- Email: [email protected]
The microwave spectrum and structure of chlorine isocyanate
JOURNAL
OF
The
MOLECUL.LR
SPECTROSCOPY
Microwave
&?,
of Chemistry,
(1972)
Spectrum and Structure lsocyanate
W. H. HOCKING Depadment
547-566
University
of Chlorine
and M. C. L. GERRY
of British
Colwnbia,
Vancouver
8, B.C.,
Cartada
The microwave spectra of three isotopic species of chlorine isocyanate, ClNCO, have been measured in the frequency region 8-37 GHz. Spectra have been observed for molecules in both the ground and excited vibrational states, and have yielded values for the rotational const.ants, inertial defects, centrifugal distortion constants, and nuclear quadrupole coupling constants for both chlorine and nitrogen. The molecule has been shown to be planar, with the following internuclear parameters: r(ClN) = 1.703 f 0.0114, = 1.218 f 0.012 B, r(NC) r(C0) = 1.165 f 0.008 A, < (ClNC) = 119” 22’ z!z l”, < (NCO) = 171” 24’ f 1” 30’, with Cl and 0 trans. The principal values of the chlorine nuclear quadrupole coupling tensor were calculated, and were found to be consistent with the derived struct,ure. INTRODUCTION
The preparation of chlorine isocyanatc, CINCO, has been reported recently (1). This molecule is isoelectronic with two others whose structures have unusual features. For one, silyl isocyanate, SiH&CO, the microwave spectrum is consist,ent with a linear heavy atdm chain (.2), but electron diffraction results suggest it to be bent (5’). In the ot’her, chlorine azide, ClIY3 , the azide chain, which is usually linear, has been recently shown to be bent (4). Accordingly we have measured the rotational speckurn of several isotopic species of chlorine isocyanate to determine its structural parameters, and particularly to discover whether these too show unusual features. This article gives a full account of this st.udy’, which has yielded, besides rotational constants and internuclear parameters, inertial defects, centrifugal distortion constants and nuclear quadrupole coupling constants. EXPERIMENTAL Chlorine isocyar1at.c was prepared by the pyrolysis of t.richloroisocyanuric acid according to the method of Nachbaur and Gottardi (1). Commercial trichloroisocyanuric acid (Baker Chemical) was placed in a Pyrex tube and heated slowly over eight hours from 150 to 200°C. A portion of the sample was sublimed and pyrolgsed at 310°C further along the tube. The pyrolysis products were collected
1A preliminary
account
has appeared in Chen~. Gown. 448 (1970). 547
Copyright
@ 1972 by Academic
Press,
Inc.
HOCKING
AND
GERRY
in vacua at 77°K; they were then fractionally distilled from the collection trap, with the middle portion being retained for spectroscopic study. Samples prepared in this way were essentially free of interfering impurities. The sample was stored at 77”K, at which temperature it was indefinitely stable. To obtain the sample enriched with 1*0, alkaline hydrolysis of cyanuric chloride with H2180 was first carried out; on acidification, labeled cyanuric acid was deposited and then isolated. The product was then converted to trichloroisocyanuric acid as follows: chlorine gas was bubbled t’hrough a 0.40 ICI suspension of the cyanuric acid in a 1.25 M sodium acetate solution initially at pH 6.5, until the pH dropped to 2. The labeled trichloroisocyanuric acid which precipitated was isolated, dried, and pyrolysed as described above. The microwave spectrum was obtained in the frequency region 5-37 GHz using a 100 kHz Stark modulated spectrometer having a 7-foot X-band cell. This spectrometer was of conventional design, except that in the frequency region 