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CW optical-optical double-resonance excitations of 39K2 Rydberg states
JOURNAL OF MOLECULAR SPECTROSCOPY
137,304-3 l l ( 1989)
CW Optical-Optical Double-Resonance Excitations of 3gK2Rydberg States HE WANG, ’ LI LI,’ A. M. LYYRA,~ AND W. C. STWALLEY 3 Centerfor Laser Science and Engineering, University of Iowa, Iowa City, Iowa 52242-1294 One ‘4 state, one ‘IIg state, and several ‘2: states of ‘9Kain the energy region 28 522-30 050 cm-’ have been observed by cw optical-optical double-resonance(OODR) fluorescenceexcitation techniques. Absolute vibrational numberings of the ‘4 state, the ‘II, state, and one of the ‘Zi states have been assignedand major molecularconstants for these three states have been determined. 0 1989 Academic Press,Inc. I. INTRODUCTION
Rydberg states of alkali dimers have been interesting to spectroscopists for many years. Excellent experimental results have been reported for Na2 and Li2 (I-5). Although highly excited K2 Rydberg states near the ionization limit have been observed by two- and three-photon ionization with unresolved rotational structure ( 6-7)) very little is known about the lower members of the Rydberg series. Engelke and Schtile reported transitions into Rydberg states by Doppler-free two-photon excitation in the energy region of 3 1 000-32 000 cm -’ (8). Normally, two-photon transitions are rare and only occur by coincidence; it is therefore difficult to study the Rydberg states systematically by that method. Sub-Doppler OODR spectroscopy, on the other hand, has proven to be a very powerful technique for study of Rydberg states even in the high-energy region where the density of energy levels is very high. In this paper we report our experimental investigation of Rydberg states of 39K2 with cw sub-Doppler OODR fluorescence excitation spectroscopy in the energy region 28 522-30 050 cm-’ above the potential minimum of the ground state. II. EXPERIMENTAL DETAILS
The experimental setup is shown in Fig. 1. Potassium vapor was generated in a five-arm stainless steel heat-pipe oven allowing spectral observation perpendicular to the laser axis. The heat pipe was operated at an equilibrium pressure of l-2 Torr of Ar buffer gas. An Ar+ laser-pumped CR 599-21 dye laser operated with DCM dye was used as the pump laser to excite 39K2 B’lI,-X12: transitions. A Kr+ laser-
’ Also Department of Physics and Astronomy. 2 Permanent address:Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, People’s Republic of China. 3 Also Department of Chemistry and Department of Physics and Astronomy. 0022-2852/89 $3.00 CopyrightQ 1989 by Academic Press, Inc. All rightsof reproductionin any form reserved.
304
305
K2 RYDBERG STATES
COMPUTER
CHOPPER fI t
\
I I
,
A
6 MONOCHROMATOR
PREAMPLIFIER
FIG. I. OODR experimental set-up. The single-mode operation of the CR 599-2 1dye laser was monitored with a spectrum analyzer (SA) and a scope.
pumped CR 699-29 Autoscan ring dye laser, operated with LD700 dye, was used as a probe laser. Iodine laser-induced fluorescence was used for absolute frequency calibration for both lasers. The pump and probe beams, after being modulated atfr and f2,respectively, were combined using a dichroic mirror (that passes X < 6900 A and reflects h > 7000 A) and then the copropagating beams were focused at the center of the heat-pipe oven. When the pump laser frequency was tuned to a selected B’II, D’, J’ + X’Z: u”, J” transition and held fixed, the probe laser was scanned and the OODR fluorescence to low vibrational levels of the A ‘Z L state was detected with a filter-PMT-lock-in system at a frequency offi - fi . The OODR fluorescence was also dispersed with a 0.5-m monochromator. The excitation scheme is shown in Fig. 2. B’II, v’ = 2, J’ = 14e/f, v’ = 0, S = 14e, and v’ = 4, J’ = 55e/f levels were selected as intermediate levels, which were excited from X’Z: 2)” = 0, 1, and 4, respectively, with large Franck-Condon factors. Transition frequencies were calculated from molecular constants given by Heinze et al. (9). Due to the high density of rovibrational transitions (calculations show that at least 10 B ‘II, + X ‘Zi transitions could be simultaneously excited at any pump frequency even with a narrow-band ( 1 MHz) CW dye laser), extra intermediate levels other than the selected one could also have been populated. In order to identify the OODR signals via the desired intermediate levels from those via unexpected intermediate levels, we first populated the selected B’II, v’, J’ level by pumping the B’II, v’, J’, +- X12: v”, J” = J’ - 1 transition, scanning the probe laser, then pumping the B’II, v’, J’ + k1 TZg d’, J”
306
WANG ET AL.
