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Resolution of the Q branch in the ν3 fundamental of PF5
JOURNAL OF MOLECULAR
SPECTROSCOPY
137,204-2 14 ( 1989)
Resolution of the Q Branch in the
v3
Fundamental of PF5
H. PRINZ AND W. A. KREINER Abteilung Physikalische Chemie, University of Urn, West Germany
The ~3fundamental of phosphorus pentafhroride, PF5, has been investigated with a laser sideband spectrometer. A line width of 2 X lo-’ cm-’ was observed with the saturation technique, which was sufficient to resolve the @branch K structure. Four hundred sixty-seven transition frequencies up to J” = 76 have been measured with an accuracy of +200 kHz. The spectrum was fitted with a symmetric rotor program including three terms of sixth order. As a result, 11 parameters have been determined, yielding an overall standard deviation of 207 kHz. With the present resolution of 600 kHz no indication of splitting due to Berry rotation was found. o 1989 Academic PIWS,IIIC. 1. INTRODUCTION
The infrared spectrum of a fairly heavy molecule like phosphorus pentafluoride, PF,, has been a challenging problem in high-resolution spectroscopy for several years. The Q branch of the v3 fundamental was first observed at 944.8 cm-’ by Griffith et al. (I). Schatz and Reichmann (2) derived the first rotational constants from a partly resolved spectrum. The K structure was not resolved in a spectrum recorded with 0.014 cm-’ resolution by Palma et al. in 1982 (3) while Dana et al. derived nine spectroscopic constants from a Fourier transform spectrum with 1.6 X lob3 cm-’ resolution in 1985 (4). The K structure of the v3 P and R branch was resolved in 1983 with a diode laser in a pulsed supersonic free jet by Takami and Kuze (5). Single lines around 940 cm-’ have been observed by BordC et al. with saturation spectrosCOPY (6, 7). PFS is a subject of considerable theoretical interest because of the presence of the phenomenon of pseudorotation first suggested by Berry (8). This fast intramolecular rearrangement process may explain the observation that NMR data show only one fluorine resonance (9) although electron diffraction (10, I I), infrared, and Raman (12, 13) data indicate the presence of a D3h trigonal bipyramidal configuration. The spectroscopic consequences of different tunnelling mechanisms have been discussed by Brocas and Fastenakel (14). With the advent of laser sideband saturation spectroscopy using microwave modulation frequency resolution (1.5), absolute accuracy and tunability are achieved in the infrared region which are comparable to those of conventional microwave spectroscopy. In addition, this technique produces infrared frequencies directly rather than the wavelengths. Since sub-Doppler resolution can be achieved with this method its application to the Q branch of a heavy molecule looked promising. However, since the spectral brightness so far available is relatively low this method can only be applied to strongly absorbing bands. The u3 fundamental of PFS seemed to fill the necessary 0022-2852189
$3.00
Copyright Q 1989 by Ademic F’ress,Inc. All ri#~ts of nwoduction in any fomt reserved.
204
205
vj OF PFs
requirements. We were also interested in investigating the spectrum at fairly high quantum numbers J in order to check whether a symmetric rotor Hamiltonian up to sixth order can describe the observed transition frequencies satisfactorily. 2. EXPERIMENTAL
PROCEDURE
The spectrometer has been described already (15). With this technique the overall spectral coverage in the infrared is determined by the CO2 laser lines available (e 1Op36 of 13C02 at 882 cm-’ and =9R40 of CO2 at 1090 cm-‘). It should be mentioned that sideband spectroscopy with a CO laser has been reported (16) as well as generation of sidebands at higher mw modulation frequencies (17). As infrared source a DC sealedoff COZ laser was used which could also be operated with other CO2 isotopes. The output (between 5 and 10 W) was modulated at frequencies between 12 and 18 GHz via the electrooptic effect in a CdTe crystal. The crystal was placed in a copper housing designed as a tunable microwave resonator with a bandwidth of 30 MHz. The microwave, generated in a synthesizer (HP 8673 E), was amplified up to 20 W by a travelling wave tube. A few mW of tunable IR power were obtained in either sideband. The cell consisted of a 1.2-m J-band waveguide equipped with a Stark septum leaving a gap of 7.65 mm. Because the sideband radiation is polarized perpendicularly with respect to the carrier, one can separate most of the unmodulated laser power (the carrier) from the sidebands by reflection on suitably oriented Brewster polarizers. Part of the carrier radiation was fed into the COZ fluorescence cell in order to stabilize the laser via the 4.3~pm emission Lamb dip. For this purpose the piezo mounted laser mirror was jittered at a frequency of 400 Hz. The sideband radiation traversed the absorption cell twice in order to allow saturation dips to be observed. A grid polarizer in front of the detector provided additional suppression of the carrier. The reflected beam was usually tilted at a slight angle in order to produce spatial separation. During part of the measurement a slightly different arrangement was chosen in order to produce collinear direction of saturation and detection beams (Fig. 1). In this case a partly transmitting mirror was positioned at the far end of the absorption cell, perpendicular to the incoming beam. The reflected
SIDEBAND
IN
STARK
CELL
R.98%
DET
FIG. 1. Optical arrangements used to observe saturation dips. In the version with the partly transmitting mirror (top) probe beam and saturation beam are nearly parallel; this avoids line broadening introduced when there is an angle between them (bottom).
206
PRINZ AND KREINER
PF5 V3= 1
a,2 (12)
12530 co2
50
45
40
35
MHZ
lOP18
FIG. 2. Frequency modulated lines in the Q-branch of the ys fundamental. Ten sweeps have been averaged. The two features at the let? side are most likely due to thermal effects in the modulator, while the sharp spike in the center is an artifact produced by the synthesizer. In addition, saturation dips ofweaker transitions can be recognized.
power (98%) was still strong enough to saturate most of the transitions. The transmitted portion of the radiation (2%) could be used to detect the saturation signal, with the incoming beam acting as the probe. No monochromator was used to eliminate one of the sidebands.
us
LS
P2,(45)
15 125
30
35
40
45
uns
co2 1OP 25 FIG. 3. The two strong lines, just resolved on the recording, coincide with the upper and lower sideband, respectively. The baseline is due to frequency modulation of the Doppler profile and the bandwidth of the modulator, which are of the same order [Aun(PFs) = 34 MHz; Ayr.,oD= 30 MHz].
207
vj OF PFI
12 420 co2 10 PlB
us
FIG. 4. Series of Q-branch lines, partly blended. The assigned transitions coincide with the upper sideband of the P18 laser line in the IO-pm band of the regular CO2 isotope.
3. OBSERVATION AND RESULTS
Examples of saturation dips observed are given in Figs. 2 to 5. Half width (FWHM) is 2600 kHz and absolute accuracy was G +200 kHz in most cases; this was limited by spectral impurity introduced mainly into the laser cavity via the stabilization system and other sources of mechanical noise.
PF5 V3=
1
us
16930
R6u61
35
40
45
MHZ
cop 1OP 8 FIG. 5. Assignment refers to the strong line, while the unassigned lines were just checked with respect to the sideband they coincide with by changing their carrier frequencies slightly and observing their relative shifts.
