JOURNAL OF MOLECULAR SPECTROSCOPY 123,237-246 (I 987)

A Spin-Orbit 2’fI, - 23&g Perturbation in Na,: Hypetfine Splittings, Perturbation Matrix Elements,

and Electronic Structure Implications

LI LI’ AND ROBERT W. FIELD

Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachus~ts 02139

A perturbation between the Nar 2’114, u = u* - 11 (u * =68+2)and2’II,o=27,J= 13 and 14 levels is observed by Perturbation Facilitated Optical-Optical Double Resonance Spec- troscopy. The local (J = 13) and electronic spin-orbit perturbation matrix elements, respectively, are 0.096( 13) and -3.5 cm-’ (1 q uncertainty). The relatively large size of the interaction matrix element implies that the 2311, and Z’II, states both have appreciable ~:3p LCAO-MO character at short internuclear distance (the potential curves cross near R = 3.4 A). The 2’II, u = I)* - 11, J = 13 and 14 levels are observable by virtue of their admixed 2’II, u = 27 character (20 and - 5%, respectively), but the resolved magnetic hyperhne splitting

c,_,~~= -4,73(21)MHz, c,_,~~= -5.10(63)MHz

c,_,~~ = -4.32(29) MHz, c+,~ = -4.13(30) MHz

reflects the mixed-a 2311, character of these levels. The hfs in the 2311, state is very similar to that in b311z. (I’&) because the hfs originates primarily from the 02s orbital which is nominally singly occupied for both ‘II states. o 1987 Academic ores, I~C.

I. INTRODUCTION

The Na2 A’Z+ - b311, spin-orbit perturbations give rise to several levels of mixed singlet - triplet’character. The technique of Perturbation Facilitated Optical-Optical Double Resonance (PFOODR) spectroscopy has taken advantage of these mixed levels to gain access to six triplet states of Na2, a3Z:, b311,, 13Ag, 2’II,, 3311,, and 43Z,+ (Z-4). Owing to the expected small size of the spin-orbit interaction in Na2, singlet - triplet perturbations among the higher-lying states should be rare. Several pertur- bations among low Rydberg states were observed by PFOODR (4). The present paper deals with a 23lI2, - 2’II, interaction. The existence of this interaction implies that there will be numerous and somewhat stronger 2311, - ‘I& interactions which could affect si~cantly the collisional interconversion of singlet and triplet Nat and suggests new PFOODR studies (by two-photon pulsed 2’II, - 231T, + X’Z$ excitation followed by excitation or stimulated emission into ‘A, states).

The purpose of this paper is to provide the evidence for the assignment of the observed PFOODR transitions, to report the values of the observed perturbation in- teraction matrix elements and hyperhne splittings, and to interpret these electronic properties.

’ Permanent address: Qinghai Institute of Salt Lake, Xining, Qinghai, People’s Republic of China.

237 0022-2852187 $3.00 Copyrisht 0 1987 by Academic Press, Inc.

All rights of ltpmduction in Bay form resewed.

238 LI AND FIELD

2’~gv=27.J=13f

15990.514 cm-’ 23~2pv=v*-ll, J= 13f

(33147.354 cm-’ I 15990 756 cm-’

( 33147 596 cm-‘)

15990.602 cm-’

33 147 442 cm-‘I

Probe Loser Frequency-+

FIG. 1. A portion of the PFOODR excitation spectrum recorded from the b3110u 1)’ = 25, S = 13e inter- mediate level. Probe laser frequencies, upper-level term values (in parentheses), and upper-level assignments are given above the PFOODR lines.

II. EXPERIMENTAL DETAILS

The details of PFOODR spectroscopy have been presented in Refs. (Z-4). Na vapor was produced in a linear heat pipe oven operated at -500°C with He buffer gas. Two copropagating, single-mode, frequency-stabilized, cw dye lasers were used as pump and probe lasers. The PFOODR fluorescence excitation spectrum was recorded by fixing the pump laser frequency on a selected A’Z$ - b311, + X’Z: pump transition and scanning the frequency of the probe laser. Transitions into triplet states were detected by monitoring the resultant PFOODR fluorescence with a suitable filter/ photomultiplier combination. In addition to PFOODR excitation spectra, PFOODR- resolved fluorescence spectra were recorded by fixing both pump and probe lasers on aspecific3Ag(A=0,1,2)+A-b + X transition and dispersing the resultant PFOODR fluorescence with a scanning l-m monochromator.

