 mJ/cm* for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state. The auto-ionization rate is calculated to be 6.6 x 1Or3 s-l so the auto-ionization rate will not limit the process.

RIS schemes of type (0, + wz+ w3) Three-color process consisting of two resonance steps followed by photo-ionization

by an infrared photon. h,=285.2 nm, A2=552.8 nm, A3=1064 nm.


Data for RIS scheme of type (0, +02 t 03) [ 1, 31

Lifetimes and photo-ionization cross section from excited states [3, 4, 61 ~(3s3p ‘P1”)=2.01 ns, T(3s4d ‘&)=55 ns. The power in Al required to saturate the excitation to the 3s3p rPlo level is 96 W/cm*.

An estimate of the energy required in A2 to saturate the second step from this level to the 3s4d ID2 level, within the absorption bandwidth delivered while the first step is being pumped is 6.8 x 10m4 ml/cm*. The photo-ionization cross section of the 3s4d ‘D2 level by 1064 nm radiation has been calculated to be 34 x lo-l8 cm*. This corresponds to a laser energy requirement of 5.5 mJ/cm* for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state.

RIS schemes of type (2q+w,): [F] One-color process consisting of a two-photon transition to the resonant level followed

by photo-ionization with a third photon of same color as used for the initial step. X,=355.1 or 355.9 nm.

Data for RIS schemes of type (20, to,) [l]

Lifetimes and photo-ionization cross section from excited states [4, 6, 7, F] T(3s5d ID*)=46 ns, ~(3.~6s ‘So)=204 ns. A calculation of the two-photon excitation cross section for these transitions reports

a value of 1.2 x 1O-49 cm*s for the 3s5d ‘D2 level and 6.8 X lO+l cm*s for the 3~6s ‘5, level. Calculations of the photo-ionization cross sections from these levels by 355 nm radiation are uncertain but indicate a relatively low cross section particularly for the 3s6F i& level. It has been reported [F] that the ratio of signal intensity of the ‘D2 to the ‘S,, was about 3:l.

Isotope data [8-lo] Stable isotopes: 24Mg (78.99%) Z=O; 2sMg (10.00%) 1=5/2; 26Mg (11.01%) Z=O. Unstable isotopes: *‘Mg I=112 ~=9.462 min; *aMg I=0 7=20.90 h.

Isotope shiftslhfs [ 1 l-131 The isotope shift of the indicated levels of the Mg isotopes are given in the following

table relative to the level in 24Mg.

Isotope shift (lo-” cm-‘)

366 E. B. SALOMAN

The Mg isotopes with even isotope mass number have no hyperfine structure (I=O). The hfs interaction constants for the 3s3p ‘Pi” level in 25Mg are: A=-0.26 X 10V3 cm-i and 0.53 x 10m3 cm-’ > B > 0.

Laser schemes For 285.2 nm, Nd:YAG pumped frequency doubled Rhodamine 590 dye laser; for

301 nm, Nd:YAG pumped frequency doubled Rhodamine 610 dye laser; for 355-356 nm, Nd:YAG pumped TMQ dye laser; for 552.8 nm, Nd:YAG pumped Rhodamine 590 dye laser; for 1064 nm, Nd:YAG direct IR.

Atom reservoirs and sources Several methods have been used to produce magnesium atoms for RIS studies.

These include evaporation from a tungsten filament [F] (a tungsten filament was reported to be 20 times more effective than rhenium), evaporation from a heated Mg ribbon [D], and sputtering a solid sample with an argon ion beam [A, E].

RIS references

[A] P. Gelin, 0. Gobcrt, B. Dubreuil, J. L. Debrun and R. L. Inglebert, Studies on the analysis of trace metallic elements in semiconductors using RIMS, in Resonance Ionization Spectroscopy 1988, Eds, T. B. Lucatorto and J. E. Parks, p.201. Institute of Physics, Bristol (1989).

[B] P. Gelin, J. L. Debrun, 0. Gobert, R. L. Inglebert and B. Dubreuil, Nucf. Instrum. Metho& B 40/41, 290 (1989).

[C] D. J. Bradley, C. H. Dugan, P. Ewart and A. F. Purdie, Phys. Rev. A 13, 1416 (1976). [D] R. E. Bonanno, C. W. Clark and T. B. Lucatorto, fhys. Rev. A 34, 2082 (1986). [E] 0. Gobert, SpectromCtrie de masse par ionisation laser resonnante. Etude des processus multiphotoniques

et applications B I’analyse des materiaux solides, These, I’Universite d’orleans (1989). [F] E. C. Apel, J. E. Anderson, R. C. Estler, N. S. Nogar and C. M. Miller, Appl. Opr. 26, 1045 (1987). [G] B. Dubreuil, private communication (1990). The cross section reported in Ref. [A] is incorrect.

