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An analysis of the F′(0u+) ion-pair state of I2 by optical-optical double resonance
JOURNAL OF MOLECULAR
SPECTROSCOPY
117,89- 10 1 ( 1986)
An Analysis of the F’(Ol) Ion-Pair State of I2 by Optical-Optical Double Resonance TAKASHI ISHIWATA, ATSUTO TOKUNAGA,
TSUTOMU
SHINZAWA,
AND IKUZO TANAKA Department of Chemistry, Tokyo Institute of Technology, Ohokayama, Meguro, Tokyo 152, Japan An optical-opticaldouble resonance technique utilizing a stepwise three-photon transition has been applied to study the F’(O:) ion-pair state of I2 which correlates with I-(‘S) + I+(‘D) at the dissociation limit. Two pulsed tunable dye lasers are used to excite the molecules to appropriate levels of the B’II(O:) state, and subsequently into the F’(O:) state by a simultaneous two-photon transition. The optical-optical double resonance excitation spectra show vibrational progressions consisting of 0, Q, and S branches in accordance with the selection rule (AJ = 0, 22) of the F(O:)-B311(O:) two-photon transition. The absolute vibrational numbering of the F’(O:) state is established by the direct observation of the F’(O:)-X’Z: fluorescence interpreted using the FranckCondon factor calculations. Dunham parameters of the F’(O:) state, based on a global leastsquares fit analysis of 136 1 transitions (u’ = O-38, J’ = 6- 108), are Y, = 5 1706.237(2),
Y10= 131.00041(83),
YZO= -0.5 16270(143)
Y,, = 4.2640( 104) X 10m3,
Y, = -4.5797(330) x 10-5.
Y,, = 2.8381(376) X lo-’
Y,, = 0.02194899(46),
Y,, = -9.2508(99) X 10~‘.
Y,, = 8.359(79) x lo-’
Y,, = -8.550( 167) X 10-9,
and Y,, = -2.632(37) X 10s9
(all in cm-’ with 1 SD in parentheses).
0
1986 Academic press. IK.
1. INTRODUCTION
The ultraviolet emission spectrum of I2 has been studied many times both from a theoretical and an experimental point of view (I-5). While in the earlier works some confusion existed regarding the interpretation of the spectrum, it appears that the numerous bands observed in the discharge experiments are of the charge transfer type, originating from ion-pair states and terminating on low-lying valence states (6). Since the spectrum is extremely congested due to the high density of the states, the analysis requires high resolution when using conventional spectroscopy. Furthermore, many possible transitions between the excited states and also with the ground state overlap in the same spectral region. In view of these difficulties, an optical-optical double resonance (OODR) technique has recently been introduced to clarify the assignment of the emission spectrum. The results are quite useful for sorting out the emission bands, and more than half of the 20 ion-pair states correlating with I-(‘S) + If(3P, ‘D, ‘S) have been spectroscopically identified (7-15). In this paper we present the results of OODR analysis on the F’(0:) ion-pair state of Iz, which tends toward I-(‘S) + I+(‘D) at the dissociation limit. In accordance with the pump-probe scheme, F’(O:)-B311(O:)-X’Z~, the OODR excitation spectra re89
0022-2852186 $3.00 Copyri&t 0 1986 by Academic Press. Inc. All rights of reproduction in any form reSXXd
90
ISHIWATA ET AL.
vealed the F’(0:) state in the vibrational progressions consisting of the 0, Q, and S branches, and our observations were made on the vibrational levels 2)’= 0 through u’ = 38. A set of the molecular constants obtained from a Dunham-type expression is given as well as an RKR potential curve of the F’(0:) state. Furthermore, the OODR emission is resolved to show that the F’(O:)-X’Z,+ transition is responsible for the 235~nm emission observed in the discharge. The results reported here confirm the essential features previously derived (16), while the determination of the molecular constants has been significantly improved. 2. EXPERIMENTAL
DETAILS
The experimental setup used in the present work is very similar to that described previously (I 7). Briefly, the OODR excitation of I2 was performed by two tunable dye lasers which were pumped by the divided outputs of an XeCl excimer laser. The I2 molecules in the X’Z,+ ground state were first excited to the B311(O:) state by a pump laser (vi), and subsequently to the F’(0:) state by a probe laser (vz) in a simultaneous two-photon transition, The pump laser frequency was adjusted to a P- or R-branch transition of the B311(O:)-X’Z; system by monitoring the near-infrared fluorescence and assigned using their molecular constants. The probe laser was scanned to probe the vibrational progressions arising from the excitation of 12 to the F’(O:) state by monitoring the F’(O:)-X12,+ emission band through a 25-cm monochromator. Both of the laser beams were aligned to propagate in parallel and then both were focused into the ultraviolet fluorescence cell. A photomultiplier signal was amplified 10 times by a preamplifier and detected by a boxcar integrator. The output of dye laser was vertically polarized. In order to examine anisotropic characters of the two-photon transitions originating from the B311(O:) state, the polarization angle of the probe laser could be changed. The optical components used for this purpose consisted of a polarizer, a double Fresnel rhomb, and a single Fresnel rhomb. In a separate experiment, the two laser frequencies were adjusted to excite the desired F’(O$B311(O:)-X’Z~ transition, and the fluorescence spectrum was recorded by using a 50-cm monochromator in the second order. 3. RESULTS AND DISCUSSION
In the OODR experiments of IZ through the pump-probe excitation scheme, F’(O:)-B311(O:)-X’Z,‘, the double resonance signals were detected in three types of transitions induced by an overall three-photon process: Type I
Vl
+
&2)
Type II
Vl
+
hl
Type III
v2
+
G2).
+
v2)
The type I transition denotes the (1 + 2) photon process which corresponds to the excitation of 12to the appropriate level of the B311(O:) state by pump frequency (vi) and thence to the F’(0:) ion-pair state in the simultaneous two-photon transition by probe frequency (2~~) alone. On the other hand, the process involving two photons
THE F’(0,) ION-PAIR STATE OF I2
91
in the type II transition proceeds by the combination of pump and probe lasers (Y, + v2) due to the temporal overlap of pump and probe pulses. Both the type I and II transitions appear in the spectrum as vibrational progressions with regular intervals, while they can be distinguished by the dependence of their line intensities on the time delay between two laser pulses and more easily identified by the polarization effects on their transition strength. In the type III transition, the excitation of molecules is performed by the probe laser alone and only if the double resonance conditions of the two transition components are satisfied at a given frequency. The previous analysis of the F’(O:) state was based on transitions of this type but they appeared too sparse to permit a systematic analysis. Figure 1 shows a typical OODR spectrum corresponding to the type I transition. It was obtained by probe photons with (a) vertical and (b) circular polarization, while the pump laser was operated with vertical polarization. The pump laser (vJ was adjusted to a photon energy of 18 356.15 cm-’ which is in resonance with the (26-O)PSs transition of the B311(O&X’Zl system. The spectrum was recorded by installing an intracavity etalon in the probe laser, whose frequency was determined by reference to the B311(O:)-X’Z,+ spectrum of I2 (18). A sample pressure was 0.3 Torr and there was no time delay between pump and probe laser pulses. Under these conditions, the relaxation of the intermediate B311(O:) state does not occur during the excitation. The excited states which are able to combine with the B31’I(Oz)state by a coherent twophoton absorption are 0:) 1u, and 2, in Hund’s case c notation in accordance with the rotational selection rules,
17196 Wavenumber
( cm-’
)
FIG. 1. A typical OODR excitation spectrum of the type I transition taken under high-resolution (FWHM = 0.04 cm-‘). The probe laser is (a) vertically and (b) circularly polarized. The pump frequency ( 18356.15 cm-‘) is in resonance with a (26-O)& transition of the B’II(O:)-X’Z: system. The spectrum shows closely spaced rotational lines, which correspond to the two-photon transitions from the B311(O:)state; (9-26)0,, (17 913.76 cm-‘), Q,, (17 196.05 cm-i), and SW (17 198.39 cm-‘).
92
ISHIWATA
ET AL.
AJ = 0, k2
for 0+-O+ transition
(1)
AJ = 0, kl, +2
for l-O+ and 2-O+ transitions.
(2)
The appearance of three rotational lines is consistent with the symmetry of the F’(0:) ion-pair state and they can be attributed to the 0, Q, and S branches in order with increasing frequency of the probe laser. Furthermore, the polarization effects of the transition strength appear in the F’(Oz)-B311(O:) transition because of the anisotropic character of the coherent twophoton absorption. Their transition strengths (6) depend on (1) a factor specified by J” and J’, analogous to the Honl-London factors appearing in one-photon transitions, (2) an intrinsic factor characteristic to the particular vibronic transition, and (3) a factor dependent on the polarization vector of the two photons absorbed simultaneously, as discussed in detail by McClain and Harris (19). In the case of 0+-O+ transition, we can obtain the intensity ratio of the 0 and S branches:
Subscripts 1 and c designate linearly and circularly polarized photons, respectively. It is obvious that the value of 3/2 in Eq. (3) agrees with our observations and the excitation
0
*
17150
17170
17160 Wavenumber
17180
(cm’)
RG. 2. A Fortrat diagram of the (0-14)F’(O:)-B%(O:)
transition.
