JOURNAL OF MOLECULAR SPECTROSCOPY127, 178-185
(1988)
Rotational Spectrum of Butyronitrile: Dipole Moment, Centrifugal
Distortion Constants and Energy Difference between Conformers
G. WLODARCZAK, L. MARTINACHE, AND J. DEMAISON
Laboratoire
de Spectroscopie Hertzienne, Associe au CN.R.S.
Universite de Lille l, P5
F59655 Villeneuve D'Ascq Cedex, France
AND
K.-M. MARSTOKK AND HARALD MØLLENDAL
Department
ofChemistry,
The University
of Oslo, N-0315 Oslo 3, Norway
The molecular rotational spectrum of butyronitrile has been investigated in the vibrational
ground state up to 300 GHz. High J transitions have been measured for the two isomers and
fitted to a centrifugally distorted Hamiltonian inciuding some sextie coefficients. The results of
the analysis are sufficient for the predietion of all strong transitions throughout the millimeterwave range. The molecular dipole moment components were calculated from measured Stark
effect shifts as /loa = 3.597(59) D and /loh= 0.984(15) D for the anti form and /loa= 3.272(37) D
and /loh= 2.139(30) D with /loepreset at zero debye for the gauche form. It has been found from
intensity measurements
that the anti form is slightly more stable than the gauche form with an
energy difference of l.1 (3) kl mol-I.
@ 1988 Academic
Press, Inc.
INTRODUCTION
Butyronitrile (CH3CH2CH2CN)was previously studied in the eentimeter-wave range
by Hirota (1) who showed that two isomerie forms exist. He determined the rotational
eonstants for the ground and several exeited vibrational states but as the lines were
broad, he eould not determine the quadrupole eoupling eonstants. The dipole moments
of the two eonformers and their relative stability were not determined by him. Later
Kaushik (2) determined the quartie eentrifugal distortion eonstants of the gauche form
in its ground state using the measurements of Hirota. Reeently, the quadrupole hyperfine strueture due to the nitrogen nucleus was investigated by using a mierowave
Fourier transform speetrometer (3).
Butyronitrile is a possible eandidate for interstellar deteetion. In faet some eoineidenees between a ealculated speetrum and som e U lines have already been noted (4).
For this reason we have measured the millimeter-wave speetrum of both forms of
butyronitrile and earried out a eomplete eentrifugal distortion analysis so that aeeurate
measurements and predietions would be available for radioastronomers. We have also
determined the energy differenees between the anti and the gauche eonformations as
well as the dipole moments.
EXPERIMENT
AL DET AILS
The sample of butyronitrile was obtained eommereially from Merek-Sehuehardt
(Hohenbrunn, FRG) and was used without further purifieation. The millimeter-wave
0022-2852/88 $3.00
Copyright@ 1988 by AcademicPress,Inc.
All rights of reproduction in any form reserved.
178
179
ROTATIONAL SPECTRUM OF BUTYRONITRILE
transitions were measured with a computer-controlled spectrometer with superheterodyne detection (Lille). Details ofthis instrument have been reported elsewhere (5).
The dipole moments and the relative intensities were measured with a Stark effect
spectrometer (Oslo).
SPECTRAL ANALYSIS
The largestcomponent of the dipole moment is /-Lafor both forms, so the a-typeRbranch spectra were searched first. Their assignments were relatively easy because the
spectra are strong and because the constants of Hirota (1) and Kaushik (2) could be
used for a first prediction. The assignment was then continued using the "bootstrap"
method as described by Kirchhoff(6) and the calculation of the standardized residuals
t(.:lVi)was systematically used to check the assignment of each individual line. The
aROIseries was measured up to J = 46 and K- = 34 for the gauche form and up to J
= 63 and K- = 23 for the anti form. For the gauche form, a number of characteristic
quartets of very low K and high J could be easily identified. They are essentially due
to the EO splittings of the levels (7) and appear as a symmetrical quartet (see Fig. 1).