III. OBSERVATIONS AND PFOODR LINE ASSIGNMENTS

Many rotation-vibration levels of the 52 = 0 and 1 components of the 2’II, state have been observed by PFOODR spectroscopy (I, 4). Definitive 9, J, and .e#assign- ments could be made because the pump laser populated only one known o, fl, J, e/f intermediate level (I, 4). When the pump laser was tuned to excite the AiZ: 2)’ = 22 - b3110u 2)’ = 25, J’ = 13e, 14e, and 16e levels and the probe laser was tuned through the predicted region of the 23II0g v = u * - 11, J = J’ f 1 e levels, the expected 23II0g + b3110,, transitions (R, P doublet, 300-MHz FWHM lines) were absent. However, about 7 cm-’ above the expected Q = 0 + 9’ = 0 transitions, a more complicated PFOODR spectrum was observed. Not only were there more than two PFOODR excitation lines, but most of the lines exhibited resolved hyperfme splittings. Figure 1 shows a portion of the PFOODR spectrum from the nominal’ b3110u u’ = 25,

2 Mixed levels are named by their predominant basis state character. For example, the “nominal” b3110u u’ = 25, J’ = 13e level is the one of the two A’Z: u’ = 22 - b%,. u’ = 25, S = 13e mixed levels which has greater b-‘II. than A’Z: character.

Na2 2’fI, - 2%, PERTURBATION 239

2’rIgv-27, J=l3e

15987 092 cm-’

( 33 147.352 cm-‘)

\\ I I I I I I 1 I I

- 30cMHZ

Probe Laser Frequency -

23~2~v=v*-ll. J=l3e

15987.332cme’

(33147 592 cm-‘) I 4

I =3+-I=3

I 16C17 14+15 12tl3

15~16 , 13714 /

FIG. 2. A portion of the PFOODR excitation spectrum recorded from the b’IIo. u’ = 25, J’ = 14e inter- mediate level. Probe laser frequencies, upper-level term values (in parentheses), and upper-level assignments are given above the PFOODR lines.

J’ = 13e intermediate level. Figure 2 is a higher-resolution scan in the same energy region, but the intermediate level is b3110u, 2)’ = 25, J’ = 14e (rather than 13e). The probe laser frequencies and calculated term values (relative to E = 0 at R, of X’Z,‘) are given above the corresponding lines in Figs. 1 and 2.

The evidence supporting our assignments of the 23IIZg - 2’II, perturbation complex will now be presented. The key hypothesis is that the perturbed levels appear in the PFOODR spectrum because of their 2’II, u = 27 character, the 23II2, v = o* - 11 character being both A52 = 2 and Franck-Condon inaccessible from b3110U u’ = 25. PFOODR excitations via nominal b311 iU o’ = 2 1, J’ = 16e and b3110U u’ = 14, J’ = 11 e, 12e, 13e intermediate levels were attempted. No PFOODR transitions were observed in the target region via the nominal b311 I u 2)’ = 2 1, S = 16e level. However, very strong 23II08 D = u* - 11 + b3110U u’ = 14, J’ = 1 le, 12e, 13e R and P transitions were observed at their predicted wavenumbers, although no PFOODR transitions were detected into the levels observed via b3110U u’ = 25, J’ = 13e.

The observed levels and the intermediate levels from which they were accessed are summarized in Table I. The e and f parity components of both nominal 2lII, and 23II, J = 13 and 14 levels were observed. Four of the observed levels listed in Table I could not be assigned.3

The 2’II, u = 27 assignment is based on the following facts:

(i) The observed term values agree satisfactorily (- 1 cm-‘) with those calculated from the molecular constants reported by Taylor et al. (5). Table I lists the Toa

3 In addition to the expected OODR transitions into high-lying states via the pump-selected intermediate level, additional transitions frequently appear in the OODR excitation spectrum. These extra transitions could appear from collisionaNy populated intermediate levels or from levels accidentally populated by the pump or probe laser.