K, POTENTIALS 32 28 -
“9 \ 7%
1 + h
24 -
20-
-FLUORESCENCE
‘g 8 w
16 12 -
8-PUMP 4-
FIG. 2. Kz OODR fluorescence spectroscopy. The ‘Zl curve (r, = 29 363.005 cm-‘) overlaps the ‘4 state (r, = 29 349.582 cm-‘), but is centered at larger internuclear distance.
= J’ + 1 transition and scanning the probe again. Only those double resonance lines which appeared at the same frequency with the same intensity during both scans are the OODR signals through our selected B’TI, u’, J’ intermediate level. III. RESULTS AND DISCUSSION
From a B’II, intermediate level (e- orf-parity), ‘Z:, ‘Zg, ‘I&, and ‘A, Rydberg states can be reached by OODR excitation. Our detection of the fluorescence from the Rydberg states to the low vibrational levels of the A ‘Z I: state favors the observation of the ‘El and ‘I’&states since ‘Ag and ‘2; states cannot directly radiate to the A ’ Z : state. More than 100 levels in the energy region of 28 522-30 050 cm-r have been observed. Among them, 42 have been assigned to a ‘A, state, 35 to a ‘I& state, 12 to a ‘2: state, and 39 to eight other higher-energy ‘2: states (not reported here). The electronic assignment of the Rydberg states is based on the excitation spectral pattern and resolved fluorescence to the A ‘2: state. ‘2: v + B’II, o’, J’e excitation results in a P and an R line and ‘2: II + B ‘II, v’, J'fexcitation results in only a Q line. ‘TIJ ‘Ag II + B’II, u’, J’e/f transitions, on the other hand, should contain all three (P, Q, and R) lines, but the Q lines for the transition ‘I&V * B’II, v’, J’e/ f were
307
K2 RYDBERG STATES
too weak to be observed in our experiment. By observing the P and R lines from both e and f parity of the intermediate state, the ‘IIg state was distinguished from the ‘Z’ states. The ‘A, state can be readily distinguished since it cannot directly radiate to ihe A ’ Z : state. Table I gives the 42 ‘A, levels, Table II the 35 ‘I& levels, and Table III the 12 ‘Xi levels. Their vibrational and rotational quantum numbers, e- orf-symmetry, term values above the X ‘2: potential minimum, intermediate levels, and probe laser frequencies are also given in those tables. The A-doubling of the ‘A, state and the ‘I& state were not resolved with our accuracy (0.01 cm-‘). The vibrational numberings given in Tables I, II, and III were determined by comparisons of the calculated FranckCondon factors of the ‘Ag, ‘IIg, ‘2: + B’II, systems and the ‘II,, ‘2: + A’Z: systems with the observed intensity patterns. For the given v-numberings of the above
TABLE I Energy Levels and Assignments of the Rydberg State ‘A8and the Corresponding Intermediate States (B’II. (v’, J’)) INTERMEDIATE v' .I'
* a)
PROBE (cm-l)
T (cm-l)
ASSIGNMENT " J 0 0 0
13e a) 14f a) 15e a)
1 1
1
13e a) 14f a) 15e a)
29582.110* 29586.789* 29591.559*
1 1
54e/f 55f/e 56e/f
13959.925 13961.125 13962.410
29532.176* 29533.376* 29534.661*
2 2 2
:2; "; 15e =I
55e/f 55e/f 55&!/f
13799.144 13803.839 13808.549
29650.824* 29655.519* 29660.229*
2 2 2
54e/f 55f/e 56e/f
2 2 2
14e/f 14e/f 14e/f
14096.192 14097.375 14098.645
29668.442* 29669.626* 29670.896*
4 4 4
13e/f 14f/e 15e/f
4 4 4
55e/f 55e/f 55e/f
13933.907 13938.500 13943.178
29785.587 29790.ia0 29794.858
4 4 4
54e/f 55f/e 56e/f
2 2 2
14e 14e 14e
14162.904 14164.072 14165.326
29735.155* 29736.323* 29737.577*
5 5 5
13e 14f 15e
4 4 4
55e/f 55e/f 55e/f
13999.080 14003.395 14007.725
29850.760 29855.076 29859.405
5 5 5
54e/f 55f/e 56e/f
2 2 2
14e 14e 14e
13820.381 13821.592 13822.887
29392.632*
2 2 2
14e 14e 14e
13890.537 13891.745 13893.021
29462.788* 29464.400* 29465.272*
4 4 4
55e/f Me/f 55e/f
13730.430 13735.109 13739.879
2 2 2
14e 14e 14e
4 4 4
29393.843* 29395.138*
Data used to fit Dunham Constants. Also observed via B%I,,v'-O,J'-14e intermediate level