For the gauche form a large number of /-Lblines could be identified without too much
difficulty whereas for the anti form only three /-Lblines could be assigned without
ambiguity. This is due to the fact that the /-Lb/
/-La
ratio is much smaller for the anti form
and that the spectrum is very crowded, so that the relatively weaker /-Lblines are often
IMHz
'--'
FIo. 1. Symmetrical quartet at 179.07 GHz due to the EO splitting (transitions
311.30; 322.31
312.30; 32'.31
312.30).
322.3'
311.30; 321.31 ......
180
WLODARCZAK
ET AL.
blended with stronger Ilalines. None of the measured transitions were observed to be
split, either by internal rotation or by nuclear quadrupole interaction. The newly
measured frequencies are listed in Table I for the anti form and in Table Il for the
gauche form. In order to derive the molecular parameters the spectrum was fitted to
the Hamiltonian ofWatson (8) using the l' representation. The centimeter-wave transitions of Refs. (1) and (3) were also taken into account. Both A- and S-reduction were
tried, the latter in a notation due to van Eijck (9) and to Typke (10) who also coded
the program. Although both forms are near-symmetric the S-reduction did not give
better results. So for the final fit, the A-reduction was adopted because computer
programs using it are more currently available. The rotational and centrifugal distortion
constants are presented in Table III together with their standard deviation and their
correlation matrix. Some sextic centrifugal distortion constants could be determined
for both forms. However, the highest sextie contribution is only 5.39 MHz for the
transition 4823,25 4723,24of the anti form whereas it is -51.63 MHz for the transition
-
T ABLE I
Newly
J
3
23
35
o
35
2
35
6
35
7
35
8
35
9
35 10
35 Il
35 12
36 O
36
I
36
I
36
I
36 2
36 2
36 3
36 3
36 4
36 4
36 5
36 5
36 6
36 7
36 8
36 13
36 14
36 15
36 16
36 17
36 18
37
O
37
l
43
2
48
I
48 2
48 2
48 2
48 3
48 4
48 4
48 5
48 5
48 6
48 6
48 7
48 8
48
9
48 10
.)....
Measured
K.Ko'-J
20
35
33
29
28
27
26
25
24
23
36
36
35
36
34
35
33
34
32
33
31
32
31
30
29
24
22
22
20
19
18
37
37
42
47
47
46
46
46
45
44
44
43
42
43
42
41
40
39
22
34
34
34
34
34
34
34
34
34
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
36
36
42
47
47
47
47
47
47
'fl
47
47
47
47
47
47
47
47
K.
2
o
2
6
7
8
9
10
I1
12
O
O
1
I
2
2
3
3
4
4
5
5
6
7
8
13
14
15
16
17
18
O
I
I
1
2
2
2
3
4
4
5
5
6
6
7
8
9
10
in tIiz. ..-c. in kHz.
Rotational
Ko
21
34
32
26
27
26
25
24
23
22
35
35
34
35
33
34
32
33
31
32
30
31
30
29
28
23
21
21
19
18
17
36
36
41
46
46
45
45
45
44
43
43
42
41
42
41
40
39
38
o...
210682.22
152420.07
156362.10
154794.60
154778.85
154773.84
154775.62
154782.18
154792.35
154805.40
156709.22
159988.78
159984.27
156376.78
160851.40
158511.09
159816.20
159295.56
159360.35
159324.49
159258.14
159256.97
159218.77
159201.12
159194.99
159241.59
159259.85
159280.32
159302.83
159327.32
159353.76
16099!I.16
160691.64
211442.58
211856.19
210741.48
214343.66
214343.68
212219.54
212517.79
212766.64
212415.06
212430.89
212320.77
212320.28
212267.79
212241.20
212230.19
212229.67
Transitions
0.-<:.
