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Rotational spectrum of butyronitrile: Dipole moment, centrifugal distortion constants and energy difference between conformers
JOURNAL OF MOLECULAR SPECTROSCOPY
127, 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 SpectroscopicHertzienne, AssociPau C.N.R.S. Universite’de Lille I, P5 F59655 VilleneuveD’Ascq Cedex, France AND
K.-M. MARSTOKK AND HARALD MLLENDAL Departmentof Chemistry, The Universityof 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 including some sextic coefficients. The results of the analysis are sufficient for the prediction of all strong transitions throughout the millimeterwave range. The molecular dipole moment components were calculated from measured Stark effect shifts as p. = 3.597(59) D and pb = 0.984( 15) D for the anti form and p. = 3.272(37) D and pb = 2. I39(30) D with g< preset 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 1.1(3) kJ mol-I. o 1988 AcademicRW, IIIC. INTRODUCTION
Butyronitrile (CH3CH2CH2CN) was previously studied in the centimeter-wave range by Hirota (1) who showed that two isomeric forms exist. He determined the rotational constants for the ground and several excited vibrational states but as the lines were broad, he could not determine the quadrupole coupling constants. The dipole moments of the two conformers and their relative stability were not determined by him. Later Kaushik (2) determined the quartic centrifugal distortion constants of the gauche form in its ground state using the measurements of Hirota. Recently, the quadrupole hyperfine structure due to the nitrogen nucleus was investigated by using a microwave Fourier transform spectrometer (3). Butyronitrile is a possible candidate for interstellar detection. In fact some coincidences between a calculated spectrum and some U lines have already been noted (4). For this reason we have measured the millimeter-wave spectrum of both forms of butyronitrile and carried out a complete centrifugal distortion analysis so that accurate measurements and predictions would be available for radioastronomers. We have also determined the energy differences between the anti and the gauche conformations as well as the dipole moments. EXPERIMENTAL
DETAILS
The sample of butyronitrile was obtained commercially from Merck-Schuchardt (Hohenbrunn, FRG) and was used without further purification. The millimeter-wave 0022-2852/88 $3.00 Copyrisk0 1988 by Academic Press, Inc. All rights
of reproductionin any form resewed.
178
ROTATIONAL
SPECTRUM
OF BUTYRONITRILE
179
transitions were measured with a computer-controlled spectrometer with superheterodyne detection (Lille). Details of this instrument have been reported elsewhere (5). The dipole moments and the relative intensities were measured with a Stark effect spectrometer (Oslo). SPECTRAL ANALYSIS
The largest component of the dipole moment is pa for both forms, so the u-type Rbranch spectra were searched first. Their assignments were relatively easy because the spectra are strong and because the constants of Hirota (I) 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(Avi) was systematically used to check the assignment of each individual line. The ‘Ro, series 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 & lines could be identified without too much difficulty whereas for the anti form only three ,.&blines could be assigned without ambiguity. This is due to the fact that the &&/paratio is much smaller for the anti form and that the spectrum is very crowded, so that the relatively weaker pb lines are often
FIG. 1. Symmetrical quartet at 179.07 GHz due to the EO splitting (transitions 322,,, + 3 1,,lO; 32,,3, + 31 I.30;322.31+ 3lb 32,,3, + 314.
180
WLODARCZAK
ET AL.
blended with stronger pa lines. 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 II for the gauche form. In order to derive the molecular parameters the spectrum was fitted to the Hamiltonian of Watson (8) using the I’ representation. The centimeter-wave transitions of Refs. (I) and (3) were also taken into account. Both A- and Sreduction were tried, the latter in a notation due to van Eijck (9) and to Typke (IO) who also coded the program. Although both forms are near-symmetric the Sreduction 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 sextic contribution is only 5.39 MHz for the transition 4823,25f 4723,24of the anti form whereas it is -5 1.63 MHz for the transition
TABLE 1 Newly Measured Rotational Transitions for an&Butyronitrile= J KmKm 23
<-
J
K,
Ka
.I KD I(. 47 12 Th
2,2249Le
-26
47
13
212266,32
-j;
47 47
14 3-l 21228759 15 33 212312.29
23 8
32 3,
47 47
I6 I7
31 30
212340.,9 212371.06
4 22
18
31
19 20 21
30 28 27
47 47 47
I8 19 20
30 29 27
2124M.72 2,244,.,, 2,2430.03
22 65 30
2:&.22'~~;
43
12
34 32 26
1524iTLO? 156362.10
15 -23 7
4) 46 48
13 36 14 35 15 34
34
7
27
15477.385 15477384
-18
48 46
16 17
15477562 154762.18 154792.35
-98 -19
48 4) 41 46
432226 48 23
25
35
6
29
35 35
7 8
28 27
34826
35 35
9 10
26 25
34 34
9 ,O
25 24
35
I,
24
35 12 36036
23
34 34
11 12
23 22
36235 36333
KS Ke q-
21
0 2 6
20 35 33
36 I 35 36 136 36234
J
2
34 34 34
3 0 2
36136
9
22
35 35
,54794&a
35
035
154605.40 15670922
35
0
35
l59988.76
35 35
I 34 135
15998427 156376.76
-u
-3 -54 5
-45 -38
37
35
axa.
..-c.