308
WANG ET AL. TABLE II Energy Levels and Assignments of the Rydberg State ‘IIs and the Corresponding Intermediate States (B’II, (u’, S)) INTERMEDIATE v'
T
PROBE
J'
(cm-l)
ASSIGNPIENT
(cm-1)
"
J
0 0
13 15
0 0
14e/f 16e
13098.335 13097.809
28522.905 28525.358
0 0
14e 14e
13168.969 13171.439
28593.530 28596.008
13 15
0 0
14e 14e
13239.195 13241.633
28663.764 28666.203
13 15
0 0
14e 14e
13309.031 13311.461
28733.601 28736.031
13 15
0 0
14e 14e
13378.453 13380.892
28803.023 28805.462
13 15
0 0
14e 14e
13447.454 13449.880
28072.024 20674.450
13 15
2
2
14e 14e
13368.380 13370.785
28940.631 28943.035
6 6
13 15
2 2
14e/f 14e/f
13436.572 13438.971
29008.823 29011.222
7 7
13 15
2 2
14e/f 14e/f
13504.320 13506.706
29076.571 29078.957
8 8
13 15
2 2
14e/f 14e/f
13571.647 13574.035
29143.897 29146.2135
9 9
13 15
2 2
14e/f 14e/f
13638.503 13640.854
29210.754 29213.105
10 10
13 15
2 2
14e/f 14e/f
13704.942 13707.286
29277.193 29279.537
11 11
13 15
TABLE III Energy Levels and Assignments of the Rydberg State ‘2; and the Corresponding Intermediate States (B’II, (v’, J’)) INTERMEDIATE v' J'
Term Value (cm-')
ASSIGNMENT " J
2 2 2
14e 14f 14e
13829.266 13830.350 13831.547
29401.517 29402.601 29403.798
:
4 4 4
55e 55f 55e
13659.079
0
13663.348 13667.725
29510.759 29515.028 29519.405
0
0
54 55 56
4 4 4
55e 55f 55e
13722.197 13726.528 13730.913
29573.877 29578.208 29582.593
1 1 1
54 55 56
2
14e 14f 14e
13956.140 13957.211 13958.382
29528.391 29529.462 29530.633
2
13
;
:I: a)
z a)
PROBE (cm-l)
0
Also observed via B1llu~'-0, J'-14e intermediate level.
13 14 15
a) a)
a)
WY
K2 RYDBERG STATES TABLE IV Molecular Constants of the ‘As, ‘IIt, and One of the ‘Zi States of 39K2; The Number in Parentheses is 1g Uncertainties
lAE Te 0, uexe WJe Be =e De R,(A)
lnP,
29349.5l32(0.008) 70.8690(93)
28479.730(0.039) 71.0437(94)
0.3178(38) -0.0125(4) 0.04338(3) 0,244(2)x10-3 0.676(80)x10-7 4.4585(15)
0.1918(15) -0.999(82)x10-3 0.04265(M) 0.180(26)x10-3 ___ 4.4967(95)
29363.005(0.01) 62.631(45) -0.266(16) ___ 0.039172(5) ___ ___ 4.6918(3)
three states, molecular constants can be fitted and hence RKR potential curves and Franck-Condon factors can be calculated. Only the Franck-Condon factors calculated from the u-numberings in Tables I, II, and III give satisfactory agreement with observations. Vibrational numbering and molecular constants of the A ‘2 : state have been obtained from observation of the A ‘Z : o’ = 12- 18 levels by Ross et al. (IO). In order to confirm the A ’ Z : v-numbering and observe the A1I2: II’= 0- 11 levels, we resolved the fluorescence from more than 15 different vibrational-rotational levels of the ‘Xi states to the A ‘Z: state. The o’ = O-1 1 levels have been observed and no levels below u’ = 0 were found. It is not the purpose of this paper to discuss the A ‘22: state; the results will be reported elsewhere ( 11) . Table IV lists the molecular constants of the ‘AZ, ‘I&, and one of the ‘2: states. It can be seen that the first two states in Table IV have similar w,, w,x,, B,, and cy, values to the K: ‘2: state ( 7) and they are also very similar to those of the A ‘L:L state (Table 5 of Ref. (10)). The same similarity has been seen for Na2 (12). From the similarity of the constants, we can roughly estimate the asymptotic limits of those Rydberg states. By adding the dissociation energy of the K: ‘Zi state ( 7) to the T,
TABLE V K2 ‘A, RKR Potential Energy Curve; Yoo= -0.00995 ”
%(cm-l)
G(v) + y,, (cm-l)
&n(A)
&ax(A)
0
0.04326 0.04301 0.04277 0.04253 0.04228 0.04204
35.344 105.536 174.981 243.603 311.326 378.076
4.3091 4.2075 4.1408 4.0883 4.0440 4.0049
4.6217 4.7512 4.0459 4.9269 5.0000 5.0682
1 2 3 4 5
R, - 4.459 A
WANG
310
ET AL.