-Il
15
-25
7
-18
-43
-48
-19
-3
-54
5
-45
-38
10
-67
27
142
-21
30
8
-17
33
-14
t4
-12
-31
-35
-27
-25
-19
33
26
53
96
-135
-101
-115
-118
-37
19
165
22
82
-7
64
20
35
-9
50
J K.
48 12
48 13
48 14
48 15
48 16
48 17
48 18
48 19
48 20
48 21
482226
48 23
49 O
49
I
49 2
49 4
49 16
49 17
492030
50
O
50
3
50
7
50
8
50
9
50 10
50 Il
50 12
50 13
50 14
50 20
51 O
51
I
64 6
64 6
64
7
64 8
64 9
64 10
64 11
64 12
64 13
64 14
64 15
64 16
64 17
64 18
64 19
642045
64 21
for anti-Butyronitrilea
Ko ,37
36
35
34
32
31
31
30
28
27
25
49
49
48
46
34
33
50
48
44
43
42
41
40
39
37
37
31
51
51
59
58
58
57
56
55
54
53
51
50
50
48
47
46
45
43
J
K.
'fl
12
47 13
47 14
47 15
47 16
47 17
47 18
47 19
47 20
47 21
47 22
47 23
48 O
48
l
48 2
48 4
48 16
48 17
482029
49 O
49 3
49 7
49 8
49 9
49 10
49 ti
49 12
49 13
49 14
492030
50
O
50
1
63
6
63
6
63
7
63 8
63 9
63 lO
63 Il
63 12
63 13
63 14
63 15
63 16
63 17
63 18
63 19
632044
63 21
Ko
36
35
34
33
31
30
30
29
27
26
25
24
48
48
47
45
33
32
49
47
43
42
41
40
39
38
36
36
50
50
58
57
57
56
55
54
53
52
50
49
49
47
46
45
44
42
0.-<:.
o...
-26
212249.06
212266.32
-32
23
212267.59
212312.29
8
212340.19
4
212371.06
22
212404.72
22
212441.11
65
212480.03
30
-25
212521.49
212565.54
12
-45
212611.99
212476.62
63
212378.48
18
215077.17
16
216949.09
-13
216757.71
18
216789.07
49
216899.87
9
216767.70
-74
221009.11
-70
221112.20
29
221080.73
25
221066.76
5
221064.35
5
221070.19
13
49
221082.34
221099.49
12
221121.05
9!1
221319.17 -131
221059.01
-76
220979.61
-50
283158.51
-13
283171.68
82
283022.98 289
282943.15
-6
26269!1.81
-41
262677.00
-BO
282670.71
-60
262675.72
-67
282689.55
-68
-79
282910.51
282937.54 -24
282969.81
-3
283006.76 -24
283048.15
54
263093.46
-3
263142.77
64
263195.66
17
ROTATIONAL
SPECTRUM
OF BUTYRONITRILE
181
T ABLE Il
Newly
Measured
J Kp Ko <25 5 21
26 6 21
26 7 19
26 10 17
26 11 16
26 12 15
26 13 14
26 14 13
26 15 12
26 17 10
26 18 9
26 19 8
I 27
28
28 2 27
28
l 27
28 2 27
29 5 25
30 4 27
30
4 26
30 5 26
30 7 23
31 2 29
31 3 29
31 2 29
31 3 29
31 3 28
31 4 28
31 3 28
31 4 27
31 5 27
31 5 26
7 25
31
31 7 24
31 8 23
32 2 30
32 3 30
32 2 30
32 3 30
32 4 29
32 4 28
32 4 28
32 10 23
32 10 22
32 12 21
32 13 20
32 14 19
33
2 31
33 3 31
33 2 31
33 3 31
33 3 30
33 4 30
33 3 30
33 4 30
33 4 29
34 2 32
34 3 32
34 2 32
34 3 32
34 6 28
35 6 29
Rotational
Transitions
O.-c.
J Kp Ko
o.p.