47 47
21 22
26 25
212521.49 212565.54
-25 12
47
23
24
212611.99
45
49049 49 149
48 46
0 I
48 46
212476.62 212378.48
63 18
160651.40 158511.09 159816.20
-67
49248
27 142
49446 49 16
46 48
2 4
47 45
21507717 216949.09
16 -13
34
48
16
33
216757.7,
18
33 3, 32 30 3,
159295s 159360.35 159324.49
-21 30 8
49 17 33 492030 50 054
46 46 4)
17 20 0
32 29 49
216789.07 216899.87 216767.70
49 9 -74
159258.14 159256.97
49 49
3 7
47 43
22tw9.,, 221112.20
-79 29
49 49
8 9
42 41
221060.73 22,066.76
25 5
35233 35 2 35 3
34 32
3 4 4 5 5
10
36 36 36
3 4 4
34 32 33
36 36
5 5
3, 32
35 35 35 35 35
6 7
31 30
35 35
6 7
30 29
159218.77 159201.12
-I7 33 -14 14
50345
36 36
35
8
28
159194.99
-12
50
942 10 4,
49
10
40
221064.35
5
159241.59
-31 -35
50
II
4
49
I,
39
221070.19
13
50 50
36829 36 36
13 14
24 22
35 35
13 14
23 2,
36
15
22
35
15
21
36 36 36 37 37
16 17 18 0 I
20 19 18 37 37
35 35 35 36
43242 46 I 47 46 2 47
42 47 47 47 47 47 47 47
16 19 17 18 IS 17 036 1.36 I 41 I 46 2 46 2 45 2 46 3 43 4 44 4 43
159259.85 159280.32
-27
159Jo2.83
46544 40543 a, 6 42 46 6 43 40 7 42 43 8 4, 43 940
47 47 47
47 47
0 9
40 39
-25 159327.32 -19 159353.76 33 1&?996.,6 26 16069164 63 211442.56 96 2,,856.,9 -135 210741.46 -10, 214543.66 -115 214343.66 -,,a 212219.54 -37 212517.79 19 212766.64 165 212415.D6 22 2,2uo.s9 62 212320.77 -7 212320.211 a4 212267.79 20 21274,M 35 212230.19 -9
48
47
,O
38
21222967
43 246 48246 48345 46 445 48444
10
39
36
47 47
a)mp.inMks*.inUiz.
5 5 6 6 7
43 42 4, 42 4,
50
50 50 50
744
843
12 13
39 37
49 43
12 13
36 36
221082.34 221099.49
49 12
50 14 50 M 51 0 5, I M 6 64 6 64766 64 8 64 9 64 10 64 II 64 12 64 ,3 64 14 64 15 64 16 64 17 64 18 64 19 64 20
37 3, 5, 5, 59 58
49 49
14 38 20 30
22,,2,.05 22,3,9.,7
96 -131
57 Z6 55 54 53 51 50 50 48 47 46 45 45
50 50 63 63 63 63 63 63 63 63 63
0 , 6 6 7 8 9 10 1, I2 13
50 50 56 57 57 56 55 54 53 52 50
221059.0, 229979.6, 263158.5, 283171.66 263022.98 282943.15 282696.8, 282677.W 282870.7, 282875.72 28266955
-76 -50 -13 82 269 d -4, -60 -60 -87 -en
64 2,
43
63 63 63 63 63 63 63 63
14 49 15 49 16 47 I7 4 18 45 19 44 20 44 21 42
282910.5, 262937.64 262969.8, 283006.76 283043.15 263093.46 26314277 26319366
-79 -24 -3 -24 54 -3 64 17
ROTATIONAL
181
SPECTRUM OF BUTYRONITRILE TABLE II
Newly Measured Rotational Transitions for gauche-Butyronitrile” J K, K. a25 5 2,
J 24
4
20
18299023
26
6
21
25
6
20
15762825
26
7
19
25
7
18
157477.90
26
10
17
25
10
16.
156295.53
-12
2e
II
16
25
I,
15
156141.79
96
36
32
26
12
15
25
12
14
ls6032.20
13
36
10 27
26
,3
14
25
13
13
15595449
-21
36
26
14
13
25
14
12
1559oo.13
39
26
15
I2
25
15
,I
15586329
23
26
17
IO
25
17
9
155827.91
K,
up.
K.
26
18
9
25
18
8
26
19
8
2s
19
26
,
27
27
26
2
27
28
1
2?
28
2
27
29
5
30 3Q
..-c.
J
Ka Km c-
KD Km
J
am.
..-c.