818 GHz the source was a phase-stabilized Hewlett-Packard 84OOB Microwave Spectroscopy Source. Above 18 GHz an appropriate OK1 klystron was used as the source; its frequencies were measured by comparison with the output of a Micro-Now 1OlC Frequency i\lultiplier Chain whose fundamental was continuously monitored with a Hewlett-Packard .524.5LFrequency Counter. Gaseous samples of chlorine isocyanate for microwave spectroscopic study wore taken from the vapor above the bulk liquid sample held at approximately -80°C. At this temperat.ure liquid chlorine isocyanate polymerizes very slowly, but still has a significant vapor pressure. The micromavc cell was cooled with dry ice; the samples were stable in the cell for about five minutes. Pressures of .‘,-2.5 p were used, depending on t)he intensity of t.he lines being studied. OBSERVED
SPECTRA
a7(3’4N’2C16() :tnd The spectra of three isotopic species, 35C1’4N12C’80,were observed in both the ground and excited vibrational st!ates. Transitions of molecules in two excited vibrational stat,es were measured for 3sC114N’2C160, and in one excit’ed state for the other isotopic species. From the relative intensities and frequencies these were found to be excited states of the same vibration, with a frequency of less than ZOO cm-‘. Numerous a- and b-type transit’ions were assigned and measured for all isotopic species in all vibrational state*. The u-type transitions were fairly easily assigned as R-branches of a slightly asymmetric near-prolate rotor; rpsolut,ion of transitions with different values of E1 , which is often difficult for such a molecule, was easy in this case and provided evidence of large centrifugal distortion. Three series of b-type P- and R-branches were observable, and were measured up to J = 30; these had the forms Jo,_, - (J - ~)L.T-I , JLM - (J - 1)s-2 , and J,,., - (J - 1)2,5--3 . These transit,ions also showed evidence of large centrifugal distort’ion. Both the a- and b-type transitions were of comparable intensity. All transitions showed considerable hyperfine structure due to nuclear quad35C114N12~16~,
MICROWAVE
SPECTRUM
OF ClNCO
549
rupole coupling of the molecular rotation with the nuclear spins of chlorine and nitrogen. The structure due to chlorine was large and easily resolved; that of nitrogen was smaller, and resolution was more difficult. The quadruple coupling was used to confirm all rotational assignments. The entire measured spectrum was analysed, first for the nuclear quadrupole coupling constants, and then for the rotational and centrifugal distortion constants using the methods described in the following section. Some representative observed transitions of 35Cl’4N12C’60, along with their assignments and the splittings calculated using the derived quadrupole coupling constants are given in Table I. In Table II are given the frequencies of all the observed rotational transitions with nuclear quadrupole hyperfine structure removed, along with t,he calculated frequencies and centrifugal distortion corrections. ANALYSIS ;lTuclear
Quadrupole
OF THE
SPECTRA
Coupling