24 4 20 182990.23
43
25 6 20 157628.25
I
25
7 18 157477.90
25
25 10 16 156296.53 -12
25 11 15 156141.79
96
13
25 12 14 156032.20
25 13 13 155954.49 -21
39
25 14 12 155900.13
155863.29
23
25 15 Il
-9
25 17 9 155827.91
5
25 18 8 155824.65
25 19 7 155828.81
-13
27
I 26 157495.25
-19
27
l 26 157503.23 -40
27 2 26 157482.64
54
27 2 26 157490.60
15
28 4 24 189805.28
-3
-5
29 3 26 178167.69
29 4 25 182703.13 -91
29 4 25 192210.43 -19
29
7 22 182961.27
6
30 2 28 177803.90 -19
30 2 28 177857.94 -10
30
3 28 177721.22
-5
30
3 28 177775.23 -26
30 3 27 182248.22 -72
30 3 27 183077.55
-9
30 4 27 181050.65 -25
30 5 26 178318.43
55
30 5 26 185532.39 154
-39
30 5 25 192803.61
30 7 24 188156.51
-45
30
7 23 189515.12 -46
30 8 22 187858.13
23
31 2 29 183183.36
13
31
2 29 183218.50
28
31
3 29 183129.35
29
31 3 29 183164.45
2
31 3 28 188119.54 -36
31 4 27 192927.96 -87
31 5 27 185714.09 -95
31 10 22 192852.63
31
31 10 21 192854.42
30
56
31 12 20 192320.23
31 13 19 192158.76
43
81
31 14 18 192040.62
32 2 30 188564.34 -22
17
32 2 30 188587.13
2
32 3 30 188529.24
32 3 30 188551.94 -39
3 29 192871.17 -35
32
32 3 29 193259.00
-6
32
4 29 192301.88 -57
32
4 29 192689.70 -41
-95
32 5 28 192663.51
33 2 31 193946.21
-47
26
33 2 31 193960.95
33 3 31 193923.55
41
33 3 31 193938.16 -16
33 6 27 212120.06 -39
34 6 28 218287.17 -89
for gauche-Butyronitrile'
J Kp Kø <35
7 29
35 8 28
35 9 27
35
9 26
36
4 32
36 10 27
36 10 26
36 11 26
36 11 25
36 12 25
36 13 24
36 14 23
36 16 21
36 16 21
36 17 20
36 18 19
36 20 16
36 21 15
36 22 14
36 23 14
36 24 12
36 25 11
36 26 11
36 27 9
36 27 10
36 28 8
36 32 4
37 3 34
37 3 34
37 4 34
38
I 37
38 3 36
38 2 36
38 3 35
38 3 35
38 4 35
39 O 39
39
2 37
39
3 37
39
2 37
39
3 37
40
O 40
47 14 34
47 17 31
47 19 29
47 20 27
47 21 26
47 22 26
47 23 24
47 24 23
47 25 23
47 26 22
47 27 21
47 28 20
47 29 18
47 30 18
47 31 17
47 33 14
47 34 13
48 5 43
48 6 43
J Kp Ko
34 7 28
34 8 27
34 9 26
34
9 25
35
5 31
35 10 26
35 10 25
35 11 25
35 11 24
35 12 24
35 13 23
35 14 22
35 16 20
35 16 20
35 17 19
35 18 18
35 20 15
35 21 14
35 22 13
35 23 13
35 24 11
35 25 10
35 26 10
35 27 8
35 27 9
35 28 7
35 32 3
36 3 33
36 4 33
36 4 33
37 2 36
37 2 35
37 3 35
37 3 34
37 4 34
37 4 34
38
I 38
38 2 36
38 2 36
3 36
38
38
3 36
39
l 39
46 14 33
46 17 30
46 19 28
46 20 26
46 21 25
46 22 25
46 23 23
46 24 22
46 25 22
46 26 21
46 27 20
46 28 19
46 29 17
46 30 17
46 31 16
46 33 13
46 34 12
47 5 42
47
6 42
O.-c.
o.p.