34
7
28
21243375
58
26
34
a
27
2t268.29
50
27
34
9
26
2,1628.%
136
34
9
25
2,,938.0,
II
35
5
31
211527.01
-63
35
10
iS
217402.36
0
IO 26
35
IO
25
217418.12
56
1,
26
35
I,
25
216940.59
5
z6
I,
25
35
,I
24
216941.74
63
-9
36
12
25
35
12
24
21664X.17
45
43
3s
729
I
35
8
25
55
9
35926 4
7
155824.65
5
36
13
24
35
I3
23
216367.23
62
7
155826.8,
-13
36
14
23
35
14
22
216188.17
95
I 28
157495.25
-19
36
16
2,
35
16
20
21595660
69
27
1 26
15750333
-40
36
I6 2,
35
I6
20
215956.57
27
2
I
157482.64
54
ss
17
20
35
17
19
21sea5.1a
27
2
26
,574%bO
I5
34
111 19
35
111 16
25
28
4
24
165%0528
-3
36
20
(6
36
20
15
215784%
4
27
29
3
26
178167.69
-5
36
21
15
35
21
14
21577922
100
4
26
29
4
25
,62703.13
-9,
36
22
14
36
22
13
215783m
39
30
5
26
29
4
25
m210.43
-19
J(, 23
14
35
23
13
2,5797.53
-4
30 31
7 23 229
r) 30
7 2
22 28
,6298,37 6 ,77eJ23.90 -19
36 36
24 25
I2 I,
35 35
24 25
I, 10
21s319.22 215847.8,
m -62
31 3, 3,
329 229 329
30 30
2 3
26 26
177657.94 17772l.22
-10 -5
36 36
26 27
11 9
35 35
26 27
10 8
215682.85
-70
215923.59
-75
30
3
28
177775.23
-26
36
27
10
35
27
9
215923.60
-67
31 3,
328 426
Jo 30
3 3
27 27
182246.22 ,63077.55
-72 -9
36266 Zh 32
4
35 35
26 32
7 3
215%9.54 -109 216198.45 -IE
31
328
30
4
27
18105065
-25
37
3
34
3, 3,
4 5
27 27
30 30
5 5
26 2e
17031843 18553239
55 154
37 37
3 4
34 34
36 36
3 4
33 33
214265.30 214147.29
-6 -26
36
4
33
2142258,
-12
31 3, 31 31 32 32
526 72s 7 24 823 2 30
30 30 30
5 7 7
25 24 23
192603.61 ,6615M, 18951512
-39 -45 -6
38
1 37
37 37 37
2 2 3
36 35 35
211401.39 215476.23 2,5469.85
105 60 17
30 31 3,
8 2 2
22 29 29
1878% 13 163183.36 1832218.50
23 I3 28
34 34 34
219628.21 219549.67 2,9eo,64
29 -9 -28
29 29 28
, JB 2 36
21274302 220854.X
-37 40
4 5
27 27
29 2 -36 -07 -95
38 36
3, 3,
113129.35 16316445 168119.54 19292796 185714.09
35 35 35 39 37
3 4 4
3 3 3
3 3 4 0 2
37 37 37
3, 3, 3,
36 36 38 39 39 39 39 39
3 2 3
37 37 37
36 3-s 38
2 3 3
36 36 36
220855.81 2200s1.79 220853.34
3a 29 2,
22 2, M
192852.63
31
192654.42 192320.23
30 56
0 40 14 34 17 3,
39 46 46
1 14 17
39 33 M
21812930 282874 I8 2820702,
-60 -32 28
19 29
86 102
32 32 32
3 2 3 4
30 30 30 29
58 336 36236
2Kmx.30
66 77 101 97
32 32 32 32
4 28 4 20 10 23 10 22
32
I2
2,
31 3, 31
10 10 12
32 32
13 14
20 19
3, 31
13 14
19 16
192158.76 19M4062
43 8,
47 47
20
27
46 45
19 20
28 26
281801.94 2817,683
33 33 33
2 3
31 3,
x) Jo 30
16556434 ,8050713 18652924
-22 17 2
47 47 47
21 22 23
26 26 24
2, 22
25 25
28165667 28,‘,,7.41
79 23
3,
2 2 3
46 46
2
32 32 32
46
23
23
28,5%02
36
33 33 33
3 3 4
31 30 30
192671.17 ,932sP.OO ,9230,.m WC8970
-35 -6 -57 -4,
47 47 47
24 25 26
23 23 22
30 30
30 29 29 r) 29
-39
3 4
3 3 3 4 4
16855194
33 33
32 32 32 32 32
47 47
27 28
2, 2Q
46 46 46 46 46
24 25 26 27 26
22 22 2, 20 19
26158994 261597.15 2816,614 26,64?.57 281684.43
52 6 4 -29 14
33 34 34 34 34 34 3s
4 2 3 2 3 6 6
29 32 32 32 32 28 29
32 33 33
5 2 2
26 3, 3,
19256351 193946.2,
-95 -47
d 46 46
29 30 3,
17 17 (6
281731.64 281766.68 281648.86
-76 -79 16
3 3 6 6
3, 3, 27 28
26 41 -16 -39
2-9 1s 30 ,a 3, 17
33 33 33 34
193960.95 19392355 193938.16 212120.06
47 47 47
45 46 47
33 34 5
13 12 42
28199238 282072.85 261724.06
121 179 36
2L3287.17
-89
47
6
42
281635.76
-4
40 47 47
47 33 47 34 46543 4.3643
14 I3
a) sxp I"tw. e.-c.ine-k
4734,13f 4634,12of the gauche form. Only two correlation coefficients are greater than 0.9 for the two forms: p(AJ, GJ) = 0.961 and ~(6~, (pJ) = 0.944 for the gauche form and p(B, A,) = 0.928 and p(AJ, a_,) = 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 ~b lines of high J for the anti form, the constants A and AK may not be determined as accurately as their standard deviation seems to indicate.
gauche formb
2.443 (169)
pJlmHr
91
136
- 219.5(27) 0.046349(82) 0.269(96) 0.457(38) 0.2915(54) 5.596(106)
- 10.8429 (32)
1.000
1.000 - 0.322 0.296 - 0.246 0.196 0.856 - 0.564 - 0.449 - 0.096 0.055 - 0.057
- 0.082 0.307 0.108 0.147 0.814 - 0.481 0.190 0.145 - 0.038 - 0.362 - 0.017
1.000 0.374 0.928 0.103 0.176 0.551 0.530 0.772 0.090 0.050
1.000 0.568 0.825 0.018 - 0.221 0.347 0.102 0.811 0.021 0.212 0.025
-
-
-
1.000
1.000 0.489 0.211 0.319 0.380 0.393 0.537 0.134 0.328
O.C82 0.321 0.357 0.013 0.828 0.001 0.295 0.052
o.soo
1.000 0.239 - 0.118 0.389 0.500 0.905 0.025 0.198
1.000 - 0.265 0.128 - 0.102 0.276 0.961 - 0.214 - 0.203 0.224
0.130 - 0.301 - 0.249 - 0.249 0.766 - 0.614
1.000
1.000 0.175 0.212 - 0.709 - 0.078 0.828 0.368 - 0.491
1.000 - 0.418 - 0.367 0.012 0.017 - 0.025
1.000 - 0.489 0.412 0.115 - 0.180 - 0.346 0.071
b) OJK = @K = PK = 0 assumed. c) Standard deviation of the fit. d) 'QJK= @K = 4~ = $JK = 0 assumed.