266 lOP26 266 10126 266 lOP26 266 lOP26
-25 -77 lo* 292
P g (36, 936.29010, 939.202915 9,9.20,5*7
P o 02) P , 02,
P 6 (32, 9,9.245662 P 9 (32, 9,9.257045
-16.05,54
-15.474,*
-15.65546
-15.3967,
-15.09611
-14.75966
-14.36135
-13.9630,
-11.50467
-13.00661
-12.4667,
-11.69066
13.5111,
1,.5,,1,
13.59296
266 10126
266 lOP26
266 1op2*
266 1OP26
266 IOPZO
266 1OP26
266 1OP26
266 lOP20
266 1OP26
266 1OP26
266 1OP26
266 lOP26
266 1OP26
266 10126
266 10124
-64 -99
-114 -65
P 5 124, 941.106973 P 6 (24, 941.114,46 P , (24, 941.123059 P 6 (24, 941.1,,116 P 9 124, 941.144520
16.66617
17.42551
-13.54970
-1,.5296,
-13.46976
-I,.,6970
266 lOP26
266 10126
266 10126
266 10126
266 10126
266 10126
466
446
P,, 140, 937.367015
PII 140, 9,7.,*5005
9M.242289
125
-140
P 4 124, 941.100937
16.36666
266 lOP26
429
P,2 140, 9,7.,50,59
P , 061
-109
P , 124, 941.096246
15.92762
266 lOP26
407
Pl, (40, 9,7.3,5041
-15
-79
P 2 (24, 941.092696
15.50*4,
266 lOP26
41,
PIO (401 9,7.,21056
P 2 (36, 9,6.216951
-71
P , (24, 941.090606
15.12922
266 lOP26
436
P g (40, 9,7.,04409
-127
-115
P o (24, 941.090214
14.74992
266 lOP26
,*0
P * (401 9,7.291091
P 1 116, 9H.236944
-359
P 5 (26.1 940.17097,
14.49062
266 lOP26
160
-146
-416
P 4 (26, 940.164946
14.21127
266 lOP26
-1
-294
P , (26, 940.160267
14.0,1*7
266 10126
9M.236265
-425
P 2 (26, 940.156917
P o 06,
-357
P 1 (26, 940.154911
13.69274
306 -,61
9,9.2*,790
Pll 021 P o (26, 940.154242
211
Plo 1321 939.269746
234
256
19, 255
P 6 (32, 939.226967 P 7 02,
939.235657
242 294
939.219621
P 5 02,
144
P , (32, 939.208927 P 4 (32, 919.213606
224
9M.276964
P 2 132) 9,9.20556(1
P 4 06,
P 7 (36, 9M.266959
1,.8,2,0
P , (40, 937.267107
266 10P26
5
-16.19265
266 lOP26
9,6.260266
266 lOP28
159
266 lOP26
-27
P 6 06)
-16.29227
266 10124
266 10124
266 lOP24
266 lOP24
266 10124
266 lOP24
266 lOP24
266 lOP24
266 lOP24
266 10124
266 1OP24
266 lOP24
266 lOP24
266 lOP24
266 lOP24
266 10P24
266 lOP24
266 lOP26
266 lOP26
266 1OP26
266 lOP26
266 1OP26
266 1OP26
266 lOP26
266 1OP26
266 lOP26
266 lOP26
266 lOP26 266 1OP26
2, -1
938.246954
P 5 (361 936.252954
-16.,5195
266 10126
P 4 061
-16.37160
266 lOP26
266 10126
P 6 140, 9,7.276456
-I4
P14 144, 9,6.,476,,
405
-61
Pl, (44, 936.369444
P 5 (40, 9,7.2711,*
-50
P12 (44, 9,6.,5,270
,49
-101
Pll (44, 916.337964
441
-214
9,6.3240,4
PlO 04,
P 4 (40, 937.265144
-239
P g (44, 916.311414
P , (40, 937.260494
-266
P 4 (44, 9,6.,00125
,29
-x25
P , (44, 936.290164
140
-,26
P 6 (44) 936.24151,
P 2 (40, 937.257164
-,50
P 5 ,441 916.274231
P , (40, 9,7.255164
-415
P 4 (44, 936.266255
,l
-24,
P , (44, 9,6.26,615
276
-392
P 2 (44, 9,6.260292
P o 140, 9,7.254501
-364
P , (44, 9,6.256,01
Pl5 (44, 9,6.407115
-436
P 0 (44, 9,6.2516,6
vj of PF5 : Observed Transitions
TABLE I
-13.22966
17.66014
17.53632
17.23676
16.97554
16.75451
16.57357
16.43294
16.,,251
16.2722,
16.25210
-11.3056,
-11.46645
-11.62678
-11.72722
-11.70735
-11.60741
17.65346
17.4324,
17.05166
16.71100
‘6.41046
16.14997
15.9297,
15.74941
15.6091,
15.50905
15.44904
15.42*91
-11.9,02*
-12.27022
-12.57016
-12.4,Oll
-1,.0499*
P,
PO (41
(41 945.5,710,
945.5,64,4
P 6 (16, 942.956646
P , (161 942.946567
P 6 (16, 942.939630
P 5 (16, 942.9,24,6
P 4 (161 942.926391
P , (161 942.921667
P 2 (16, 942.918329
P , (16, 942.916313
P o (16, 942.915640
-174
-120
-144
-159
-116
-,55
-105
-117
-192
266 lOP16
266 lOP16
266 lOP22
266 lOP22
266 lOP22
266 lOP22
266 10122
266 10122
266 10122
266 10122
266 10122
-13.28449
-1,.,0455
17.24725
16.9450,
16.6*,11
16.46149
16.26022
16.13919
16.03054
15.97610
15.95190
11.b6191
11.59521
266 lOP36
266 3OP1b
266 1OPlb
266 1OPU
-61
332
-6
11.13316
12.23776
12.Ib269
11.,920,
266 lOPl(1
266 1OPlb
266 lOP14
266 lOSlb
266 10916
266 lOPl6
266 1OPlb
266 1OPlb
126
-12
,011
2b
5
110
15
-350
9,
69
62
b4
51
122
(10) 946.191453
Q 9 (11, 946.,6,7,4
Q,, (11, 946.394709
,,,o 132, 946.366696
Qll 112) 946.3.92b33
Q12 (12) 946.390325
Qll (1,) 946.369912
Q12 (1,) 946.3b5446
QIJ (1,) 946.402296
946.366441
$0
$2
Q14 (141 946.406625
Pl, (151 946.173600
P14 (15) 946.391161
12.44b69
13.946,5
12.57013
266 ,013,
266 1011,
266 loPI*
266 1OPlb
266 1OPlb
266 1OPlb
39
8,
(5
52
33
Q16 (16) 946.416353
Q,5 (17) 946.17b654
Q16 (1,) 946.39952b
Q17 (11) 946.421154
a,, (lb1 946.36171,
12.03606
11.23644
13.07454
12.923,)
266 3OPlb
9,
120
12.33769
12.14796
11.68409
12.51406
12.06964
11.645b2
12.42566
Q,5 (16, 946.395471
266 1OPlb
266 lOPl6
266 lOP16
11.61611
12.32bO6
266 ,OP,b
266 1OPlb
11.94435
266 ,OP,b
Q15 (151 946.411311
Q,, (10
(14) 946.171609
12.65,12
266 ,OP,b
-3,
Q 9 (10, 946.37b654
12.24109
ll.b9Ib2
95
Q ,
946.3b6552
12.09924
266 3OPlb
35
Q 9 I 9)
946.1Ob21
Q , I 7)
11.b3694
266 1OPlb
122
946.377102
946.315071
Q 6 1 I)
11.62250
12.04456
266 lOP,b
266 ,OP,b
137
101
11.61bI6
Q 6 ( 9)
946.361997
Q 6 1 61
266 1OPlb
11.67796
946.367OOb
946.374569
Q 5 , 6)
I9
266 1OPlb
Q , , 9,
946.374465
Q 4 ( 5,
590
11.625bO
11.94435
l,.b4,4,
946.375904
946.369169
Q , I 5)
266 3OP3b
266 lOP3b
6,
134
266 1OPlb
I6
f 61
946.374699
Q , C 4)
946.37526*
946.316654
3,
Q , C 31
p2t
(191 946.433627
(201 946.3bb904
60
-15
Q21 (2,) 946.402,66
946.407566
-76 -43
Q,, (27) 946.425304
60
3b
-45
-90
99
-4
-19
-166
I6
11
-36
-6
90
Q24 (211 946.392303
Q26 (26, 946.4b642b
Q25 (26) 946.452050
Q24 126) 946.419034
P2, (26) 946.367301
P25 (25) 946.4IIb14
Q24 (25) 946.444717
Q2, 125) 946.413123
P22 (25) 946.302615
Q24 (24, 946.46955,
42, ,241 946.411661
022 120
Qzl (24, 946.,76613
92, (2,) 966.461656
43
-55
Q20 (23) 946.,,4759
Q22 (231 946.433,32
42
P22 (22) 946.45411,
266 ,OPlb
266 lOP16
266 10116
266 lOP16
266 10116
266 1OPlb
266 1OP3b
266 lOP16
266 1OPlb
266 1OPlb
266 lOPl6
266 lOPl6
266 lOI,
266 ion*
266 lOPlO
266 IOPl.9
266 lOPl6
266 lOPlO
266 lOPl6
a66 lOPl6
266 1OP36
2,
-5,
(22, 946.425140
Q20 (22, 946.,9,522 ,,21
266 lOP16
266 IOP16
266 lOPl6
266 3OP,b
266 10110
266 1OPlb
266 lOP16
266 1OPlb
266 10116
266 LOP16
266 1OP16
266 10116
266 lOPI
266 1OPlb
-7b
,l
1
-51
-64
71
-36
-26
-53
51
20
31
113
Q19 (22) 946.371262
Q23 (21) 946.646927
Q2o (21) 946.41930,
Q19 (21) 946.393034
Q16 (21) 946.366123
Q20 (20, 946.460100