93
THE F’(0,) ION-PAIR STATE OF I2 TABLE I Observed Double Resonance Transitions of I2 (cm-‘) Proke transition(cm-5 -P 0
Q
Probe transition(an-l) -P
S
v'=2 3
17354.44 17354.85 17355.35 418.43 418.84 419.34
v'=2 3
17353.62 17354.36 17355.16 417.64 418.34 419.15
v'=2 3
0
Q
S
v'=2 3
17338.92 17342.03 17345.22 402.73 405.82 408.99
R78
v'=2 3
17336.00 17339.40 17342.91 399.74 403.13 406.62
17354.34 17354.78 17355.33 418.34 418.80 419.34
P79
v'=2 3
17336.42 17339.79 17343.25 400.16 403.52 406.97
17353.51 17354.27 17355.13 417.50 418.25 419.11
Rs4
v'=2 3
17333.30 17336.95 17340.71 397.00 400.65 404.38
17353.36 17354.18 17355.06 417.34 418.16 419.05
'84
v'=2 3
17334.23 17337.78 17341.46 397.94 401.50 405.15
v'=2 3
17352.25 17353.36 17354.56 416.24 417.34 418.53
%9
v'=2 3
17330.89 17334.80 17338.75 394.58 398.45 402.39
v'=2
17353.23 17354.06 17355.00
'87
v'=2 3
17332.83 17336.52 17340.33 396.52 400.20 404.00
v'=2
17352.07 17353.22 17354.46
v'=2 3
17353.08 17353.96 17354.94 417.06 417.95 418.92
R92
v'=2 3
17329.42 17333.44 17337.54 397.06 393.07 401.14
v'=2
17351.91 17353.08 17354.38 415.86 417.06 418.33
P90
v'=2 3
17331.38 17335.23 17339.17 398.88 395.07 402.80
v'=2 3
17352.25 17353.36 17354.56 416.06 417.33 418.53
535
v'=2 3
17327.90 17332.03 17336.27 391.52 395.64 399.86
v'=2 3
17350.89 17352.31 17353.81 414.85 416.26 417.75
P35
v'=2 3
17350.68 17352.13 17353.68 414.66 416.09 417.63
R40
v'=2 3
17349.07 17350.80 17352.66 413.M) 414.74 416.58
v'=2
17349.30 17351.01 17352.82 413.26 414.95 416.76
R46
v'=2 3
17347.46 17349.48 17351.57 411.39 413.40 415.49
P47
v'=2 3
17347.74 17349.72 17351.79 411.66 413.64 415.68
(13-o)Pll
R16
P41
R52
v'=2 3
17345.70 17347.98 17350.34 411.86 409.59 414.21
P59
v'=2 3
17344.08 17346.58 17349.18 407.96 410.44 413.00
R64
v'=2 3
17341.63 17344.42 17347.31 405.47 408.25 411.11
'60
v'=2 3
17343.75 17346.30 17348.93 407.60 410.15 412.76
R65
v'=2 3
17341.27 17344.07 17347.03 405.09 407.91 410.84
'65
v'=2 3
17342.00 17344.75 17347.59 405.84 408.58 411.40
v'=2 3
17339.34 17342.39 17345.54 403.13 406.17 409.31
R70
(13-o)P73
17333.91 17337.93 397.53 401.56
P93
R98
R16
R27
v'=2 3
17326.34 17330.60 17334.96 389.91 394.52 398.52
v'=a
17173.75 17174.11 17174.57
v'=O
17173.02 17173.69 17174.45
v'=a 4
17173.66 17174.06 17174.57 430.66 431.08 431.58
v'=o 4
17172.88 17173.62 17174.42 429.86 431.38 430.59
v'=4
17430.55 17431.02 17431.57
v'=4
17429.75 17430.49 17431.34
v'=o
17173.34 17173.90 17174.54
v'=O
17172.48 17173.34 17174.28
v'=O
17173.14 17173.78 17174.49
v'+
17172.20 17173.14 17174.18
v'=o
17172.49 17173.34 17174.29
v'=o
17171.40 17172.56 17173.81
v'=O 4
17172.34 17173.24 17174.23 429.32 431.17 430.20
v'=O 4
17171.23 17172.43 17173.73 428.14 429.32 430.60
ISHlWATA ET AL.
94
TABLE I-Continued F-r* transition(~31~~1 plrmp 0
(14-O)P*,
R32
Q
S
v'=o 1 4
17171.57 17172.68 17173.89 236.53 237.66 238.84 428.50 429.58 430.78
VW
17170.30 17171.71 17173.23 235.26 236.66 238.17 427.17 428.55 430.04
1 4
Probe transitionCan-l) _P
'28
v'=O
17171.40 17172.56 17173.82
R33
v'=O
17170.10 17171.56 17173.13
0
clli-o,P,, v'=O 1 4 5
Q
S
17163.59 17166.16 17168.80 230.98 233.59 228.41 422.54 425.15 420.02 488.05 482.95 485.47
'65
v'=O 1 4 5
17161.26 17164.11 17167.08 228.92 231.85 420.35 423.28 417.54 483.25 486.15 480.44
R70
v'=O 4 5
17159.46 17162.55 17165.71 421.79 415.63 418.66 484.63 478.48
P73
v'=U :
17159.09 17162.24 17165.44 421.47 230.17 415.23 223.85 418.29 226.96
'32
v'=l
17235.64 17236.97 17238.39
R37
v'=l
17234.17 17235.82 17237.54
P35
V'=O 1 4 5
17170.10 17171.56 17173.11 235.04 236.50 238.05 426.95 428.38 429.92 489.94 491.39 492.91
R78
V'=O 1 4 5
17168.57 17170.33 17172.20 233.48 235.24 237.10 425.32 427.06 428.89 488.29 490.02 491.87
v'=O 1 4 5
17156.36 17159.79 17163.32 227.99 221.06 224.49 419.15 412.31 415.69 481.95 478.48
P74
v'=5
17477.66 17480.78 17483.99
P37
v'=O
17169.68 17171.24 17172.87
R79
v'=5
17474.68 17478.09 17481.60
R42
v'=O
17168.09 17169.94 17171.89
'78
v'=O
17157.15 17160.49 17163.95
R40
5
478.08
471.14
484.30
P40
v'=O
17169.03 17170.71 17172.48
%3
v'=O
17154.28 17157.91 17161.65
R45
VW
17167.33 17169.31 17171.40
P79
P41
v'=O 1 4 5
17168.80 17170.52 17172.34 233.72 235.44 237.26 425.56 427.27 429.05 488.56 490.23 492.04
v'=O 4 5
17156.76 17160.14 17163.62 419.50 412.74 416&X 482.29 475.56 478.88
%4
v'=O 4 5
17153.84 17157.53 17161.32 416.97 409.62 413.24 479.72 472.40 476.02
v'=O 1 4 5
17167.07 17169.09 17171.23 231.97 233.98 236.11 423.73 425.73 427.83 486.71 488.68 490.78
'84
v'=5
17473.32 17476.85 17480.48
%J9
v'=4 5
17407.25 17411.10 17415.04 477.74 469.93 473.81
P46
v'=O 1
17167.59 17169.54 17171.56 232.48 234.43 236.45
'87
v'=5
17471.92 17475.59 17479.33
R51
v'=Cl 17165.70 17167.95 17170.30 1 230.57 232.80 235.15
R92
v'=4 5
17405 77 17409.75 468:49 472.45 17476.50
P47
v'=4 5
17424.01 17425.96 17428.03 486.99 488.92 490.97
P%l
v’=4
%2
v'=4 5
17421.98 17424.23 17426.59 484.93 487.16 489.52
$5
v'=4 5
17404.24 17408.35 17412.55 475.21 466.94 471.03
P54
v'=O 1
17165.41 17167.72 17170.09 230.30 232.56 234.93
P91
v'=O
17151.64 17155.53 17159.52
%6
v'=O
17148.35 17152.55 17156.85
R59
v'=O 1
17163.26 17165.87 17168.57 228.11 230.70 233.37
'92
v'=o
17151.17 17155.11 17159.15
v'=O 4 5
17163.91 17166.41 17169.02 420.36 422.85 425.41 483.29 485.75 488.31
%7
v'=O
17147.86 17152.11 17156.46
P93
v'=4 5
17406.28 17410.20 468.99 472.91 17476.91
v'=o 4 5
17161.60 17164.43 17167.34 417.91 420.69 423.56 480.81 483.57 486.45
%e
v'=4 5
17402.70 17406.92 17411.24 473.86 465.36 469.58
R46
P59
%4
5
17470.47
17411.53 474.26
THE F’(0,)
ION-PAIR
STATE OF 12
95
TABLE I-Continued Probe transition(an-l) -P 0
Q
Probe transition(cm-l) -P
S
(14-OJP97
v'=O
17148.80 17152.99 17157.25
R102
v'=O
17145.35 17149.83 17154.40
(22-O)Pg
v'=7 10
17242.02 17242.42 425.95
R13
v'=7 10
17241.20 17241.78 425.12 425.70 17426.35
58
v'=7 10 11 19
17240.91 17241.61 424.81 425.52 17426.29 485.31 485.99 486.76 955.26 955.92 956.66
R__ LL
v'=7 10 11 19
17241.17 17242.23 17424.09 425.03 426.07 484.56 485.51 486.54 954.44 955.37 956.35 17178.77
0
(22-0)R65
Q
s
v'=6 7 10
17169.59 17172.39 17175.27 231.59 234.38 237.26 415.04 417.79 420.63
p73
v'=6 7 10 19
17167.92 17170.98 17174.10 229.90 232.93 236.07 413.23 416.24 419.34 942.08 945.00 948.01
R77
v'=6 7 10 19
17228.08 411.32
'84 RX6 G’6-O)P2q
v'=6
17169.44 17172.85 231.37 234.75 414.57 417.91 943.03 946.27 17168.09 17171.69
v'=6
17166.35 17170.21
v'=8 9 16 17 20 21 25
17136.52 17137.68 17138.96 197.80 198.96 2cO.21 615.54 616.68 617.87 673.69 674;82 676;03 846.02 847.13 848.33 959.16 960.27 961.47 18126.41 18127.48 18128.68
'27
v'=6
R31
v'=6
17178.15
'32
v'=7 10 11
17239.09 17240.40 17241.77 422.93 424.22 483.38 484.66 486.04
P31
v'=8 9
17136.29 17137.52 17138.87 197.55 198.80 200.13
R36
v'=7 10 11
17238.13 17239.68 17241.29 421.90 423.44 425.05 482.34 483.85 485.49
*36
v'=8 9
17135.35 17136.90 17138.54 196.62 198.16 199.77
p37
v'=6 19
17176.15 17177.67 952.18 953.62 17955.16
R49
v'=8 9
17133.31 17135.40 17137.58 194.51 196.60 198.78
R41
v'=6 19
17175.09 17176.86 950.88 952.58 17954.35
P55
'42
v'=7 10
17237.39 17239.11 17240.90 421.13 422.84 424.64
R46
v'=7 10
17236.19 17238.17 17240.23 419.88 421.84 423.88
v'=8 9 16 17 20 21 22 25 26
17132.58 17134.85 17137.20 193.76 196.05 198.39 610.98 613.17 615.47 669.05 671.24 673.54 841.16 843.33 845.60 897.84 900.01 902.26 954.16 956.33 958.58 18121.17 18123.32 18125.53 176.21 178.34 180.55
v'=6 7
17174.50 17176.40 17178.39 236.61 238.49 240.48
v'=8
17130.40 17133.13 17135.95
v'=6 I
17173.25 17175.42 17177.64 235.33 237.48 239.71
R68
v'=8 9 16 17 20 21 22 25 26
17129.53 17132.43 17135.42 190.67 193.55 196.53 607.38 610.19 613.11 665.39 668.20 671.09 837.32 840.10 842.95 893.93 896.70 899.56 950.20 952.97 955.56 18117.03 18119.77 18122.59 172.00 174.73
P74
v'=8 9
17128.63 17131.71 17134.86 189.76 192.80 195.95
R77
v'=8 9 16 17 20 21 22 25 26
17127.45 17130.73 17134.11 188.52 191.79 195.15 604.90 608.09 611.38 662.88 666.05 669.31 834.68 837.81 841.03 891.23 894.35 897.58 947.45 950.59 953.79 18114.16 18117.24 169.09 172.16 18175.32
'46 R50
P48
v'=lO
17419.87 17421.84 17423.87
R52
v'=lO
17418.49 17420.70 17423.00
P54
v'=7 10 19
17234.87 17237.10 17139.43 418.49 420.70 423.00 948.11 950.24 952.47
R58
v'=7 10 19
17233.41 17235.91 17238.49 416.98 419.43 421.99 946.37 948.76 951.22
P59
v'=7 10
17233.68 17236.12 17238.66 417.24 419.64 422.16
R63
v'=7 10
17232.14 17234.83 17237.62 415.60 418.28 421.03
'61
v'=6 7 10
17171.15 17173.69 17176.30 233.18 235.70 238.32 416.70 419.20 421.81
R64
ISHIWATA
96
ET AL.