TABLE VI Kz ‘IIs RKR Potential Energy Curve; Y, = 0.00234 v
0
1 2 3 4 5 6 7 8 9 10 11
%(cm-l)
G(v) + y,,
bin(A)
%nax(A)
0.04256 0.04238 0.04220 0.04202 0.04184 0.04166 0.04148 0.04130 0.04111 0.04093 0.04075 0.04057
35.476 106.133 176.397 246.263 315.724 384.774 453.408 521.619 589.401 656.749 723.657 790.118
4.3466 4.2435 4.1758 4.1225 4.0777 4.0386 4.0036 3.9719 3.9428 3.9157 3.8905 3.8667
4.6585 4.7851 4.8766 4.9537 5.0224 5.0856 5.1447 5.2008 5.2544 5.3061 5.3561 5.4048
(cm-l)
Re - 4.497 A
values of our Rydberg states in Table IV, we found that the ‘Ag state and the ‘2: state very likely dissociate to the 4s6d atomic limit and the ‘I& state likely dissociates to either the 457~ or the 4~5 d atomic limit. As another result of this potential curve similarity, the strongest ’ Z,,+ ‘II, - A ‘2 : transitions are the Av = 0 transitions whose Franck-Condon factors are about one order of magnitude larger than the sum of those of all other transitions. Tables V, VI, and VII show the RKR potential curves for the ‘A*, ‘I&, and ‘2: states, respectively. IV. CONCLUSION
One ‘Ag, one ‘I&, and several ‘2: Rydberg states have been observed by cw OODR fluorescence excitation spectroscopy via B ‘II, intermediate levels. Molecular constants of the ‘A* state, the ‘II, state and one of the ‘Z,+ states have been obtained. We observe a striking similarity of the major molecular constants (o,, w,x,, B,, a,) of the ‘4 and ‘I& Rydberg states to those of the “2: ion ground state and the A’Z+U state.
TABLE VII K2 ‘Zi RKR Potential Energy Curve ”
%(cm-l)
G(V) + y,, (cm-l)
hi,,(A)
%mx(A)
0 1 2
0.03917 0.03917 0.03917
31.382 94.545 158.238
4.5291 4.4146 4.3384
4.8604 4.9864 5.0740
R, - 4.692 A
Kz RYDBERG STATES
311
ACKNOWLEDGMENTS We thank Professors R. W. Field and D. D. Konowalow for helpful discussions. This work was supported by National Science Foundation Grant CHE 86- 17954. RECEIVED: May 18, 1989 REFERENCES 1. N. W. CARLSON,A. J. TAYLOR, K. M. JONES,AND A. L. SCHAWLOW,Phys. Rev. A 24,822-834 ( 1981). 2. R. A. BERNHEIM,L. P. GOLD, AND T. TI~ON, J. Chem. Phys. 78,3635-3646 (1983). 3. S. MARTIN, J. CHEVALEYRE, M. CHR. B~RDAS, S. VALIGNAT, AND M. BROYER, J. Chem. Phys. 79, 4132-4141 (1983). 4. L. LI AND R. W. FIELD, J. Mol. Spectrosc. 117, 245-282 ( 1986). 5. X. XIE AND R. W. FIELD, J. Mol. Spectrosc. 117,228-244 ( 1986). 6. A. F. J. VAN RAAN, J. E. M. HAVERKORT, B. L. MEHTA, AND J. KORVING, J. Phys. B: At. Mol. Phys. 15, L669-675 (1982). 7. M. BROYER, J. CHEVALEYRE, G. DELACRETAZ, S. MARTIN, AND L. WOSTE, Chem. Phys. Lett. 99, 206-212 (1983). 8. F. ENGELKEAND V. SCHOHLE,Chem. Phys. Lett. 123,289-294 ( 1986). 9. J. HEINZE, U. SCHOHLE,AND F. ENGELKE, J. Chem. Phys. 87,45-53 ( 1987). 10. A. J. Ross, P. CROZET, C. EF’FANTIN,J. D’INCAN, AND R. F. BARROW, J. Phys. B: At. Mol. Phys. 20, 6225-6231 (1987). II. A. M. LYYRA,W.-T. LUH, L. LI, H. WANG, AND W. C. STWALLEY, submitted to J. Chem. Phys. 12. P. LABASTIE,B. TRIBOLLET, M. BROYER, M. C. BORDAS.AND J. CHEVALEYRE,Mol. Phys. 59,29-40 (1986).
