Fourier Transform Infrared Emission Spectroscopy of NaCl ...bernath.uwaterloo.ca/publicationfiles/1997/171.pdf · The infrared emission spectra of NaCl and KCl have been recorded

JOURNAL OF MOLECULAR SPECTROSCOPY 183, 360–373 (1997)ARTICLE NO. MS977292

Fourier Transform Infrared Emission Spectroscopy of NaCl and KCl

R. S. Ram,* M. Dulick,† ,‡ B. Guo,‡ K.-Q. Zhang,‡ and P. F. Bernath* ,‡

*Department of Chemistry, University of Arizona, Tucson, Arizona 85721; †National Solar Observatory, National Optical Astronomy Observatories,Tucson, Arizona 85726; and ‡Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1

Received November 25, 1996; in revised form March 3, 1997

The infrared emission spectra of NaCl and KCl have been recorded at high resolution with a Fourier transformspectrometer. A total of 929 lines belonging to 8 vibrational bands, 1–0 to 8–7, for Na35Cl, 252 lines of 1–0, 2–1,and 3–2 bands of Na37Cl, and 355 lines of 1–0, 2–1, 3–2, and 4–3 bands of K35Cl have been measured and combinedwith the existing microwave and millimeter-wave data to obtain a set of refined molecular constants. The data forNa35Cl and Na37Cl have also been fitted to determine the Dunham Yij constants and mass-reduced Dunham constantsUij . In one fit all Uij’s were treated as adjustable parameters while in a second fit only Ui 0’s and Ui 1’s were allowed tovary freely with the remaining Uij constants determined by the constraints imposed by the Dunham model. In addition,the internuclear potential energy parameters were determined by fitting the entire NaCl data set to the eigenvalues ofthe Schrodinger equation containing a parameterized potential energy function. q 1997 Academic Press

INTRODUCTION fit using the Dunham equations. In a separate study, Ueharaet al. (13) investigated the infrared emission spectra of KClat a resolution of 0.1 cm01 and provided a set of DunhamDiatomic alkali halides are high temperature species ofcoefficients for the ground electronic state.fundamental importance. Their low vapor pressures and

Some matrix isolation studies of NaCl and KCl are alsohighly ionic nature present challenges for gas phase experi-available. Martin and Schaber (8) observed the infraredmental studies (1) . There are many studies of NaCl (2–9)spectra of NaCl while Ismail et al. (14) observed both NaCland KCl (2–4, 10–14) in the near-ultraviolet and micro-and KCl in a solid argon matrix.wave regions. NaCl (2, 3) and KCl (10–12) have a long

Extensive microwave data for NaCl and KCl have beenseries of unresolved bands in the near ultraviolet which havepublished (5, 9) . In the initial work of Honig et al. (5) ,been called ‘‘fluctuation bands’’ (15) . These bands ariseseveral alkali halide molecules were investigated and theyfrom transitions between individual vibrational levels of onereported rotational constants and electric dipole moments.electronic state and a rather flat portion of the potential curveIn another study, Clouser and Gordy (9) measured the milli-of the other state. The ground state of these molecules aremeter-wave molecular beam absorption spectra of NaCl,relatively well characterized experimentally by infrared andKCl, and several other alkali chlorides. In this work theymicrowave studies.measured a number of pure rotational transitions in severalThe NaCl and KCl molecules are important species in thevibrational levels of the ground state and reported improvedcombustion of coal. Coal contains substantial amounts ofvalues for Be , ae and ge for most of the molecules studied.inorganic material that are responsible for slagging and foul-They also provided indirect estimates for the vibrational con-ing of coal-fired power plants. NaCl and KCl can, in princi-stants.ple, be monitored by the absorption or emission using the

The alkali halides have dissociative UV absorption spec-vibration–rotation bands.tra. Silver et al. (16) measured the absolute UV dissociationThe low resolution infrared spectra of NaCl and KCl werecross sections for gas phase NaCl and Novick et al. (17)first observed in absorption by Rice and Klemperer (4) ,measured the photodetachment spectra of the alkali halidewho determined the ground state vibrational constants ve

negative ions NaCl0 , NaBr0 , and NaI0 .and vexe from band head positions in conjunction with theThe ionic nature of the alkali halide ground states has ledground state B values, previously reported by Honig et al.