TABLE I-Continued Probe transition (an-l) bP 0
(30-0)P15 "'=;; 15 R18
";;;.z 409:91
Q
S
17112.02 17112.67 232.58 233.23 410.47 411.10
v'=lO 12 15
17111.10 17111.88 17112.74 231.64 232.41 233.27 409.53 410.29 411.14
v'=lO 12 15
17110.70 17111.69 17112.75 231.24 232.21 233.27 409.10 410.04 411.10
R28
v'=lO 12 15
17110.25 17111.46 17112.75 230.76 231.94 233.24 408.58 409.76 411.02
Pjl
v'=lO 12 15
17110.15 17111.40 17112.73 230.67 231.89 233.21 408.48 409.69 411.00
R34
v'=lO 12 15
17109.65 17111.11 17112.65 230.15 231.58 233.10 407.92 409.35 410.85
v'=lO 12 15
17109.55 17111.04 17112.63 230.03 231.51 233.07 407;El 409.27 410;83
R40
v'=lO 12 15
17109.00 17110.71 17112.50 229.45 231.16 232;91 407.19 408.86 410.62
P50
v'=lO 12 15
17108.03 17110.07 17112.22 228.43 230.46 232.57 406.10 408.10 410.19
v'=lO 12 15
17107.39 17109.63 17111.97 227.73 229.98 232.30 405.36 407.55 409.85
Psi
v'=lO 12 15
17106.55 17109.05 17111.64 226.84 229.33 231.91 404.39 406.84 409.39
R64
v'=lO 12 15
17105.81 17108.53 17111.33 226.05 228.76 231.53 403.53 406.20 408.94
'67 v'=lO 12 15
17105.65 17108.43 17111.25 225.91 228.64 231.46 403.37 406.06 408.86
R70
v'=lO 12 15
17104.89 17107.85 17110.90 225.08 228.02 231.04 402.46 405.36 408.36
P73
v'=;; 15
17;;;.7$ 17107.72 17110.82 227.87 230.95 402:25 405.21 408.24
R76
v'=lO 12 15
17103.89 17107.10 17110.41 224.03 227.21 230.49 401.30 404.46 407.70
'81 v'=lO 12 15 Rs4
'25
p37
R53
v'=lO 12 15
Probe transition Can-l) m 0 (30-O)Pgo "'=;;
Q
S
15
17398.83
17105.50 17109.31 225.46 402.48 17406.22
v'=12 15
17397.73
17224.67 401.58 17405.53
p97 v'=lO 12 15
17397.27
17104.50 224.35 401.22 17405.24
RlOO v'=lO 15
17396.12
17103.73 400.27 17440.36
Rg3
(31-O)Pg
v'=ll 13 18 19
17137.74 17138.06 17138.46 257.82 550.29 550.60 551.00 607.76 608.06 608.46
R12
v'=;; 18 19
17137.45 17137.98 17138.57 257.73 549.97 550.48 551.07 607.43 607.95 608.52
'25
v'=ll 13 14
17136.66 17137.64 257.37 17258.42 315.66 316.63 317.70
R28
v'=ll 13 14
17136.24 17137.43, 17138.69 255.94 257.13 315.22 316.39 317.69
P31
v'=ll 14
17136.15 17137.37 17138.71 315.12 316.35 317.66
v'=ll 14
17135.69 17137.13 17138.67 314.64 316.06 317.57
v'=ll 13 18 19
17138.19 17136.84 17138.57 254;84 256.47 258.24 547.37 548.98 550.68 604.78 606.40 608.08
v'=ll 13 18 19
17134.65 17136.52 17138.46 254.26 256.11 546.73 548.55 550.44 604.12 605.94 607.83
P50
v'=ll 14
17134.19 17136.22 17138.34 315.01 313.01 317.11
R53
v'=ll 14
17133.59 17135.82 17138.16 312.36 314.57 316.88
v'=ll 13 18 19
17133.33 17135.66 17138.08 252.90 255.20 257.58 547.41 545.14 549;77 602.52 604.76 607.11
R60
v'=ll 13 18 19
17132.69 17135.24 17137.85 252.22 254.72 257.31 544.33 546.81 549.38 601.68 604.15 606.71
17103.38 17106.72 17110.15 223.48 226.80 230.19 400.70 403.98 407.35
P66
v'=ll 13 14
17132.15 17134.85 17137.65 251.62 254.30 310.78 313.44 316.20
17102.50 17106.06 17109.66 222.55 226.05 229.68 399.67 403.16 406.72
R6g
v'=ll 13 14
17131.45 17134.36 17137.36 250.87 253.76 309.96 312.87 315.83
R34 P41
R44
P57
THE F’(0.)
ION-PAIR
STATE OF 12
97
TABLE I-Continued Probe transition(~II-~) m 0
'82
R85 p95
RY8
S
18 19
17131.16 17134.16 17137.24 309.67 312.63 315.69 542;46 545.36 548.36 599.72 602.64 605.65
v'=ll 14 18 19
17130.41 17133.63 17136.91 308.83 312.02 315.28 544.64 541.50 547.84 598.77 601.89 605.08
v'=ll 14
17129.79 17133.17 17136.63 308.16 311.50 314.93
v'=ll 14
17129.01 17132.59 17136.25 307.27 310.82 314.45
v'=ll 14
17127.69 17131.62 17135.62 309.67 313.63
v'=ll 14
17126.85 17130.97 17135.17 308.90 313.09
(31-O)P73 "'=;g
R76
Q
PlO2 v'=ll 17 18 19 RlO5 v'=ll 17 18 19
17479.04 536.50 593.63
17477.95 535.37 592.45
17130.70 483.16 17487.35 540.60 544.78 597.70 601.88 17130.04 482.27 17486.66 539.66 544.08 596.73 601.10
(33-o)Plo v'=L3
17191.47 17191.82 17192.27
R13 v'=13
17191.18 17191.76 17192.40
v'=13
17190.89 17191.65 17192.51
v'=13
17190.55 17191.52 17192.59
P20 R23
v'=13
17187.99 17190.23 17192.55
P72
v'=13
17186.18 17189.13 17192.14
y3
v'=13
17188.90 17192.03
R53
Probe transition(cm-l) _P 0
Q
S
(39-o)P23 v'=27 29 31 32 33 34
17815.89 17816.76 17817.70 924.54 926.31 925.39 18031.97 18032.82 18033.73 085.19 086.96 086.05 138.18 139.cxl 139.94 190.83 191.67 192.59
v'=25 27 29 31 32 33 34
17705.37 17706.83 17708.38 815.21 816.67 818.21 923.77 925.23 926.75 18031.16 18032;58 18034.09 084.38 085.79 087.30 137.32 138.74 140.24 192.87 189.97 191.37
v'=21 27 29 31 32
17481.37 17483.45 17485.63 814.51 816.53 818.67 927.12 922.98 925.01 18030.26 18032.29 18034.39 085.44 087.55 083.44
(39-o)P53 v'=33 34
18136.37 18138.37 18140.42 188.96 193.04 190.94
v'=21 25
17481.27 17483.51 17485.85 704.58 706.79
v'=27
17813.84 17816.44 17819.14 922.24 924.82 18029.42 18031.97 18034.63 087.74 082.54 085.08 140.57 135.41 137.95 193.10 187.95 190.48
R36
P53
R55
'67
32 33 34
R78
v'=27 29 31 32 33 34
(40-o)P51 v’=29 35 P74
v'=29 35 38
17813.29 17816.40 17819.59 921.59 924.65 18028.61 18031.69 18034.84 084.74 137;52 193.14 186.99 190.01 17900.32 17902.34 18216.67 18218.58 18220.58 17898.36
17897.62 17900.47 17903.41 18215.40 18218.20 18221.08 370.42 373.20 376.05
of I2 from the B311(O:) state proceeds through a coherent two-photon transition by the probe photons alone. The molecular constants of the F’(OL) state were obtained from a term value analysis. For this purpose, the probe frequencies (v2) measured in the type I transition are converted to energies all referred to the potential minimum of the X’ZZ state by the equation T;; = hv, + 2hu2 + G”(v) + F’:(J). (5) The pump frequency (Y,) and the term value of the ground state (G”(v) + F;(J)) were calculated from the constants derived by Luc from the B%I(O:)-X’Z: absorption spectrum (20). At this time, the previous u’ numbering of the F’(Oz) state appears to remain valid, since we could not observe any lower vibrational levels than that previously labeled u’ = 0. Rotational assignment of the OODR spectrum was straight-
98
ISHIWATA ET AL. TABLE II Dunham Parameters of the F’(0:) State for I2 (cm-‘) 51706.237(2)')
Yoo
131.00041(83)
y10
-0.516270(143)
Y20 Y30 Y40 y50
x 1O-3 x 10-5
2.8381(376)
x 1O-7
0.02194899(46)
y01
-9.2508(99)
Yll
x 10-5 -7
8.359(79)
Y21
x 10
-8.550(167)
y31
x lo-' -9 x 10
-2.632(3?)
