Notizen 1253 T h e v4 R o t a t i o n V i b r a t i o n B a n d
o f D i c y a n o a c e t y l e n e
F l e m m i n g W i n t h e r a n d M a r e n K e t e l s e n
Abteilung Chemische Physik, Institut für Physikalische Chemie, Universität Kiel, Kiel, Germany
M a r i o n N i e d e n h o f f a n d Koichi M . T. Y a m a d a I. Physikalisches Institut, Universität zu Köln, Köln, Germany
Z. Naturforsch. 47 a, 1253-1254 (1992);
received October 8, 1992
The v4 fundamental band of dicyanoacetylene has been recorded in a 60 m-Herriot cell with a PC-controlled diode laser spectrometer. Transitions were measured in the range from 2232 to 2250 c m- 1 with a resolution of 0.005 c m- 1. Although the upper state is perturbed, v0 = 2245.374 (3) c m "1
and B'-B" = — 1.016 (10) • 10~4 c m "1 could be obtained.
D i c y a n o a c e t y l e n e ( N C - C = - C N ) w a s p r e p a r e d as d e s c r i b e d in [1] a n d the v4 f u n d a m e n t a l w a s r e c o r d e d w i t h a d i o d e laser s p e c t r o m e t e r in K ö l n [2]. F o r the p r e s e n t e d m e a s u r e m e n t s , t h e laser w a s c o n t r o l l e d by a P C a n d the s p e c t r a were digitally r e c o r d e d . T e c h n i c a l details of the spectrometer will be published elsewhere.
T h e spectral r e s o l u t i o n w a s 0.005 c m "1 (limited by D o p p l e r r e s o l u t i o n ) a n d the lines were c a l i b r a t e d with N20 lines f r o m [3].
I n o r d e r t o r e c o r d the v4 b a n d , w h i c h is very w e a k , a H e r r i o t cell w i t h a p a t h l e n g t h of 60 m w a s u s e d w i t h a s a m p l e p r e s s u r e less t h a n 100 P a . T h e m e a s u r e m e n t s w e r e c a r r i e d o u t at r o o m t e m p e r a t u r e .
D u e to t h e m a n y low lying v i b r a t i o n a l levels of d i c y a n o a c e t y l e n e , several line series of s i m i l a r inten- sity o v e r l a p t h e m a i n b a n d . T h u s t h e e x p e c t e d g a p b e t w e e n P a n d R b r a n c h of t h e I < -1 b a n d c o u l d n o t b e seen clearly. C o n s e q u e n t l y t h e c o r r e c t J n u m b e r i n g h a d t o be f o u n d f r o m the spin statistics a n d t h e g r o u n d s t a t e r o t a t i o n a l c o n s t a n t s . F o r t h e I * < - 1 * t r a n s i t i o n t h e lines with J" even a r e e x p e c t e d t o b e t w o t i m e s as i n t e n s e as the o d d ones. T h e g r o u n d states c o n s t a n t s h a v e b e e n r e p o r t e d in [1]: ß0 = 445.8699(10)
• 1 0 "4 a n d D0 = 1 0 . 4 9 ( 4 ) - 1 0 "1 0 c m "1. T h e s e values a r e in g o o d a g r e e m e n t w i t h t h o s e f o u n d f o r t h e v4
m a i n b a n d in t h e p r e s e n t s t u d y : B" = 445.87(2) • 1 0 "4
a n d D" = 11.3(9)- 1 0_ l oc m_ 1.
Reprint requests to Dr. K. M. T. Yamada, I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-5000 Köln 41, Germany.
S i m i l a r t o t h e v5 b a n d , AB = B'-B" is negative in t h e v4 b a n d , as well as in the n u m e r o u s h o t b a n d s seen in t h e s p e c t r u m . F r o m the e x p e c t e d r a n g e of B" v a l u e s f o r t h e l o w e r levels it c a n be d e d u c e d t h a t the b a n d c e n t e r s of t h e h o t b a n d s a r e all at lower f r e q u e n c i e s
Table 1. v- 1 -4 Band of dicyanoacetylene. Line frequencies in cm .