Nuclear quadrupole coupling was observed for both chlorine and nitrogen. The theory of such coupling by two nuclei has been treated by Bardeen and Townes (6). In chlorine isocyanate the coupling of nitrogen is very much less than that of chlorine, and the following coupling scheme is approximated very closely : II + J = F1 ; I2 + F, = F. Here 11 and 12 are the nuclear spins of chlorine and nitrogen, respectively. In general, the well-known quadrupole Hamiltonian is diagonal in II, IZ and F, but can have elements both diagonal and off -diagonal in J and F1 (7). However, in chlorine isocyanate the quadrupole couplings of both nuclei are sufficiently small so that elements off -diagonal in J can be ignored. Preliminary coupling constants obtained from the spectrum using first-order perturbation theory (i.e., ignoring elements off-diagonal in F1) were used in the full matrix scheme to predict the quadrupole hyperfine patterns. In virtually all cases the elements off-diagonal in Fl gave negligible contributions to the patterns, and could therefore be ignored. The analysis thus used the following expression for the quadrupole energy of a given rotational level: E
= 3AdAo Q
M&21~
-
+ 1) l)J(2J
Pa’> -
4I1(I1 + ljJ(J + 1) - l)(J + 1>(2J + 3)
1
cc
,3(P “) _ ’
J(J
W(b,) [X&(l) - x (l)] b, [3Al(Al + 1) - 4IdIz + lP0’~ + 111 +[3Az(Az + 1) - 4J(J + W’dF1 + 111
+ .‘* + 1612(2I2 - l>J(2J - l)(J + 1) . (25 + 3)F1(2Fl - l)(K + 1) (2F1 + 3) x . . x
[3(P,2) - J(J + 1)1x.&>
+
(“)
+
l>jx
aa(1)
(1)
7 - xccc91 P 1[Xbzm
; W(bp)
550
HOCKING TABLE I
AND GERRY
SOME REPRESENTATIVE TRPNSITIONS OF 35C114N12C160 IN THE GROUND VIWATIONAL
F,'
F'
F,"
F"
Unsplit line:
313 + 212
STATEaTb
Observed Frequency Ohs 17 950.00'
ouadrupole Correction Observed Calculatede Calc
17 950.1Zd
512 512 512 7/z
712 512 512 512
3/2 312 312 312 312 512
;;; 312 312 3/2 912 312 ;;g
;;; l/2 l/2 512 712 312 ;;;
512 l/2 l/2 l/2 712 II2 712 l/2
712 512 l/2 312 312 712 312 5/2 l/2
17 17 17 17 17 17 17
947.52 948.08 949.90 949.90 950.59 951.03 951.38 951.98 951.3&
-2.48 -1.92 -0.10 -0.10 0.59 1.03 1.38 1.98 1.38
-2.43 -1.90 -0.08 -0.08 0.56 0.95 1.35 2.01 1.35
9/2 11/2 912 912 912 912
712 712 712
9/2 712 912
17 951.98 17 952.42 17 953.28
1.98 2.42 3.28
2.04 2.44 3.26
'4,3 + 54,2
3/z l/2 512 512 312 3/2
17 17 17 17 17 17
945.84 945.84 946.15 946.80 946.80 947.52
-4.16 -4.16 -3.85 -3.20 -3.20 -2.48
-4.17 -4.17 -3.89 -3.23 -3.23 -2.55
Unsplit line:
Obs 36 507.9GC
cak
36 507.a6d
64,2 + 54,1 1312 13/Z 1312 1112 1112 11/2 15/Z 15/2 1512 9/2 912 912
1112 15/2 1312 912 1312 11/z 13/2 17/Z 15/2 712 1112 9/2
1112 11/2 11/2 912 912 912 13/2 13/Z 1312 712 712 l/2
120,12 + 11, ,, 2112 2112 2112 2712 27/2 2712 2312 2312 2312 25/2 2512 2512
21/2 2312 1912 2712 2912 2512 2312 2512 2112 2512 2712 2312
1912 1912 1912 2512 2512 2512 2112 2112 2112 2312 2312 2312
221,21t212,20
912 13/2 11/2 712 11/z 9/2 11/i 15/2 13/2 512 q/2 772 Unsplit line: 1912 2112 1712 2572 27/2 2312 21/2 2312 19/2 23/2 2572 2112 Unsplit line-
36 36 36 36 36 36 36 36 36 36 36 36
502.77 502.77 503.25 505.15 505.15 505.6C' 510.89 510.89 511.51 513.36 513.38 513.0')
Obs 30 011.62‘ 30 30 30 30 30 30 30 30 30 30 30 30
008.85 009.14 009.14 009.59 009.89 009.89 013.14 013.43 013.43 013.94 014.20 014.20
Obs 10 485.40' 10 lo 10 10 10 10 10 10 10 10 10 10
482.70 4e3.03 483.03 483.03 483.37 483.37 487.30 487.63 487.63 487.63 488.02 488.02
-5.19 -5.19 -4.71 -2.81 -2.81 -2.36 2.93 2.93 3.55 5.42 5.42 5.93 C?llC Y.77 -2.48 -2.48 -2.03 -1.73 -1.73 1.52 1.81 1.81 2.32 2.50 2.58 C
-5.28 -5.19 -4.66 -2.88 -2.76 -2.27 2.81 2.91 3.51 5.18 5.35 5.e9 30 011.6gd -2.76 -2.50 -2.46 -2.00 -1.73 -1.70 1.55 l.El 1.84 2.31 2.57 2.60 10 485.53d -2.73
2.25 2.27 2.60 2.62
MICROWAVE
SPECTRUM
OF ClNCO
551
TABLE I (continued)
aAll transition frequencies are in MHz. bEstimated uncertainty in transition frequencies is t 0.10 MHz. 'Hypothetical unsplit frequencies with hyperfine structure removed. dFrequency calculated using the rotational constants and centrifugal distortion constants obtained in the analysis. eFrequency shift due to quadrupale coupling calculated using the constants in Table 111.