to the development of simple potential energy functions such(5) in a microwave study. The high-resolution infrared vi-as the Rittner model (18–20) . There are a number of theo-bration–rotation spectra of Na35Cl and Na37Cl have beenretical calculations of electronic structure and other proper-studied by Horiai et al. (6) and Uehara et al. (7) by infraredties available for NaCl (21–29) and KCl (30–35) . Boundsdiode laser spectroscopy. These measurements were used toand Hinchliffe (23) performed ab initio calculations of thedetermine a set of Dunham parameters Yij for the groundSCF pair potential and polarizability of NaCl and Leasurestate of NaCl. The potential constants for the ground state

were also calculated by Uehara et al. (7) in a least squares et al. (26) calculated the electronic structure. Swaminathan

3600022-2852/97 $25.00Copyright q 1997 by Academic PressAll rights of reproduction in any form reserved.

AID JMS 7292 / 6t1b$$$241 05-07-97 16:24:46 mspa

INFRARED EMISSION SPECTROSCOPY OF NaCl AND KCl 361

TABLE 1The R Head Positions ( in cm01 ) of Vibration–Rotation Bands in the 1–0 Sequence of K 35Cl

FIG. 1. A compressed portion of infrared bands of KCl marking theband heads in the 1–0 sequence of K35Cl.

et al. (28) calculated the potential energy of NaCl with largeatomic basis sets and extensive configuration interaction.Bounds and Hinchliffe (32) studied the polarizability of KCland Zeiri and Balint-Kurti (34) studied the potential energycurves and transition dipole moments of NaCl, KCl, andseveral other alkali halides.

Some of the alkali halides are also of astrophysical impor-tance. Recently the presence of NaCl and KCl, along withAlCl and AlF, has been established in the carbon star IRC particularly important since high-quality spectroscopic pa-

rameters are necessary for infrared searches for these mole-/ 10216 by millimeter-wave astronomers (36) . Normallymetals are depleted onto grains in the interstellar medium cules.

In this paper we report on the observation of vibration–but this discovery indicates that metal-containing moleculesare more abundant in cool circumstellar envelopes. Unfortu- rotation bands of Na35Cl, Na37Cl, and K35Cl. Eight bands,

1–0, 2–1, 3–2, 4–3, 5–4, 6–5, 7–6, and 8–7, for Na35Cl,nately, the infrared spectra of many of the metal halide di-atomic molecules have not been investigated at high resolu- three bands, 1–0, 2–1, and 3–2, for Na 37Cl, and four bands,

1–0, 2–1, 3–2, and 4–3, for K35Cl have been observed attion and their vibrational constants are not precisely known.The high-resolution studies of these molecules are, therefore, a resolution of 0.01 cm01 . Analysis of the data has provided

improved molecular constants and the Dunham coefficientsYij for these species. The Na35Cl and Na37Cl data sets havealso been fitted together to obtain mass-reduced Dunhamconstants Uij and the constants of a parameterized potentialenergy function.

EXPERIMENTAL

The high-resolution emission spectra of Na35Cl, Na37Cl,and K35Cl were recorded with a Bruker IFS 120HR Fouriertransform spectrometer at the University of Waterloo. Themolecules were vaporized in an alumina tube furnace byheating NaCl or KCl gradually until the operating tempera-ture of 10007C was achieved. A 3.5 mm mylar beam splitterand a Si:B detector (NaCl) or a 4 K bolometer (KCl) wereused to record the spectra. The cell was pressurized withabout 5 Torr of argon to avoid the deposition of the solidmaterial on the KRS-5 windows. The resolution was 0.01FIG. 2. An expanded portion of the 1–0 band of Na35Cl near the R

head. cm01 for both molecules. The final interferograms for NaCl

Copyright q 1997 by Academic Press

AID JMS 7292 / 6t1b$$$242 05-07-97 16:24:46 mspa

RAM ET AL.362

TABLE 2Observed Rotational Lines ( in cm01 ) in the Vibration–Rotation Bands of Na35Cl and Na37Cl