J R(J)OBS P(J)OBS J R(J)OBS P(J)OBS
5 2244.9225 66 2250.8747
6 2244.8328 67 2250.9491
7 2244.7409 68 2251.0240 2238.8396
8 2244.6519 69 2238.7358
9 2244.5596 70 2251.1723 2238.6317
10 2244.4712 71 2238.5278
11 2246.4268 2244.3781 72 2238.4231
12 2246.5124 2244.2885 74 2238.2147
13 2244.1979 75 2238.1084
16 2246.8576 77 2237.8980
17 2246.9431 84 2252.1866
18 2243.7359 85 2252.2577
19 2247.1140 86 2252.3282
20 2243.5497 87 2252.3992
24 2247.5378 88 2252.4695
25 2247.6222 89 2252.5399
26 2247.7057 90 2252.6095
27 2247.7889 91 2252.6787
28 2247.8716 2242.8010 92 2252.7486 2236.2978 29 2247.9555 2242.7059 93 2252.8167 2236.1898 30 2248.0383 2242.6111 94 2252.8875 2236.0813
31 2242.5157 95 2252.9574 2235.9713
32 2248.2034 2242.4194 96 2253.0241 2235.8617
33 2248.2857 97 2253.0922 2235.7540
34 2248.3679 98 2253.1603 2235.6416
35 2248.4472 99 2253.2275 2235.5327
36 2248.5305 100 2253.2965 2235.4224
37 2241.9404 101 2253.3648
38 2241.8435 102 2253.4309 2235.2022
39 2248.7724 2241.7458 103 2253.4980 2235.0916
40 2241.6490 104 2253.5652 2234.9792
41 2241.5509 105 2234.8680
42 2249.0136 2241.4533 107 2234.6462
43 2241.3563 108 2234.5358
44 2249.1753 2241.2582 112 2234.0868
45 2249.2543 2241.1595 113 2233.9749
46 2249.3343 2241.0614 115 2233.7479
47 2249.4134 2240.9630 116 2254.3475 2233.6352
48 2249.4930 117 2254.4110 2233.5210
50 2249.6470 118 2254.4752 2233.4076
51 2249.7252 119 2233.2943
53 2240.3656 120 2254.6031 2233.1780
54 2240.2651 121 2233.0652
55 2240.1658 122 2254.7298
56 2240.0621 123 2254.7923
57 2239.9622 124 2254.8549
58 2250.2692 2239.8616 125 2254.9161
59 2250.3458 2239.7607 126 2254.9780 2232.4895
60 2250.4222 2239.6583 128 2232.2598
62 2250.5744 130 2232.0251
65 2250.7994 132 2231.7925
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1254 Notizen than the main band. However, the insufficient accu- racy of the line positions due to line overlapping did not allow us to identify the hot bands from their B"
values.
A seen in the low resolution spectrum [4], the v4
band system is overlapped by another one of approx- imately the same intensity. Within our frequency range (2232 to 2250 c m- 1) we could not detect any line series belonging to the second band system. This suggests that the absorption maximum at 2226 c m- 1
in the low resolution spectrum must be interpreted as the center Q branch of a perpendicular band. If the observed absorption minimum near 2232 cm - 1 is the center gap of a parallel band, the R branch of this band should have been observed in our spectrum. The assignment of the 2226 c m- 1 band, a difference band 2 v5 - v9, presumably, shall be discussed in a forthcom- ing paper [5].
Attempts to fit the lines of the v4 band to a low order polynomial were unsuccessful, indicating that
the upper state is perturbed, probably by Coriolis coupling with a combination state nearby. The (v2 = 1, vg = l) state, which is of /7U symmetry, is the most likely candidate for the interaction partner. Since no transitions to this level have been observed, it was possible to analyze the v4 band rigorously.
Table 1 lists the observed lines. We have obtained v0 = 2245.374(3) c m- 1 and B'-B" = -1.016(10) • 1 0- 4
c m- 1 from a sixth order polynomial fit of the lines.
The errors given are confidence limits, not the stan- dard errors of the fit, which are not realistic in view of the perturbation and the many overlapping hot bands.
Acknowledgement
This work was supported in part by the Deutsche Forschungsgemeinschaft (Grant SFB 301).
[1] F. Winther, M. Schönhoff, R. LePrince, A. Guarnieri, D. N. Bruget, and D. McNaughton, J. Mol. Spectrosc.
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[2] M. Niedenhoff, K. M. T. Yamada, and G. Winnewisser, J.
Mol. Spectrosc. 145, 290 (1991).
[3] G. Guelachvili and K. Narahari Rao, Handbook of Infra- red Standards, Academic Press, Florida 1986.
[4] F. A. Miller and R. B. Hannan, Jr., J. Chem. Phys. 21, 110 (1953).
[5] F. Winther, M. Ketelsen, and A. Guarnieri, to be pub- lished.