yo2
a)
4.2640(104) -4.5797(330)
Quoted
uncertainty
deviation. energies
"fit
is 0.0175
data in Table
is one standard
to the F'(Oi) cm -1
.
term
Calculated
from
I (v = O-38, J = 6-108).
forward from the selection rule of AJ = 0 and *2, because the rotational quantum number of the pumped B’II(0:) state was known for each set of experiments. In several instances, the same final state was accessed by using two or more different pump frequencies involving different initial and intermediate states in the excitation scheme. In any case the final state term values are consistent with each other within the estimated accuracy of the frequency calibration of the probe laser (~0.02 cm-‘). In the measurements, we intended to probe the F’(0:) ion-pair state with a reasonably wide distribution of J value. In particular, much time was spent sampling the lower vibrational levels for two reasons: (1) to derive an accurate potential curve of the F’(0:) state, in which the equilibrium internuclear distance is one of the dominant factors; and (2) to clarify the existence of perturbation by the surrounding ion-pair states which are expected to appear in the lower vibrational levels largely because of the importance of the Franck-Condon overlap on perturbations between two states (I 7). However, no trace of perturbation could be found, and a Fortrat diagram of the (O-14) P”(O:)-B311(O:) transition is given as an example in Fig. 2. The term values of the F’(0:) state calculated from the OODR transition frequencies in Table I were submitted to a global least-squares fit to the Dunham expansion,
(6) The raw data included in 136 1 transitions in the F’(O:)-B311(0,‘) system with 0 =Sv G 38 and 6 < J =S108. The results of this analysis are shown in Table II. The standard deviation of the fit is 0.0175 cm-’ and the coefficients can be used to regenerate all P’(0:) term values in the fitted range within 0.06 cm-‘. The molecular constants in
THE F’(0,)
ION-PAIR
99
STATE OF Iz
TABLE III RKR Potential Curve of the F’(O,+)State
v
l G(v)+YOO
" (cm-l)
El
Turning inner
0.000
-0.5
-0.25 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
3)
a)(cm-l)
3.4791
32.739
65.393 195.374 324.360 452.374 579.439 705.574 830.804 955.144 1078.616 1201.236 1323.022 1443.990 1564.155 1683.533 1802.138 1919.983 2037.080 2153.443 2269.084 2384.012 2498.241 2611.779 2724.637 2836.825 2948.351 3059.225 3169.457 3279.053 3388.022 3496.373 3604.114 3711.252 3817.796 3923.753 4029.131 4133.939 4238.183 4341.873 4445.016
t
Yoo = 0.02 cm-l vibrational energy
point (i) outer
0.0219029 8121 7228 6351 5488 4640 3806 2986 2178 1383 0599 0.0209827 9065 8314 7573 6481 6117 5402 4696 3996 3302 2615 1934 1257 0586 0.0199918 9255 8594 7935 7280 6626 5972 5320 4667 4014 3360 2704 2046 1386
1s
the Dunham levels.
3.4355 .4183 .3773 .3506 .3291 .3121 .2969 .2834 .2710 -2598 .2492 .2395 .2303 -2216 .2133 .2055 .1979 .1907 .1838 .1771 .2707 .1645 .1584 .1526 .1469 .1414 .1361 .1308 .1258 -1208 .1160 .1113 .1067 .1023 .0979 .0936 .0895 .0855 .0815 .0?77
correction
3.5257 .5459 .5990 -6377 .6705 .6998 .7268 .7521 .7761 .7989 .8210 .8422 .8629 .8830 .9026 .9217 .9405 .9589 .9771 .9949 4.0125 .0298 -0469 .0638 .0805 .0971 .1135 .1297 -1458 .lblB .1771 .1934 .2091 .2246 .2401 .2555 .2708 .2861 .3013 .3164
to the
Table II were used to construct an RKR potential curve of the F’(0:) ion-pair state. The RKR turning points for the observed vibrational levels are given in Table III. Figure 3 shows the vibrational progression of emission spectrum originating from a v = 0, J = 60 level of the F’(0:) state. The absolute wavelength position of the expected P and R doublet of the F’(O:)-X’Z: was calculated by using the molecular constants of the X’Z;; state (21). The results agreed with our observations within the experimental accuracy of 0.2 A, even though the P and R branches were not resolved in the spectrum. We then calculated the Franck-Condon factors of the transitions
100
ISHIWATA ET AL
3
Ji L 10
r
2
A .In c 0, c 1
0 -1 1
I
I
I
I
230
226
234
Wavelength
(nm
111 I
I
/
238
)
FIG. 3. The F’(O:)-X’Zg+ fluorescence spectrum of I*. The excitation process is F’(Oi) (S
PII
&
PZf .
The Franck-Condon factors for the F’(O:)-X’Z: transition at (a) u’ = 0, J’ = 60 and (b) I)’= 2, J’ = 42 [see the spectrum shown in Fig. 2 of Ref. (16)] were calculated to be V
35
36
37
38
39
40
41
42
43
44
45
46
41
4 96
11 186
27 319
62 476
127 606
239 629
413 492
649 237
926 26
1192 47 60
FCF x IO’ 7 V
19
45
48
49
50
51
52
53
54
55
56
57
58
59
1374 318
1408 600
1269 578
995 249
668 2
316 238
173 868
66 1358
17 1308
3 839
355
90
10
between the X’Z: and F’(O:) states to confirm the intensity distribution of the emission spectrum. As shown in Fig. 3, the calculations can obviously reproduce the characteristic intensity distribution. The transition terminates on the high vibrational levels of the ground state as expected since the internuclear distance of P’(0:) ion-pair states is much longer (re = 3.479 A) than that of the ground state [r, = 2.67 A (20)]. The low-u’ level of the ion-pair state should then display in emission a band system whose intensity distribution is modulated according to the probability distribution of the upper vibrational wavefunction. An envelope of the spectrum in Fig. 3 shows a single intensity maximum which indicates that the fluorescence originates from the 2)’= 0
THE F’(0.) ION-PAIR STATE OF I2
101
level. Furthermore, the intensity distribution of Fig. 2 in Ref. (16) is also consistent with the calculation. Our results on the F’(0:) state are consistent with a simple picture describing the ion-pair states of IZ, whereby they group in accordance with ionic asymptotes (1, 2, 6). Among the 20 ion-pair states correlating with I-(‘S) + I+(3P, ‘D, ‘S), the 6 states [0’(2,), P( I&, D(O:), E(O& y( l.), and 6(2,)] which belong to the lowest group correlating with I-(‘S) + I+(3P2)lie at around 40 000 cm-’ above the ground state. The next higher group correlating with I-(‘S) + If(3P,,, 3P,) has been identified to lie at around 47 000 cm-‘. There is a close family likeness in their equilibrium internuclear distances and vibrational frequencies (typically r, = 3.6 .& and o, = 100 cm-‘). The F’(O:) state is expected to correlate with I-(‘S) + I+(‘D), while its energy level and potential curve are somewhat different. It is characterized by a larger vibrational frequency and smaller equilibrium internuclear distance as compared with other ion-pair states and its position is about 2000 cm-’ lower than the empirical predictions: T, = 51 706.2 cm-‘, o, = 131.0 cm-‘, and r, = 3.48 A. It should be pointed out that a similar tendency of strong bonding character of the F’(0:) state is predicted by Jaffe from his theoretical model (3). ACKNOWLEDGMENT The authorsaregratefulto Dr. J. T. Hougen of the National Bureauof Standardsfor supplyingthe RKR and FCF computerprogram. RECEIVED:
September 3, 1985 REFERENCES
1. R. S. MULLIKEN,J. Chem. Phys. 55,288-309 (1971). 2. G. DAS ANDA. C. WAHL, J. Chem. Phys. 69,53-62 (1978). 3. R. L. JAFFE, privatecommunicationcited in Ref. (13). 4. J. A. COXON, “Molecular Spectroscopy”(The Chemical Society, Ed.), Vol. 1, pp. 177-228, Billing, London, 1978. 5. K. P. HUBERANDG. HERZBERG, “Molecular Spectraand Molecular Structure,”Vol. IV, “Constants of Diatomic Molecules,” pp. 330-337, Van Nostrand-Reinhold,New York, 1978.
A. L. GUY, K. S. VISWANATHAN, ANDJ. TELLINGHUISEN, Chem. Phys. Lett. 73,582-588 (1980). J. TELLINGHUISEN, J. Mol. Specfrosc. 94,231-252 (1982). J. P. PEROT, M. BROYER,J. CHEVALEYRE, ANDB. FEMELAT, J. Mol. Spectrosc. 98, 161-167 (1983). J. TELLINGHUISEN, Chem. Phys. Lett. 99,373-376 (1983). 10. J. C. D. BRAND,A. R. HOY, A. K. KALKAR,ANDA. B. YAMASHITA,J. Mol. Spectrosc. 95, 350-358 6. 7. 8. 9.
(1983). 11. G. W. KING, I. M. LITTLEWOOD, ANDJ. R. ROBINS,Chem. Phys. 56, 145-156 (1981). 12. J. C. D. BRANDANDA. R. HOY, J. Mol. Spectrosc. 97,379-386 (1983). 13. K. S. VISWANATHAN ANDJ. TELLINGHUISEN, J. Mol. Spectrosc. 101,285-299 (1983). 14. K. WIELAND,J. TELLINGHUISEN, ANDA. NOBS,J. Mol. Spectrosc. 41,69-83 (1972). 15. K. S. VI~WANATHAN, A. SUR, ANDJ. TELLINGHUISEN, J. Mol. Spectrosc. 86, 393-405 (198 1). 16. T. ISHIWATA,H. OHTOSHI,M. SAKAKI,ANDI. TANAKA,J. Chem. Phys. 80, 1411-1416 (1984). 17. T. ISHIWATA,A. TOKIJNAGA, T. SHINZAWA,ANDI. TANAKA,J. Mol. Spectrosc. 108, 3 14-327 (1984). 18. S. GERSTENKORN AND P. Luc, “Atlas du spectre d’absorption de la mob&de I’iode,” CNRS, Paris, 1978. 19. W. M. M&LAIN AND R. A. HARRIS,“Excited States” (E. C. Lim, Ed.), Vol. 1, pp. l-56, Academic
Press, New York, 1978. 20. P. Luc, J. Mol. Specfrosc. 80,41-55 (1980). 21. J. TELLINGHUISEN, M. R. MCKFZEVER, ANDA. SUR,J. Mol. Spectrosc. 82, 225-245 (1980).