212483.75 -58
212458.29 -50
211828.06 136
211938.01
11
211527.01 -83
217402.38
O
7
217418.12
216940.59
5
216941.74
63
216609.17
46
216367.23
62
216188.17
95
215956.60
89
215956.57
68
77
215885.18
215835.30 101
215784.95
97
215779.22 100
215783.85
39
-4
215797.53
215819.22
28
215847.81 -82
215882.85 -70
215923.59 -75
215923.60 -67
215969.54 -109
216198.45 -18
214265.30
-6
214147.29 -28
214225.81 -12
211401.39 105
215476.23
80
17
215469.85
29
219628.21
219549.67
-9
219601.64 -28
212743.02 -37
220854.26
40
220855.81
36
220851.79
29
220853.34
21
218129.30 -60
282874.18 -32
282070.21
28
281801.94
86
281716.83 102
281656.67
79
281617.41
23
281596.02
36
281589.94
52
281597.15
6
281616.14
-9
281645.57 -29
14
281684.43
281731.64 -76
281786.66 -79
281848.86
16
281992.38 121
282072.85 179
281724.06
36
-4
281635.78
aj e'p. I" MH,.e.-c l" ,H<.
of the gauche form. Only two correlation coefficients are greater than
0.9 for the two forms: p(D.;, <pJ)= 0.961 and p(o;, CPJ)= 0.944 for the gauche form
and p(B, D.J)= 0.928 and p(D.;, <pJ)= 0.905 for the anti form. The standard frequency
deviation was 76 and 91 kHz for the gauche and anti forms, respectively, which is
comparable to the experimental accuracy. As it was nearly impossible to identify Jlb
lines of high J for the anti form, the constants A and D.Kmay not be determined as
accurately as their standard deviation seems to indicate.
4734,13 +- 4634,12
00
N
TABLE III
Rotational
9auche formb
A/MHz
10 060.3826 (91)
B/MHz
C/MHz
and Centrifugal
Distortion
Constants
and Correlation
Matrix
of Butyronitrilea
l. 000
(118)
- 0.082
l. 000
2 705.44668 (116)
0.307
0.568
l. 000
0.108
l. 000
0.147
0.825
0.018
0.800
"JK/kHz
3.35269 (75)
- 19.2003 (20)
0.C82
- 0.265
l. 000
"K/kHz
61.12 (32)
0.814
- 0.221
0.128
0.175
l. 000
- 0.481
0.347
0.321
- 0.357
- 0.102
0.212
- 0.489
l. 000
0.190
0.145
- 0.102
- 0.013
0.276
- 0.709
0.412
- 0.457
l. 000
0.811
0.828
0.961
- 0.078
0.115
- 0.096
0.150
l. 000
0.828
- 0.180
0.224
0.493
- 0.146
l. 000
0.368
- 0.346
0.944
- 0.569
- 0.172
0.353
l. 000
- 0.491
0.071
- 0.381
0.825
0.194
- 0.483
- 0.552
3267.66767
"/kHz
6/kHz
1.03685 (43)
'K/ kHz
7.900 (18)
,,/mHz
6.995 (155)
<PK/Hz
- 0.49457 (136)
- 0.038
0.021
- 0.001
J/mHz
2.443 (169)
- 0.362
0.212
- 0.295
- 0.214
- 0.203
- 0.017
- 0.025
- 0.052
0.224
28.0 (46)
JK/mHz
Numberof l ines
a/kHzC
anti
r-'
O
l. 000
ti
;I>
::o
162
n
76
formd
A/MHz
23 667.848 (30)
B/MHz
2 268.14737 (97)
C/MHz
"/kHz
"JK/KHz
"K/kHz
l. 000
t!1
...,
- 0.322
l. 000
2 152.96476 (84)
0.296
0.374
l. 000
0.40038 (34)
- 0.246
0.928
0.489
l. 000
0.196
- 0.103
0.211
0.239
- 10.8429 (32)
- 219.5 (27)
;I>
r-'
l. 000
0.856
- 0.176
0.319
- 0.118
0.130
l. 000
- 0.564
0.551
0.389
- 0.301
- 0.418
l. 000
- 0.449
- 0.096
0.530
- 0.380
- 0.393
- 0.249
- 0.367
0.499
l. 000
0.772
0.537
0.500
0.905
- 0.249
0.012
0.258
0.156
l. 000
'K/kHz