a) A reduction, representatian 1' , standard ertws in parenthesas, shown in units of the last digit,
olkHzC
Number of lines
AK/kHz 6JkHz GK/kHz oJ/mH2 +&iz rn@z
AJK/KHz
0.40038 (34)
2 152.96476 (84)
C/MHz
AJ/kHz
2 268.14737 (97)
23 667.848 (30)
76
162
B/MHz
A/MHz
anti formd
o/kHrC
Number of lines
28.0 (46)
- 0.49457 (136)
rnKd/HZ
aJKlmNz
6.995 (155)
- 19.2003(20) 61.12(32) 1.03685(43) 7.900(18)
3.35269 (75)
10 060.3826(91) 3 267.66767 (118) 2 705.44668 (116)
BJ/mHz
AJK/kHz AKlkHt GJ/kHz 6K/kHz
AJkHz
C/MHz
B/MHZ
A/MHz
1.000 0.499 0.258 - 0.120 0.123
1.000 - 0.457 - 0.096 0.224 0.944 - 0.381
1.000 0.156 0.036 0.039
1.000 0.150 0.493 - 0.569 0.825
1.000 0.028 0.398
1.000 - 0.146 - 0.172 0.194
Rotational and Centrifugal Distortion Constants and Correlation Matrix of Butyronitrile”
TABLE III
1.000 - 0.093
1.000 0.353 - 0.483
1.000
1.000 - 0.552
1.000
ROTATIONAL
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 0.7 152 1 D (I 1). For each second-order coefficient shown in Tables IV and V a 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 conformation. However, an imaginary value was found for pcL,.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 u-type low JR-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
TABLE IV Stark Coefficient and Dipole Moment of anti-Butyronitrile
Transition
Cal<.
ohs.
30,3
*
zo,*
IMl = '
-6.06(7)
-6.07
41.4
+
3,,3
IHI = '
-3.12(4)
-3.12
4
+
31.2
I,3
M
=o
-4.15(5)
IHI = 1 3
I,2
Dipole
+
M
%,I
nerent
: p
d
-31.2(4)
=o
Uncertainties represent
-5.20
-4.92(5)
= 3.597(59)
ptot -
-4.13 -28.0
= 3.729(58)
me
D
,
ub
= 0.984(15)
D.
scandard
deviation.
II
WLODARCZAK
184
ET AL.
TABLE V Stark Coefficients and Dipole Moment of gauche-Butyronitrile
Transition
21,l
+
'1.0
4
+
30.3
f
3,,2
0.4
41.3
Dipole
manent
ObS.
I4 = 0 /MI
=
,
Calc
5.780)
5.64
-0.111(l)
-0.115
/HI
-
2
1.40(2)
1.29
H
-
0
1.57(Z)
1.62
IHI
=
1
/Ml
= 2
-1.32(2)
-1.23
IHI
= 3
-5.08(7)
-4.80
: II
0.856(10)
= 3.272(37)
0
,
ub
0.905
= 2.139(30)
D
,
5 u
=
0 D
(preset)
(
Ptot -
P
Uncertainties
represent
one
standard
= 3.909(41)
D.
deviation.
to be 1. The internal energy difference was found to be Egauche- Eanti = 1.1(3) kJ mol-‘. The anti conformation is thus more stable than the gauche by 1.1(3) kJ mol-‘. 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 predictions 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), Cl (15, 16) NC (17) and C = CH (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 de la Recherche Scientifique (ATP PCMI) and by the EPR Nerd/Pas-de-Calais. RECEIVED:
April
6, 1987 REPERENCES
1. E. HIROTA, .I Chem. Phys. 37, 2918-2920 (1962). 2. V. K. KAUSHIK, Spectrochim. Acta, Part A 35, 85 l-855 (1979). 3. J. DEMAISON AND H. DREIZLER, Z. Naturjbrsch., A 37, 199-200 (1982). 4. B.E. TURNER, in “Interstellar Molecules” (B. H. Andrew, Ed.), p. 45, Reidel, Dordrecht, 1980. 5. J. BURIE,D.BOUCHER,J.DEMAISON,ANDA.DUBRULLE,J. Phys.(OrsayFr.)43,1319-1325(1982x
ROTATIONAL
SPECTRUM
OF BUTYRONITRILE
185
6. W. H. KIRCHHOFF,J. Mol. Specfrosc. 41, 333-380 (1972). 7. E. K. Gau, J. Mol. Spectrosc. 16, 378-405 (1965). 8. J. K. G. WATSON, in “Vibrational Spectra and Structure” (J. R. Durig Ed.), Vol. 6, Elsevier, Amsterdam, 1977. 9. B. P. VAN EIJCK,J. Mol. Spectrosc. 53,246-249 (1974). 10. V. TYPKE, J. Mol. Spectrosc. 63, 170-179 (1976). 11. J. S. MUENTER,J. Chem. Phys. 48,4544-4547 (1968). 12. C. H. TOWNESAND A. L. SCHAWLOW,“Microwave Spectroscopy,” p. 372, McGraw-Hill, New York, 1955. 13. B. H. ELLINGSEN,K. M. MARSTOKK, AND H. ~LLENDAL, J. Mol. Struct. 48,9-23 (1978). 14. E. HIROTA, J. Chem. Phys. 37,283-291 (1962). IS. T. SARACHMAN,J. Chem. Phys. 39,469-473 (1963). 16. K. YAMANOUCHI,N. SUGIE,H. TAKEO,C. MATSUMURA,AND K. KUCHITSU,J. Phys. Chem. 88,23 152320 (1984). 17. M. J. FULLERAND E. B. WILSON, J.