TABLE II
Transition 35C114N12C160 31,3 - 21,2
ASSIGNED TRANSITIONS OF CHLORINE ISOCYANATEa'b
Unsplit lineC
Calculated Frequencyd
Distortion corrd
Ground Vibrational State 5.0
17 950.12
1.30
-30 022.23
13.36
24 297.16
24 297.21
-0.51
23 932.54
23 932.69
1.55
30.3 - 21.2
-30 022.24
40,4 - 30,3 4 1,4 - 31,3 41,3 - 31,2
24 674.65
24 674.68
1.87
42,3 - 32,2 4 2,2 - 32,1
24 311.04
24 310.98
8.36
24 316.32
24 316.30
8.37
43,2 - 33,1
24 323.65
24 323.54
19.45
43.1 - 33,0 4 0,4 - 31,3 5 0,5 - 40.4
24 323.65
24 323.55
19.45
-23 675.00
-23 675.14
11.55
30 367.18
30 367.17
-1.00
51,5 - 41.4
29 914.38
29 914.58
1.64
51,4 - 41,3
30 841.96
30 841.92
1.92 10.10
52,4 - 42,3
30 387.76
30 387.71
52,3 - 42,2
30 398.34
30 398.35
10.11
53,3 - 43,2
30 404.68
30 404.57
23.96
53,2 - 43,1
30 404.68
30 404.59
23.96
54,2 - 44,1
30 423.42
30 423.33
43.36 43.36
54.1 - 44.0
30 423.42
30 423.33
50,5 - 41,4
-17 240.58
-17 240.66
9.00
60,6 - 50,5
36 434.24
36 434.24
-1.72
61,6 - 51,5
35 895.56
35 895.62
1.54
61,5 - 51.4
37 008.23
37 008.21
1.69
36 463.78
36 463.75
11.59
36 482.46
36 482.36
11.61
36 485.05
36 485.67
28.22
36 485.85
36 485.72
28.22
36 507.96
36 507.86
51.50
64,2 - 54,1
36 507.96
36 507.86
51.50
65,2 - 55,1
36 537.04
36 537.31
El.43 81.43
62,5 - 52,4 62,4 - 52,3 63,4
53,3
63,3 - 53,2 64,3 - 54,2
65.1 - 55.0
36 537.04
36 537.31
60,6 - 51,5
-10 720.92
-10 720.99
5.64
90,9 - El.8
9 320.90
9 320.96
-10.22
'00,10- 91,9
16 151.15
16 151.23
-17.72
"0,11-'01,10
23 049.59
23 049.66
-26.49
'20.12-"1,ll
30 011.62
30 011.69
-36.59
HOCKING
AND
TABLE II Transition
Unsplit line‘
35C,14N12C160
GkXKY
(continued)
Calculated Frequencyd
Distortion Come
Ground Vibrational State (cont'd)
'30 13-121 12
37 032.40
37 032.41
-48.10
16,:15-l52:14
-36 021.94
-36 022.04
-13.84
'71 M-162
15
-28 462.68
-28 462.75
-51.79
181:17-172:16
-20 824.51
-20 824.51
-93.29
'91,w'82,17
-13 108.93
-13 108.85
-138.48
221,21-2'2,20
10 485.40
10 485.54
-297.78
231,22-222,Zl
18 492.95
18 493.02
-359.27
241,23-232,22
26 568.23
26 568.24
-425.17
251,24-242,23
34 708.94
34 708.78
-495.61
241,24-232,21
-35 027.80
-35 027.70
-151.37
251,25-242,22
-32 536.70
-32 536.67
-164.64
261,26_252.23
-30 279.58
-30 279.60
-173.89
271,2J-262.24
-28 263.55
-28 263.56
-178.38
281,28-2J2,25
-26 495.0‘
-26 495.13
-177.34
2g1,29-282,26