AID JMS 7292 / 6t1b$$7292 05-07-97 16:24:46 mspa


TABLE 2—Continued


AID JMS 7292 / 6t1b$$7292 05-07-97 16:24:46 mspa

RAM ET AL.364

TABLE 2—Continued


AID JMS 7292 / 6t1b$$7292 05-07-97 16:24:46 mspa


TABLE 2—Continued


AID JMS 7292 / 6t1b$$7292 05-07-97 16:24:46 mspa

RAM ET AL.366

TABLE 2—Continued


AID JMS 7292 / 6t1b$$7292 05-07-97 16:24:46 mspa


TABLE 2—Continued


AID JMS 7292 / 6t1b$$7292 05-07-97 16:24:46 mspa

RAM ET AL.368

TABLE 3Observed Rotational Lines ( in cm01 ) in the Vibration–Rotation Bands of K35Cl

AID JMS 7292 / 6t1b$$7292 05-07-97 16:24:46 mspa


TABLE 3—Continued

and KCl involved coaddition of 100 and 400 scans, respec- The measurements of strong and unblended Na35Cl lines areexpected to have a precision of about {0.003 cm01 . Thetively.

The spectra were measured using the PC-DECOMP, a uncertainty in the measurements of Na37Cl lines is expectedto be somewhat worse because of the weaker intensity andprogram developed by J. Brault at the National Solar Obser-

vatory. This program determines the position of individual overlapping from the major isotopomer. The lines of KClare much weaker in intensity than NaCl, and K37Cl lineslines by fitting a Voigt lineshape function to each line. The

spectra were calibrated using the measurements of H2O lines could not be identified in our spectra. The K35Cl lines areexpected to be accurate to, at best, {0.005 cm01 .(37) which were also present in our spectra as an impurity.


AID JMS 7292 / 6t1b$$$242 05-07-97 16:24:46 mspa

RAM ET AL.370

TABLE 4 350 to 387 cm01 . The intensity of the higher vibrationalRotational Constants ( in cm01 ) of the X1S/ State of NaCl bands decreases slowly with increasing vibration and it be-

comes difficult to identify the bands with £ ú 8 because ofoverlapping and the decline in intensity. In contrast to theprevious infrared observations of Horiai et al. (6) and Ueh-ara et al. (7) , we have identified a number of P lines. Theintensity of the Na37Cl isotopomer is about 33% of the inten-sify of Na35Cl as expected. The rotational lines only in the1–0, 2–1, and 3–2 bands of Na37Cl were identified andincorporated in the fit. A part of the high-resolution spectrumof the 1–0 band of NaCl near the R head is provided in Fig.1 where some R lines of Na35Cl have been marked.

The rotational lines belonging to the 1–0, 2–1, 3–2, and4–3 bands of K35Cl were identified in our high-resolutionspectra although band heads up to 12–11 can be clearlyseen. A part of the compressed spectrum of KCl showingthe band heads is presented in Fig. 2 and a list of observedband heads is provided in Table 1. For technical reasons(the use of a bolometer) the KCl data are relatively poorcompared to NaCl and a much less extensive analysis wascarried out.

As expected for a 1S/ – 1S/ transition, each band consistsof one R and one P branch. The wavenumbers of the ob-served transitions of NaCl and KCl are provided in Tables2 and 3 respectively. The wavenumbers of NaCl and KClwere fit to the customary energy level expression:

F£(J) Å T

£/ B

£J(J / 1) 0 D

£[J(J / 1)]2

RESULTS AND DISCUSSION / H£[J(J / 1)]3 .

[1]

The vibration–rotation bands of NaCl and KCl are locatedin the 340–390 and 240–300 cm01 regions, respectively. In the final least-squares fit, approximate weights for the

individual rotational lines were chosen on the basis of signal-The bands form R heads and the rotational structure of bandswith high £ values is heavily overlapped. Our Loomis–Wood to-noise ratio as well as freedom from blending. We have

also included the previous microwave measurements ofprogram was very helpful in identifying the connecting R andP lines in each band, particularly in the severely overlapped Honig et al. (5) and Clouser and Gordy (7) , with appro-

priate weights in our final fit. The spectroscopic constantsregions. For KCl essentially all of the lines are blended.The observed spectrum of NaCl consists of eight vibra- for the X 1S/ state of NaCl and KCl obtained from the fit

of the combined infrared and microwave data are providedtion–rotation bands, 1–0 to 8–7, of Na35Cl spread from