Data references

[l] W. C. Martin and R. Zalubas, J. Whys. Chem. Ref. Data 9, 1 (1980). (21 V. Kaufman and W. C. Martin, J. Phys. Chem. Ref. Data M (1991). [3] W. L. Wiese and G. A. Martin, Atomic Transition probabilities, in CRC Handbook of Chemistry and

Physics, 70th Edn. Eds, R. C. Weast and D. Lide, p.E-338. CRC Press, Boca Raton (1989). [4] Compilation of experimental lifetime measurements in Ref. [5]. [5] R. Moccia and P. Spixxo, 1. Phys. B 21, 1133 (1988). (61 Calculated using the Hartree-Fock code with relativistic corrections of R. D. Cowan, The Theory of

Atomic Sfructure and Spectra, University of California Press, Berkeley (1981). [7] R. Moccia and P. Spiro, J. Phys. B 21, 1145 (1988). [8] N. E. Holden, R. L. Martin and I. L. Barnes, Pure Appf. Chem. 55. 1119 (1983). [9] P. Raghavan, Atom. Data Nucl. Data Tables 42. 189 (1989).

[lo] P. M. Endt and C. van der Leun, Nucl. Phys. A 310, 1 (1978). [ll] L. Hallstadius and J. E. Hansen, Z. Phys. A 285, 365 (1978). [12] L. Hallstadius, Z. Phys. A 291, 203 (1979). [13] H.-J. Kluge and H. Sauter, Z. Phys. 270, 295 (1974).


Data sheet for RIWRIMS schemes Mercury

Hs 2=80

Ground state [l] ls22s22p63s23p6 3d104s24p64d’04f45s2 5p65d’06s2 ‘So


RIS has been applied to the analysis of mercury by several groups. MIZIOLEK [A] used a two-photon excitation from the 6.r2 ‘S,-, ground state to the 7s ‘So excited level followed by photo-ionization using a third photon from the same laser (a so called 2wl+01 process). He reported a detection limit of 5 x lo8 atoms/cm3 limited by noise ion production from his cell windows and by the nonresonant multiphoton ionization of impurities. He estimates that by using a time-of-flight mass spectrometer and a saturated volume of 10 -4 cm3, detection limits lower than 10%m3 should be attainable. DYER et al. [B, C] carried out isotopically selective RIS using a multistep excitation process. The mercury atoms were excited from their ground state to the 6p 3P10 resonant level by the first laser, then excited to the 8s ‘S,, level by the second laser. The atom is then either photo-ionized from this level by using the second harmonic of the Nd:YAG pump laser or excited to an auto-ionizing state (so called O1+W2+O3 or 01+W2+WA’ 3 processes). These processes allow for isotopically selective excitation in addition to the high atomic selectivity of several relatively low-powered discrete steps. BUSHAW [D] excited mercury atoms from their ground state to the 6p 3P10 level as above and then used the second laser to excite the 7s 3S1 level. Another photon from the second laser then photo-ionized the atom with the assistance of a nearby auto-ionizing level in the continuum (a so called wI+wZ+O~ process). This scheme has the advantages of the preceeding scheme. He reports a sensitivity of 220 fg in a 100 ml air sample or 2.2 pg/l. CRANE et al. [E] investigated several RIS schemes with the object of designing efficient isotope separation schemes for mercury. Those considered here begin with the excitation of the atoms from their ground state to the 6p 3P10 resonant level. One scheme follows this with excitation to an auto-ionizing state (a so called wl+wA: p recess) using 197 nm radiation which though somewhat difficult to obtain is becoming available in many laboratories. The other schemes follow the first step with an excitation to a level of the 7d configuration followed by photo- ionization using the direct IR of a Nd:YAG (a so called 01+02+w3 process). This process also has the advantages of the others with several discrete steps. The analysis of trace quantities of mercury is important in monitoring for environmentally dangerous quantities of this element in the air, water and food supply. A Grotrian diagram of the RIS schemes in mercury is shown in Fig. 9 [l-3, E]. The energy values quoted are for 198Hg.

RIS schemes of type (2w,+o,): [A] One-color process consisting of a two-photon transition to the resonant level followed

by photo-ionization with a photon of the same color as used in the initial step. h,=312.8 nm.

Data for RIS schemes of type (2w,+o,) [2]

368 E. B. SALOMAN

90099 cni

887s IS,

63828 cm-l

285.7

I f

8~78 h?nq.g

nm 435. 95, ;;;r;

nm

_LJ_ I

I I 312.8 nm

856~ “P; 39412 cm-’

u/ 84184 cri’

53

312.8 nm

253.7 nm 312.8 nm

_ 0 cm-’

I@ ‘s 0

Fig. 9. Grotrian diagram of resonance ionization spectroscopy schemes in mercury.