Mol. Spectrosc. 58,414-426 (1975). 18. F. J. WODARCZYKAND E. B. WILSON,J. Chem. Phys. 56, 166-176 (1972).
127, 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 SpectroscopicHertzienne, AssociPau C.N.R.S. Universite’de Lille I, P5 F59655 VilleneuveD’Ascq Cedex, France AND
K.-M. MARSTOKK AND HARALD MLLENDAL Departmentof Chemistry, The Universityof 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 including some sextic coefficients. The results of the analysis are sufficient for the prediction of all strong transitions throughout the millimeterwave range. The molecular dipole moment components were calculated from measured Stark effect shifts as p. = 3.597(59) D and pb = 0.984( 15) D for the anti form and p. = 3.272(37) D and pb = 2. I39(30) D with g< preset 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 1.1(3) kJ mol-I. o 1988 AcademicRW, IIIC. INTRODUCTION
Butyronitrile (CH3CH2CH2CN) was previously studied in the centimeter-wave range by Hirota (1) who showed that two isomeric forms exist. He determined the rotational constants for the ground and several excited vibrational states but as the lines were broad, he could not determine the quadrupole coupling constants. The dipole moments of the two conformers and their relative stability were not determined by him. Later Kaushik (2) determined the quartic centrifugal distortion constants of the gauche form in its ground state using the measurements of Hirota. Recently, the quadrupole hyperfine structure due to the nitrogen nucleus was investigated by using a microwave Fourier transform spectrometer (3). Butyronitrile is a possible candidate for interstellar detection. In fact some coincidences between a calculated spectrum and some U lines have already been noted (4). For this reason we have measured the millimeter-wave spectrum of both forms of butyronitrile and carried out a complete centrifugal distortion analysis so that accurate measurements and predictions would be available for radioastronomers. We have also determined the energy differences between the anti and the gauche conformations as well as the dipole moments. EXPERIMENTAL
DETAILS
The sample of butyronitrile was obtained commercially from Merck-Schuchardt (Hohenbrunn, FRG) and was used without further purification. The millimeter-wave 0022-2852/88 $3.00 Copyrisk0 1988 by Academic Press, Inc. All rights
of reproductionin any form resewed.
178
ROTATIONAL
SPECTRUM
OF BUTYRONITRILE
179
transitions were measured with a computer-controlled spectrometer with superheterodyne detection (Lille). Details of this instrument have been reported elsewhere (5). The dipole moments and the relative intensities were measured with a Stark effect spectrometer (Oslo). SPECTRAL ANALYSIS
The largest component of the dipole moment is pa for both forms, so the u-type Rbranch spectra were searched first. Their assignments were relatively easy because the spectra are strong and because the constants of Hirota (I) 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(Avi) was systematically used to check the assignment of each individual line. The ‘Ro, series 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 & lines could be identified without too much difficulty whereas for the anti form only three ,.&blines could be assigned without ambiguity. This is due to the fact that the &&/paratio is much smaller for the anti form and that the spectrum is very crowded, so that the relatively weaker pb lines are often
FIG. 1. Symmetrical quartet at 179.07 GHz due to the EO splitting (transitions 322,,, + 3 1,,lO; 32,,3, + 31 I.30;322.31+ 3lb 32,,3, + 314.
180
WLODARCZAK
ET AL.
blended with stronger pa lines. 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 II for the gauche form. In order to derive the molecular parameters the spectrum was fitted to the Hamiltonian of Watson (8) using the I’ representation. The centimeter-wave transitions of Refs. (I) and (3) were also taken into account. Both A- and Sreduction were tried, the latter in a notation due to van Eijck (9) and to Typke (IO) who also coded the program. Although both forms are near-symmetric the Sreduction 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 sextic contribution is only 5.39 MHz for the transition 4823,25f 4723,24of the anti form whereas it is -5 1.63 MHz for the transition
TABLE 1 Newly Measured Rotational Transitions for an&Butyronitrile= J KmKm 23
<-
J
K,
Ka
.I KD I(. 47 12 Th
2,2249Le
-26
47
13
212266,32
-j;
47 47
14 3-l 21228759 15 33 212312.29
23 8
32 3,
47 47
I6 I7
31 30
212340.,9 212371.06
4 22
18
31
19 20 21
30 28 27
47 47 47
I8 19 20
30 29 27
2124M.72 2,244,.,, 2,2430.03
22 65 30
2:&.22'~~;
43
12
34 32 26
1524iTLO? 156362.10
15 -23 7
4) 46 48
13 36 14 35 15 34
34
7
27
15477.385 15477384
-18
48 46
16 17
15477562 154762.18 154792.35
-98 -19
48 4) 41 46
432226 48 23
25
35
6
29
35 35
7 8
28 27
34826
35 35
9 10
26 25
34 34
9 ,O
25 24
35
I,
24
35 12 36036
23
34 34
11 12
23 22
36235 36333
KS Ke q-
21
0 2 6
20 35 33
36 I 35 36 136 36234
J
2
34 34 34
3 0 2
36136
9
22
35 35
,54794&a
35
035
154605.40 15670922
35
0
35
l59988.76
35 35
I 34 135
15998427 156376.76
-u
-3 -54 5
-45 -38
37
35
axa.