TABLE 5Rotational Constants ( in cm01 ) of the X 1S/ State of KCl


AID JMS 7292 / 6t1b$$$242 05-07-97 16:24:46 mspa


TABLE 7in Tables 4 and 5, respectively. The molecular constantsDunham Constants ( in cm01 ) of the X 1S/ State of KClobtained in this study are in excellent agreement with values

reported earlier from infrared studies (5, 7) but are moreprecise by an order of magnitude because of the inclusionof extensive data with high J and £ values along with purerotational lines. The rotational lines of Na35Cl, Na37Cl, andK35Cl were fit to the Dunham energy level expression (38)

E(£, J) Å ∑ Yij(£ / 1/2) i[J(J / 1)] j . [2]

The Dunham constants (Yij) for the X 1S/ state of NaCl andKCl obtained from these fits are provided in Tables 6 and7, respectively.

In another fit the combined Na35Cl and Na37Cl data setswere fit to the following expression to determine a set ofmass-reduced Dunham Uij coefficients and Born–Oppenhei-mer breakdown constants Dij (39, 40) :

E(£, J) Å ∑ Uijm0 ( i/2 j ) /2 (£ / 1/2) i[J(J / 1)] j

[3]1 S1 / me

MA

DAij /

me

MB

DBijD .

me is electron mass, MA and MB are masses of two atomicall of the parameters for a power series potential are uniquelycenters A and B, respectively, and DA

ij and DBij are Born–

determined by the Ui 0 and Ui 1 constants (41, 42) . ThisOppenheimer breakdown constants for atoms A and B. Itmeans that Uij’s with j § 2 can be expressed in terms ofturns out that no D parameters were necessary in our fits.Ui 0’s and Ui 1’s. In the second fit, therefore, Ui 0’s and Ui 1’sTwo fits of the combined NaCl data were obtained. In thewere treated as adjustable parameters with the remainingfirst fit all Uij parameters were allowed to vary. The constantsUij’s fixed to the values satisfying these constraints. Theobtained from this fit are reported in Table 8 under theconstants obtained from this fit are also reported in Table 8column heading ‘‘unconstrained.’’ These unconstrained Uijunder the column heading ‘‘constrained.’’and Yij values of Tables 6 and 7 are thus empirical coeffi-

There is no doubt that the Dunham constants reproducecients of polynomial fits. According to the Dunham modelthe transition wavenumbers over the range of £ and J valuesobserved. It is well known, however, that this model is inade-quate for extrapolating beyond the range of experimentalTABLE 6measurements. The full advantage of high-quality, high-res-Dunham Constants ( in cm01 ) of the X 1S/ State of NaClolution spectra is achieved when the extracted spectroscopicinformation can also be applied in predicting the spectrawell beyond the range of experimental measurements. Theinherent failure of the Dunham model has led to the develop-ment of a more sophisticated approach of fitting observedmeasurements directly to the eigenvalues of the Schrodingerequation containing a parameterized potential energy func-tion (43–46) . The Born–Oppenheimer potential UBO is rep-resented by

UBO Å De{1 0 exp[0b(R)]}2 /{1 0 exp[0b(`)]}2 ,

[4]

where

b(R) Å z ∑ bi zi , [5]


AID JMS 7292 / 6t1b$$$243 05-07-97 16:24:46 mspa

RAM ET AL.372

TABLE 9b(`) Å ∑ bi , [6]Internuclear Potential Energy Parameters ( in cm01 )

for the X 1S/ State of NaCland

z Å (R 0 Re ) / (R / Re ) . [7]

We call this approach to data reduction the parameterizedpotential model and the method is described in more detailin several previous publications (45, 46 ) . This fit providesa set of bi parameters which describe (Eq. [4 ] ) the in-ternuclear potential function (45, 46 ) . These parametersfor NaCl are provided in Table 9. Only statistically deter-mined parameters are listed in this table along with 1suncertainties.