-24 980.30
-24 980.33
-169.96
301,30-2g2,27
-23 724.62
-23 724.58
-155.43
35C,14N12C160 40,4 - 30,3 41,4 - 31,3 41,3 - 31.2 42,3
32,2
42,2 - 32,l 43,2 - 33,1 43.1 - 33.0 40,4
31,3
50,5 - 50,4 51,5 - 41,,4 51,4 - 41,3 52,4 - 42,3 52,3 - 42,2 53,3 - 43,2 53,2
43,l
54,2 - 44.1
24 017.91
1.66
24 792.51
24 792.59
1.99
24 413.00
24 412.99
8.89
24 418.54
24 418.60
8.90
24 426.33
24 426.32
20.66
-0.53
24 426.33
24 426.32
20.66
-25 219.04
-25 219.10
14.14
30 493.34
30 493.44
-1.04
30 020.88
30 021.03
1.77
30 959.21
30 989.25
2.05
30 515.17
30 515.17
10.74
30 526.36
30 526.38
10.76
30 533.70
30 533.05
25.45
30 533.20
30 533.05
25.45
30 553.09
30 552.97
46.05
30 553.09
30 552.97
46.05
-18 743.56
11.44
36 585.40
36 585.44
-1.79
51,5
36 023.12
36 023.27
1.68
- 51,4
37 184.92
37 184.90
1.83
44,0
50,5
41,4
60,6 - 50,5 Y,5
24 398.41
24 017.75
-18 743.52
54,l
61.6
First Excited Vibrational State vz = 1 24 398.20
6235
52,4
‘2,4
52,3
63,4 - 53,3 63,3
53,2
64,3
54,2
64,2
54,1
65,2
55,l
‘5.1 - 55,o
36 616.64
36 616.64
12.35
36 636.46
36 636.25
12.37
36 640.18
36 ‘39.87
30.00
36 640.18
36 639.92
30.00
36 663.64
36 6‘3.43
54.72
36 663.64
36 6‘3.43
54.72
3‘ ‘94.33
36 694.70
86.49
36 ‘94.33
36 694.70
86.49
MICROWAVE
SPECTRUM TABLE II
Transition
Unsplit lineC
35C1'4N12C'6D
OF ClNCO
(continued)
Calculated Frequencyd
Distortion Car?
First Excited Vibrational State v5 = 1 (cont'd)
-12179.19 60,6 - 51,5
.Ba 14 905.62
14 905.70
-16.80
21 864.70
21 864.76
-26.04
28 889.99
28 889.94
-36.68
'30,13-'21,lZ
35 976.10
35 976.09
-48.80
171 16-162 15
-32 410.85
-32 410.91
-25.51
181'17-172'16
-24 679.52
-24 679.55
-69.27
1gl:18-182:17
-16 867.55
-16 867.50
-116.90
'00,10- 91,9 "0.11-'01.10
231 22-222 21 241'23-232'22
15 150.41
15 150.51
-349.37
23 336.83
23 336.83
-418.69
31 591.21
31 591.11
-492.75
24
-34 728.54
-34 728.52
-161.22
2g1:29-282:26
-31 813.55
-31 813.57
-152.95
-30 760.17
-30 760.17
-137.98
251:24-242:23 271 27-'%
,
,
3ol 30-2g2 27
-
Second Excited Vibrational State v5 = 2
50.5 - 40,4
30 611.68
30 611.89
51,5 - 41,4
30 119.98
30 120.22
1.67
51,4 - 41.3
31 127.90
31 128.15
2.28
52;4 - $2.3
30 635.02
30 634.87
11.40
52,3 - 42.2
30 646.40
30 646.59
11.43
53.3 - 43,2
30 654.10
30 653.88
27.12
-1.18
53,2 - 43,1
30 654.10
30 653.91
27.12
54,2 - 44,1
30 675.22
30 fi75.17
49.11