240 LI AND FIELD

TABLE I

PFOODR Upper Level Term Values’ and Assignments

Intermediate Level J'

Tv,~

33 158.165e 21ng (27.17) -1.004 33 155.192f (27.16) -1.040

33 152.427e 33 152.422e 2h-1~ -1.040 33 149.854e 33 149.831f

2’11g (27,15) kg (27414) -1.044f

33 149.408e 33 149.386f 33 147.5961 33 147.589e

2%x29 (v*-11.14)

33 147.442 33 147.419 2b2 (v -11.13) ““as igned P

33 147.354f 33 147.350e 2hlg (27,13) -1.lUb 33 145.189 unassigned 33 145.144e 2kg (27.12) -1.065 33 144.952 33 142.292e unassign$d

33 140.582e 25rIOg (v*-11.14)

33 138.965e 33 138.939e 23rIOg (v*-11.13)

33 137.487e 23nog (v*-11,121

33 136.127e 2’iTOg (v*-11.11) 23r10g (v -11, IO)

a) In cm-' relative to T=O at re of X'rg'. b) From nominal b%I@, v'=14 intermediate level. c) From nominal b%Q, v'=25 intermediate level. d) From both nominal Al&' v'=22 and ban 7 v'=25 interwdiate levels. e) The elf parity of the upper level is g ven beside the observed term value. f) In cm-'. TcALc iape from nmlecular constants reported in Ref. [5].

- TcALC. The observed and calculated rotational constants for n = 27 are 0.0869 and 0.0873 cm-‘.

(ii) Spectra of resolved fluorescence from 3A, Rydberg states into the a3Z: and b311, states have been discussed elsewhere (2-4). When the nearly perturbation-free levels, which are assigned in Table I as 2’II, u = 27, J = 15e and 16f; were excited the resulting fluorescence spectra showed that the predominant character of the upper levels was ‘I& and that the triplet character was undetectably small.

(iii) Although almost all ‘A, q J + b3110u 2)’ = 25 - A’Z: 2)’ = 22, J’ = 14e + XiI;,f o” = 2, J” = 15 PFOODR lines were stronger by a factor of -2 when excited via the nominal b3110,, rather than the nominal A’Z: intermediate level, the OODR lines in Table I, including the transitions into J = I3 and 14 nominal 23II, levels, were stronger via the A’Z: intermediate. This implies that the nominal singlet-singlet transition character is more important than the nominal triplet-triplet character. This

. . is not surprising as 3II, 6 3II0U transitions are forbidden. The only 23II2, D = u* - 11 levels with appreciable 2’II, v = 27 character are J = 13 and 14.

(iv) The PFOODR excitation spectra display a typical perpendicular transition P, Q, R 1:2: 1 pattern, thus the upper singlet state can only be a ‘I& state.

(v) The b311i, o’ = 21, J’ = 16e and b3110,, u’ = 14, J’ = 13e, 14e, 15e levels are perturbed respectively by AIL’: u’ = 17 and u’ = 8. The absence of PFOODR excitation spectra into 2lII, 11 = 27 (all J) and 23IIzg u = u* - 11, J = 13, 14 levels from these intermediate levels is due to smaller Franck-Condon factors (q,,) than for the A’ZZ 0’ = 22 level:

2’rI,-A’z: (0, 07

27,22 27, 17 27, 8

4uf

6.81 x 10-2 4.24 X lo-’ 9.88 x lo-”

Naz 2’II, - 291ti PERTURBATION 241

(vi) The observation of PFOODR transitions into 23II0, IJ = V* - 11 from b3110U V’ = 14 but not from u’ = 25 and 2 1 implies small Franck-Condon factors for the (u, u’) = (u* - 11, 25) and (u* - 11, 21) transitions. Since the 2311, potential curve is not yet known (uncertain absolute vibrational numbering, effects of 2311, - 3311, perturbations), it is impossible to confirm this hypothesis by computed 2311E-b311, Franck-Condon factors.