SPECTROSCOPY
117,89- 10 1 ( 1986)
An Analysis of the F’(Ol) Ion-Pair State of I2 by Optical-Optical Double Resonance TAKASHI ISHIWATA, ATSUTO TOKUNAGA,
TSUTOMU
SHINZAWA,
AND IKUZO TANAKA Department of Chemistry, Tokyo Institute of Technology, Ohokayama, Meguro, Tokyo 152, Japan An optical-opticaldouble resonance technique utilizing a stepwise three-photon transition has been applied to study the F’(O:) ion-pair state of I2 which correlates with I-(‘S) + I+(‘D) at the dissociation limit. Two pulsed tunable dye lasers are used to excite the molecules to appropriate levels of the B’II(O:) state, and subsequently into the F’(O:) state by a simultaneous two-photon transition. The optical-optical double resonance excitation spectra show vibrational progressions consisting of 0, Q, and S branches in accordance with the selection rule (AJ = 0, 22) of the F(O:)-B311(O:) two-photon transition. The absolute vibrational numbering of the F’(O:) state is established by the direct observation of the F’(O:)-X’Z: fluorescence interpreted using the FranckCondon factor calculations. Dunham parameters of the F’(O:) state, based on a global leastsquares fit analysis of 136 1 transitions (u’ = O-38, J’ = 6- 108), are Y, = 5 1706.237(2),
Y10= 131.00041(83),
YZO= -0.5 16270(143)
Y,, = 4.2640( 104) X 10m3,
Y, = -4.5797(330) x 10-5.
Y,, = 2.8381(376) X lo-’
Y,, = 0.02194899(46),
Y,, = -9.2508(99) X 10~‘.
Y,, = 8.359(79) x lo-’
Y,, = -8.550( 167) X 10-9,
and Y,, = -2.632(37) X 10s9
(all in cm-’ with 1 SD in parentheses).
0
1986 Academic press. IK.
1. INTRODUCTION
The ultraviolet emission spectrum of I2 has been studied many times both from a theoretical and an experimental point of view (I-5). While in the earlier works some confusion existed regarding the interpretation of the spectrum, it appears that the numerous bands observed in the discharge experiments are of the charge transfer type, originating from ion-pair states and terminating on low-lying valence states (6). Since the spectrum is extremely congested due to the high density of the states, the analysis requires high resolution when using conventional spectroscopy. Furthermore, many possible transitions between the excited states and also with the ground state overlap in the same spectral region. In view of these difficulties, an optical-optical double resonance (OODR) technique has recently been introduced to clarify the assignment of the emission spectrum. The results are quite useful for sorting out the emission bands, and more than half of the 20 ion-pair states correlating with I-(‘S) + If(3P, ‘D, ‘S) have been spectroscopically identified (7-15). In this paper we present the results of OODR analysis on the F’(0:) ion-pair state of Iz, which tends toward I-(‘S) + I+(‘D) at the dissociation limit. In accordance with the pump-probe scheme, F’(O:)-B311(O:)-X’Z~, the OODR excitation spectra re89
0022-2852186 $3.00 Copyri&t 0 1986 by Academic Press. Inc. All rights of reproduction in any form reSXXd
90
ISHIWATA ET AL.
vealed the F’(0:) state in the vibrational progressions consisting of the 0, Q, and S branches, and our observations were made on the vibrational levels 2)’= 0 through u’ = 38. A set of the molecular constants obtained from a Dunham-type expression is given as well as an RKR potential curve of the F’(0:) state. Furthermore, the OODR emission is resolved to show that the F’(O:)-X’Z,+ transition is responsible for the 235~nm emission observed in the discharge. The results reported here confirm the essential features previously derived (16), while the determination of the molecular constants has been significantly improved. 2. EXPERIMENTAL
DETAILS
The experimental setup used in the present work is very similar to that described previously (I 7). Briefly, the OODR excitation of I2 was performed by two tunable dye lasers which were pumped by the divided outputs of an XeCl excimer laser. The I2 molecules in the X’Z,+ ground state were first excited to the B311(O:) state by a pump laser (vi), and subsequently to the F’(0:) state by a probe laser (vz) in a simultaneous two-photon transition, The pump laser frequency was adjusted to a P- or R-branch transition of the B311(O:)-X’Z; system by monitoring the near-infrared fluorescence and assigned using their molecular constants. The probe laser was scanned to probe the vibrational progressions arising from the excitation of 12 to the F’(O:) state by monitoring the F’(O:)-X12,+ emission band through a 25-cm monochromator. Both of the laser beams were aligned to propagate in parallel and then both were focused into the ultraviolet fluorescence cell. A photomultiplier signal was amplified 10 times by a preamplifier and detected by a boxcar integrator. The output of dye laser was vertically polarized. In order to examine anisotropic characters of the two-photon transitions originating from the B311(O:) state, the polarization angle of the probe laser could be changed. The optical components used for this purpose consisted of a polarizer, a double Fresnel rhomb, and a single Fresnel rhomb. In a separate experiment, the two laser frequencies were adjusted to excite the desired F’(O$B311(O:)-X’Z~ transition, and the fluorescence spectrum was recorded by using a 50-cm monochromator in the second order. 3. RESULTS AND DISCUSSION
In the OODR experiments of IZ through the pump-probe excitation scheme, F’(O:)-B311(O:)-X’Z,‘, the double resonance signals were detected in three types of transitions induced by an overall three-photon process: Type I
Vl
+
&2)
Type II
Vl
+
hl
Type III
v2
+
G2).
+
v2)
The type I transition denotes the (1 + 2) photon process which corresponds to the excitation of 12to the appropriate level of the B311(O:) state by pump frequency (vi) and thence to the F’(0:) ion-pair state in the simultaneous two-photon transition by probe frequency (2~~) alone. On the other hand, the process involving two photons
THE F’(0,) ION-PAIR STATE OF I2
91
in the type II transition proceeds by the combination of pump and probe lasers (Y, + v2) due to the temporal overlap of pump and probe pulses. Both the type I and II transitions appear in the spectrum as vibrational progressions with regular intervals, while they can be distinguished by the dependence of their line intensities on the time delay between two laser pulses and more easily identified by the polarization effects on their transition strength. In the type III transition, the excitation of molecules is performed by the probe laser alone and only if the double resonance conditions of the two transition components are satisfied at a given frequency. The previous analysis of the F’(O:) state was based on transitions of this type but they appeared too sparse to permit a systematic analysis. Figure 1 shows a typical OODR spectrum corresponding to the type I transition. It was obtained by probe photons with (a) vertical and (b) circular polarization, while the pump laser was operated with vertical polarization. The pump laser (vJ was adjusted to a photon energy of 18 356.15 cm-’ which is in resonance with the (26-O)PSs transition of the B311(O&X’Zl system. The spectrum was recorded by installing an intracavity etalon in the probe laser, whose frequency was determined by reference to the B311(O:)-X’Z,+ spectrum of I2 (18). A sample pressure was 0.3 Torr and there was no time delay between pump and probe laser pulses. Under these conditions, the relaxation of the intermediate B311(O:) state does not occur during the excitation. The excited states which are able to combine with the B31’I(Oz)state by a coherent twophoton absorption are 0:) 1u, and 2, in Hund’s case c notation in accordance with the rotational selection rules,
17196 Wavenumber
( cm-’
)
FIG. 1. A typical OODR excitation spectrum of the type I transition taken under high-resolution (FWHM = 0.04 cm-‘). The probe laser is (a) vertically and (b) circularly polarized. The pump frequency ( 18356.15 cm-‘) is in resonance with a (26-O)& transition of the B’II(O:)-X’Z: system. The spectrum shows closely spaced rotational lines, which correspond to the two-photon transitions from the B311(O:)state; (9-26)0,, (17 913.76 cm-‘), Q,, (17 196.05 cm-i), and SW (17 198.39 cm-‘).
92
ISHIWATA
ET AL.
AJ = 0, k2
for 0+-O+ transition
(1)
AJ = 0, kl, +2
for l-O+ and 2-O+ transitions.
(2)
The appearance of three rotational lines is consistent with the symmetry of the F’(0:) ion-pair state and they can be attributed to the 0, Q, and S branches in order with increasing frequency of the probe laser. Furthermore, the polarization effects of the transition strength appear in the F’(Oz)-B311(O:) transition because of the anisotropic character of the coherent twophoton absorption. Their transition strengths (6) depend on (1) a factor specified by J” and J’, analogous to the Honl-London factors appearing in one-photon transitions, (2) an intrinsic factor characteristic to the particular vibronic transition, and (3) a factor dependent on the polarization vector of the two photons absorbed simultaneously, as discussed in detail by McClain and Harris (19). In the case of 0+-O+ transition, we can obtain the intensity ratio of the 0 and S branches:
Subscripts 1 and c designate linearly and circularly polarized photons, respectively. It is obvious that the value of 3/2 in Eq. (3) agrees with our observations and the excitation
0
*
17150
17170
17160 Wavenumber
17180
(cm’)
RG. 2. A Fortrat diagram of the (0-14)F’(O:)-B%(O:)
transition.