137,304-3 l l ( 1989)
CW Optical-Optical Double-Resonance Excitations of 3gK2Rydberg States HE WANG, ’ LI LI,’ A. M. LYYRA,~ AND W. C. STWALLEY 3 Centerfor Laser Science and Engineering, University of Iowa, Iowa City, Iowa 52242-1294 One ‘4 state, one ‘IIg state, and several ‘2: states of ‘9Kain the energy region 28 522-30 050 cm-’ have been observed by cw optical-optical double-resonance(OODR) fluorescenceexcitation techniques. Absolute vibrational numberings of the ‘4 state, the ‘II, state, and one of the ‘Zi states have been assignedand major molecularconstants for these three states have been determined. 0 1989 Academic Press,Inc. I. INTRODUCTION
Rydberg states of alkali dimers have been interesting to spectroscopists for many years. Excellent experimental results have been reported for Na2 and Li2 (I-5). Although highly excited K2 Rydberg states near the ionization limit have been observed by two- and three-photon ionization with unresolved rotational structure ( 6-7)) very little is known about the lower members of the Rydberg series. Engelke and Schtile reported transitions into Rydberg states by Doppler-free two-photon excitation in the energy region of 3 1 000-32 000 cm -’ (8). Normally, two-photon transitions are rare and only occur by coincidence; it is therefore difficult to study the Rydberg states systematically by that method. Sub-Doppler OODR spectroscopy, on the other hand, has proven to be a very powerful technique for study of Rydberg states even in the high-energy region where the density of energy levels is very high. In this paper we report our experimental investigation of Rydberg states of 39K2 with cw sub-Doppler OODR fluorescence excitation spectroscopy in the energy region 28 522-30 050 cm-’ above the potential minimum of the ground state. II. EXPERIMENTAL DETAILS
The experimental setup is shown in Fig. 1. Potassium vapor was generated in a five-arm stainless steel heat-pipe oven allowing spectral observation perpendicular to the laser axis. The heat pipe was operated at an equilibrium pressure of l-2 Torr of Ar buffer gas. An Ar+ laser-pumped CR 599-21 dye laser operated with DCM dye was used as the pump laser to excite 39K2 B’lI,-X12: transitions. A Kr+ laser-
’ Also Department of Physics and Astronomy. 2 Permanent address:Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, People’s Republic of China. 3 Also Department of Chemistry and Department of Physics and Astronomy. 0022-2852/89 $3.00 CopyrightQ 1989 by Academic Press, Inc. All rightsof reproductionin any form reserved.
304
305
K2 RYDBERG STATES
COMPUTER
CHOPPER fI t
\
I I
,
A
6 MONOCHROMATOR
PREAMPLIFIER
FIG. I. OODR experimental set-up. The single-mode operation of the CR 599-2 1dye laser was monitored with a spectrum analyzer (SA) and a scope.
pumped CR 699-29 Autoscan ring dye laser, operated with LD700 dye, was used as a probe laser. Iodine laser-induced fluorescence was used for absolute frequency calibration for both lasers. The pump and probe beams, after being modulated atfr and f2,respectively, were combined using a dichroic mirror (that passes X < 6900 A and reflects h > 7000 A) and then the copropagating beams were focused at the center of the heat-pipe oven. When the pump laser frequency was tuned to a selected B’II, D’, J’ + X’Z: u”, J” transition and held fixed, the probe laser was scanned and the OODR fluorescence to low vibrational levels of the A ‘Z L state was detected with a filter-PMT-lock-in system at a frequency offi - fi . The OODR fluorescence was also dispersed with a 0.5-m monochromator. The excitation scheme is shown in Fig. 2. B’II, v’ = 2, J’ = 14e/f, v’ = 0, S = 14e, and v’ = 4, J’ = 55e/f levels were selected as intermediate levels, which were excited from X’Z: 2)” = 0, 1, and 4, respectively, with large Franck-Condon factors. Transition frequencies were calculated from molecular constants given by Heinze et al. (9). Due to the high density of rovibrational transitions (calculations show that at least 10 B ‘II, + X ‘Zi transitions could be simultaneously excited at any pump frequency even with a narrow-band ( 1 MHz) CW dye laser), extra intermediate levels other than the selected one could also have been populated. In order to identify the OODR signals via the desired intermediate levels from those via unexpected intermediate levels, we first populated the selected B’II, v’, J’ level by pumping the B’II, v’, J’, +- X12: v”, J” = J’ - 1 transition, scanning the probe laser, then pumping the B’II, v’, J’ + k1 TZg d’, J”
306
WANG ET AL.