(vii) Resolved fluorescence spectra from the levels at T = 33 149.386 and 33 147.589 cm-‘, assigned in Table I as 23II2, v = u* - 11, J = 14fand J = 13e, into the a3Z: and b311, states show that the upper states have significant 2311, character. Similarly, the spectra originating from the J = 13e levels at T = 33 147.589 (23II,) and T = 33 147.350 cm-’ (2lII, v = 27) into a3Z: and b311, have identical patterns, implying that the nominal 2’II, level borrows all of its ability to fluoresce into 3h, states from the nearby 2311, state.

(viii) The 2311, state has an -3~cm-’ spin-orbit splitting as determined from the separations of Q = 0, 1 components of several vibrational levels (4). The 23II~, 2) = o* - 11, J = lo- 14 e levels have been observed directly via b3110U 1)’ = 14, S = 1 l-l 3 e levels and assigned definitively. That the two 2311, levels observed via A’Z+ u’ = 22 - b3110U u’ = 25 levels lie -7 cm -’ higher than the 23II0g levels of the sami J value make the R = 2 assignment unquestionable.

IV. PERTURBATION MATRIX ELEMENT

Spin-orbit perturbations between Rydberg states are unusual for electronic and Franck-Condon reasons. Because of their large size, Rydberg orbit& have small spin- orbit coupling constants. Rydberg states built on the same ion-core state have nearly identical potential energy curves, therefore the only Rydberg - Rydberg vibrational overlap factors (u~u’) appreciably different from zero are u - u’ = 0 or + 1. The 23II~Z - 2’II, perturbation is between states of very different vibrational quantum numbers. It is observable because the molecular constants of the 2311, state are not at all Rydberg- like; thus the 2311, state’s potential energy curve crosses those of most low-energy Rydberg states. The 2311, - 2’II, curve crossing is at R, z 3.4 A, and the measured perturbation matrix element samples the character of the 27rg orbital at R = R,!

‘l-I - 311 perturbations can arise from the spin-orbit term, H”, which allows an interaction between ‘II, and ‘II, case (a) basis functions (AQ = 0 selection rule). At J = 13 the 2311, state has mixed-Q character. In particular, if the spin-orbit constant for 2’II, is A = 3 cm-’ and the rotational constant is B = 0.062 cm-‘, then the nominal 3II2g J = 13 eigenstate is

IC3&g’) = (1 - c:2Y213n2g) + G213~lg), (1)

where Cl2 N 2”*BJfA = 0.38. (2)

This means that the nominally forbidden 2’II, - 2311, spin-orbit interaction is smaller than the allowed 2’II, - 23111g interaction by a factor of 0.38.

Figure 3 shows the deviations (Toss - TCALC) of the observed 2’II, u = 27 term values of e-parity levels from values calculated using the constants of Ref. (5). The

4 The absolute vibrational numbering of the 2%, state is uncertain. R, = 3.4 A corresponds to U* = 70.

242 LI AND FIELD

-I IO

P -I I 2

12 13 14 I5 16 17 J

FIG. 3. (Tom - TcALc) versus J for the Z’II, u = 27 e-parity rotational levels observed in the PFOODR excitation spectra. Note the large level shift for J = 13.

straight line is from a least-squares fit which excluded the J = 13 and 14 levels. It is evident that the J = 13 level is shifted more than the others. The standard deviation is c = 0.016 cm-‘, whereas J = 13 is shifted by 0.048 cm-‘. The shift of J = 14 is slightly smaller than the detection threshold (2~). Using the observed J = 13 level shift, 6( 13) = 0.048( 16) cm-‘, and the separation between nominal 23II~g and 2’II, levels, AE( 13) = 0.240(6) cm-‘, the deperturbed level spacing at J = 13 is

AE0(13)=AE(13)-2]6(13)(=0.144(33)cm-’, (3)

and the local interaction matrix element, Hnn( 13), is given by

&n(J) = [W(JY2~* - (~“(JY2)21”2

Hnn( 13) = 0.096( 13) cm-‘.