Q16 (20) 946.3bb904
$6
Q3, (20) 946.365340
Q
Q,b 119) 946.606101
QII (19) 946.365131
Q36 (16) 946.427514
Q,, (16) 946.403936
946.391576
946.504725
Q2b (201
00,
946.373505
946.503109
01) 01) 02) 02) (32) 1121 132, (33) (33) 031
Q,. Q,3 Q24 Q,, Q3o 931 Qj2 P29 P31 Q32
13.342b6
12.35349
15.17530
l4.,44IO
13.15492
12.20591
14.917Ob
1,.92695
12.97771
12.06911
14.66952
11.71993
12.83110
11.94312
14.4327,
946.512b66
946.512b67
946.4703b9
946.3b9546
946.565605
946.422231
946.30643
946.534150
946.493107
946.45,9,1
(34, 946.4,6690
946.395607
Q,2 (34, 946.479147
Qjl
Q30 00
P,, (33) 946.556116
P32 03)
946.4619b6
(11,
Q29
13.52360
16.31529
13.6b422
14.95703
266
3OPlb
266 1OPlb -33
-114
12.45259
266 10136
-bI
1,.2b24b
15.96Ibb
15.96792
266 lOPl4
266 1OPlb
14.69446
12.27095
16.949,)
15.67540
14.44256
11.25015
12.09992
16.62694
lb6
I5
266 lOP16
266 1OPlb
3
115
266 lOPl6
266 lOPlO
266 1OP16
266 lOPl6
266 lOPl6
266 lOP36
IOPlb
15.39354 266
14.20127 266 1OPlb
13.04999 266 1013)
266 3OPlb
266 1OPlb
11.9,966
15.1224b lop,*
266
13.97065
12.b59b6
11.7699b
16.01416
14.b619b
33.15071
12.6bO3b
11.65091
l5.,23b5
14.61217
13.5414b
12.53162
11.52256
15.44411
14.,7301
266 3OPlb
266 10136
266 lOP16
-144
163
70
-3
-bb
-204
137
4,
-22
-,oe
946.415534
01,
Qzb
11.b2I59 12.6552,
209
113
-44
-132
266 lOP16
266 lOP3.9
6b
-161
266 1OPlb
266 1OPlb
266 lOPl6
266 IOPlb
266 1OPlb
266 1OPlb
266 10116
266 1OPlb
266 10116
266 1OPlb
266 10116
41
-56
-137
-21*
I4
16
-4
-06
-366
3b
-2
-166
,,3o (30, 946.524454
Q29 (301 946.464666
Q2( (30) 946.446245
Q2, (101 946.409192
Q26
Q29 (29, 946.514409
!,2b (29, 946.475976
Q,, (29) 946.43b9Ob
P2( (29) 946.403205
Q25 (29) 946.36bb66
946.461664
Q21 (20
P26 (20) 946.431929
Q25 I20
Q24 (20) 966.364564
Q2, (27) 966.495396
Q26 (27) 946.459666
Q2, (31, 946.3Ib49I
14.20655
1,.3,795
12.51000
11.72276
13.99311
13.16297
12.,7546
11.62b64
13.76643
12.25163
12.25164
11.54522
1,.5923b
12.b451,
12.13053
13.40932
12.10229
-121
9
Qj2 (35, 946.444452
Q,, (I51 946.4**263
54
212
-179
Q,, t,*) 946.56699,
a,5 (391 946.431207
254
-122
946.550411
,,,*(42, 946.456*21
3,
,,,*(41) 946.49*4*2
01,
-,4*
Qj7 (41) 946.447929
Q
14*
-22,
Qj6 (41) 946.,9*761
-1*7
t,,6(40, 946.439391
t,,,(40, 946.5,9170
-192
2*2
Q,5 (40, 946.391676
946.57***4
*9
Q,, (39, 946.521277
Q,* 09,
-25
946.47905,
(39,
266 lOPl*
1,*
946.51774,
Q,6 00
Qj6
266 lOPl*
-47
12.5471,
14.02115
15.5,66(
266 lOPl*
266 lOP,*
266 lOPl*
14.2*772
11.0936*
16.75646
Q2,
140
946.516244
*,* III) 945.4,*4,9
Q4( (47) 946.565272
-64
-177
,26
33
-140
P4, (47) 946.5065*4
-22,
Q42 (471 946.449294
-26
-69
-154
4,s
-19,
22,
20
-165
no
-22
-9*
-95
-104
15*
-57
-171
-310
11
-149
-112
111
-56
-20,
-,07
,1*
61
-*7
-207
**
15.*4,*4
266 ,OPl*
266 lOPl*
266 lOPl*
266 lOPI*
266 ,OPl*
266 lOP,*
266 lOPI*
266 lOPl*
266 tOPI*
266 lOPI*
266 lOPl*
266 lOPl*
266 1OPl*
266 lOPI*
266 lOPI*
266 lOPI*
266 lOPI*
266 lOP,*
266 lOPl*
266 lOPI*
266 1OPl*
266 lOPl*
266 lOPl*
945.509110
-1,.909*4
Q45 (52) 946.37716,
P29 (52) 945.584556
Q2* (52) 945.5466,7
p27 (52, 945.510017
Q25 (52, 945.440*65
Q24 (52, 945.400306
Q47 (511 946.552755
P47 (51) 946.552753
P46 (51) 946.4900,7
16.77957
-16.24215
-13,
-150
-264
,*5
65
-77
-350
-15
-45
-,*
199
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Q45 (51, 946.4211722 -172
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Q2( (51) 945.525690
Q25 (51, 945.491165
Q46 (50, 946.5406*,
P45 I501 946.47932,
Q14 (501 946.419362
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Q45 (49) 946.52*964
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17.17*67
15.46004
1,.7*313
12.14132
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-12.71656
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-14.1529*
16.02902
15.1510,
11.51475
11.92000
-12.10,*6
-13.46105
266 lOPI* 266 lOPl*
-14.07942
16.49000
14.*526*
266 lOPl*
266 lOPl*
266 lOPl*
1,.25696
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266 lOPl*
266 lOPlO
P45 (40) 946.577642
11.7999,
266 lOPl*
946.517597
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16.16156
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266 lOPl*
PI, 00
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266 lOPI*
266 IOP,*
266 lOPl*
I-Continued
P41 (47) 946.393396
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1,.7651*
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17.94706 *2o (47, 945.535970
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16.42990
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17.59057
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16.11409
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QIo (461 946.,*545*
266 lOPl*
266 lOPl*
Q17 (46, 945.500134 Ql* (46, 945.531422
14.67*96
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266 lOPl*
266 lOPl*
266 lOPl*
266 lOPI*
266 lOPI*
266 ,OPl*
266 lOPI*
266 lOPI*
266 lOPl*
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946.469*11
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266 lOPlO
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Q,5 00
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Ql5 (44) 945.554646
Q41 (43, 946.573977
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Q,, (43) 946.414192
Pjg (42) 946.50*12*
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15.51424
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17.62636
16.27109
266 ,OPl*
-261
946.507560
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266 lOP,*
266 lOP,*
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266 lOPI*
266 lOPl*
266 ,OPl*
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266 lOPl*
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TABLE
16.*01*1
266 lOPI*
266 10110
266 lOPl*
266 lOPl*
266 lOPl*
266 lOPl*
266 lOPI*
266 lOP,*
266 lOP,*
266 lOP,*
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266 lOPI*
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266 lOPl*
266 lOPI*
13.16476 14.96232
266 ,OP,*
-14.12371
-16.01439
16.45049
14.65164
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266 ,OP,8
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266 lOPl2