K, POTENTIALS 32 28 -
“9 \ 7%
1 + h
24 -
20-
-FLUORESCENCE
‘g 8 w
16 12 -
8-PUMP 4-
FIG. 2. Kz OODR fluorescence spectroscopy. The ‘Zl curve (r, = 29 363.005 cm-‘) overlaps the ‘4 state (r, = 29 349.582 cm-‘), but is centered at larger internuclear distance.
= J’ + 1 transition and scanning the probe again. Only those double resonance lines which appeared at the same frequency with the same intensity during both scans are the OODR signals through our selected B’TI, u’, J’ intermediate level. III. RESULTS AND DISCUSSION
From a B’II, intermediate level (e- orf-parity), ‘Z:, ‘Zg, ‘I&, and ‘A, Rydberg states can be reached by OODR excitation. Our detection of the fluorescence from the Rydberg states to the low vibrational levels of the A ‘Z I: state favors the observation of the ‘El and ‘I’&states since ‘Ag and ‘2; states cannot directly radiate to the A ’ Z : state. More than 100 levels in the energy region of 28 522-30 050 cm-r have been observed. Among them, 42 have been assigned to a ‘A, state, 35 to a ‘I& state, 12 to a ‘2: state, and 39 to eight other higher-energy ‘2: states (not reported here). The electronic assignment of the Rydberg states is based on the excitation spectral pattern and resolved fluorescence to the A ‘2: state. ‘2: v + B’II, o’, J’e excitation results in a P and an R line and ‘2: II + B ‘II, v’, J'fexcitation results in only a Q line. ‘TIJ ‘Ag II + B’II, u’, J’e/f transitions, on the other hand, should contain all three (P, Q, and R) lines, but the Q lines for the transition ‘I&V * B’II, v’, J’e/ f were
307
K2 RYDBERG STATES
too weak to be observed in our experiment. By observing the P and R lines from both e and f parity of the intermediate state, the ‘IIg state was distinguished from the ‘Z’ states. The ‘A, state can be readily distinguished since it cannot directly radiate to ihe A ’ Z : state. Table I gives the 42 ‘A, levels, Table II the 35 ‘I& levels, and Table III the 12 ‘Xi levels. Their vibrational and rotational quantum numbers, e- orf-symmetry, term values above the X ‘2: potential minimum, intermediate levels, and probe laser frequencies are also given in those tables. The A-doubling of the ‘A, state and the ‘I& state were not resolved with our accuracy (0.01 cm-‘). The vibrational numberings given in Tables I, II, and III were determined by comparisons of the calculated FranckCondon factors of the ‘Ag, ‘IIg, ‘2: + B’II, systems and the ‘II,, ‘2: + A’Z: systems with the observed intensity patterns. For the given v-numberings of the above
TABLE I Energy Levels and Assignments of the Rydberg State ‘A8and the Corresponding Intermediate States (B’II. (v’, J’)) INTERMEDIATE v' .I'
* a)
PROBE (cm-l)
T (cm-l)
ASSIGNMENT " J 0 0 0
13e a) 14f a) 15e a)
1 1
1
13e a) 14f a) 15e a)
29582.110* 29586.789* 29591.559*
1 1
54e/f 55f/e 56e/f
13959.925 13961.125 13962.410
29532.176* 29533.376* 29534.661*
2 2 2
:2; "; 15e =I
55e/f 55e/f 55&!/f
13799.144 13803.839 13808.549
29650.824* 29655.519* 29660.229*
2 2 2
54e/f 55f/e 56e/f
2 2 2
14e/f 14e/f 14e/f
14096.192 14097.375 14098.645
29668.442* 29669.626* 29670.896*
4 4 4
13e/f 14f/e 15e/f
4 4 4
55e/f 55e/f 55e/f
13933.907 13938.500 13943.178
29785.587 29790.ia0 29794.858
4 4 4
54e/f 55f/e 56e/f
2 2 2
14e 14e 14e
14162.904 14164.072 14165.326
29735.155* 29736.323* 29737.577*
5 5 5
13e 14f 15e
4 4 4
55e/f 55e/f 55e/f
13999.080 14003.395 14007.725
29850.760 29855.076 29859.405
5 5 5
54e/f 55f/e 56e/f
2 2 2
14e 14e 14e
13820.381 13821.592 13822.887
29392.632*
2 2 2
14e 14e 14e
13890.537 13891.745 13893.021
29462.788* 29464.400* 29465.272*
4 4 4
55e/f Me/f 55e/f
13730.430 13735.109 13739.879
2 2 2
14e 14e 14e
4 4 4
29393.843* 29395.138*
Data used to fit Dunham Constants. Also observed via B%I,,v'-O,J'-14e intermediate level
