Notizen 585
Quadrupole Coupling in the
Microwave Spectrum of Ethylisothiocyanate
An Application of Microwave FourierTransform Spectroscopy
W. Kasten, H. Dreizler, and R. Schwarz
Abteilung C h e m i s c h e Physik im Institut f ü r Physikalische C h e m i e der Universität Kiel
Z. Naturforsch. 38 a, 5 8 5 - 5 8 6 (1983);
received March 12, 1983
We investigated the m i c r o w a v e spectrum of ethyliso- thiocyanate, C H3C H2 N C S , for the nitrogen q u a d r u p o l e coupling. T h e spectrum was first measured and assigned by Sakaizumi. O h a s h i , and Y a m a g u c h i [1], By c o m p a r i n g the measured rotational constants with those resulting f r o m an assumed structure they concluded that the synperi- planar (eis) form was m e a s u r e d .
By use of Microwave F o u r i e r T r a n s f o r m ( M W F T ) spectroscopy [2, 3] we were able to resolve the nitrogen q u a d r u p o l e hfs. T h e s a m p l e was purchased f r o m Ega Chemie, Steinheim, with a 95% purity and used after vacuum distillation. T h e spectra were recorded at temper- atures of — 60 ° C and pressures down to 0.2 mTorr.
T h e half width at half height was usually 30 kHz. We believe that our m e a s u r e m e n t s are more precise than those reported. O u r m e a s u r i n g error is less than 20 kHz*.
Figure 1 gives an example. T h e measured lines are given in Table 1. T h e h y p e r f i n e structure was analyzed by first order p e r t u r b a t i o n theory. T h i s a p p r o x i m a t i o n was checked by calculations using diagonalisation of a suffi- ciently large H a m i l t o n i a n s u b m a t r i x [4],
We f u r t h e r proved that no line within the range of our spectrometer is sensitive enough to the off diagonalelement /_.db of the q u a d r u p o l e coupling tensor. T h e results for the hfs-analysis are given in T a b l e 2. T h e standard deviation of the fit is 8 kHz for a m e a n splitting of 230 kHz.
In the course of our analysis we p e r f o r m e d a centrifugal distortion analysis to f o u r t h o r d e r with the Hamiltonian of van Eijck [5] and T y p k e [6],
As the selection of lines with mostly AJ = 1, AK_ = 0, AK+ = 1 is very u n f a v o u r a b l e , nine correlation coefficients are higher than 0.99. So we set as in [1] D'K = 0, Sj = 0 and /?6 = 0. T h e results are given in T a b l e 3. We included the lines of Table 1 and those lines of Table 1 of [1]** not measured by us.
* We monitor our high stability reference quartz by comparison with the normal frequency of D C F 77 Main- flingen.
** Lines of T a b l e 1 of [1] m a r k e d with c) were e x e m p t e d .
Reprint requests to Prof. Dr. H. Dreizler, Institut f ü r Physi- kalische C h e m i e der Universität Kiel, Olshausenstr. 40, D-2300 Kiel, Haus S 12c.
T h e standard deviation of the fit of 52 lines m e a s u r e d by [1] and 17 lines measured by us are 210 kHz.
Using the full fourth o r d e r H a m i l t o n i a n [6] the s t a n d a r d deviation decreases to 192 kHz taking all lines. W h e n we take v = ( X , 0 ' o b s — vc a i c )2/ " )l / 2 a s a measure of precision, we get 37 kHz for the 17 lines measured by M W F T - spectroscopy a n d 204 k H z for those of Table 1 of [1]. But as the correlation is high, we think that the set of constants of Table 3 is a good basis for f u r t h e r work.
We further repeated the calculations of the rotational constants by fitting the s a m e structural p a r a m e t e r s with the assumptions of T a b l e 3 of [1] by a /-0-structure. T h e results are in agreement with [1].
Only few determinations of the hfs in isothiocyanates have been reported. T h e coupling constants are given in Table 4. T h e information for these molecules is too limited to determine the principal axes c o m p o n e n t s of the cou- pling tensor.
We thank the m e m b e r s of our g r o u p for help and discus- sions, the Deutsche F o r s c h u n g s g e m e i n s c h a f t and F o n d s der C h e m i e for funds. O n e of us (W.K.) thanks for a fellowship of the F o n d s der C h e m i e . All calculations were made at the University C o m p u t i n g Centre.