54,) - 44,0
30 675.22
30 675.17
49.11
60,6 - 50.5
36 727.15
36 727.23
-2.04
61,6 - +,5
36 142.09
36 142.16
1.49
62,5 - 52,4
36 760.16
36 760.15
13.06
62,4 - 52,3
36 780.85
36 780.66
13.12
63,4 - 53,3
36 785.10
36 784.83
31.93
63,3 - 53,2
36 785.10
36 784.89
31.93
64,3 - !j4,2
36 E10.08f
36 810.02
58.32
64,2 - 54,l
36 810.0Bf
36 810.02
58.32
65,2 - 55,l
36 B43.21f
36 843.42
92.24
65.1 - 55,0
36 B43.21f
36 843.42
92.24
60,6 - 51,5
-13 839.62
-13 839.64
11.02
'00 lo- 91 9
13 448.62
13 448.64
-14.87
-13 259.17
-13 259.17
-139.08
11 172.71
11 172.71
-329.15
201'19‘~92'1B 23 1'22-222'*, . . 37C,14N12C160 31,3 - 21.2
Ground Vibrational State 17 544.92 17 544.95
40,4 - 30,3
23 742.74
23 742.82
-0.49 1.62
1.30
41,4 - 31,3
23 392.41
23 392.51
41.3 - 31,2
24 105.30
24 105.35
1.83
42,3 - 32,2
23 756.10
23 756.02
8.16
42,2 - 32,l
23 760.94
23 760.95
8.17
43,2 - 33,1
23 768.30
23 768.19
18.97
43.1 - 33,0
23 768.30
23 768.20
18.97
TABLE II Transition 37C,14N12C160 -____ +I,4 50,5
- 31,3 40,4
51,5 - 41,4 51,4 - 41,3 52,4
42,3
52,3
42,2
53.3 - 43,2 53,2
43,1
54,2
44,l
54.1 - 44.0 50.5
41,4
60.6 - 50,5 b1,6 - 51,5 61,s - 51,4 '2,5 - 52,4 62,4
52,3
63,4 - 53,3 b3,3 - '3,2
Unsplit lineC
(continued)
Calculated Freq"encyd
Distortion Corre
Ground Yibrational State [cont'd) -24 000.85
-24 000.91
11.46
29 674.45
29 674.43
-0.96
29 239.31
29 239.44
1.61
30 130.30
30 130.36
1.89
29 695.09
29 694.06
9.86
29 703.9%
29 703.93
9.87
29 710.4%
29 710.36
23.37
29 710.48
29 710.37
23.37
29 723.81
29 728.68
42.28 42.2%
29 728.81
29 728.6%
-17 718.83
-17 718.93
8.98
35 603.42
35 603.46
-1.65 1.52
35 085.53
35 085.57
36 154.52
36 154.47
1.67
35 631.45
35 631.47
11.32 11.34
35 648.83
35 648.73
35 652.68
35 652.59
27.54
35 652.68
35 652.64
27.54
35 674.39
35 674.27
50.23
'4,2 - 54.1
35 674.39
35 674.27
50.23
65,2 - 55,1
35 702.75
35 703.00
79.41
35 702.75
35 703.00
79.41
-11 354.87
-11 354.91
5.71
% 203.30
8 203.34
-9.66
14 867.56
14 867.60
-16.93
21 598.03
21 598.0%
-25.41
b4,3
54,2
65.1 - 55,o 60,b - 51,5 90,9 - *I,.¶ '00,10- 91,9 11 0,11-'01,lO 120 12-1'1 1,
28 390.55
2% 390.57
-35.19
130:13-121:12
35 240.44
35 240.49
-46.33
171,16-'62,15
-30 601.00
-30 601.37
-46.18
-23 160.82
-23 160.32
-86.32
-15 645.78
-15 645.73
-130.03
15 130.62
15 130.71
-343.39
22 994.61
22 994.63
-407.06
30 922.38