..-c.
47 47
21 22
26 25
212521.49 212565.54
-25 12
47
23
24
212611.99
45
49049 49 149
48 46
0 I
48 46
212476.62 212378.48
63 18
160651.40 158511.09 159816.20
-67
49248
27 142
49446 49 16
46 48
2 4
47 45
21507717 216949.09
16 -13
34
48
16
33
216757.7,
18
33 3, 32 30 3,
159295s 159360.35 159324.49
-21 30 8
49 17 33 492030 50 054
46 46 4)
17 20 0
32 29 49
216789.07 216899.87 216767.70
49 9 -74
159258.14 159256.97
49 49
3 7
47 43
22tw9.,, 221112.20
-79 29
49 49
8 9
42 41
221060.73 22,066.76
25 5
35233 35 2 35 3
34 32
3 4 4 5 5
10
36 36 36
3 4 4
34 32 33
36 36
5 5
3, 32
35 35 35 35 35
6 7
31 30
35 35
6 7
30 29
159218.77 159201.12
-I7 33 -14 14
50345
36 36
35
8
28
159194.99
-12
50
942 10 4,
49
10
40
221064.35
5
159241.59
-31 -35
50
II
4
49
I,
39
221070.19
13
50 50
36829 36 36
13 14
24 22
35 35
13 14
23 2,
36
15
22
35
15
21
36 36 36 37 37
16 17 18 0 I
20 19 18 37 37
35 35 35 36
43242 46 I 47 46 2 47
42 47 47 47 47 47 47 47
16 19 17 18 IS 17 036 1.36 I 41 I 46 2 46 2 45 2 46 3 43 4 44 4 43
159259.85 159280.32
-27
159Jo2.83
46544 40543 a, 6 42 46 6 43 40 7 42 43 8 4, 43 940
47 47 47
47 47
0 9
40 39
-25 159327.32 -19 159353.76 33 1&?996.,6 26 16069164 63 211442.56 96 2,,856.,9 -135 210741.46 -10, 214543.66 -115 214343.66 -,,a 212219.54 -37 212517.79 19 212766.64 165 212415.D6 22 2,2uo.s9 62 212320.77 -7 212320.211 a4 212267.79 20 21274,M 35 212230.19 -9
48
47
,O
38
21222967
43 246 48246 48345 46 445 48444
10
39
36
47 47
a)mp.inMks*.inUiz.
5 5 6 6 7
43 42 4, 42 4,
50
50 50 50
744
843
12 13
39 37
49 43
12 13
36 36
221082.34 221099.49
49 12
50 14 50 M 51 0 5, I M 6 64 6 64766 64 8 64 9 64 10 64 II 64 12 64 ,3 64 14 64 15 64 16 64 17 64 18 64 19 64 20
37 3, 5, 5, 59 58
49 49
14 38 20 30
22,,2,.05 22,3,9.,7
96 -131
57 Z6 55 54 53 51 50 50 48 47 46 45 45
50 50 63 63 63 63 63 63 63 63 63
0 , 6 6 7 8 9 10 1, I2 13
50 50 56 57 57 56 55 54 53 52 50
221059.0, 229979.6, 263158.5, 283171.66 263022.98 282943.15 282696.8, 282677.W 282870.7, 282875.72 28266955
-76 -50 -13 82 269 d -4, -60 -60 -87 -en
64 2,
43
63 63 63 63 63 63 63 63
14 49 15 49 16 47 I7 4 18 45 19 44 20 44 21 42
282910.5, 262937.64 262969.8, 283006.76 283043.15 263093.46 26314277 26319366
-79 -24 -3 -24 54 -3 64 17
ROTATIONAL
181
SPECTRUM OF BUTYRONITRILE TABLE II
Newly Measured Rotational Transitions for gauche-Butyronitrile” J K, K. a25 5 2,
J 24
4
20
18299023
26
6
21
25
6
20
15762825
26
7
19
25
7
18
157477.90
26
10
17
25
10
16.
156295.53
-12
2e
II
16
25
I,
15
156141.79
96
36
32
26
12
15
25
12
14
ls6032.20
13
36
10 27
26
,3
14
25
13
13
15595449
-21
36
26
14
13
25
14
12
1559oo.13
39
26
15
I2
25
15
,I
15586329
23
26
17
IO
25
17
9
155827.91
K,
up.
K.
26
18
9
25
18
8
26
19
8
2s
19
26
,
27
27
26
2
27
28
1
2?
28
2
27
29
5
30 3Q
..-c.
J
Ka Km c-
KD Km
J
am.
..-c.