266 lOPlO
266 lOPlO
266 lOPlO
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16.12150
16.221100
16.36792
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16.76a40
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266 lOPlO
266 lOPlO
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266 lOPlO
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162
953.412a40
953.4401aa
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I 2 ,401 954.09a555
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I ,
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227
I g ,161 951.470262
I o (40) 954.095aa6
199
I a ,161 953.45a900
2111
156
255
I 4 (16, 953.426430
-13.44655
I 4 ,461 955.0967a9
I 6 (46) 955.110012
9 2 (50, 955.729476
II, 150, 955.727490
-12.96694
-I,.14619
266 1OP 4
I 9 ,461 955.139994
-425
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I , ,461 955.092135
I 5 ,461 955.102771
226 2,a
202
241
107
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296
119
229
304
254
299
241
212
200
237
221
243
114
202
191
-153
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266 1OP 6
-139
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II1 146) 955.Oa6825
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RI4 ,451 955.139245
2,, 145) 955.115917
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RI5 (45, 955.073275
R14 (45) 955.053962
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954.977423
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II4 1451 954.93419,
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RIO ,401 954.162575
9 9 ,401 954.149a99
2 a (40) 954.1X1560
P , (40) 954.12(556
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266 1OP a
266 1OP a
266 1OP 2
-13.46659
16.06750
266 lOPlO
266 101 6
16.04749
266 lOPlO
517
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266 lOPlO
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951.422162
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266 lOPlO
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266 lOPlO
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266 lOPlO
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266 lOPlO
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-l4.12034
266 lOPlO
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211
-14.42159
266 lOPlO
-252
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953.416141
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266 lOPlO
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266 lOPI
-226
9 4 (IO, 952.311690
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R 6 (JO, 952.391006
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17.056al
266 lOPI
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266 lOI
16.55,57
266 lOPl2
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16.09056
266 10112
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951.12a992
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k,,
266 1OP 6
266 10s 6
266 1OP 6
266 1OP 4
266 10) 6
266 1OP a
266 1OP a
266 10s a
266 ,OP 6
266 1OP a
266 1OP a
266 IOP 2
266 ,OP 6
266 10s a
266 1OP a
266 1OP a
266 1OP 2
266 10s 4
266 101 a
266 10s a
266 1OP 6
266 1OP 6
266 1OP 4
266 1OP 8
266 1OP 4
266 101 a
266 10s a
266 IOP a
266 ,OP II
266 1OP 6
266 1OP 2
266 1OP 4
266 109 6
266 1OP a
266 1OP 6
TABLE I-Continued
-12.7470,
-13.65559
-11.71511
-1,.1,510
17.a341,
16.93100
14.,1**1
16.53946
16.39994
16.,0049
16.24075
16.22oa2
17.al227
17.11292
16.45370
15.113456
15.25556
14.71665
14.21165
1,.75a*4
1,.,,9*9
12.96100
12.62194
l2.,22a4
12.06166
11.8444,
11.66502
11.52555
11.4258,
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11.34614
-11.4673,
-11.641,4
-12.12726
-12.4a717 -353
955.143396 955.750690 955.759,0* 955.769255 955.780530
1 5 ISO) P 6 (50) II 7 (50) I 2 ,501 150) ,501
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955.79,1,1
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-139
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-230
-289
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-316
II, ,501 955.732793 101 6
101 6
6
266 101 6
266 101
266 101 6
266 101 6
266 101 6
266 101 6
266
266
-,,.747,2
-12.12511
-12.46,lO
-12.16130
-1,.0196a
-13.23627
-13.4171,
-I,.55620
213
uj OF PFs
The spectrum of the u3fundamental (parallel band) shows a symmetric top rotational structure. The lines observed are collected in Table I. Four hundred sixty-seven transitions have been assigned ranging in the rotational quantum number from J” = 2 up to J” = 76. In the fit we used the Hamiltonian H = BJ(J + 1) + (.4 - B)K2 - &J*(J + H5J3(J
+ 1)2 - DJKJ(J + l)K2 - DKK4
+ 1)3 + HJKJ2(J + 1)2K2 + HKJJ(J + 1)K4 + HKK6,
where the last two terms were found not to contribute significantly to the fit. From the observed frequencies 11 parameters have been determined (Table II). The root mean square of the fit was 207 kHz 4 6.90 X 10P6 cm-‘. From the spectrum no triplet structure due to Berry pseudorotation has been found. Application of DC voltage up to approximately 3000 V cm-’ on some of the lines did not show any indication of a Stark effect. 4. DISCUSSION
The advantages and limitations of the laser sideband technique have been demonstrated by the observation of IR transitions of the v3 fundamental of phosphorous pentafluoride. The spectral brightness of this source is high enough to saturate transitions and to completely resolve the Q branch, with all its K structure, up to fairly high J values. This technique has the advantage that, unlike a beam method, obser-
TABLE II Spectroscopic Constants of the us Fundamental -1 cm
"0 B"
B’_ B”
946.378527(5)
0.104516(l)
0.10451904(2)
6.7330(2) x 1O-4
2.03 0)
x lo-*
2.000 (2) x 10-8
- D;'
-1.37 (2) x 10-Y
-1.418(15)x 10-9
DS
-1.06 (9) x lo-*
-8 -1.288 (5) x 10
4.26 (9) x lo-'
4.51 (5) x 10-Y
-2.97 (9) x lo-'
-2.998 (1) x 10-Y
- 0;;
El" J
-6.4 (4) x lo-l4
";
-6.2 (5) x lo-l4
- HiI;
a) V.Dana.J.Bord4.L
b, &KJ
946.37847(7)
6.732(l) x 1O-4
0; - D;'
";K
b
-4.9460(Z)x 1O-4
D" J
D;K
Thia work
-4.9431(6)x 1O-4
A’_A”_(B’_B”)
D;
Dana et al?