308
WANG ET AL. TABLE II Energy Levels and Assignments of the Rydberg State ‘IIs and the Corresponding Intermediate States (B’II, (u’, S)) INTERMEDIATE v'
T
PROBE
J'
(cm-l)
ASSIGNPIENT
(cm-1)
"
J
0 0
13 15
0 0
14e/f 16e
13098.335 13097.809
28522.905 28525.358
0 0
14e 14e
13168.969 13171.439
28593.530 28596.008
13 15
0 0
14e 14e
13239.195 13241.633
28663.764 28666.203
13 15
0 0
14e 14e
13309.031 13311.461
28733.601 28736.031
13 15
0 0
14e 14e
13378.453 13380.892
28803.023 28805.462
13 15
0 0
14e 14e
13447.454 13449.880
28072.024 20674.450
13 15
2
2
14e 14e
13368.380 13370.785
28940.631 28943.035
6 6
13 15
2 2
14e/f 14e/f
13436.572 13438.971
29008.823 29011.222
7 7
13 15
2 2
14e/f 14e/f
13504.320 13506.706
29076.571 29078.957
8 8
13 15
2 2
14e/f 14e/f
13571.647 13574.035
29143.897 29146.2135
9 9
13 15
2 2
14e/f 14e/f
13638.503 13640.854
29210.754 29213.105
10 10
13 15
2 2
14e/f 14e/f
13704.942 13707.286
29277.193 29279.537
11 11
13 15
TABLE III Energy Levels and Assignments of the Rydberg State ‘2; and the Corresponding Intermediate States (B’II, (v’, J’)) INTERMEDIATE v' J'
Term Value (cm-')
ASSIGNMENT " J
2 2 2
14e 14f 14e
13829.266 13830.350 13831.547
29401.517 29402.601 29403.798
:
4 4 4
55e 55f 55e
13659.079
0
13663.348 13667.725
29510.759 29515.028 29519.405
0
0
54 55 56
4 4 4
55e 55f 55e
13722.197 13726.528 13730.913
29573.877 29578.208 29582.593
1 1 1
54 55 56
2
14e 14f 14e
13956.140 13957.211 13958.382
29528.391 29529.462 29530.633
2
13
;
:I: a)
z a)
PROBE (cm-l)
0
Also observed via B1llu~'-0, J'-14e intermediate level.
13 14 15
a) a)
a)
WY
K2 RYDBERG STATES TABLE IV Molecular Constants of the ‘As, ‘IIt, and One of the ‘Zi States of 39K2; The Number in Parentheses is 1g Uncertainties
lAE Te 0, uexe WJe Be =e De R,(A)
lnP,
29349.5l32(0.008) 70.8690(93)
28479.730(0.039) 71.0437(94)
0.3178(38) -0.0125(4) 0.04338(3) 0,244(2)x10-3 0.676(80)x10-7 4.4585(15)
0.1918(15) -0.999(82)x10-3 0.04265(M) 0.180(26)x10-3 ___ 4.4967(95)
29363.005(0.01) 62.631(45) -0.266(16) ___ 0.039172(5) ___ ___ 4.6918(3)
three states, molecular constants can be fitted and hence RKR potential curves and Franck-Condon factors can be calculated. Only the Franck-Condon factors calculated from the u-numberings in Tables I, II, and III give satisfactory agreement with observations. Vibrational numbering and molecular constants of the A ‘2 : state have been obtained from observation of the A ‘Z : o’ = 12- 18 levels by Ross et al. (IO). In order to confirm the A ’ Z : v-numbering and observe the A1I2: II’= 0- 11 levels, we resolved the fluorescence from more than 15 different vibrational-rotational levels of the ‘Xi states to the A ‘Z: state. The o’ = O-1 1 levels have been observed and no levels below u’ = 0 were found. It is not the purpose of this paper to discuss the A ‘22: state; the results will be reported elsewhere ( 11) . Table IV lists the molecular constants of the ‘AZ, ‘I&, and one of the ‘2: states. It can be seen that the first two states in Table IV have similar w,, w,x,, B,, and cy, values to the K: ‘2: state ( 7) and they are also very similar to those of the A ‘L:L state (Table 5 of Ref. (10)). The same similarity has been seen for Na2 (12). From the similarity of the constants, we can roughly estimate the asymptotic limits of those Rydberg states. By adding the dissociation energy of the K: ‘Zi state ( 7) to the T,
TABLE V K2 ‘A, RKR Potential Energy Curve; Yoo= -0.00995 ”
%(cm-l)
G(v) + y,, (cm-l)
&n(A)
&ax(A)
0
0.04326 0.04301 0.04277 0.04253 0.04228 0.04204
35.344 105.536 174.981 243.603 311.326 378.076
4.3091 4.2075 4.1408 4.0883 4.0440 4.0049
4.6217 4.7512 4.0459 4.9269 5.0000 5.0682
1 2 3 4 5
R, - 4.459 A
WANG
310
ET AL.