34
7
28
21243375
58
26
34
a
27
2t268.29
50
27
34
9
26
2,1628.%
136
34
9
25
2,,938.0,
II
35
5
31
211527.01
-63
35
10
iS
217402.36
0
IO 26
35
IO
25
217418.12
56
1,
26
35
I,
25
216940.59
5
z6
I,
25
35
,I
24
216941.74
63
-9
36
12
25
35
12
24
21664X.17
45
43
3s
729
I
35
8
25
55
9
35926 4
7
155824.65
5
36
13
24
35
I3
23
216367.23
62
7
155826.8,
-13
36
14
23
35
14
22
216188.17
95
I 28
157495.25
-19
36
16
2,
35
16
20
21595660
69
27
1 26
15750333
-40
36
I6 2,
35
I6
20
215956.57
27
2
I
157482.64
54
ss
17
20
35
17
19
21sea5.1a
27
2
26
,574%bO
I5
34
111 19
35
111 16
25
28
4
24
165%0528
-3
36
20
(6
36
20
15
215784%
4
27
29
3
26
178167.69
-5
36
21
15
35
21
14
21577922
100
4
26
29
4
25
,62703.13
-9,
36
22
14
36
22
13
215783m
39
30
5
26
29
4
25
m210.43
-19
J(, 23
14
35
23
13
2,5797.53
-4
30 31
7 23 229
r) 30
7 2
22 28
,6298,37 6 ,77eJ23.90 -19
36 36
24 25
I2 I,
35 35
24 25
I, 10
21s319.22 215847.8,
m -62
31 3, 3,
329 229 329
30 30
2 3
26 26
177657.94 17772l.22
-10 -5
36 36
26 27
11 9
35 35
26 27
10 8
215682.85
-70
215923.59
-75
30
3
28
177775.23
-26
36
27
10
35
27
9
215923.60
-67
31 3,
328 426
Jo 30
3 3
27 27
182246.22 ,63077.55
-72 -9
36266 Zh 32
4
35 35
26 32
7 3
215%9.54 -109 216198.45 -IE
31
328
30
4
27
18105065
-25
37
3
34
3, 3,
4 5
27 27
30 30
5 5
26 2e
17031843 18553239
55 154
37 37
3 4
34 34
36 36
3 4
33 33
214265.30 214147.29
-6 -26
36
4
33
2142258,
-12
31 3, 31 31 32 32
526 72s 7 24 823 2 30
30 30 30
5 7 7
25 24 23
192603.61 ,6615M, 18951512
-39 -45 -6
38
1 37
37 37 37
2 2 3
36 35 35
211401.39 215476.23 2,5469.85
105 60 17
30 31 3,
8 2 2
22 29 29
1878% 13 163183.36 1832218.50
23 I3 28
34 34 34
219628.21 219549.67 2,9eo,64
29 -9 -28
29 29 28
, JB 2 36
21274302 220854.X
-37 40
4 5
27 27
29 2 -36 -07 -95
38 36
3, 3,
113129.35 16316445 168119.54 19292796 185714.09
35 35 35 39 37
3 4 4
3 3 3
3 3 4 0 2
37 37 37
3, 3, 3,
36 36 38 39 39 39 39 39
3 2 3
37 37 37
36 3-s 38
2 3 3
36 36 36
220855.81 2200s1.79 220853.34
3a 29 2,
22 2, M
192852.63
31
192654.42 192320.23
30 56
0 40 14 34 17 3,
39 46 46
1 14 17
39 33 M
21812930 282874 I8 2820702,
-60 -32 28
19 29
86 102
32 32 32
3 2 3 4
30 30 30 29
58 336 36236
2Kmx.30
66 77 101 97
32 32 32 32
4 28 4 20 10 23 10 22
32
I2
2,
31 3, 31
10 10 12
32 32
13 14
20 19
3, 31
13 14
19 16
192158.76 19M4062
43 8,
47 47
20
27
46 45
19 20
28 26
281801.94 2817,683
33 33 33
2 3
31 3,
x) Jo 30
16556434 ,8050713 18652924
-22 17 2
47 47 47
21 22 23
26 26 24
2, 22
25 25
28165667 28,‘,,7.41
79 23
3,
2 2 3
46 46
2
32 32 32
46
23
23
28,5%02
36
33 33 33
3 3 4
31 30 30
192671.17 ,932sP.OO ,9230,.m WC8970
-35 -6 -57 -4,
47 47 47
24 25 26
23 23 22
30 30
30 29 29 r) 29
-39
3 4
3 3 3 4 4
16855194
33 33
32 32 32 32 32
47 47
27 28
2, 2Q
46 46 46 46 46
24 25 26 27 26
22 22 2, 20 19
26158994 261597.15 2816,614 26,64?.57 281684.43
52 6 4 -29 14
33 34 34 34 34 34 3s
4 2 3 2 3 6 6
29 32 32 32 32 28 29
32 33 33
5 2 2
26 3, 3,
19256351 193946.2,
-95 -47
d 46 46
29 30 3,
17 17 (6
281731.64 281766.68 281648.86
-76 -79 16
3 3 6 6
3, 3, 27 28
26 41 -16 -39
2-9 1s 30 ,a 3, 17
33 33 33 34
193960.95 19392355 193938.16 212120.06
47 47 47
45 46 47
33 34 5
13 12 42
28199238 282072.85 261724.06
121 179 36
2L3287.17
-89
47
6
42
281635.76
-4
40 47 47
47 33 47 34 46543 4.3643
14 I3
a) sxp I"tw. e.-c.ine-k
4734,13f 4634,12of the gauche form. Only two correlation coefficients are greater than 0.9 for the two forms: p(AJ, GJ) = 0.961 and ~(6~, (pJ) = 0.944 for the gauche form and p(B, A,) = 0.928 and p(AJ, a_,) = 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 ~b lines of high J for the anti form, the constants A and AK may not be determined as accurately as their standard deviation seems to indicate.