The 2’II, character admixed into the nominal 23IIzz J = 13 level is

Cnn( 13) = [6( 13)/AE( 13)]“2 = 0.45(7).

The nominal ]‘23112,‘) eigenstate is

/‘23rI,‘) = (1 - c:p( 1 - c&,)“2123rI,,)

+ C,2( 1 - C&J”2123II,,)

+ GI&‘%)

(4)

(5)

(6) thus the relative intensity for excitation into the J = 13 nominal 23112, and 2’II, levels (via the AiZ: character of the intermediate level) should be given by the fractional 2 ‘I& character,

Cn,( 1 3)2 = 0.20(5) for ‘23112g’

(1 - C,,( 13)2) = 0.80(5) for ‘2lII,‘.

Similar calculations, which confirm the J = 13 analysis, can be made for the J = 14e level. Values of AE( 14e) = -0.446(6) and 6( 14e) = -0.024( 16) cm-’ from Table I and Fig. 3, respectively, lead to a value of Hnn( 14) = 0.101(33) cm-‘. The predicted values of Hnn( 14) = (14/l 3)Hnn( 13) = 0.103 cm-’ and 6( 14) = -0.02 1

Na2 2’II, - 23112, PERTURBATION 243

cm-’ (derived from B(2’Q) = 0.0869, B(23II~J = 0.0639, and AE”(13) = 0.144(33) cm-‘) agree satisfactorily with the observed values.

One also expects that transitions into nominal 23&g and 2’II, levels from a common intermediate level will have - 1:4 and 1:20 intensity ratios for J = 13 and 14, respec- tively. However, in Figs. 1 (J = 13f upper levels) and 2 (J = 13e upper levels), it appears that the transitions into nominal 23II, and 2’II, levels have comparable intensities. This is a consequence of the fluorescence detection scheme being optimized for 2311, + a’Z: and against 2’II, + A’Z: (I, 4). When filters peaking at 360 nm were used’ the 2’II, + A’Z+ 2) = 22 P(14) line became stronger than the 23II2R f A’Zf u = 22 P( 14) line by a factor of 6.

V. HYPERFINE SPLITTINGS OF 2311, u = u* = 11, J = 13 AND 14 LEVELS

The observed hyperline splitting of the J = 13 and 14 levels of the 23II, state provides further evidence in support of the 52 = 2 assignment. In Ref. (4) the hyperfine splittings of the 2311, and 3311, Q = 0 and 1 levels were reported and discussed. The relationship between the total hypertine splitting in an OODR excitation line and the splittings in the intermediate and final levels, for copropagating pump and probe beams, was shown to be (4)

Au = IV,,,- T.-I) - 2(7’.‘.~+1- G~-I)(w/Q~)~, (7)

where Au is the total hyperline splitting of an OODR excitation line (the splitting between the F = J + I + F’ = J’ + I + F” = J” + Z and F = J - Z f F’ = J’ - Z 6 F” = J” - I components), TF is the term value of a hyperline component, and Vpb and vpp are probe and pump laser frequencies. As for the b311, state, hyperfine splittings of the 2311, state arise primarily from magnetic dipole terms

(JZFjHMD(JIF) = (c/2)[F(F+ 1) - J(J+ 1) - I(Z+ l)], (8)

where c is a phenomenological J, Cl, elfaependent hyperline constant. The 23111g levels are observed (4) to have very small c values and their hyperfine splittings are not resolved in our PFOODR spectra. The 23II0g levels have resolvable hyperfine splittings and their c values, like those for b3110u levels (6), are positive (4).