0.046349 (82)
0.269 (96)
,,/mHz
0.457 (38)
"K/Hz
0.2915 (54)
0.055
0.090
0.134
0.025
0.766
0.017
- 0.120
0.036
0.028
l. 000
K/Hz
5.596 (106)
- 0.057
0.050
- 0.'328
0.198
- 0.614
- 0.025
0.123
0.039
0.398
- 0.093
6/ kHz
Numberof l ines
o/kHzc
136
91
a) A reduction, representation
lr, standard
b) JK = <PK = K = O assumed.
c) Standard deviation of the fit.
d) "JK = <PK= J = JK = O assumed.
errors
in parenthes2s,
shown in units
of the last
di9it.
l. 000
ROTA TIONAL SPECTRUM OF BUTYRONITRILE
183
DIPOLE MOMENTS
Stark coefficients of low J transitions were used to determine the dipole moment.
Comparatively large Stark splittings were measured in order to minimize possible
quadrupole coupling effects. A DC voltage was applied between the Stark septum and
the cell with the modulating square wave voltage superimposed. The DC field strength
was calibrated using the OCS J = 2
1 transition with the dipole moment of OCS
taken to be 0.71521 D (11). For each second-order coefficient shown in Tables IV and
Va standard deviation was estimated. A least-squares fit using a diagonal weight
matrix was performed. The weights were chosen as the inverse squares of the standard
deviations of the Stark coefficients shown in Tables IV and V.
In the case of anti-butyronitrile, the c-axis dipole moment component was preset
at zero debye. The final results are shown in Table IV.
Initially, all three dipole moment components were fitted for the gauche confor-
-
mation. However,an imaginary value was found for 1Lc. In the final fit, this dipole
moment component was preset at zero debye. The results are shown in Table V.
ENERGY DIFFERENCE
The intensities of several a-type low J R-branch transitions were used to determine
the energy difference between the anti and gauche conformations of butyronitrile.
The comparisons were made at room temperature and at -40°C. The formula of Ref.
(12) was used to calculate the internal energy difference between the two conformers.
This formula requires the determination of the half-width of the transitions. Accurate
determination of the half-width is very difficult in a case such as this. It was therefore
assumed that the half-width is proportional to the dipole moment (13). The statistical
weight of gauche was assumed to be 2, while the statistical weight of anti was assumed
TABLEIV
Stark Coefficient and Dipole Moment
of anti-Butyronitrile
6v E-2; [(MHz V-2 em2)x 106]
Obs.
Transition
30,3
20,2
41,4
31,3
41,3
31,2
IMI = 1
-6.06(7)
-6.07
IMI = 1
-3.12(4)
-3.12
M = o
-4.15(5)
-4.13
-31.2(4)
IMI = 1
31,2
Dipole
21,1
moment,
M = O
"a
represent
-28.0
-5.20
-4.92(5)
= 3.597(59)
"~
Uneertainties
Cale .
D
, "b =
0.984(15)
= 3.729(58) D.
ane
standard
deviation.
D
184
WLODARCZAK ET AL.
T ABLE V
Stark Coefficients
and Dipole Moment
of gauehe-Butyronitrile
I.v E-2/[(MHZ v-2 em2)xI05J
Transition
21,1
40,4
Obs.