93
THE F’(0,) ION-PAIR STATE OF I2 TABLE I Observed Double Resonance Transitions of I2 (cm-‘) Proke transition(cm-5 -P 0
Q
Probe transition(an-l) -P
S
v'=2 3
17354.44 17354.85 17355.35 418.43 418.84 419.34
v'=2 3
17353.62 17354.36 17355.16 417.64 418.34 419.15
v'=2 3
0
Q
S
v'=2 3
17338.92 17342.03 17345.22 402.73 405.82 408.99
R78
v'=2 3
17336.00 17339.40 17342.91 399.74 403.13 406.62
17354.34 17354.78 17355.33 418.34 418.80 419.34
P79
v'=2 3
17336.42 17339.79 17343.25 400.16 403.52 406.97
17353.51 17354.27 17355.13 417.50 418.25 419.11
Rs4
v'=2 3
17333.30 17336.95 17340.71 397.00 400.65 404.38
17353.36 17354.18 17355.06 417.34 418.16 419.05
'84
v'=2 3
17334.23 17337.78 17341.46 397.94 401.50 405.15
v'=2 3
17352.25 17353.36 17354.56 416.24 417.34 418.53
%9
v'=2 3
17330.89 17334.80 17338.75 394.58 398.45 402.39
v'=2
17353.23 17354.06 17355.00
'87
v'=2 3
17332.83 17336.52 17340.33 396.52 400.20 404.00
v'=2
17352.07 17353.22 17354.46
v'=2 3
17353.08 17353.96 17354.94 417.06 417.95 418.92
R92
v'=2 3
17329.42 17333.44 17337.54 397.06 393.07 401.14
v'=2
17351.91 17353.08 17354.38 415.86 417.06 418.33
P90
v'=2 3
17331.38 17335.23 17339.17 398.88 395.07 402.80
v'=2 3
17352.25 17353.36 17354.56 416.06 417.33 418.53
535
v'=2 3
17327.90 17332.03 17336.27 391.52 395.64 399.86
v'=2 3
17350.89 17352.31 17353.81 414.85 416.26 417.75
P35
v'=2 3
17350.68 17352.13 17353.68 414.66 416.09 417.63
R40
v'=2 3
17349.07 17350.80 17352.66 413.M) 414.74 416.58
v'=2
17349.30 17351.01 17352.82 413.26 414.95 416.76
R46
v'=2 3
17347.46 17349.48 17351.57 411.39 413.40 415.49
P47
v'=2 3
17347.74 17349.72 17351.79 411.66 413.64 415.68
(13-o)Pll
R16
P41
R52
v'=2 3
17345.70 17347.98 17350.34 411.86 409.59 414.21
P59
v'=2 3
17344.08 17346.58 17349.18 407.96 410.44 413.00
R64
v'=2 3
17341.63 17344.42 17347.31 405.47 408.25 411.11
'60
v'=2 3
17343.75 17346.30 17348.93 407.60 410.15 412.76
R65
v'=2 3
17341.27 17344.07 17347.03 405.09 407.91 410.84
'65
v'=2 3
17342.00 17344.75 17347.59 405.84 408.58 411.40
v'=2 3
17339.34 17342.39 17345.54 403.13 406.17 409.31
R70
(13-o)P73
17333.91 17337.93 397.53 401.56
P93
R98
R16
R27
v'=2 3
17326.34 17330.60 17334.96 389.91 394.52 398.52
v'=a
17173.75 17174.11 17174.57
v'=O
17173.02 17173.69 17174.45
v'=a 4
17173.66 17174.06 17174.57 430.66 431.08 431.58
v'=o 4
17172.88 17173.62 17174.42 429.86 431.38 430.59
v'=4
17430.55 17431.02 17431.57
v'=4
17429.75 17430.49 17431.34
v'=o
17173.34 17173.90 17174.54
v'=O
17172.48 17173.34 17174.28
v'=O
17173.14 17173.78 17174.49
v'+
17172.20 17173.14 17174.18
v'=o
17172.49 17173.34 17174.29
v'=o
17171.40 17172.56 17173.81
v'=O 4
17172.34 17173.24 17174.23 429.32 431.17 430.20
v'=O 4
17171.23 17172.43 17173.73 428.14 429.32 430.60
ISHlWATA ET AL.
94
TABLE I-Continued F-r* transition(~31~~1 plrmp 0
(14-O)P*,
R32
Q
S
v'=o 1 4
17171.57 17172.68 17173.89 236.53 237.66 238.84 428.50 429.58 430.78
VW
17170.30 17171.71 17173.23 235.26 236.66 238.17 427.17 428.55 430.04
1 4
Probe transitionCan-l) _P
'28
v'=O
17171.40 17172.56 17173.82
R33
v'=O
17170.10 17171.56 17173.13
0
clli-o,P,, v'=O 1 4 5
Q
S
17163.59 17166.16 17168.80 230.98 233.59 228.41 422.54 425.15 420.02 488.05 482.95 485.47
'65
v'=O 1 4 5
17161.26 17164.11 17167.08 228.92 231.85 420.35 423.28 417.54 483.25 486.15 480.44
R70
v'=O 4 5
17159.46 17162.55 17165.71 421.79 415.63 418.66 484.63 478.48
P73
v'=U :
17159.09 17162.24 17165.44 421.47 230.17 415.23 223.85 418.29 226.96
'32
v'=l
17235.64 17236.97 17238.39
R37
v'=l
17234.17 17235.82 17237.54
P35
V'=O 1 4 5
17170.10 17171.56 17173.11 235.04 236.50 238.05 426.95 428.38 429.92 489.94 491.39 492.91
R78
V'=O 1 4 5
17168.57 17170.33 17172.20 233.48 235.24 237.10 425.32 427.06 428.89 488.29 490.02 491.87
v'=O 1 4 5
17156.36 17159.79 17163.32 227.99 221.06 224.49 419.15 412.31 415.69 481.95 478.48
P74
v'=5
17477.66 17480.78 17483.99
P37
v'=O
17169.68 17171.24 17172.87
R79
v'=5
17474.68 17478.09 17481.60
R42
v'=O
17168.09 17169.94 17171.89
'78
v'=O
17157.15 17160.49 17163.95
R40
5
478.08
471.14
484.30
P40
v'=O
17169.03 17170.71 17172.48
%3
v'=O
17154.28 17157.91 17161.65
R45
VW
17167.33 17169.31 17171.40
P79
P41
v'=O 1 4 5
17168.80 17170.52 17172.34 233.72 235.44 237.26 425.56 427.27 429.05 488.56 490.23 492.04
v'=O 4 5
17156.76 17160.14 17163.62 419.50 412.74 416&X 482.29 475.56 478.88
%4
v'=O 4 5
17153.84 17157.53 17161.32 416.97 409.62 413.24 479.72 472.40 476.02
v'=O 1 4 5
17167.07 17169.09 17171.23 231.97 233.98 236.11 423.73 425.73 427.83 486.71 488.68 490.78
'84
v'=5
17473.32 17476.85 17480.48
%J9
v'=4 5
17407.25 17411.10 17415.04 477.74 469.93 473.81
P46
v'=O 1
17167.59 17169.54 17171.56 232.48 234.43 236.45
'87
v'=5
17471.92 17475.59 17479.33
R51
v'=Cl 17165.70 17167.95 17170.30 1 230.57 232.80 235.15
R92
v'=4 5
17405 77 17409.75 468:49 472.45 17476.50
P47
v'=4 5
17424.01 17425.96 17428.03 486.99 488.92 490.97
P%l
v’=4
%2
v'=4 5
17421.98 17424.23 17426.59 484.93 487.16 489.52
$5
v'=4 5
17404.24 17408.35 17412.55 475.21 466.94 471.03
P54
v'=O 1
17165.41 17167.72 17170.09 230.30 232.56 234.93
P91
v'=O
17151.64 17155.53 17159.52
%6
v'=O
17148.35 17152.55 17156.85
R59
v'=O 1
17163.26 17165.87 17168.57 228.11 230.70 233.37
'92
v'=o
17151.17 17155.11 17159.15
v'=O 4 5
17163.91 17166.41 17169.02 420.36 422.85 425.41 483.29 485.75 488.31
%7
v'=O
17147.86 17152.11 17156.46
P93
v'=4 5
17406.28 17410.20 468.99 472.91 17476.91
v'=o 4 5
17161.60 17164.43 17167.34 417.91 420.69 423.56 480.81 483.57 486.45
%e
v'=4 5
17402.70 17406.92 17411.24 473.86 465.36 469.58
R46
P59
%4
5
17470.47
17411.53 474.26
THE F’(0,)
ION-PAIR
STATE OF 12
95
TABLE I-Continued Probe transition(an-l) -P 0
Q
Probe transition(cm-l) -P
S
(14-OJP97
v'=O
17148.80 17152.99 17157.25
R102
v'=O
17145.35 17149.83 17154.40
(22-O)Pg
v'=7 10
17242.02 17242.42 425.95
R13
v'=7 10
17241.20 17241.78 425.12 425.70 17426.35
58
v'=7 10 11 19
17240.91 17241.61 424.81 425.52 17426.29 485.31 485.99 486.76 955.26 955.92 956.66
R__ LL
v'=7 10 11 19
17241.17 17242.23 17424.09 425.03 426.07 484.56 485.51 486.54 954.44 955.37 956.35 17178.77
0
(22-0)R65
Q
s
v'=6 7 10
17169.59 17172.39 17175.27 231.59 234.38 237.26 415.04 417.79 420.63
p73
v'=6 7 10 19
17167.92 17170.98 17174.10 229.90 232.93 236.07 413.23 416.24 419.34 942.08 945.00 948.01
R77
v'=6 7 10 19
17228.08 411.32
'84 RX6 G’6-O)P2q
v'=6
17169.44 17172.85 231.37 234.75 414.57 417.91 943.03 946.27 17168.09 17171.69
v'=6
17166.35 17170.21
v'=8 9 16 17 20 21 25
17136.52 17137.68 17138.96 197.80 198.96 2cO.21 615.54 616.68 617.87 673.69 674;82 676;03 846.02 847.13 848.33 959.16 960.27 961.47 18126.41 18127.48 18128.68
'27
v'=6
R31
v'=6
17178.15
'32
v'=7 10 11
17239.09 17240.40 17241.77 422.93 424.22 483.38 484.66 486.04
P31
v'=8 9
17136.29 17137.52 17138.87 197.55 198.80 200.13
R36
v'=7 10 11
17238.13 17239.68 17241.29 421.90 423.44 425.05 482.34 483.85 485.49
*36
v'=8 9
17135.35 17136.90 17138.54 196.62 198.16 199.77
p37
v'=6 19
17176.15 17177.67 952.18 953.62 17955.16
R49
v'=8 9
17133.31 17135.40 17137.58 194.51 196.60 198.78
R41
v'=6 19
17175.09 17176.86 950.88 952.58 17954.35
P55
'42
v'=7 10
17237.39 17239.11 17240.90 421.13 422.84 424.64
R46
v'=7 10
17236.19 17238.17 17240.23 419.88 421.84 423.88
v'=8 9 16 17 20 21 22 25 26
17132.58 17134.85 17137.20 193.76 196.05 198.39 610.98 613.17 615.47 669.05 671.24 673.54 841.16 843.33 845.60 897.84 900.01 902.26 954.16 956.33 958.58 18121.17 18123.32 18125.53 176.21 178.34 180.55
v'=6 7
17174.50 17176.40 17178.39 236.61 238.49 240.48
v'=8
17130.40 17133.13 17135.95
v'=6 I
17173.25 17175.42 17177.64 235.33 237.48 239.71
R68
v'=8 9 16 17 20 21 22 25 26
17129.53 17132.43 17135.42 190.67 193.55 196.53 607.38 610.19 613.11 665.39 668.20 671.09 837.32 840.10 842.95 893.93 896.70 899.56 950.20 952.97 955.56 18117.03 18119.77 18122.59 172.00 174.73
P74
v'=8 9
17128.63 17131.71 17134.86 189.76 192.80 195.95
R77
v'=8 9 16 17 20 21 22 25 26
17127.45 17130.73 17134.11 188.52 191.79 195.15 604.90 608.09 611.38 662.88 666.05 669.31 834.68 837.81 841.03 891.23 894.35 897.58 947.45 950.59 953.79 18114.16 18117.24 169.09 172.16 18175.32
'46 R50
P48
v'=lO
17419.87 17421.84 17423.87
R52
v'=lO
17418.49 17420.70 17423.00
P54
v'=7 10 19
17234.87 17237.10 17139.43 418.49 420.70 423.00 948.11 950.24 952.47
R58
v'=7 10 19
17233.41 17235.91 17238.49 416.98 419.43 421.99 946.37 948.76 951.22
P59
v'=7 10
17233.68 17236.12 17238.66 417.24 419.64 422.16
R63
v'=7 10
17232.14 17234.83 17237.62 415.60 418.28 421.03
'61
v'=6 7 10
17171.15 17173.69 17176.30 233.18 235.70 238.32 416.70 419.20 421.81
R64
ISHIWATA
96
ET AL.