1111111 iJLu-iJ 11111111111111111111111111111111 n 1111111u l u i l m l
Fig. 1. Section of 1.5 M H z below a 12.5 M H z recording near the 42 3 - 322 transition of C H3C H2N C S . T e m p e r a t u r e - 6 0 ° C , pressure 0.4 mTorr. D a t a aquisition: 1024 data points filled with zeros u p to 4096 data points, 20 ns sample interval, time d o m a i n averaging 218 cycles, f r e q u e n - cy domain averaging 30 cycles, spectral point distance
12.5 kHz, line frequencies by three point interpolation.
0340-4811 / 83 / 0500-0583 $ 01.3 0 / 0 . - Please order a reprint rather t h a n m a k i n g y o u r own copy.
586 Notizen T a b l e 1. M e a s u r e d r o t a t i o n a l t r a n s i t i o n s of e t h y l i s o t h i o c y a n a t e .
v
unspii
t iso b t a i n e d a d d i n g t h e h f s - c o r r e c t i o n s t o t h e f r e q u e n c i e s v0t>s of t h e hfs c o m p o - nents. T r a n s i t i o n s b e l o w t h e line c o u l d not b e r e s o l v e d .
J'KLK; --JK.K+ F'- -F Vobs
''unsplit
A Vhfs.obs A Vhfs.calc32I -
220
34 2
— 2 - 3 - 1
10 182.119 10 181.518 10 181.184
10 1 8 1 . 6 5 2 0 . 6 0 1 0 . 3 3 4
0 . 6 0 4 0 . 3 3 5
303 —
2o:
24 3
- 1 - 3 - 2
10 167.423 10 167.306
10 167.326 0 . 1 1 7 0 . 1 1 0
3,3
— 2,2
34 2
- 2 - 3 - 1
9 9 2 2 . 4 4 6 9 9 2 2 . 2 5 9
9 9 2 2 . 3 1 5 0 . 1 8 7 0 . 1 6 6
322 -221
34 2
- 2 - 3 - 1
10 175.409 10 174.810 10 174.478
10 174.944 0 . 5 9 9 0 . 3 3 2
0 . 6 0 2 0 . 3 3 4
4(14-
3()3
35 4
- 2 - 4 - 3
13 5 4 8 . 4 8 9 13 5 4 8 . 4 2 1
13 5 4 8 . 4 3 9 0 . 0 6 8 0 . 0 5 1
431- 4 ,2- 330 331
4 53 - 3 - 4 - 2
13 5 7 1 . 6 7 6 13 5 7 1 . 1 2 7 13 5 7 0 . 8 9 2
13 5 7 1 . 2 5 3 0 . 5 4 9 0 . 2 3 5
0 . 5 5 8 0 . 2 1 6
4,3
—
3,2 4 5- 3
- 4 13 8 9 6 . 6 8 7
13 8 9 6 . 5 9 6 13 8 9 6 . 6 3 4 0 . 0 9 1 0 . 0 7 6
4 ,4-
3,3 4 5- 3 - 4
13 2 2 7 . 7 3 5
13 2 2 7 . 6 5 1 13 2 2 7 . 6 8 2 0 . 0 8 4 0 . 0 7 1
423 -322
45 - 3
- 4 13 5 6 5 . 2 9 8
13 5 6 5 . 0 4 2 13 5 6 5 . 1 1 0 0 . 2 5 6 0 . 2 5 5 3
_ 2
13 5 6 4 . 9 6 20 . 0 8 0 0 . 0 6 6
3 _ 2
13 5 6 4 . 9 6 2541 - 542 - 440
441
5 64 - 4 - 5 - 3
16 9 6 6 . 2 9 0 16 9 6 5 . 8 0 3 16 9 6 5 . 6 3 3
16 9 6 5 . 9 2 1 0 . 4 8 7 0 . 1 7 0
0 . 5 0 5 0 . 1 5 1
523
-422
56 4
- 4 - 5 - 3
16 9 8 7 . 6 2 7 16 9 8 7 . 4 6 3
16 9 8 7 . 5 2 0 0 . 1 6 4 0 . 1 4 2
505 -404
46 5
- 3 - 5 - 4
16 9 2 2 . 7 4 3 16 9 2 2 . 7 0 6