Lifetimes and photo-ionization cross section from excited state ~(7s ISo) = 32 ns [4]. For photo-ionization to the continuum by 312.8 nm radiation a calculation by means

of a Hartree-Fock code [5] for the 7s ‘S,, level gives an estimate for the cross section of 0.66 x lo-i8 cm*. This corresponds to a laser energy requirement of 970 ml/cm2 for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state. It has been reported [A] that the power necessary to have the two-photon transition occur is sufficient to saturate the photo-ionization.

RZS scheme of type (o,+wA$: [E] Two-color two-photon process consisting of a resonance step followed by excitation

to an auto-ionizing state. X,=253.7 nm, &=197.2 nm.

Data for RIS schemes of type (o,+oAi) [l, 2, 6, E]

x (-0 Low. Level El t--9 Ren. Leval E, (cm-l) f,

Xl 253.6507 6s2 %a 0.0000 686 3P,O 6~ !

sp,* 39412.4585 0.0247 197.2267 6s6p 39412.4585 ‘Pn 90099. 0.27

Lifetime and auto-ionization rates from excited state [6, 71 ~(ti6p 3P10)=117 ns. The power in A, required to saturate the excitation to the 6.~6~ 3P,o level is estimated

to be 36 W/cm*. An estimate of the energy, E,,,, needed in the 197.2 nm radiation to saturate the second step of this process going to the 6p2 3Po auto-ionizing level within the absorption bandwidth delivered while the first step is being pumped, is calculated to be 0.28 mJ/cm*. Using data given in Ref. [E] a value of 0.3 mJ/cm* is obtained for the 197.23 nm transition. Calculations indicate that the auto-ionization rate for the 6p2 “P,, level is 2.4 x lOI s-l, so the auto-ionization rate will not limit the RIS processes.


RIS schemes of type (wI+02+w& (ol+02+o_J, or (01+02+oAj): [B-E] Two- or three-color process consisting of two resonance steps followed by photo-

ionization or by excitation to an auto-ionizing state. Photo-ionization may be enhanced by nearby auto-ionizing states. h1=253.7 nm.

Data for RIS schemes of type (w,+~~~~+uJ,(w~+~~+w,),or (w,+w,+w*:) [l-3,6, E]

Low. Lsvel El (cm-l) Rer. Lsvel f,

Xl 253.6507 6s2 IS, 0.0000 39412.4585 0.0247 x2 265.2043 6s6p 3P1°

6s6p 3Pl0 39412.4585 6974 3D2 77108.0168 0.068

Xl 253.6507 6s' 'S, 0.0000 6s6p 3P10 39412.4585 0.0247 265.3683 6s6p 3P1° 39412.4585 6s7d 3D, 77084.7224 0.037

I 4 x2 253.6507 265.5130 6s6p 6s' 'So 3Pi0 39412.4585 0.0000 6s6p 6s7d 3P,O 'D2 39412.4585 77064.1854 0.0247 0.019

Xl 253.6507 6s' 'S, 0.0000 6s6p 3P10 39412.4585 0.0247 -42 285.6939 6s6p 3P10 39412.4585 6s8s Is, 74404.676 4.X-4

4 253.6507 6s2 'So 0.0000 6s6p JP,' 39412.4585 0.0247 x2 285.6939 6s6p 3Pl0 39412.4585 6s8s Is, 74404.676 4.5E-4 x3 696.41 6s8s Is, 74404.676 5de6s26p 3P10 88760. 0.187

Xl 253.6507 6s2 'S, 0.0000 6s6p 3P10 39412.4585 0.0247 435.8337 6S6P 3P,O 39412.4585 6~7s 3S, 62350.5411 0.159

Lifetimes and photo-ionization cross section from excited state [4, 6-8, E] ~(6s6p 3P,“)=117 ns; ~(6s7s l&)=32 ns; ~(6.~7s 3S1)=8.0 ns. T(6s7d ‘&)=35 ns; T(6s7d 3D2)=18.1 ns; T(6s7d 301)=13.4 ns; ~(6.~8s ‘&)=80 ns. The power in hl required to saturate the excitation to the 6.~6~ 3P10 level is estimated

to be 36 W/cm*. An estimate of the energy, E,,*, needed in A2 to saturate the second step of these processes going to discrete excited states within the absorption bandwidth delivered while the first step is being pumped, is given in the following table for the designated transition wavelengths.