2.7 (4) x lo-l5
ctrosc.ll4,42 (1985)
and blIKErrors in the order of constants
214
PRINZ AND KREINER
vation is not confined to low rotational quantum numbers. However, the low power levels presently available limit application to strongly absorbing bands. The resolution so far achieved is still considerably lower than that achieved with sophisticated waveguide lasers (6). In the vicinity of the vg fundamental (between 936 cm-’ and 952 cm-‘) our spectrometer covers =55% of this spectral range, employing MW modulation from 12 to 18 GHz. 5. ACKNOWLEDGMENTS
Substantial support of the Deutsche Forschungsgemeinschaft fessors Dr. H. Jones and Dr. A. Ruoff for critical comments. RECEIVED:
is gratefully acknowledged. We thank Pro-
April 24, 1989 REFERENCES
1. J. E. GRIFFITHS,R. P. CARTER,JR.,AND R. R. HOLMES,J. Chem. Phys. 41,863-876 (1964). 2. J. S~HATZ AND S. REICHMANN,J. Chem. Phys. 57,4571-4575 (1972). 3. M. L. PALMA, J. BORD~,J. DUPR~, AND C. MEYER,J. Phys. Les U/is, Fr. 43,869-874 (1982). 4. V. DANA, J. BORD~, L. HENRY, AND A. VALENTIN,J. Mol. Spectrosc. 114,42-48 (1985). 5. M. TAKAMI AND H. KUZE, J. Chem. Phys. 80,23 14-2318 (1983). 6. CH. BORDB,C.R. Hebd. St!ances Acad. Sci. 271,371-374 (1970). 7. CH. BORDB,J. BORDB,CH. BRYANT, CH. CHARDONNET,A. VAN LERBERGHE,AND CH. SAL~MON, Springer Ser. Opt. Sci. 49, 108-l 14 (1985). R. S. BERRY,J. Chem. Phys. 32,933-938 (1960). B. J. DALTON, J. Chem. Phys. 54,4745-4762 (1971). K. W. HANSENAND L. S. BARTELL,Znorg. Chem. 4, 1775 (1965). H. KURIMURA,S. YAMAMOTO,T. EGANEA,AND K. KUCHITSU,J. Mol. Struct. 140,79-86 (1986). R. WYATT, J. T. ROBERTS,R. E. WENTZ, ANDP. M. WILT, J. Chem. Phys. 50,255Z (1969). L. S. BERNSTEINAND IRA W. LEVIN, J. Chem. Phys. 64,3228-3236 (1976). J. BR~CASAND D. FASTENAKEL, Mol. Phys. 30, 193-198 (1975). G. MAGERL,W. SCHUPITA,J. M. FRYE, W. A. KREINER,AND T. OKA, J. Mol. Spectrosc. 107,72-83 (1984). 16. S.-C. HSU, R. H. SIZHWENDEMAN, ANDG. MAGERL,ZEEEJ. Quantum Electron. 24,2294-2301(1988). 17. W. A. KREINER,G. MAGERL,B. F~RCH, AND E. BONEK,J. Chem. Phys. 70,5015-5020 (1979). 8. 9. 10. II. 12. 13. 14. 15.
SPECTROSCOPY
137,204-2 14 ( 1989)
Resolution of the Q Branch in the
v3
Fundamental of PF5
H. PRINZ AND W. A. KREINER Abteilung Physikalische Chemie, University of Urn, West Germany
The ~3fundamental of phosphorus pentafhroride, PF5, has been investigated with a laser sideband spectrometer. A line width of 2 X lo-’ cm-’ was observed with the saturation technique, which was sufficient to resolve the @branch K structure. Four hundred sixty-seven transition frequencies up to J” = 76 have been measured with an accuracy of +200 kHz. The spectrum was fitted with a symmetric rotor program including three terms of sixth order. As a result, 11 parameters have been determined, yielding an overall standard deviation of 207 kHz. With the present resolution of 600 kHz no indication of splitting due to Berry rotation was found. o 1989 Academic PIWS,IIIC. 1. INTRODUCTION
The infrared spectrum of a fairly heavy molecule like phosphorus pentafluoride, PF,, has been a challenging problem in high-resolution spectroscopy for several years. The Q branch of the v3 fundamental was first observed at 944.8 cm-’ by Griffith et al. (I). Schatz and Reichmann (2) derived the first rotational constants from a partly resolved spectrum. The K structure was not resolved in a spectrum recorded with 0.014 cm-’ resolution by Palma et al. in 1982 (3) while Dana et al. derived nine spectroscopic constants from a Fourier transform spectrum with 1.6 X lob3 cm-’ resolution in 1985 (4). The K structure of the v3 P and R branch was resolved in 1983 with a diode laser in a pulsed supersonic free jet by Takami and Kuze (5). Single lines around 940 cm-’ have been observed by BordC et al. with saturation spectrosCOPY (6, 7). PFS is a subject of considerable theoretical interest because of the presence of the phenomenon of pseudorotation first suggested by Berry (8). This fast intramolecular rearrangement process may explain the observation that NMR data show only one fluorine resonance (9) although electron diffraction (10, I I), infrared, and Raman (12, 13) data indicate the presence of a D3h trigonal bipyramidal configuration. The spectroscopic consequences of different tunnelling mechanisms have been discussed by Brocas and Fastenakel (14). With the advent of laser sideband saturation spectroscopy using microwave modulation frequency resolution (1.5), absolute accuracy and tunability are achieved in the infrared region which are comparable to those of conventional microwave spectroscopy. In addition, this technique produces infrared frequencies directly rather than the wavelengths. Since sub-Doppler resolution can be achieved with this method its application to the Q branch of a heavy molecule looked promising. However, since the spectral brightness so far available is relatively low this method can only be applied to strongly absorbing bands. The u3 fundamental of PFS seemed to fill the necessary 0022-2852189
$3.00
Copyright Q 1989 by Ademic F’ress,Inc. All ri#~ts of nwoduction in any fomt reserved.
204
205
vj OF PFs
requirements. We were also interested in investigating the spectrum at fairly high quantum numbers J in order to check whether a symmetric rotor Hamiltonian up to sixth order can describe the observed transition frequencies satisfactorily. 2. EXPERIMENTAL
PROCEDURE
The spectrometer has been described already (15). With this technique the overall spectral coverage in the infrared is determined by the CO2 laser lines available (e 1Op36 of 13C02 at 882 cm-’ and =9R40 of CO2 at 1090 cm-‘). It should be mentioned that sideband spectroscopy with a CO laser has been reported (16) as well as generation of sidebands at higher mw modulation frequencies (17). As infrared source a DC sealedoff COZ laser was used which could also be operated with other CO2 isotopes. The output (between 5 and 10 W) was modulated at frequencies between 12 and 18 GHz via the electrooptic effect in a CdTe crystal. The crystal was placed in a copper housing designed as a tunable microwave resonator with a bandwidth of 30 MHz. The microwave, generated in a synthesizer (HP 8673 E), was amplified up to 20 W by a travelling wave tube. A few mW of tunable IR power were obtained in either sideband. The cell consisted of a 1.2-m J-band waveguide equipped with a Stark septum leaving a gap of 7.65 mm. Because the sideband radiation is polarized perpendicularly with respect to the carrier, one can separate most of the unmodulated laser power (the carrier) from the sidebands by reflection on suitably oriented Brewster polarizers. Part of the carrier radiation was fed into the COZ fluorescence cell in order to stabilize the laser via the 4.3~pm emission Lamb dip. For this purpose the piezo mounted laser mirror was jittered at a frequency of 400 Hz. The sideband radiation traversed the absorption cell twice in order to allow saturation dips to be observed. A grid polarizer in front of the detector provided additional suppression of the carrier. The reflected beam was usually tilted at a slight angle in order to produce spatial separation. During part of the measurement a slightly different arrangement was chosen in order to produce collinear direction of saturation and detection beams (Fig. 1). In this case a partly transmitting mirror was positioned at the far end of the absorption cell, perpendicular to the incoming beam. The reflected
SIDEBAND
IN
STARK
CELL
R.98%
DET
FIG. 1. Optical arrangements used to observe saturation dips. In the version with the partly transmitting mirror (top) probe beam and saturation beam are nearly parallel; this avoids line broadening introduced when there is an angle between them (bottom).