TABLE I-Continued Probe transition (an-l) bP 0
(30-0)P15 "'=;; 15 R18
";;;.z 409:91
Q
S
17112.02 17112.67 232.58 233.23 410.47 411.10
v'=lO 12 15
17111.10 17111.88 17112.74 231.64 232.41 233.27 409.53 410.29 411.14
v'=lO 12 15
17110.70 17111.69 17112.75 231.24 232.21 233.27 409.10 410.04 411.10
R28
v'=lO 12 15
17110.25 17111.46 17112.75 230.76 231.94 233.24 408.58 409.76 411.02
Pjl
v'=lO 12 15
17110.15 17111.40 17112.73 230.67 231.89 233.21 408.48 409.69 411.00
R34
v'=lO 12 15
17109.65 17111.11 17112.65 230.15 231.58 233.10 407.92 409.35 410.85
v'=lO 12 15
17109.55 17111.04 17112.63 230.03 231.51 233.07 407;El 409.27 410;83
R40
v'=lO 12 15
17109.00 17110.71 17112.50 229.45 231.16 232;91 407.19 408.86 410.62
P50
v'=lO 12 15
17108.03 17110.07 17112.22 228.43 230.46 232.57 406.10 408.10 410.19
v'=lO 12 15
17107.39 17109.63 17111.97 227.73 229.98 232.30 405.36 407.55 409.85
Psi
v'=lO 12 15
17106.55 17109.05 17111.64 226.84 229.33 231.91 404.39 406.84 409.39
R64
v'=lO 12 15
17105.81 17108.53 17111.33 226.05 228.76 231.53 403.53 406.20 408.94
'67 v'=lO 12 15
17105.65 17108.43 17111.25 225.91 228.64 231.46 403.37 406.06 408.86
R70
v'=lO 12 15
17104.89 17107.85 17110.90 225.08 228.02 231.04 402.46 405.36 408.36
P73
v'=;; 15
17;;;.7$ 17107.72 17110.82 227.87 230.95 402:25 405.21 408.24
R76
v'=lO 12 15
17103.89 17107.10 17110.41 224.03 227.21 230.49 401.30 404.46 407.70
'81 v'=lO 12 15 Rs4
'25
p37
R53
v'=lO 12 15
Probe transition Can-l) m 0 (30-O)Pgo "'=;;
Q
S
15
17398.83
17105.50 17109.31 225.46 402.48 17406.22
v'=12 15
17397.73
17224.67 401.58 17405.53
p97 v'=lO 12 15
17397.27
17104.50 224.35 401.22 17405.24
RlOO v'=lO 15
17396.12
17103.73 400.27 17440.36
Rg3
(31-O)Pg
v'=ll 13 18 19
17137.74 17138.06 17138.46 257.82 550.29 550.60 551.00 607.76 608.06 608.46
R12
v'=;; 18 19
17137.45 17137.98 17138.57 257.73 549.97 550.48 551.07 607.43 607.95 608.52
'25
v'=ll 13 14
17136.66 17137.64 257.37 17258.42 315.66 316.63 317.70
R28
v'=ll 13 14
17136.24 17137.43, 17138.69 255.94 257.13 315.22 316.39 317.69
P31
v'=ll 14
17136.15 17137.37 17138.71 315.12 316.35 317.66
v'=ll 14
17135.69 17137.13 17138.67 314.64 316.06 317.57
v'=ll 13 18 19
17138.19 17136.84 17138.57 254;84 256.47 258.24 547.37 548.98 550.68 604.78 606.40 608.08
v'=ll 13 18 19
17134.65 17136.52 17138.46 254.26 256.11 546.73 548.55 550.44 604.12 605.94 607.83
P50
v'=ll 14
17134.19 17136.22 17138.34 315.01 313.01 317.11
R53
v'=ll 14
17133.59 17135.82 17138.16 312.36 314.57 316.88
v'=ll 13 18 19
17133.33 17135.66 17138.08 252.90 255.20 257.58 547.41 545.14 549;77 602.52 604.76 607.11
R60
v'=ll 13 18 19
17132.69 17135.24 17137.85 252.22 254.72 257.31 544.33 546.81 549.38 601.68 604.15 606.71
17103.38 17106.72 17110.15 223.48 226.80 230.19 400.70 403.98 407.35
P66
v'=ll 13 14
17132.15 17134.85 17137.65 251.62 254.30 310.78 313.44 316.20
17102.50 17106.06 17109.66 222.55 226.05 229.68 399.67 403.16 406.72
R6g
v'=ll 13 14
17131.45 17134.36 17137.36 250.87 253.76 309.96 312.87 315.83
R34 P41
R44
P57
THE F’(0.)
ION-PAIR
STATE OF 12
97
TABLE I-Continued Probe transition(~II-~) m 0
'82
R85 p95
RY8
S
18 19
17131.16 17134.16 17137.24 309.67 312.63 315.69 542;46 545.36 548.36 599.72 602.64 605.65
v'=ll 14 18 19
17130.41 17133.63 17136.91 308.83 312.02 315.28 544.64 541.50 547.84 598.77 601.89 605.08
v'=ll 14
17129.79 17133.17 17136.63 308.16 311.50 314.93
v'=ll 14
17129.01 17132.59 17136.25 307.27 310.82 314.45
v'=ll 14
17127.69 17131.62 17135.62 309.67 313.63
v'=ll 14
17126.85 17130.97 17135.17 308.90 313.09
(31-O)P73 "'=;g
R76
Q
PlO2 v'=ll 17 18 19 RlO5 v'=ll 17 18 19
17479.04 536.50 593.63
17477.95 535.37 592.45
17130.70 483.16 17487.35 540.60 544.78 597.70 601.88 17130.04 482.27 17486.66 539.66 544.08 596.73 601.10
(33-o)Plo v'=L3
17191.47 17191.82 17192.27
R13 v'=13
17191.18 17191.76 17192.40
v'=13
17190.89 17191.65 17192.51
v'=13
17190.55 17191.52 17192.59
P20 R23
v'=13
17187.99 17190.23 17192.55
P72
v'=13
17186.18 17189.13 17192.14
y3
v'=13
17188.90 17192.03
R53
Probe transition(cm-l) _P 0
Q
S
(39-o)P23 v'=27 29 31 32 33 34
17815.89 17816.76 17817.70 924.54 926.31 925.39 18031.97 18032.82 18033.73 085.19 086.96 086.05 138.18 139.cxl 139.94 190.83 191.67 192.59
v'=25 27 29 31 32 33 34
17705.37 17706.83 17708.38 815.21 816.67 818.21 923.77 925.23 926.75 18031.16 18032;58 18034.09 084.38 085.79 087.30 137.32 138.74 140.24 192.87 189.97 191.37
v'=21 27 29 31 32
17481.37 17483.45 17485.63 814.51 816.53 818.67 927.12 922.98 925.01 18030.26 18032.29 18034.39 085.44 087.55 083.44
(39-o)P53 v'=33 34
18136.37 18138.37 18140.42 188.96 193.04 190.94
v'=21 25
17481.27 17483.51 17485.85 704.58 706.79
v'=27
17813.84 17816.44 17819.14 922.24 924.82 18029.42 18031.97 18034.63 087.74 082.54 085.08 140.57 135.41 137.95 193.10 187.95 190.48
R36
P53
R55
'67
32 33 34
R78
v'=27 29 31 32 33 34
(40-o)P51 v’=29 35 P74
v'=29 35 38
17813.29 17816.40 17819.59 921.59 924.65 18028.61 18031.69 18034.84 084.74 137;52 193.14 186.99 190.01 17900.32 17902.34 18216.67 18218.58 18220.58 17898.36
17897.62 17900.47 17903.41 18215.40 18218.20 18221.08 370.42 373.20 376.05
of I2 from the B311(O:) state proceeds through a coherent two-photon transition by the probe photons alone. The molecular constants of the F’(OL) state were obtained from a term value analysis. For this purpose, the probe frequencies (v2) measured in the type I transition are converted to energies all referred to the potential minimum of the X’ZZ state by the equation T;; = hv, + 2hu2 + G”(v) + F’:(J). (5) The pump frequency (Y,) and the term value of the ground state (G”(v) + F;(J)) were calculated from the constants derived by Luc from the B%I(O:)-X’Z: absorption spectrum (20). At this time, the previous u’ numbering of the F’(Oz) state appears to remain valid, since we could not observe any lower vibrational levels than that previously labeled u’ = 0. Rotational assignment of the OODR spectrum was straight-
98
ISHIWATA ET AL. TABLE II Dunham Parameters of the F’(0:) State for I2 (cm-‘) 51706.237(2)')
Yoo
131.00041(83)
y10
-0.516270(143)
Y20 Y30 Y40 y50
x 1O-3 x 10-5
2.8381(376)
x 1O-7
0.02194899(46)
y01
-9.2508(99)
Yll
x 10-5 -7
8.359(79)
Y21
x 10
-8.550(167)
y31
x lo-' -9 x 10
-2.632(3?)