16 9 2 2 . 7 1 6 0 . 0 3 7 0 . 0 3 1
5 ,4-
4,3 5 4 6- 4 - 3 - 5
17 3 6 7 . 2 4 6 17 3 6 7 . 2 2 3 17 3 6 7 . 1 9 5
17 3 6 7 . 2 1 8 0 . 0 2 3 0 . 0 2 8
0 . 0 1 5 0 . 0 2 7
524 -423
56 4
- 4 - 5
- 3
16 9 5 4 . 1 0 8 16 9 5 3 . 9 7 0
16 9 5 4 . 0 1 5 0 . 1 3 8 0 . 1 3 8
1 0 , 9 - 10,10 10
11 9
- 10 - 11 - 9
9 175.183 9 174.940
9 1 7 5 . 0 2 0 0 . 2 4 3 0 . 2 4 3
202 -
loi 3 2- 2
- 1 6 7 8 1 . 0 5 0 6 7 8 1 . 0 5 0 0 . 0 0 0 0 . 0 4 0
5 , 5 - 4,4 5 - 4
4 - 3 16 5 3 1 . 2 9 5 16 5 3 1 . 2 9 5 0 . 0 0 0 0 . 0 1 5
6 - 5 0 . 0 2 9
T a b l e 2. N i t r o g e n q u a d r u p o l e c o u p l i n g c o n s t a n t s of et- h y l i s o t h i o c y a n a t e ( M H z ) . T h e e r r o r s a r e s t a n d a r d er- rors.
= Xhh + Xcc - 1 . 8 7 3 ( 1 8 ) Xtui 1.873 ( 1 8 ) 7 - ~ Xhh - Xcc - 0 . 6 5 6 ( 3 5 ) Xhh - 1 . 2 6 4 ( 2 6 )
correlation
c o e f f i c i e n t 0 . 0 0 8 Xcc - 0 . 6 0 9 ( 2 6 )
T a b l e 3. R o t a t i o n a l [ M H z ] a n d c e n t r i f u g a l [kHz]
d i s t o r t i o n constants of e t h v i s o t h i o c y a n a t e . E r r o r s are s t a n d a r d errors. A s s u m p t i o n in s q u a r e b r a c k e t s , x: a s y m m e t r y p a r a m e t e r . ( C . D ' j ) : h i g h e s t c o r r e l a t i o n .
A 14 188.5 (5.4) D'K [0]
B 1 779.274 (6) SJ f0]
C 1 612.130 (6) R'I [0]
D'I 1.53 (4) X - 0 . 9 7 3 4 1 9
D'JK - 3 6 . 8 4 (9) (C. D'J) 0.855
T a b l e 4. Q u a d r u p o l e c o u p l i n g c o n s t a n t s [ M H z ] of s o m e i s o t h i o c y a n a t e s .
Xau Xhh Xcc
H N C S [7] 1 . 1 1 4 ( 2 6 ) - 0 . 5 3 0 ( 7 1 ) - 0 . 5 8 5 ( 7 1 )
C H i N C S [8] 1 . 9 0 ( 3 ) - -
C H , C H ^ N C S 1.873 ( 1 8 ) - 1 . 2 6 4 ( 2 6 ) - 0 . 6 0 9 ( 2 6 )
[1] T. Sakaizumi. O. Ohashi. and I. Yamaauchi, Bull.
Chem. Soc. Japan 49,948 (1976).
[2] G. Bestmann and H. Dreizler, Z. Naturforsch. 3 7 a , 58 (1982).
[3] G. Bestmann. H. Dreizler. H. Mäder. and U. Andresen.
Z. Naturforsch. 35 a, 392 (1980).
[4] D. Hübner and M. Stolze, program N Q H F S , Diplom- arbeiten Kiel 1980.
[5] B. P. van Eijck, J. Mol. Spectrosc. 53,246 (1974).
[6] V. Tvpke. J. Mol. Spectroscop. 63, 170 (1976). formula (6), program VT26.
[7] K. Yamada, M. Winnewisser. G. Winnewisser, L. B.
Szalowski. and M. C. L. Gerry. J. Mol. Spectrosc. 79, 295 (1980).
[8] R. G. Lett and W. H. Flygare, J. Chem. Phys. 47, 4730 (1967).