TABLE VI Kz ‘IIs RKR Potential Energy Curve; Y, = 0.00234 v
0
1 2 3 4 5 6 7 8 9 10 11
%(cm-l)
G(v) + y,,
bin(A)
%nax(A)
0.04256 0.04238 0.04220 0.04202 0.04184 0.04166 0.04148 0.04130 0.04111 0.04093 0.04075 0.04057
35.476 106.133 176.397 246.263 315.724 384.774 453.408 521.619 589.401 656.749 723.657 790.118
4.3466 4.2435 4.1758 4.1225 4.0777 4.0386 4.0036 3.9719 3.9428 3.9157 3.8905 3.8667
4.6585 4.7851 4.8766 4.9537 5.0224 5.0856 5.1447 5.2008 5.2544 5.3061 5.3561 5.4048
(cm-l)
Re - 4.497 A
values of our Rydberg states in Table IV, we found that the ‘Ag state and the ‘2: state very likely dissociate to the 4s6d atomic limit and the ‘I& state likely dissociates to either the 457~ or the 4~5 d atomic limit. As another result of this potential curve similarity, the strongest ’ Z,,+ ‘II, - A ‘2 : transitions are the Av = 0 transitions whose Franck-Condon factors are about one order of magnitude larger than the sum of those of all other transitions. Tables V, VI, and VII show the RKR potential curves for the ‘A*, ‘I&, and ‘2: states, respectively. IV. CONCLUSION
One ‘Ag, one ‘I&, and several ‘2: Rydberg states have been observed by cw OODR fluorescence excitation spectroscopy via B ‘II, intermediate levels. Molecular constants of the ‘A* state, the ‘II, state and one of the ‘Z,+ states have been obtained. We observe a striking similarity of the major molecular constants (o,, w,x,, B,, a,) of the ‘4 and ‘I& Rydberg states to those of the “2: ion ground state and the A’Z+U state.
TABLE VII K2 ‘Zi RKR Potential Energy Curve ”
%(cm-l)
G(V) + y,, (cm-l)
hi,,(A)
%mx(A)
0 1 2
0.03917 0.03917 0.03917
31.382 94.545 158.238
4.5291 4.4146 4.3384
4.8604 4.9864 5.0740
R, - 4.692 A
Kz RYDBERG STATES
311
ACKNOWLEDGMENTS We thank Professors R. W. Field and D. D. Konowalow for helpful discussions. This work was supported by National Science Foundation Grant CHE 86- 17954. RECEIVED: May 18, 1989 REFERENCES 1. N. W. CARLSON,A. J. TAYLOR, K. M. JONES,AND A. L. SCHAWLOW,Phys. Rev. A 24,822-834 ( 1981). 2. R. A. BERNHEIM,L. P. GOLD, AND T. TI~ON, J. Chem. Phys. 78,3635-3646 (1983). 3. S. MARTIN, J. CHEVALEYRE, M. CHR. B~RDAS, S. VALIGNAT, AND M. BROYER, J. Chem. Phys. 79, 4132-4141 (1983). 4. L. LI AND R. W. FIELD, J. Mol. Spectrosc. 117, 245-282 ( 1986). 5. X. XIE AND R. W. FIELD, J. Mol. Spectrosc. 117,228-244 ( 1986). 6. A. F. J. VAN RAAN, J. E. M. HAVERKORT, B. L. MEHTA, AND J. KORVING, J. Phys. B: At. Mol. Phys. 15, L669-675 (1982). 7. M. BROYER, J. CHEVALEYRE, G. DELACRETAZ, S. MARTIN, AND L. WOSTE, Chem. Phys. Lett. 99, 206-212 (1983). 8. F. ENGELKEAND V. SCHOHLE,Chem. Phys. Lett. 123,289-294 ( 1986). 9. J. HEINZE, U. SCHOHLE,AND F. ENGELKE, J. Chem. Phys. 87,45-53 ( 1987). 10. A. J. Ross, P. CROZET, C. EF’FANTIN,J. D’INCAN, AND R. F. BARROW, J. Phys. B: At. Mol. Phys. 20, 6225-6231 (1987). II. A. M. LYYRA,W.-T. LUH, L. LI, H. WANG, AND W. C. STWALLEY, submitted to J. Chem. Phys. 12. P. LABASTIE,B. TRIBOLLET, M. BROYER, M. C. BORDAS.AND J. CHEVALEYRE,Mol. Phys. 59,29-40 (1986).