206
PRINZ AND KREINER
PF5 V3= 1
a,2 (12)
12530 co2
50
45
40
35
MHZ
lOP18
FIG. 2. Frequency modulated lines in the Q-branch of the ys fundamental. Ten sweeps have been averaged. The two features at the let? side are most likely due to thermal effects in the modulator, while the sharp spike in the center is an artifact produced by the synthesizer. In addition, saturation dips ofweaker transitions can be recognized.
power (98%) was still strong enough to saturate most of the transitions. The transmitted portion of the radiation (2%) could be used to detect the saturation signal, with the incoming beam acting as the probe. No monochromator was used to eliminate one of the sidebands.
us
LS
P2,(45)
15 125
30
35
40
45
uns
co2 1OP 25 FIG. 3. The two strong lines, just resolved on the recording, coincide with the upper and lower sideband, respectively. The baseline is due to frequency modulation of the Doppler profile and the bandwidth of the modulator, which are of the same order [Aun(PFs) = 34 MHz; Ayr.,oD= 30 MHz].
207
vj OF PFI
12 420 co2 10 PlB
us
FIG. 4. Series of Q-branch lines, partly blended. The assigned transitions coincide with the upper sideband of the P18 laser line in the IO-pm band of the regular CO2 isotope.
3. OBSERVATION AND RESULTS
Examples of saturation dips observed are given in Figs. 2 to 5. Half width (FWHM) is 2600 kHz and absolute accuracy was G +200 kHz in most cases; this was limited by spectral impurity introduced mainly into the laser cavity via the stabilization system and other sources of mechanical noise.
PF5 V3=
1
us
16930
R6u61
35
40
45
MHZ
cop 1OP 8 FIG. 5. Assignment refers to the strong line, while the unassigned lines were just checked with respect to the sideband they coincide with by changing their carrier frequencies slightly and observing their relative shifts.
266 lOP26 266 10126 266 lOP26 266 lOP26
-25 -77 lo* 292
P g (36, 936.29010, 939.202915 9,9.20,5*7
P o 02) P , 02,
P 6 (32, 9,9.245662 P 9 (32, 9,9.257045
-16.05,54
-15.474,*
-15.65546
-15.3967,
-15.09611
-14.75966
-14.36135
-13.9630,
-11.50467
-13.00661
-12.4667,
-11.69066
13.5111,
1,.5,,1,
13.59296
266 10126
266 lOP26
266 1op2*
266 1OP26
266 IOPZO
266 1OP26
266 1OP26
266 lOP20
266 1OP26
266 1OP26
266 1OP26
266 lOP26
266 1OP26
266 10126
266 10124
-64 -99
-114 -65
P 5 124, 941.106973 P 6 (24, 941.114,46 P , (24, 941.123059 P 6 (24, 941.1,,116 P 9 124, 941.144520
16.66617
17.42551
-13.54970
-1,.5296,
-13.46976
-I,.,6970
266 lOP26
266 10126
266 10126
266 10126
266 10126
266 10126
466
446
P,, 140, 937.367015
PII 140, 9,7.,*5005
9M.242289
125
-140
P 4 124, 941.100937
16.36666
266 lOP26
429
P,2 140, 9,7.,50,59
P , 061
-109
P , 124, 941.096246
15.92762
266 lOP26
407
Pl, (40, 9,7.3,5041
-15
-79
P 2 (24, 941.092696
15.50*4,
266 lOP26
41,
PIO (401 9,7.,21056
P 2 (36, 9,6.216951
-71
P , (24, 941.090606
15.12922
266 lOP26
436
P g (40, 9,7.,04409
-127
-115
P o (24, 941.090214
14.74992
266 lOP26
,*0
P * (401 9,7.291091
P 1 116, 9H.236944
-359
P 5 (26.1 940.17097,
14.49062
266 lOP26
160
-146
-416
P 4 (26, 940.164946
14.21127
266 lOP26
-1
-294
P , (26, 940.160267
14.0,1*7
266 10126
9M.236265
-425
P 2 (26, 940.156917
P o 06,
-357
P 1 (26, 940.154911
13.69274
306 -,61
9,9.2*,790
Pll 021 P o (26, 940.154242
211
Plo 1321 939.269746
234
256
19, 255
P 6 (32, 939.226967 P 7 02,
939.235657
242 294
939.219621
P 5 02,
144
P , (32, 939.208927 P 4 (32, 919.213606
224
9M.276964
P 2 132) 9,9.20556(1
P 4 06,
P 7 (36, 9M.266959
1,.8,2,0
P , (40, 937.267107
266 10P26
5
-16.19265
266 lOP26
9,6.260266
266 lOP28
159
266 lOP26
-27
P 6 06)
-16.29227
266 10124
266 10124
266 lOP24
266 lOP24
266 10124
266 lOP24
266 lOP24
266 lOP24
266 lOP24
266 10124
266 1OP24
266 lOP24
266 lOP24
266 lOP24
266 lOP24
266 10P24
266 lOP24
266 lOP26
266 lOP26
266 1OP26
266 lOP26
266 1OP26
266 1OP26
266 lOP26
266 1OP26
266 lOP26
266 lOP26
266 lOP26 266 1OP26
2, -1
938.246954
P 5 (361 936.252954
-16.,5195
266 10126
P 4 061
-16.37160
266 lOP26
266 10126
P 6 140, 9,7.276456
-I4
P14 144, 9,6.,476,,
405
-61
Pl, (44, 936.369444
P 5 (40, 9,7.2711,*
-50
P12 (44, 9,6.,5,270
,49
-101
Pll (44, 916.337964
441
-214
9,6.3240,4
PlO 04,
P 4 (40, 937.265144
-239
P g (44, 916.311414
P , (40, 937.260494
-266
P 4 (44, 9,6.,00125
,29
-x25
P , (44, 936.290164
140
-,26
P 6 (44) 936.24151,
P 2 (40, 937.257164
-,50
P 5 ,441 916.274231
P , (40, 9,7.255164
-415
P 4 (44, 936.266255
,l
-24,
P , (44, 9,6.26,615
276
-392
P 2 (44, 9,6.260292
P o 140, 9,7.254501
-364
P , (44, 9,6.256,01
Pl5 (44, 9,6.407115
-436
P 0 (44, 9,6.2516,6
vj of PF5 : Observed Transitions
TABLE I
-13.22966
17.66014
17.53632
17.23676
16.97554
16.75451
16.57357
16.43294
16.,,251
16.2722,
16.25210
-11.3056,
-11.46645
-11.62678
-11.72722
-11.70735
-11.60741
17.65346
17.4324,
17.05166
16.71100
‘6.41046
16.14997
15.9297,
15.74941
15.6091,
15.50905
15.44904
15.42*91
-11.9,02*
-12.27022
-12.57016
-12.4,Oll
-1,.0499*
P,
PO (41
(41 945.5,710,
945.5,64,4
P 6 (16, 942.956646
P , (161 942.946567
P 6 (16, 942.939630
P 5 (16, 942.9,24,6
P 4 (161 942.926391
P , (161 942.921667
P 2 (16, 942.918329
P , (16, 942.916313
P o (16, 942.915640
-174
-120
-144
-159
-116
-,55
-105
-117
-192
266 lOP16
266 lOP16