Our measurements of NaCl rotational lines are in goodagreement with the measurements of Horiai et al. (6 ) andUehara et al. (7 ) where they overlap. The present set ofDunham constants for Na 35Cl and Na 37Cl (Table 6) arealso in excellent agreement with the previous values (6,

TABLE 8 7 ) . Because of our more extensive data set includingMass Reduced Dunham Constants ( in cm01 ) bands up to 8–7, however, the present constants for

for the X 1S/ State of NaCl Na 35Cl are more precise than the previous values (5, 7 ) .A comparison of present band head positions of KCl withthose reported by Uehara et al. (13 ) indicates that onaverage their values are about 0.07 cm01 higher than thepresent measurements. At this point it is worth mentioningthat Uehara et al.’s spectra were recorded at a resolutionof 0.1 cm01 whereas the present spectra were recorded at0.01 cm01 resolution. Thus the present molecular con-stants of KCl in Tables 5 and 7 are much more precisethan previous values of Uehara et al. (13 ) . For example,the present values of Y10 , Y20 , and Y01 constants are280.0764(49) , 01.3133 (34) , and 0.12863213(33) cm01 ,respectively, compared to the corresponding values of279.963 (22) , 01.2306(83) , and 0.128631(52) cm01 , re-spectively, obtained by Uehara et al. (13 ) .

CONCLUSION

The infrared emission spectra of NaCl and KCl have beenobserved using a Fourier transform spectrometer. The vibra-tion–rotation spectra of a number of bands of Na35Cl,Na37Cl, and K35Cl have been measured and the line positionsfitted to extract molecular constants for individual vibra-tional levels and Dunham coefficients. The lines of Na35Cland Na37Cl were combined in another fit to determine themass-reduced Dunham parameters Uij . A second set of mass-reduced constants was also obtained using the same data setbut with only the Ui 0’s and Ui 1’s treated as variables andthe rest of the Uij’s were fixed by constraints imposed bythe Dunham model. The lines of NaCl have also been fit


AID JMS 7292 / 6t1b$$$243 05-07-97 16:24:46 mspa


17. S. E. Novick, P. L. Jones, T. J. Mulloney, and W. C. Lineberger, J.with a parameterized potential model to extract a potentialChem. Phys. 70, 2210–2214 (1979).energy function.

18. E. S. Rittner, J. Chem. Phys. 19, 1030–1035 (1951).19. P. Brumer and M. Karplus, J. Chem. Phys. 58, 3903–3918 (1973); J.

Chem. Phys. 64, 5165–5178 (1976).ACKNOWLEDGMENTS 20. R. L. Matcha and S. C. King, J. Am. Chem. Soc. 98, 3415–3420

(1976); J. Am. Chem. Soc. 98, 3420–3432 (1976).21. A. Laaksonen and E. Clementi, Mol. Phys. 56, 495–524 (1985).We thank Combustion Research Facility of the Sandia National Labora-22. F. Spiegelmann and J. P. Malrieu, J. Phys. B. 17, 1259–1279 (1984).tories for financial support. Support was also provided by the NASA labora-23. D. G. Bounds and A. Hinchliffe, Chem. Phys. Lett. 86, 1–6 (1982).tory astrophysics program and the Canadian Natural Sciences and Engi-24. Y. von Bergen, R. von Bergen, and B. Linder, Theoret. Chim. Actaneering Research Council (NSERC).

63, 317–322 (1983).25. L. Adamowicz and R. Bartlett, J. Chem. Phys. 88, 313–316 (1988).26. S. C. Leasure, T. P. Martin, and G. G. Balint-Kurti, J. Chem. Phys. 80,

REFERENCES 1186–1200 (1984).27. S. C. Leasure, T. P. Martin, and G. G. Balint-Kurti, Chem. Phys. Lett.

96, 447–452 (1983).1. P. Davidovits and McFadden, ‘‘Alkali Halide Vapors,’’ Academic28. P. K. Swaminathan, A. Laaksonen, G. Corongiu, and E. Clementi, J.

Press, New York, 1979.Chem. Phys. 84, 867–871 (1986).

2. H. Levi, Inaugural dissertation, Friedrich-Wilhelms University, Berlin,29. H. Nakatsuji, M., Hada, and T. Yonezawa, Chem. Phys. Lett. 95, 573–

1934.578 (1983).