For the excitation from the 6s8s IS,, level to the 5dy6s26p -7P,o auto-ionizing level by 696.41 nm light the corresponding estimate of saturation energy is 23 mJ/cm*. Calculations indicate that the auto-ionization rate for the 5d‘&*6p 3P,o is 5.3 x lOI s-l, so the auto-ionization rate will not limit the RIS process. The calculated photo- ionization cross section u from the indicated discrete level by radiation of the wavelength A and an estimate of the laser energy, Esat, required for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state is given in the following table.

Isotope data [9, lo] Stable isotopes: IyhHg (0.15%) I=O; lyxHg (10.1%) I=O; lyyHg (17.0%) I= l/2; *‘“‘Hg

(23.1%) I=O; 20’Hg (13.2%) 1=3/2; *‘12Hg (29.65%) I=O; 2’MHg (6.8%) f=O.

370 E. B. SALOMAN

* The photo-ionization of the 4~7s 3S, level by 435.83 nm fight has been reported to be assisted by auto- ionization in the wings of the Sd%r*Sp 3P10 resonance [D]. A rough calculation suggests that this resonance would not signifi~tly reduce the required saturation energy.

h In agreement with value of 13.5 ztz 2.1 x lO-LR cm2 reported in Ref. [E].

Unstable isotopes: rY3Hg I=312 ~=3.5 h; ly5Hg I=112 7=9.5 h; lg7Hg I=112 r=64.1 h; *03Hg f=5/2 r=46.59 d.

The isotope shifts of the indicated levels of the stable mercury isotopes are listed in the following table relative to 198Hg.

Isotope shift (lo-” cm-r)

Atomic Level

Isotope Mass Number 198 199 200 201 202 204

6s’ ‘S 0 -138.7 0 21.4 161.2 214.9 339.0 514.2

6s6p 3P10 - 0.8 0 0.1 0.9 1.2 1.9 2.9

6~7s 3S. - 24.4 0 3.8 28.4 37.9 59.7 90.5 _ 697s ‘S, - 25.2 0 3.9 29.3 39.1 61.6 93.4

6~x8s %, - 17.6 0 2.7 20.5 27.3 43.1 65.4

6s7d ‘D., - 11.6 0 13.5 28.4 43.1

The isotopes with even isotope mass number have no hyperfine structure. The hyperfine structure interaction constants for the 6s6p 3P10 level for the indicated isotopes are given in the following table.

Hype&e interaction constants (lo-” cm-‘)

Isotope Mass I

Dipole hfs Constant Quadrupole hfs Constant Number A B

193 -204.6 16

195 527.480

197 513.444

199 492.142

201 -181.9448 - 9.34336

lh6.494 - 8.312

The hyperfine structure splittings for the indicated levels of the stable odd isotopes of mercury are given in the following table where AE(F,F) indicates the splitting between the F and I: hyperfne levels.

RIM/RIS Data Service

Hyperfine structure splittings (10e3 cm-‘)

AE(5/2,3/2)--179.0

AE(5/2,3/2)- 68.5

Laser schemes For 197.4 nm, Nd:YAG pumped Rhodamine 590 dye laser output at 573.3 nm

Raman shifted in H2 taking the eighth anti-Stokes order [El; for 253.7 or 265.2-265.5 nm, Nd:YAG pumped frequency doubled Coumarin 500 dye laser; for 285.7 nm, Nd:YAG pumped frequency doubled Rhodamine 590 dye laser; for 312.8 nm, Nd:YAG pumped frequency doubled DCM dye laser [A]; for 435.9 nm, Nd:YAG pumped Coumarin 440 dye laser; for 532 nm, second harmonic of Nd:YAG; for 696.4 nm, Nd:YAG pumped LDS 698 dye laser; for 1064 nm, Nd:YAG direct IR.

Atom reservoirs and sources Mercury atoms present as an environmental impurity in the air or released by heat

from a surface it is adsorbed upon.

RIS references

[A] A. W. Miziolek, Anal. Chem. 53, 118 (1981). [B] P. Dyer, G. C. Baldwin, C. Kittrell. D. G. Imre and E. Abramson, Appl. Phys. Lert. 42, 311 (1983). [C] P. Dyer, G. C. Baldwin, A. M. Sabbas, C. Kittrell, E. L. Schweitzer, E. Abramson and D. G. Imre,

J. Appl. Pbys. 58, 2431 (1985). [D] B. A. Bushaw, Anal. Chem. 57, 2397 (1985). [El J. K. Crane, G. V. Erbert. J. A. Paisner, H. L. Chen, Z. Chiba, R. G. Beeler, R. Combs and S. D.

Mostek, The application of atomic vapor laser isotope separation to the enrichment of Resonance Ionization Spectroscopy 1986, Eds, G. S. Hurst and C. G. Morgan, p.251. Physics, Bristol (1987).