266 lOP22
266 lOP22
266 lOP22
266 lOP22
266 10122
266 10122
266 10122
266 10122
266 10122
-13.28449
-1,.,0455
17.24725
16.9450,
16.6*,11
16.46149
16.26022
16.13919
16.03054
15.97610
15.95190
11.b6191
11.59521
266 lOP36
266 3OP1b
266 1OPlb
266 1OPU
-61
332
-6
11.13316
12.23776
12.Ib269
11.,920,
266 lOPl(1
266 1OPlb
266 lOP14
266 lOSlb
266 10916
266 lOPl6
266 1OPlb
266 1OPlb
126
-12
,011
2b
5
110
15
-350
9,
69
62
b4
51
122
(10) 946.191453
Q 9 (11, 946.,6,7,4
Q,, (11, 946.394709
,,,o 132, 946.366696
Qll 112) 946.3.92b33
Q12 (12) 946.390325
Qll (1,) 946.369912
Q12 (1,) 946.3b5446
QIJ (1,) 946.402296
946.366441
$0
$2
Q14 (141 946.406625
Pl, (151 946.173600
P14 (15) 946.391161
12.44b69
13.946,5
12.57013
266 ,013,
266 1011,
266 loPI*
266 1OPlb
266 1OPlb
266 1OPlb
39
8,
(5
52
33
Q16 (16) 946.416353
Q,5 (17) 946.17b654
Q16 (1,) 946.39952b
Q17 (11) 946.421154
a,, (lb1 946.36171,
12.03606
11.23644
13.07454
12.923,)
266 3OPlb
9,
120
12.33769
12.14796
11.68409
12.51406
12.06964
11.645b2
12.42566
Q,5 (16, 946.395471
266 1OPlb
266 lOPl6
266 lOP16
11.61611
12.32bO6
266 ,OP,b
266 1OPlb
11.94435
266 ,OP,b
Q15 (151 946.411311
Q,, (10
(14) 946.171609
12.65,12
266 ,OP,b
-3,
Q 9 (10, 946.37b654
12.24109
ll.b9Ib2
95
Q ,
946.3b6552
12.09924
266 3OPlb
35
Q 9 I 9)
946.1Ob21
Q , I 7)
11.b3694
266 1OPlb
122
946.377102
946.315071
Q 6 1 I)
11.62250
12.04456
266 lOP,b
266 ,OP,b
137
101
11.61bI6
Q 6 ( 9)
946.361997
Q 6 1 61
266 1OPlb
11.67796
946.367OOb
946.374569
Q 5 , 6)
I9
266 1OPlb
Q , , 9,
946.374465
Q 4 ( 5,
590
11.625bO
11.94435
l,.b4,4,
946.375904
946.369169
Q , I 5)
266 3OP3b
266 lOP3b
6,
134
266 1OPlb
I6
f 61
946.374699
Q , C 4)
946.37526*
946.316654
3,
Q , C 31
p2t
(191 946.433627
(201 946.3bb904
60
-15
Q21 (2,) 946.402,66
946.407566
-76 -43
Q,, (27) 946.425304
60
3b
-45
-90
99
-4
-19
-166
I6
11
-36
-6
90
Q24 (211 946.392303
Q26 (26, 946.4b642b
Q25 (26) 946.452050
Q24 126) 946.419034
P2, (26) 946.367301
P25 (25) 946.4IIb14
Q24 (25) 946.444717
Q2, 125) 946.413123
P22 (25) 946.302615
Q24 (24, 946.46955,
42, ,241 946.411661
022 120
Qzl (24, 946.,76613
92, (2,) 966.461656
43
-55
Q20 (23) 946.,,4759
Q22 (231 946.433,32
42
P22 (22) 946.45411,
266 ,OPlb
266 lOP16
266 10116
266 lOP16
266 10116
266 1OPlb
266 1OP3b
266 lOP16
266 1OPlb
266 1OPlb
266 lOPl6
266 lOPl6
266 lOI,
266 ion*
266 lOPlO
266 IOPl.9
266 lOPl6
266 lOPlO
266 lOPl6
a66 lOPl6
266 1OP36
2,
-5,
(22, 946.425140
Q20 (22, 946.,9,522 ,,21
266 lOP16
266 IOP16
266 lOPl6
266 3OP,b
266 10110
266 1OPlb
266 lOP16
266 1OPlb
266 10116
266 LOP16
266 1OP16
266 10116
266 lOPI
266 1OPlb
-7b
,l
1
-51
-64
71
-36
-26
-53
51
20
31
113
Q19 (22) 946.371262
Q23 (21) 946.646927
Q2o (21) 946.41930,
Q19 (21) 946.393034
Q16 (21) 946.366123
Q20 (20, 946.460100
Q16 (20) 946.3bb904
$6
Q3, (20) 946.365340
Q
Q,b 119) 946.606101
QII (19) 946.365131
Q36 (16) 946.427514
Q,, (16) 946.403936
946.391576
946.504725
Q2b (201
00,
946.373505
946.503109
01) 01) 02) 02) (32) 1121 132, (33) (33) 031
Q,. Q,3 Q24 Q,, Q3o 931 Qj2 P29 P31 Q32
13.342b6
12.35349
15.17530
l4.,44IO
13.15492
12.20591
14.917Ob
1,.92695
12.97771
12.06911
14.66952
11.71993
12.83110
11.94312
14.4327,
946.512b66
946.512b67
946.4703b9
946.3b9546
946.565605
946.422231
946.30643
946.534150
946.493107
946.45,9,1
(34, 946.4,6690
946.395607
Q,2 (34, 946.479147
Qjl
Q30 00
P,, (33) 946.556116
P32 03)
946.4619b6
(11,
Q29
13.52360
16.31529
13.6b422
14.95703
266
3OPlb
266 1OPlb -33
-114
12.45259
266 10136
-bI
1,.2b24b
15.96Ibb
15.96792
266 lOPl4
266 1OPlb
14.69446
12.27095
16.949,)
15.67540
14.44256
11.25015
12.09992
16.62694
lb6
I5
266 lOP16
266 1OPlb
3
115
266 lOPl6
266 lOPlO
266 1OP16
266 lOPl6
266 lOPl6
266 lOP36
IOPlb
15.39354 266
14.20127 266 1OPlb
13.04999 266 1013)
266 3OPlb
266 1OPlb
11.9,966
15.1224b lop,*
266
13.97065
12.b59b6
11.7699b
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11.52256
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266 lOP3.9
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266 1OPlb
266 1OPlb
266 lOPl6
266 IOPlb
266 1OPlb
266 1OPlb
266 10116
266 1OPlb
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266 lOPI* 266 lOPl*
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P g 05)
IIa ,451 954.966113
II7 (45) 954.956136
R 6 ,451 954.947491
R 5 ,451 954.940176
II4 1451 954.93419,
I , (451 954.929541
II2 (45) 954.926215
II‘ 145) 954.924222
IIo ,451 954.921557
RIO ,401 954.162575
9 9 ,401 954.149a99
2 a (40) 954.1X1560
P , (40) 954.12(556
I 6 ,401 954.119am
266 1OP a
266 1OP a
266 1OP 2
-13.46659
16.06750
266 lOPlO
266 101 6
16.04749
266 lOPlO
517
-11.46751
266 lOPlO
-39,
I,( (10) 952.49*3,2
951.422162
-12.01039
266 lOPI
-,*,
hl, ,301 952.4*022,
I , 06)
-12.51294
266 lOPlO
-405
L12 ,101 952.46,456
197
-12.97522
266 lOPlO
-369
952.44ao40
Lll 00)
275
-I,.,9719
266 lOPlO
-354
RIO (10) 952.43,964
I 2 ,161 953.41aal3
-1,.77*19
266 lOPlO
-332
I ) (JO1 952.421232
II1 ,161 953.416411
-l4.12034
266 lOPlO
-,,I
I a ,101 952.409641
211
-14.42159
266 lOPlO
-252
130, 952.,99794
RI
953.416141
-14.66262
266 lOPlO
I o 06)
-14.90357
266 lOPI
-226
9 4 (IO, 952.311690
-225
-275
R 6 (JO, 952.391006
-255
I 2 (10) 952.369653
I , ,101 952.,1,001
I 5 ,301 952.3113716 -290
-191
952.361646