3. H. Beutlier and H. Levi, Z. Phys. Chem. B 24, 263–281 (1934).30. K. B. Hathaway and J. A. Krumhausl, J. Chem. Phys. 63, 4313–4316

4. S. A. Rice and W. Klemperer, J. Chem. Phys. 27, 573–579 (1957). (1975).5. A. Honig, M. Mandel, M. L. Stitch, and C. H. Townes, Phys. Rev. 96, 31. R. Hoffmann, J. Chem. Phys. 39, 1397–1412 (1963).

629–642 (1954). 32. D. G. Bounds and A. Hinchliffe, Chem. Phys. Lett. 54, 289–2916. K. Horiai, T. Fujimoto, K. Nakagawa, and H. Uehara, Chem. Phys. (1978).

Lett. 147, 133–136 (1988). 33. G. Meyer and J. P. Toennies, J. Chem. Phys. 75, 2753–2761 (1981).7. H. Uehara, K. Horiai, K. Nakagawa, and T. Fujimoto, J. Mol. Spectrosc. 34. Y. Zeiri and G. G. Balint-Kurti, J. Mol. Spectrosc. 99, 1–24 (1983).

134, 98–105 (1989). 35. S. L. Davis, B. Pouilly, and M. H. Alexander, Chem. Phys. 91, 81–888. T. P. Martin and H. Schaber, J. Chem. Phys. 68, 4299–4303 (1978). (1984).9. P. L. Clouser and W. Gordy, Phys. Rev. 134, 863–870 (1978). 36. J. Cernicharo and M. Guelin, Astron. Astrophys. 183, L10–L12 (1987).

10. P. Davidovits and D. C. Brodhead, J. Chem. Phys. 46, 2968–2973 37. J. W. C. Johns, J. Opt. Soc. Am. B 2, 1340–1354 (1985).(1967). 38. J. L. Dunham, Phys. Rev. 41, 721–731 (1932).

11. R. C. Oldenborg, J. L. Gole, and R. N. Zare, J. Chem. Phys. 60, 4032– 39. J. K. G. Watson, J. Mol. Spectrosc. 45, 99–113 (1973).4042 (1974). 40. J. K. G. Watson, J. Mol. Spectrosc. 80, 411–421 (1980).

12. K. J. Kaufmann, J. L. Kinsey, H. B. Palmer, and A. Tewarson, J. Chem. 41. E. Tiemann and J. F. Ogilvie, J. Mol. Spectrosc. 165, 377–392 (1994).Phys. 61, 1865–1867 (1974). 42. J. F. Ogilvie, J. Mol. Spectrosc. 180, 193–195 (1996).

13. H. Uehara, K. Horiai, T. Konno, and K. Miura, Chem. Phys. Lett. 169, 43. J. A. Coxon and P. Hajigeorgiou, Can. J. Phys. 70, 40–54 (1992).599–602 (1990). 44. J. A. Coxon and P. Hajigeorgiou, Chem. Phys. 167, 327–340 (1992).

14. Z. K. Ismail, R. H. Hauge, and J. L. Margrave, J. Mol. Spectrosc. 54, 45. J. M. Campbell, M. Dulick, D. Klapstein, J. B. White, and P. F. Bernath,402–411 (1975). J. Chem. Phys. 99, 8379–8384 (1993).

15. R. F. Barrow and A. D. Caunt, Proc. R. Soc., Ser. A. 219, 120–140 46. J. M. Campbell, D. Klapstein, M. Dulick, P. F. Bernath, and L. Wallace,(1953). Astrophys. J. Suppl. 101, 237–254 (1995).

16. J. A. Silver, D. R. Worsnop, A. Freedman, and C. E. Kolb, J. Chem. 47. K. P. Huber and G. Herzberg, ‘‘Constants of Diatomic Molecules,’’Van Nostrand, New York, 1979.Phys. 84, 4378–4384 (1986).


AID JMS 7292 / 6t1b$$$244 05-07-97 16:24:46 mspa

Documents

Fourier Transform Infrared Emission Spectroscopy of NaCl ...bernath.uwaterloo.ca/publicationfiles/1997/171.pdf · The infrared emission spectra of NaCl and KCl have been recorded