Data references

mercury, in Institute of

[l] C. E. Moore, Atomic Energy Levels, National Standards Reference Data Service (U.S. Nat. Bur. Stand.) NSRDS-NBS 35 Vol. 3 (1971).

[2] V. Kaufman, J. Opr. Sot. Am. 52, 866 (1962). [3] S. Gerstenkom, J. J. Labarthe and J. Verges, Phys. Scripta 15, 167 (1977). [4] E. C. Benck, J. E. Lawler and J. T. Dakin, J. Opf. Sot. Am. B 6, 11 (1989).

372 E. B. SALOMAN

[5] R. D. Cowan, The Theory of Atomic Srructure and Spectra. University of California Press, Berkeley (1981).

[6] Calculation using Hartree-Fock code of Ref. [5]. [7] J. S. Deech and W. E. Baylis, Can. J. Phys. 49, 90 (1971). [8] M. Chantepie, B. Laniepce and J. Landais, Opt. Commun. 18, 354 (1976). (91 N. E. Holden, R. L. Martin and I. L. Barnes, Pure Appl. Chem. 55, 1119 (1983).

[lo] G. H. Fuller, J. phys. Gem. Ref. Data 5, 835 (1976).


Data sheet for RWRIMS schemes Nickel

Ni 2=28

Ground state [l] ls22s22p63s23p6 3dg4s2 3F4


RIMS has been applied to the analysis of nickel by several groups. All used one- color two-photon schemes in which the atom was excited from either the ground state or a thermally populated low-lying level to a resonant state by the first photon followed by photo-ionization by a second photon of the same color (a so-called o1 + w1 process). FASSETI et al. [A] used thermal atomization and schemes in which the excitation was achieved with photons in the 294-304 nm range. MOORE et al. [B] also used thermal atomization in studying a multielement sample which included nickel. Their schemes included some with excitation in the 282-287 nm range in addition to those of Ref. [A]. GELIN er al. [C] used argon ion sputtering atomization and schemes with excitation in the 28CL305 nm range. Calculations indicate that the photo-ionization cross sections from the states reached by these schemes are rather low, so these schemes are expected to be inefficient. GELIN et al. also used excitation in the 221-236 nm range. Calculations indicate that many of the states reached by photons in this range have significant photo-ionization cross sections and therefore these schemes should be more efficient. Without specifying which line was used, they claim a detection limit for Ni of 10 ppm for real time measurements and 30 ppb for counting 18 000 shots [D]. In work reported earlier [El, this group used the 230.1 nm line. To provide a more selective and more efficient scheme, a three-color three-photon scheme is proposed (a so called w1 + w2 + o3 process). The atom is excited by the first photon

262-264 nm h221-235 nm

294-304 nm

,;a,,,,,,,,,,,,,,,,,,,,,,

30 SC.30 DZ I. D3. Gs rl,3

3 d So "d F33. pa sd F4.3. x3%1

33611 cm-‘

36601 c&' 221-235 nm

262-264 nrn 294-304 nm 299.3 nn

Fig. 10. Grotrian diagram of resonance ionization spectroscopy schemes in nickel.

374 E. B. SALOMAN

from the thermally populated a 3D3 level to the 3F2” level, then this level is excited by the second photon to the f 3G3 level which is then photo-ionized by IR radiation from a Nd:YAG pump laser. This scheme allows the intensities of the lasers driving each step to be individually optimized while having the photo-ionization take place from a state with a large cross section for the IR radiation. Analysis of nickel should be important in the study of alloys, semiconductors, and in biological systems where it constitutes an essential trace element [F]. A Grotrian diagram of the RIS schemes in nickel is shown in Fig. 10 [l, 21.

RIS schemes of type ( wI + 0,) with Al in the range 282-284 nm or 294304 nm One-color two-photon process conbisting of a resonance step (from the ground state

or a thermally populated low-lying level) followed by photo-ionization. X1 between 282 and 284 nm or 292 and 304 nm [A-C].

Data for RIS schemes of type (o,+o,) in this wavelength range [I, 3, Al

Res. Level E, (cd) f, Rs

282.1289 a 'D, 204.786 Y ‘F3’ 35639.148 5.83-3

283.4545 a 3F3 1332.153 Y ‘D,’ 36600.805 5.73-4

294.3910 a ‘D3 204.786 Y 3Dz* 34163.29 9.93-3 5.0

298.1644 a 3D, 879.813 Y 3D~' 34408.574 0.022 2.6

298.4128 a 'F, 0.000 Y 3D30 33500.854 6.93-3 4.3

299.2590 a ‘D3 204.786 SF,’ 33610.916 5.2E-3 9.4

299.4450 a 'D, 204.786 z ‘G,’ 33590.159 0.015 3.3

300.2482 a ‘D, 204.786 Y 3D3* 33500.854 0.11 90

300.3618 a 3D, 879.813 Y 3D,’ 34163.29 0.094 1.3

301.1998 a 'D, 3409.925 Y 'D,' 36600.805 0.18 0.38

301.9140 a 3F, 0.000 3F30 33112.368 6.93-3 11

303.1864 a 3F, 0.000 3F,8 32973.414 2.43-3 2.2

303.7929 33112.368 0.039 3.2

Lifetimes and photo-ionization cross section from excited states in this wavelength range