9 1 00)
-201
952.,66976
I 0 00,
-15.08422
17.056al
266 lOPI
,a
266 lOI
16.55,57
266 lOPl2
"I1 (26) 951.77935a
16.09056
266 10112
-19
"I1 (26) 951.761225
951.12a992
I6
,261
"12 ,261 951.144436
k,,
266 1OP 6
266 10s 6
266 1OP 6
266 1OP 4
266 10) 6
266 1OP a
266 1OP a
266 10s a
266 ,OP 6
266 1OP a
266 1OP a
266 IOP 2
266 ,OP 6
266 10s a
266 1OP a
266 1OP a
266 1OP 2
266 10s 4
266 101 a
266 10s a
266 1OP 6
266 1OP 6
266 1OP 4
266 1OP 8
266 1OP 4
266 101 a
266 10s a
266 IOP a
266 ,OP II
266 1OP 6
266 1OP 2
266 1OP 4
266 109 6
266 1OP a
266 1OP 6
TABLE I-Continued
-12.7470,
-13.65559
-11.71511
-1,.1,510
17.a341,
16.93100
14.,1**1
16.53946
16.39994
16.,0049
16.24075
16.22oa2
17.al227
17.11292
16.45370
15.113456
15.25556
14.71665
14.21165
1,.75a*4
1,.,,9*9
12.96100
12.62194
l2.,22a4
12.06166
11.8444,
11.66502
11.52555
11.4258,
,1.,6600
11.34614
-11.4673,
-11.641,4
-12.12726
-12.4a717 -353
955.143396 955.750690 955.759,0* 955.769255 955.780530
1 5 ISO) P 6 (50) II 7 (50) I 2 ,501 150) ,501
I g RIO
955.79,1,1
-3aa
I 4 ,501 955.1,1432
-139
-193
-230
-289
-,40
-316
II, ,501 955.732793 101 6
101 6
6
266 101 6
266 101
266 101 6
266 101 6
266 101 6
266 101 6
266
266
-,,.747,2
-12.12511
-12.46,lO
-12.16130
-1,.0196a
-13.23627
-13.4171,
-I,.55620
213
uj OF PFs
The spectrum of the u3fundamental (parallel band) shows a symmetric top rotational structure. The lines observed are collected in Table I. Four hundred sixty-seven transitions have been assigned ranging in the rotational quantum number from J” = 2 up to J” = 76. In the fit we used the Hamiltonian H = BJ(J + 1) + (.4 - B)K2 - &J*(J + H5J3(J
+ 1)2 - DJKJ(J + l)K2 - DKK4
+ 1)3 + HJKJ2(J + 1)2K2 + HKJJ(J + 1)K4 + HKK6,
where the last two terms were found not to contribute significantly to the fit. From the observed frequencies 11 parameters have been determined (Table II). The root mean square of the fit was 207 kHz 4 6.90 X 10P6 cm-‘. From the spectrum no triplet structure due to Berry pseudorotation has been found. Application of DC voltage up to approximately 3000 V cm-’ on some of the lines did not show any indication of a Stark effect. 4. DISCUSSION
The advantages and limitations of the laser sideband technique have been demonstrated by the observation of IR transitions of the v3 fundamental of phosphorous pentafluoride. The spectral brightness of this source is high enough to saturate transitions and to completely resolve the Q branch, with all its K structure, up to fairly high J values. This technique has the advantage that, unlike a beam method, obser-
TABLE II Spectroscopic Constants of the us Fundamental -1 cm
"0 B"
B’_ B”
946.378527(5)
0.104516(l)
0.10451904(2)
6.7330(2) x 1O-4
2.03 0)
x lo-*
2.000 (2) x 10-8
- D;'
-1.37 (2) x 10-Y
-1.418(15)x 10-9
DS
-1.06 (9) x lo-*
-8 -1.288 (5) x 10
4.26 (9) x lo-'
4.51 (5) x 10-Y
-2.97 (9) x lo-'
-2.998 (1) x 10-Y
- 0;;
El" J
-6.4 (4) x lo-l4
";
-6.2 (5) x lo-l4
- HiI;
a) V.Dana.J.Bord4.L
b, &KJ
946.37847(7)
6.732(l) x 1O-4
0; - D;'
";K
b
-4.9460(Z)x 1O-4
D" J
D;K
Thia work
-4.9431(6)x 1O-4
A’_A”_(B’_B”)
D;
Dana et al?
2.7 (4) x lo-l5
ctrosc.ll4,42 (1985)
and blIKErrors in the order of constants
214
PRINZ AND KREINER
vation is not confined to low rotational quantum numbers. However, the low power levels presently available limit application to strongly absorbing bands. The resolution so far achieved is still considerably lower than that achieved with sophisticated waveguide lasers (6). In the vicinity of the vg fundamental (between 936 cm-’ and 952 cm-‘) our spectrometer covers =55% of this spectral range, employing MW modulation from 12 to 18 GHz. 5. ACKNOWLEDGMENTS
Substantial support of the Deutsche Forschungsgemeinschaft fessors Dr. H. Jones and Dr. A. Ruoff for critical comments. RECEIVED:
is gratefully acknowledged. We thank Pro-
April 24, 1989 REFERENCES
1. J. E. GRIFFITHS,R. P. CARTER,JR.,AND R. R. HOLMES,J. Chem. Phys. 41,863-876 (1964). 2. J. S~HATZ AND S. REICHMANN,J. Chem. Phys. 57,4571-4575 (1972). 3. M. L. PALMA, J. BORD~,J. DUPR~, AND C. MEYER,J. Phys. Les U/is, Fr. 43,869-874 (1982). 4. V. DANA, J. BORD~, L. HENRY, AND A. VALENTIN,J. Mol. Spectrosc. 114,42-48 (1985). 5. M. TAKAMI AND H. KUZE, J. Chem. Phys. 80,23 14-2318 (1983). 6. CH. BORDB,C.R. Hebd. St!ances Acad. Sci. 271,371-374 (1970). 7. CH. BORDB,J. BORDB,CH. BRYANT, CH. CHARDONNET,A. VAN LERBERGHE,AND CH. SAL~MON, Springer Ser. Opt. Sci. 49, 108-l 14 (1985). R. S. BERRY,J. Chem. Phys. 32,933-938 (1960). B. J. DALTON, J. Chem. Phys. 54,4745-4762 (1971). K. W. HANSENAND L. S. BARTELL,Znorg. Chem. 4, 1775 (1965). H. KURIMURA,S. YAMAMOTO,T. EGANEA,AND K. KUCHITSU,J. Mol. Struct. 140,79-86 (1986). R. WYATT, J. T. ROBERTS,R. E. WENTZ, ANDP. M. WILT, J. Chem. Phys. 50,255Z (1969). L. S. BERNSTEINAND IRA W. LEVIN, J. Chem. Phys. 64,3228-3236 (1976). J. BR~CASAND D. FASTENAKEL, Mol. Phys. 30, 193-198 (1975). G. MAGERL,W. SCHUPITA,J. M. FRYE, W. A. KREINER,AND T. OKA, J. Mol. Spectrosc. 107,72-83 (1984). 16. S.-C. HSU, R. H. SIZHWENDEMAN, ANDG. MAGERL,ZEEEJ. Quantum Electron. 24,2294-2301(1988). 17. W. A. KREINER,G. MAGERL,B. F~RCH, AND E. BONEK,J. Chem. Phys. 70,5015-5020 (1979). 8. 9. 10. II. 12. 13. 14. 15.