The PFOODR transitions from the nominal A’Z: u’ = 22, J’ = 14 and the nominal b3110U 2)’ = 25, J’ = 13, 14, and 16 levels have resolved hyperfme splittings as shown in Figs. 1 and 2. The magnetic dipole hyperfme constants for b3110U u’ = 25, J’ = 13, 14, and 16 have been measured by polarization spectroscopy (7). By combining the hyperline constant for the b3110U 2)’ = 25, J’ = 13e and 14e levels (cl3 = 6.54(30) and cl4 = 5.28(9) MHz) with the observed PFOODR line splittings for transitions out of these intermediate levels, the c values for several upper levels listed in Table II could be deduced using Eqs. (7) and (8).

It is evident that the hyperfine splitting constants for the 2’II, levels are indistin- guishable from zero even for the J = 13e level, which has -20% 23II, character. The J = 13ef and 14ef levels of 23II,, which are observable by PFOODR because of their admixed 2’II, character, have resolvable hyperfine structure which is intrinsic to 2311,, being neither borrowed from 2’II, nor caused by an F-dependent 2iII, - 23II2, per-

’ At 360 urn only emission into X’Z; from collisionally populated ‘AU levels can be detected. The ‘AU

levels are populated more efficiently from Z’II, than from 2)II, levels.

244 LI AND FIELD

TABLE II

Hyperline Constants

State Y J e/f c(k) MHz c&&lo) MHz

2QI9 27 15 e -0.08(30)

2h9 27 14 e -0.30(30)

2QIg 27 14 f -0.02(30)

z3n2g v*-11 14 e -4.13(30) -4.4(4)

23n29 v*-11 14 f -4.32(29) -4.6(4)

23n29 v*-11 13 e -4.73( 21) -5.9(4)

2+I29 v*-11 13 f -5.10(63) -6.4(9)

21n9 27 13 e +0.30(19)

21ll9 27 13 f -0.06(63)

turbation interaction. The deperturbed c values, cd,,, for the J = 13efand 14eflevels of 2311, are also given in Table II. The small size of the splitting in the 2’II, J = 13e level is puzzling in view of the expected c = character in the nominal ‘II, level.

-1.2 MHz arising from the 20% ‘IIzg

Although the hyperline splitting of the A’Z: 2)’ = 22, J = 14 level could not be clearly resolved by polarization spectroscopy (7), by probing the J = 13e and 14f levels of 23II, from both the nominal A’Z: 2)’ = 22, J = 14e and b3110U v = 25, J = 14e levels, c = 3.12(22) MHz for the nominal A’Z: 2, = 22, J = 14 level could be determined. Given that the predominant contribution to the hfs at J = 13 and 14 in the nominal A’Z: and b311,, levels derives from (311JHMD1311,), the c value ratios for the nominal A’Z: and b3110U J = 14 levels, 3.12(22)/5.28(9) = 0.59(5), and b3110U J = 13 and 14 levels, 6.54(30)/5.28(9) = 1.24(8), are in excellent agreement with the corresponding ratios, 0.56 and 1.17, computed from mixing coefficients derived from the perturbation matrix element and deperturbed molecular constants of Ref. (9).

VI. CONCLUSIONS

The J = 13e, 13f, 14e, and 14flevels of 23IIz, v = u* - 11 have been observed by sub-Doppler, cw PFOODR spectroscopy. These levels owe their observability to a weak perturbation by 2’II, tr = 27. The intensity of the PFGODR transitions derives from the A’Z: character of the intermediate level and the 2*II, character of the up- per level.

The local (J = 13) value for the 2iII, v = 27 - 2311, u = u* - 11 spin-orbit perturbation matrix element is Hnn( 13) = 0.096( 13) cm-‘. From this, a value for the case (a)

(23111g2)* - 11 JH”12’II,u = 27) = Hnu( 13)/0.38 = 0.26(3) cm-’

matrix element is obtained. From this value, the eIectronic spin-orbit interaction strength could be obtained if the vibrational overlap factor (u* - 11 Iv = 27) were available. Since the absolute vibrational numbering of 2311, remains in doubt, the overlap factor cannot be reliably calculated. Alternative absolute numberings (u* = 70 and 68) give