In tabular form are listed the laser wavelength, X1, to the resonant level, the lower level, the resonant level, the lifetime, T, of the resonant level [3-51, an estimate of the laser power, P,,,, required to saturate the resonant transition, the photo-ionization

cross section of the resonant level, u, for an o1 + o1 scheme calculated by means of

a Hartree-Fock code [6], and an estimate of the energy, E,,,, delivered during the lifetime of the resonant state required to saturate the photo-ionization.

Included in this table is the relative strength (RS) of the RIS line reported in Ref. [A].

Low. Level Res. Level

II 294.3910 a 3D3 Y 3Dz0 11 660 0.39 1700 II

298.1644 a 3D, Y 3D~0 7.2 380 0.42 1600

298.4128 a 3F, Y 3D3D 10 1100 0.35 1900

299.2590 a 3D3 3F20 8.2 1700 0.33 2000

299.4450 a 3D3 z IG,' 98 88 9.OE-3 74000


300.2482 a 3D, Y =Ds' 10 93 0.35 1900

300.3618 a 3D, Y 3Dzo 11 97 0.39 1700

301.1998 a 'D, Y 'Dz' 7.1 79 0.38 1700

301.9140 a 'F, 3F30 9.2 1200 0.32 2100

303.1864 a 3F, SF,* 16 2600 0.30 2200

303.7929 a 3D. 9.2 270 0.32 2000

RIS schemes of type (w,+ wI) with Al in the range 221-235 nm One-color two-photon process consisting of a resonance step (from the ground state

or a thermally populated low-lying level) followed by photo-ionization. AI between 221 and 235 nm [C, D].

Data for RIS schemes of type (w,+o,) in this wavelength range [I, 31

law. Level El (em-‘) Rec. Iavel E, (cm-') f,

221.2150 a 3F3 1332.153 x 3P20 46522.965 3.1E-3

222.1940 a 3F, 2216.519 x 3P10 47208.228 9.63-3

223.0957 a 3D, 1713.080 x 3P2* 46522.965 6.5E-3

224.4525 a 3D, 879.813 JF," 45418.858 0.029

225.1487 a 3D, 879.813 3F3Q 45281.152 4.33-3

225.3569 a 'D, 204.786 3Gj0 44565.10 0.015

225.4800 a 3FA 0.000 J-4'* 44366.10 7.3&3

225.8148 a 3D3 204.786 3D,O 44475.158 9.4E-3

225.9563 a 3D, 879.813 3D10 45122.460 9.1%3

226.1427 a 3F, 0.000 SD,' 44206.185 5.43-3

226.6349 a 3D3 204.786 3Gq0 44314.980 2.33-3

226.7556 a 3F3 1332.153 3F,O 45418.858 4.43-3

227.1953 a 3D3 204.786 'D,' 44206.185 3.83-3

227.4662 a 3F3 1332.153 3F,O 45281.152 4.OE-3

228.7321 a 3D, 1713.080 3F20 45418.858 0.024

228.8394 a 3D, 879.813 3G," 44565.10 8.93-3

228.9984 a 3F, 0.000 J-3"* 43654.974 0.13

229.3116 a 3D, 879.813 44475.158 0.030

230.0778 a 3D3 204.786 J-3'* 43654.974 0.060

230.2941 a 3D, 1713.080 3D1° 45122.460 0.036

230.7353 a 3D, 879.813 44206.185 0.017

231.2340 a 'F, 1332.153 3G30 44565.10 0.44

231.3978 a 3F2 2216.519 3F20 45418.858 0.40

231.7161 a 3F3 1332.153 3D20 44475.158 0.22

232.0031 a 'F, 0.000 3Gq0 43089.636 0.69

232.1378 a 3F, 2216.519 3F30 45281.152 0.63

232.4654 a 'Fa 1332.153 J-4"* 44336.10 0.019

232.5797 a 'F, 1332.153 3GS0 44314.980 0.37 __

376 E. B. SALOMAN

232.9965 a ‘Fz 2216.519 sD1o 45122.460 0.26

234.5540 a ‘F, 0.000 3Da0 42621.048 0.14

234.6629 a 'F3 1332.153 3P2* 43933.428 0.033

234.7510 a 'F, 0.000 42585.296 0.018

II 234.8733 a 'D. 204.786 42767.900 0.018

* The L-S-coupling designation of this odd parity term was not provided in Ref. [l], and following the notation of that work, is not provided here.