gauche formb
2.443 (169)
pJlmHr
91
136
- 219.5(27) 0.046349(82) 0.269(96) 0.457(38) 0.2915(54) 5.596(106)
- 10.8429 (32)
1.000
1.000 - 0.322 0.296 - 0.246 0.196 0.856 - 0.564 - 0.449 - 0.096 0.055 - 0.057
- 0.082 0.307 0.108 0.147 0.814 - 0.481 0.190 0.145 - 0.038 - 0.362 - 0.017
1.000 0.374 0.928 0.103 0.176 0.551 0.530 0.772 0.090 0.050
1.000 0.568 0.825 0.018 - 0.221 0.347 0.102 0.811 0.021 0.212 0.025
-
-
-
1.000
1.000 0.489 0.211 0.319 0.380 0.393 0.537 0.134 0.328
O.C82 0.321 0.357 0.013 0.828 0.001 0.295 0.052
o.soo
1.000 0.239 - 0.118 0.389 0.500 0.905 0.025 0.198
1.000 - 0.265 0.128 - 0.102 0.276 0.961 - 0.214 - 0.203 0.224
0.130 - 0.301 - 0.249 - 0.249 0.766 - 0.614
1.000
1.000 0.175 0.212 - 0.709 - 0.078 0.828 0.368 - 0.491
1.000 - 0.418 - 0.367 0.012 0.017 - 0.025
1.000 - 0.489 0.412 0.115 - 0.180 - 0.346 0.071
b) OJK = @K = PK = 0 assumed. c) Standard deviation of the fit. d) 'QJK= @K = 4~ = $JK = 0 assumed.
a) A reduction, representatian 1' , standard ertws in parenthesas, shown in units of the last digit,
olkHzC
Number of lines
AK/kHz 6JkHz GK/kHz oJ/mH2 +&iz rn@z
AJK/KHz
0.40038 (34)
2 152.96476 (84)
C/MHz
AJ/kHz
2 268.14737 (97)
23 667.848 (30)
76
162
B/MHz
A/MHz
anti formd
o/kHrC
Number of lines
28.0 (46)
- 0.49457 (136)
rnKd/HZ
aJKlmNz
6.995 (155)
- 19.2003(20) 61.12(32) 1.03685(43) 7.900(18)
3.35269 (75)
10 060.3826(91) 3 267.66767 (118) 2 705.44668 (116)
BJ/mHz
AJK/kHz AKlkHt GJ/kHz 6K/kHz
AJkHz
C/MHz
B/MHZ
A/MHz
1.000 0.499 0.258 - 0.120 0.123
1.000 - 0.457 - 0.096 0.224 0.944 - 0.381
1.000 0.156 0.036 0.039
1.000 0.150 0.493 - 0.569 0.825
1.000 0.028 0.398
1.000 - 0.146 - 0.172 0.194
Rotational and Centrifugal Distortion Constants and Correlation Matrix of Butyronitrile”
TABLE III
1.000 - 0.093
1.000 0.353 - 0.483
1.000
1.000 - 0.552
1.000
ROTATIONAL
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 0.7 152 1 D (I 1). For each second-order coefficient shown in Tables IV and V a 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 conformation. However, an imaginary value was found for pcL,.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 u-type low JR-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
TABLE IV Stark Coefficient and Dipole Moment of anti-Butyronitrile
Transition
Cal<.
ohs.
30,3
*
zo,*
IMl = '
-6.06(7)
-6.07
41.4
+
3,,3
IHI = '
-3.12(4)
-3.12
4
+
31.2
I,3
M
=o
-4.15(5)
IHI = 1 3
I,2
Dipole
+
M
%,I
nerent
: p
d
-31.2(4)
=o
Uncertainties represent
-5.20
-4.92(5)
= 3.597(59)
ptot -
-4.13 -28.0
= 3.729(58)
me
D
,
ub
= 0.984(15)
D.
scandard
deviation.
II
WLODARCZAK
184
ET AL.
TABLE V Stark Coefficients and Dipole Moment of gauche-Butyronitrile
Transition
21,l
+
'1.0
4
+
30.3
f
3,,2
0.4
41.3
Dipole
manent
ObS.
I4 = 0 /MI
=
,
Calc
5.780)
5.64
-0.111(l)
-0.115
/HI
-
2
1.40(2)
1.29
H
-
0
1.57(Z)
1.62
IHI
=
1
/Ml
= 2
-1.32(2)
-1.23
IHI
= 3
-5.08(7)
-4.80
: II
0.856(10)
= 3.272(37)
0
,
ub
0.905
= 2.139(30)
D
,
5 u
=
0 D
(preset)
(
Ptot -
P
Uncertainties
represent
one
standard
= 3.909(41)
D.
deviation.
to be 1. The internal energy difference was found to be Egauche- Eanti = 1.1(3) kJ mol-‘. The anti conformation is thus more stable than the gauche by 1.1(3) kJ mol-‘. 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 predictions 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), Cl (15, 16) NC (17) and C = CH (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 de la Recherche Scientifique (ATP PCMI) and by the EPR Nerd/Pas-de-Calais. RECEIVED:
April
6, 1987 REPERENCES
1. E. HIROTA, .I Chem. Phys. 37, 2918-2920 (1962). 2. V. K. KAUSHIK, Spectrochim. Acta, Part A 35, 85 l-855 (1979). 3. J. DEMAISON AND H. DREIZLER, Z. Naturjbrsch., A 37, 199-200 (1982). 4. B.E. TURNER, in “Interstellar Molecules” (B. H. Andrew, Ed.), p. 45, Reidel, Dordrecht, 1980. 5. J. BURIE,D.BOUCHER,J.DEMAISON,ANDA.DUBRULLE,J. Phys.(OrsayFr.)43,1319-1325(1982x
ROTATIONAL
SPECTRUM
OF BUTYRONITRILE
185
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