yo2
a)
4.2640(104) -4.5797(330)
Quoted
uncertainty
deviation. energies
"fit
is 0.0175
data in Table
is one standard
to the F'(Oi) cm -1
.
term
Calculated
from
I (v = O-38, J = 6-108).
forward from the selection rule of AJ = 0 and *2, because the rotational quantum number of the pumped B’II(0:) state was known for each set of experiments. In several instances, the same final state was accessed by using two or more different pump frequencies involving different initial and intermediate states in the excitation scheme. In any case the final state term values are consistent with each other within the estimated accuracy of the frequency calibration of the probe laser (~0.02 cm-‘). In the measurements, we intended to probe the F’(0:) ion-pair state with a reasonably wide distribution of J value. In particular, much time was spent sampling the lower vibrational levels for two reasons: (1) to derive an accurate potential curve of the F’(0:) state, in which the equilibrium internuclear distance is one of the dominant factors; and (2) to clarify the existence of perturbation by the surrounding ion-pair states which are expected to appear in the lower vibrational levels largely because of the importance of the Franck-Condon overlap on perturbations between two states (I 7). However, no trace of perturbation could be found, and a Fortrat diagram of the (O-14) P”(O:)-B311(O:) transition is given as an example in Fig. 2. The term values of the F’(0:) state calculated from the OODR transition frequencies in Table I were submitted to a global least-squares fit to the Dunham expansion,
(6) The raw data included in 136 1 transitions in the F’(O:)-B311(0,‘) system with 0 =Sv G 38 and 6 < J =S108. The results of this analysis are shown in Table II. The standard deviation of the fit is 0.0175 cm-’ and the coefficients can be used to regenerate all P’(0:) term values in the fitted range within 0.06 cm-‘. The molecular constants in
THE F’(0,)
ION-PAIR
99
STATE OF Iz
TABLE III RKR Potential Curve of the F’(O,+)State
v
l G(v)+YOO
" (cm-l)
El
Turning inner
0.000
-0.5
-0.25 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
3)
a)(cm-l)
3.4791
32.739
65.393 195.374 324.360 452.374 579.439 705.574 830.804 955.144 1078.616 1201.236 1323.022 1443.990 1564.155 1683.533 1802.138 1919.983 2037.080 2153.443 2269.084 2384.012 2498.241 2611.779 2724.637 2836.825 2948.351 3059.225 3169.457 3279.053 3388.022 3496.373 3604.114 3711.252 3817.796 3923.753 4029.131 4133.939 4238.183 4341.873 4445.016
t
Yoo = 0.02 cm-l vibrational energy
point (i) outer
0.0219029 8121 7228 6351 5488 4640 3806 2986 2178 1383 0599 0.0209827 9065 8314 7573 6481 6117 5402 4696 3996 3302 2615 1934 1257 0586 0.0199918 9255 8594 7935 7280 6626 5972 5320 4667 4014 3360 2704 2046 1386
1s
the Dunham levels.
3.4355 .4183 .3773 .3506 .3291 .3121 .2969 .2834 .2710 -2598 .2492 .2395 .2303 -2216 .2133 .2055 .1979 .1907 .1838 .1771 .2707 .1645 .1584 .1526 .1469 .1414 .1361 .1308 .1258 -1208 .1160 .1113 .1067 .1023 .0979 .0936 .0895 .0855 .0815 .0?77
correction
3.5257 .5459 .5990 -6377 .6705 .6998 .7268 .7521 .7761 .7989 .8210 .8422 .8629 .8830 .9026 .9217 .9405 .9589 .9771 .9949 4.0125 .0298 -0469 .0638 .0805 .0971 .1135 .1297 -1458 .lblB .1771 .1934 .2091 .2246 .2401 .2555 .2708 .2861 .3013 .3164
to the
Table II were used to construct an RKR potential curve of the F’(0:) ion-pair state. The RKR turning points for the observed vibrational levels are given in Table III. Figure 3 shows the vibrational progression of emission spectrum originating from a v = 0, J = 60 level of the F’(0:) state. The absolute wavelength position of the expected P and R doublet of the F’(O:)-X’Z: was calculated by using the molecular constants of the X’Z;; state (21). The results agreed with our observations within the experimental accuracy of 0.2 A, even though the P and R branches were not resolved in the spectrum. We then calculated the Franck-Condon factors of the transitions
100
ISHIWATA ET AL
3
Ji L 10
r
2
A .In c 0, c 1
0 -1 1
I
I
I
I
230
226
234
Wavelength
(nm
111 I
I
/
238
)
FIG. 3. The F’(O:)-X’Zg+ fluorescence spectrum of I*. The excitation process is F’(Oi) (S
PII
&
PZf .
The Franck-Condon factors for the F’(O:)-X’Z: transition at (a) u’ = 0, J’ = 60 and (b) I)’= 2, J’ = 42 [see the spectrum shown in Fig. 2 of Ref. (16)] were calculated to be V
35
36
37
38
39
40
41
42
43
44
45
46
41
4 96
11 186
27 319
62 476
127 606
239 629
413 492
649 237
926 26
1192 47 60
FCF x IO’ 7 V
19
45
48
49
50
51
52
53
54
55
56
57
58
59
1374 318
1408 600
1269 578
995 249
668 2
316 238
173 868
66 1358
17 1308
3 839
355
90
10
between the X’Z: and F’(O:) states to confirm the intensity distribution of the emission spectrum. As shown in Fig. 3, the calculations can obviously reproduce the characteristic intensity distribution. The transition terminates on the high vibrational levels of the ground state as expected since the internuclear distance of P’(0:) ion-pair states is much longer (re = 3.479 A) than that of the ground state [r, = 2.67 A (20)]. The low-u’ level of the ion-pair state should then display in emission a band system whose intensity distribution is modulated according to the probability distribution of the upper vibrational wavefunction. An envelope of the spectrum in Fig. 3 shows a single intensity maximum which indicates that the fluorescence originates from the 2)’= 0
THE F’(0.) ION-PAIR STATE OF I2
101
level. Furthermore, the intensity distribution of Fig. 2 in Ref. (16) is also consistent with the calculation. Our results on the F’(0:) state are consistent with a simple picture describing the ion-pair states of IZ, whereby they group in accordance with ionic asymptotes (1, 2, 6). Among the 20 ion-pair states correlating with I-(‘S) + I+(3P, ‘D, ‘S), the 6 states [0’(2,), P( I&, D(O:), E(O& y( l.), and 6(2,)] which belong to the lowest group correlating with I-(‘S) + I+(3P2)lie at around 40 000 cm-’ above the ground state. The next higher group correlating with I-(‘S) + If(3P,,, 3P,) has been identified to lie at around 47 000 cm-‘. There is a close family likeness in their equilibrium internuclear distances and vibrational frequencies (typically r, = 3.6 .& and o, = 100 cm-‘). The F’(O:) state is expected to correlate with I-(‘S) + I+(‘D), while its energy level and potential curve are somewhat different. It is characterized by a larger vibrational frequency and smaller equilibrium internuclear distance as compared with other ion-pair states and its position is about 2000 cm-’ lower than the empirical predictions: T, = 51 706.2 cm-‘, o, = 131.0 cm-‘, and r, = 3.48 A. It should be pointed out that a similar tendency of strong bonding character of the F’(0:) state is predicted by Jaffe from his theoretical model (3). ACKNOWLEDGMENT The authorsaregratefulto Dr. J. T. Hougen of the National Bureauof Standardsfor supplyingthe RKR and FCF computerprogram. RECEIVED:
September 3, 1985 REFERENCES
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(1983). 11. G. W. KING, I. M. LITTLEWOOD, ANDJ. R. ROBINS,Chem. Phys. 56, 145-156 (1981). 12. J. C. D. BRANDANDA. R. HOY, J. Mol. Spectrosc. 97,379-386 (1983). 13. K. S. VISWANATHAN ANDJ. TELLINGHUISEN, J. Mol. Spectrosc. 101,285-299 (1983). 14. K. WIELAND,J. TELLINGHUISEN, ANDA. NOBS,J. Mol. Spectrosc. 41,69-83 (1972). 15. K. S. VI~WANATHAN, A. SUR, ANDJ. TELLINGHUISEN, J. Mol. Spectrosc. 86, 393-405 (198 1). 16. T. ISHIWATA,H. OHTOSHI,M. SAKAKI,ANDI. TANAKA,J. Chem. Phys. 80, 1411-1416 (1984). 17. T. ISHIWATA,A. TOKIJNAGA, T. SHINZAWA,ANDI. TANAKA,J. Mol. Spectrosc. 108, 3 14-327 (1984). 18. S. GERSTENKORN AND P. Luc, “Atlas du spectre d’absorption de la mob&de I’iode,” CNRS, Paris, 1978. 19. W. M. M&LAIN AND R. A. HARRIS,“Excited States” (E. C. Lim, Ed.), Vol. 1, pp. l-56, Academic
Press, New York, 1978. 20. P. Luc, J. Mol. Specfrosc. 80,41-55 (1980). 21. J. TELLINGHUISEN, M. R. MCKFZEVER, ANDA. SUR,J. Mol. Spectrosc. 82, 225-245 (1980).