Lifetimes and photo-ionization cross section from excited states in this wavelength range

In tabular form are listed the laser wavelength, hi, to the resonant level, the lower level, the resonant level, the energy of the resonant level, E,, (to avoid ambiguities in their designation), the lifetime, 7, of the resonant level from Ref. [3] and a calculation by means of a Hartree-Fock code [6], an estimate of the laser power, Psat, required to saturate the resonant transition, the photo-ionization cross section of the resonant level, CT, for an w1 + o1 scheme calculated by means of a Hartree-Fock code [6], and an estimate of the energy, ESat, delivered during the lifetime of the resonant state required to saturate the photo-ionization.

Low. Level Res. Level E, T P (cm-')

aat E (ns) (W/cm2) (lo- % cm2) (mJzm2

221.2150 a ‘F3 x sp,* 46523 9.1 4800 13 69

222.1940 a 3F2 x 3P10 47208 7.1 1600 13 69

223.0957 a 'D, 46523 9.1 5100 13 68

224.4525 a '0, 3F20 45419 1.7 3700 4.4 200

225.1487 a 'D, 3F3D 45281 1.4 42000 5.7 150

225.3569 a 'Da 3Ga0 44565 0.90 14000 8.8 100

225.4800 a 'F, J4' 44336 6.1 4000 8.8 100

225.8148 a '0, 3D2* 44475 2.8 4900 5.7 150

225.9563 a 'D, JD,' 45122 2.0 5800 6.9 130

226.1427 a ‘F, 5D,’ 44206 7.3 3500 14 63

226.6349 a ‘Da SG,” 44315 2.1 47000 8.8 100

226.7556 a ‘F, 3F2’ 45419 1.7 17000 4.4 200

227.1953 a 'Da SD,' 44206 7.3 6200 14 63

227.4662 a ‘F, 'Fae 45281 1.4 31000 5.7 150

228.7321 a ‘D, 3F20 45419 1.7 7200 4.4 200

228.8394 a 3D2 sG3* 44565 0.90 30000 8.8 99

228.9984 a ‘F, J-3' 43655 3.5 300 8.3 100

229.3116 a 3D2 3D20 44475 2.8 2000 5.7 150

230.0778 a 'DI J-3' 43655 3.5 820 8.3 100

230.2941 a ‘D1 sD1* 45122 2.0 2400 6.9 130

230.7353 a 'D, SD30 44206 7.3 1800 14 62

231.2340 a 'F3 3Ga0 44565 0.90 430 8.8 98

231.3978 a 'F2 3F20 45419 1.7 250 4.4 200

231.7161 a ‘F, 3D20 44475 2.8 200 5.7 150


232.0031 a sF, 3GsO 43090 1.2 250 9.1 94

232.1378 a 3Fz 3F30 45281 1.4 260 5.7 150

232.4654 a 3F3 J-4' 44336 6.1 1900 8.8 97

232.5797 a 3F3 sG,- 44315 2.1 280 8.8 97

232.9965 a 3F, 3D,O 45122 2.0 190 6.9 120

234.5540 a 3Fh 3D30 42621 5.0 180 13 65

234.6629 a 3F3 3P20 43933 20 180 10 a5

234.7510 a 3F, 3Fq0 42585 4.4 2000 1.4 600

234.8733 a 3D3 3F," 42768 6.0 1500 6.8 120 >

RIS schemes of type (q+ W~+WJ) Three-color process consisting of two resonance steps followed by photo-ionization

by an infrared photon. X1=299.3 nm. X2=443.1 nm. h3=1064 nm.

Data for RIS schemes of type (u,+w2+wa) [l, 31

Lifetimes and photo-ionization cross section from excited states ~(~F*“)=8.2 ns [4, 51, 7Cf3G3’)=25 ns [7]. The power in Ai required to saturate the excitation to the 3Fzo level is 1700 W/cm2.

An estimate of the energy required in X2 to saturate the second step from this level to the f 3G3” level, within the absorption bandwidth delivered while the first step is being pumped, is 7.6 X 10m3 rnJ/cm 2. For photo-ionization of the f 3G30 level by 1064 nm radiation a calculation by means of a Hartree-Fock code [6] estimates the cross section to be 13 x lo-l8 cm2. This corresponds to a laser energy requirement of 14 mJ/cm2 for photo-ionization efficiency near unity from the excited state for a pulse shorter than the lifetime of the excited state.