Naz 2’II, - 23&g PERTURBATION 245

TABLE III

Comparison of ‘II Hyperfine Constants

State Q Sign Examples

b3nu 0 00 cv=17,J=15= 8.281Hz. c,=17,5=23= 6.9Wz

2311~ 0 00 Cv+_1,J=15= 6.%Hz

3311g 0 00 C,=15,J=15= llMH2, C,=&J=2T,= mHi!

b311, 1 c-0

23ng 1 c-o

33rIg 1 c-o

b3n, 2 c<o c,=l7,J=l4= -6.42MHz

2311~ 2 cto ~~=~*_11,~=13~= -5.9Mz c,=,*_ll,J=l3f= -6.4MHz

from which I(u* - 111~ = 27)1= 0.073 and 0.027

(2311,)H”12’II,) = 3.6 or 9.6 cm-‘.

The 2311, - 2’II, spin-orbit interaction strength is sufficiently large to require sig- nificant 3p or 4p LCAO character in the 2?r, molecular orbital at an internuclear distance near the R, a 3.4 A crossing point between the 2’II, and 2311, potential curves.

This 2’II, - 2311, spin-orbit interaction is sufficiently large that these two states should perturb each other frequently. Near the energy of the 2iII,, 2311, curve crossing (see footnote 4), EC = 30 920 cm-’ (2iII, u = 3, 2311, u = o* - 43, u* w 70) these perturbations should be much stronger than the one reported here. All three 51 com- ponents of 2311, will be perturbed, but the perturbations in the nominal B = 1 com- ponent will be strongest. These perturbations will provide an opportunity for systematic examination of the hyperfine structure in the 2311, state, a basis for PFOODR studies of 3h, states, and an explanation of efficient collisional transfer between 2’II, and 2’II, states.

Although the 2311, state is a Rydberg state, its hype&e structure resembles that of the b311, state. The hyperfine structure of both states is dominated by the singly occupied 1~~3s valence orbital. The relationships between the hyperfine coupling constants and electronic configurations of Na2 triplet states will be discussed elsewhere. In Ref. (4) we compared the hyperhne splittings in the Q = 0, 1 components of the 2311, and 3311, states with those in the b311, state. In Table III we provide comparisons among these ‘II states for all three Q components. The signs and magnitudes of the hypertine constants are very similar. Atkinson et al. (6) did not observef-parity levels of the bII, state because only b311U-X’Z,+ transitions into the e levels could borrow transition probability from the A’Z:-X’Z: system. Here we have been able to observe both e- and S-parity levels of the 23II~, D = u * - 11, J = 13, 14 levels and found that the hyperfme constants for both parities of the same J are identical to within our mea- surement accuracy.

246 LI AND FIELD

ACKNOWLEDGMENT

This work was supported by a grant from the National Science Foundation (PHY83-20098).

RECEIVED: August 2 1, 1986

REFERENCES

1. LI LI AND R. W. FIELD, J. Phys. Chem. 87,3020-3022 (1983). 2. Lr LI, S. F. RICE, AND R. W. FIELD, J. Mol. Specfrosc. 105, 344-350 (1984). 3. Lr LI, S. F. RICE, AND R. W. FIELD, J. Chem. Phys. 82, I 178-1182 (1985). 4. LI LI AND R. W. FIELD, J. Mol. Spectrosc. 117, 245-282 (1986). 5. A. J. TAYLOR, K. M. JONES, AND A. L. S~HAWLOW, J. Opt. Sot. Amer. 73,994-998 (1983). 6. J. B. ATKINSON, J. BECKER, AND W. DEMTR~DER, Chem. Phys. Lett. 87, 128-133 (1982). 7. CHONGYE WANG, YINDE WANG, MINGGUANG LI, AND LI LI, J. Mol. Spectrosc. (1987), in press. 8. G. HERZBERG, “Spectra of Diatomic Molecules,” p. 282, Van Nostrand, New York, 1950. 9. J. B. ATKINSON, J. BECKER, AND W. DEMTR~DER, Chem. Phys. Lett. 87,92-97 (1982).