M '
11,0
30,3
IMI.
O
5.78 (7)
-0.111
1
IMI . 2
41,3
M
31,2
-0.115
1.29
1.57(2)
1.62
0.856(10)
0.905
IMI. 2
-1. 32(2)
-1.23
IMI. 3
-5.08(7)
-4.80
"a
.
3.272(37)
D
,
" . O D (preset)
-"-
Uneertainties
5.64
(1)
1. 40(2)
. O
IMI. 1
Dipole moment,
Cale.
represent
one
"b'
,"
standard
2.139(30)
tot
D
,
. 3.909(41) D.
deviation.
to be 1. The internal energy difference was found to be Egauche- Eanti= 1.1(3) kl
mol-I. The anti conformation is thus more stable than the gauche by 1.1(3) kl mol-I.
The quoted uncertainty represents one standard deviation.
SUMMARY
The ground states of gauche- and anti-butyronitriles have been fitted to sufficiently
high values of J and K to allow accurate predietions in the millimeter-wave range for
radioastronomical purposes.
By measuring the intensity ratio of the anti and gauche lines, it is found that the
anti ground state is more stable than the gauche ground state. In previous studies
where an electronegative substituent has been added to the n-propyl frame (F (14),
eI (15, 16), NC (17), and C == CR (18))the gauche form has been found to be more
stable than the anti form.
ACKNOWLEDGMENTS
This investigation has been supported in prt by the Centre National
PCMI) and by the EPR Nord/Pas-de-Calais.
de la Recherche
Scientifique
(A TP
RECEIVED: April 6, 1987
REFERENCES
l. E. HIROTA, J. Chem. Phys. 37, 2918-2920 (1962).
2. V. K. KAUSHIK, Speetroehim. Aeta, Part A 35,851-855
(1979).
3. J. DEMAISON ANDH. DREIZLER, Z. Naturforseh., A 37,199-200
(1982).
4. RE. TURNER, in "Interstellar Molecules" (R H. Andrew, Ed.), p. 45, Reidel, Dordrecht, 1980.
5. J. BURlE, D. BOUCHER, J. DEMAISON, AND A. DUBRULLE, J. Phys. (Orsay Fr.) 43,1319-1325
(1982).
ROT ATIONAL SPECTRUM OF BUTYRONITRILE
185
6. W. H. KIRCHHOFF, J. Mol. Speetrase. 41, 333-380 (1972).
7. E. K. GORA, J. Mol. Speetrose. 16,378-405
(1965).
8. J. K. G. WATSON, in "Vibrational
1977.
Spectra and Structure"
(J. R. Durig, Ed.), Vol. 6, Elsevier, Amsterdam,
9. B. P. VAN EIJCK, J. Mol. Speetrase. 53, 246-249 (1974).
10. V. TYPKE, J. Mol. Speetrase. 63, 170-179 (1976).
11. J. S. MUENTER, J. Chem. Phys. 48, 4544-4547 (1968).
12. C. H. TOWNES AND A. L. SCHAWLOW, "Microwave
1955.
13.
14.
15.
16.
B.
E.
T.
K.
Spectroscopy,"
p. 372, McGraw-HilI,
New York,
H. ELLINGSEN, K. M. MARSTOKK, AND H. MØLLENDAL, J. Mol. Struct. 48, 9-23 (1978).
HIROTA, J. Chem. Phys. 37, 283-291 (1962).
SARACHMAN, J. Chem. Phys. 39,469-473
(1963).
YAMANOUCHI, N. SUGlE, H. TAKEO, C. MATSUMURA, AND K. KUCHITSU, J. Phys. Chem. 88, 23152320 (1984).
17. M. J. FuLLER AND E. B. WILSON, J. Mol. Speetrase. 58, 414-426 (1975).
18. F. J. WODARCZYK AND E. B. WILSON, J. Chem. Phys. 56,166-176
(1972).