Isotope data [8-lo] Stable isotopes: 58Ni (68.27%) I=O; 60Ni (26.10%) I=O; 61Ni (1.13%) 1=3/2; 62Ni

(3.59%) I=O; 64Ni (0.91%) Z=O. Unstable isotopes: s6Ni I=0 7=6.10 d; 57Ni I=312 r=36 h; 59Ni I=312 7=7.5 x lo4 y;

63Ni 1=1/2 ~=100.1 y; 65Ni I=5/2 7=2.520 h.

Isotope shijtslhfs [9] There is no data on the isotope shifts of these lines. The even isotopes have no

hyperfine structure (I=O). For 61Ni the hyperfine interaction constants (units 10m3 cm-l) are given below for the indicated low lying state:

a 3F4: A= -7.17296 a 3F3: A= -9.98394 a 3D3: A=-15.1762 a 3D2: A= -5.72343

B= -1.8969; B= -1.4031; B= -3.4341; B=-1.8795.

Laser schemes For 221-235 nm, doubling and mixing Nd:YAG pumped Rhodamine 610 and

Rhodamine 590 dye lasers [C] or Nd:YAG pumped frequency doubled Coumarin 440 and Coumarin 460 dye lasers; for 282-284 nm, Nd:YAG pumped frequency doubled

378 E. B. SALOMAN

Rhodamine 590 dye laser [B, C]; for 294-304 nm, Nd:YAG pumped frequency doubled Rhodamine 610 dye laser [A, B, C]; for 443.1 nm, Nd:YAG pumped Coumarin 440 dye laser; for 1064 nm, Nd:YAG direct IR.

Atom reservoirs and sources The methods used to atomize Ni for RIS studies have been: evaporation of the

sample by a hot rhenium filament [A, B]; and sputtering by a pulsed argon ion beam [Cl*

RIS references

[A] J. D. Fassett, L. J. Moore, J. C. Travis and F. E. Lytle, ht. J. Mass Spectrom. Ion Proc. 54, 201 (1983).

[B] L. J. Moore, J. D. Fassett and J. C. Travis, Anal. Chem. 56, 2770 (1984). [C] P. Gelin, 0. Gobert, B. Dubreuil, J. L. Debrun and R. L. Inglebert, Studies on the analysis of trace

metallic elements in semiconductors using RIMS, in Resonance Ionization Spectroscopy 1988, Eds, T. B. Lucatorto and J. E. Parks, p. 201. Institute of Physics, Bristol (1989).

[D] P. Gelin, J. L. Debrun, 0. Gobert, R. L. Inglebert and B. Dubreuil, Nucl. Instrum. Methods B 40/41, 290 (1989).

[E) 0. Gobert, B. Dubreuil, P. Gelin, J. L. Debrun and R. L. Inglebert, Trace analysis using laser postionization of sputtered neutral atoms-Preliminary results obtained with a Nd-YAG pumped dye laser and a quadrupole mass spectrometer, in Secondary Ion Mass Spectrometry SIMS VI, Eds, A. Benninghoven, A. M. Huber and H. W. Werner, p.845. Wiley, Chichester (1988).

[F] L. J. Moore, J. E. Parks, E. H. Taylor, D. W. Beekman and M. T. Spaar, Medical and biological applications of resonance ionization spectroscopy, in Resonance Ionization Spectroscopy 1986, Eds, G. S. Hurst and C. G. Morgan, p.239. Institute of Physics, Bristol (1987).

Data references

PI [21

;:; PI

[61

;;; [91

WI

J. Sugar and C. Corliss, J. Phys. Chem. Ref. Data 14, Suppl. 2 (1985). R. H. Page and C. S. Gudeman, J. Opt. Sot. Am. B7, 1761 (1990).

J. R. Fuhr, G. A. Martin and W. L. Wiese, J. Phys. Chem. Ref. Data 17, Suppl. 4 (1988). A. Doerr and M. Kock, J. Quant. Spectrosc. Radiat. Transfer 33, 307 (1985). U. Becker, H. Kerkhoff, M. Schmidt and P. Zimmermann, J. Quant. Spectrosc. Radiat. Transfer 25. 339 (1981). R. D. Cowan, The Theory of Atomic Structure and Spectra. University of California Press, Berkeley (1981). Calculated using the Hartree-Fock code with relativistic corrections of Ref. [6]. N. E. Holden, R. L. Martin and I. L. Barnes, Pure Appl. Chem. 55, 1119 (1983). G. H. Fuller, J. Phys. Chem. Ref. Data 5, 835 (1976). P. Raghavan, Atom. Data Nucl. Data Tables 42, 189 (1989).

Documents

Saloman 1991 - Resonance Ionization Techniques