30 922.27
-475.10
-31 169.95
-31 169.89
-176.67
271,27-262,24
-29 092.76
-29 092.75
-183.29
2%7,2%-272,25
-27 250.54
-27 250.54
-184.86
2gl,29-282,26
-25 649.13
-25 649.18
-180.63
3ol>30-"2 ,27
-24 294.07
-24 294.06
-169.81
1*1,17-172,16 1g1,1%-182,17 231,22‘222,21 241,23-232,22 251,24-242,23 261,2b-252,23
37C114,,12C160
First Excited Vibrational State v
=
1
50,5 - 40,4 ---2n9fi7--
29 798.1% --
51,5 - ?,4
29 343.95
29 344.02
1.52
52,4
29 818.90
29 818.92
10.42
42,3
-1.09
52,3 - 42,2
29 829.25
29 829.34
10.45
53,3 - 43,2
29 636.26
29 836.24
24.80
53.2
43,l
29 836.26
29 836.25
24.80
54,2 - 44,l
29 055.73
29 855.73
44.92
54,1
29 855.73
29 855.73
44.92
44,o
MICROWAVE
SPECTRUM TABLE II
Transition 37C114N'2C160
Unsplit line‘
OF CINCO
555
(Continued)
Calculated Frequencyd
Distortion Came
First Excited Vibrational State v5 = 1 (cont'd)
60.6 - 50,s
35 751.51
35 751.54
$.6
- 51.5
35 210.90
35 210.94
1.35
%5
- 52,4
35 781.17
35 781.19
11.94
62,4 - 52,3 63,4 - 53.3
-1.87
35 799.44
35 799.41
11.98
35 803.74
35 803.62
29.20
35 803.74
35 803.67
29.20
64,3 - 54,2
35 826.90f
35 826.69
53.34
64,2 - 54,l
35 826.90f
35 826.69
53.34
65.2 - 55.1
35 857.lOf
35 857.27
84.38
35 857.27
84.38
63.3 - 53.2
65.1 - 55,o
35 857.10f -12 790.32
-12 790.34
8.13
13 638.49
13 638.51
-15.57
201 19‘192 18
-11 675.07
-11 675.07
-156.57
231:22-222:21
11 819.00
11 819.00
-330.63
60,6 - 51,5 '%,1a-
91,9
35C,14N12C180 31,3 - 21.2
16 Ground 985.16 Vibrational16 State 985.25 1.23
30,3 - 21,2
-30 315.61
-30 315.69
13.04
41.4 - 31.3
22 646.03
22 646.32
1.48
23 321.56
23 321.37
1.78
22 990.62
22 990.64
7.86
41,3 - 31.2 42,3 - 32,2 42.2 - 32,1
22 995.08
22 995.11
7.00
43,2 - 33,1
23 002.38
23 002.30
18.30
23 002.38
23 002.30
18.30
28 719.10
28 719.06
-0.90
28 306.64
28 306.80
1.58
29 150.56
29 150.50
1.85
20 737.47
28 737.42
9.53
43.1 - 33,o 50,5 - 40,4 51,5 - 41,4 51,4 - 41,3 52,4 - 42,3 52,3 - 42,2
28 746.39
28 746.36
9.54
53,3 - 43,2
28 753.05
28 752.97
22.55
53,2 - 43,l
28 753.05
28 752.98
22.55
28 770.71
28 770.66
40.78 40.78
54,2 - 44,l 54,l - 44,o
28 770.71
28 770.66
50,5 - 41,4
-18 249.96
-18 250.00
8.97
34 457.48
34 457.50
-1.55
'0,6 - 50,5 61.6 - 51,5 61,5 - 51,4 62,5 - 52,4 '294 - 52,3 63,4 - 53,3 63.3 - 53,2 64,3 - 54,2 '4,2 - 54.1 65.2 - 55,l 65,l - 55,0 60,6 - 51,5 '00,10- 91,9
33 966.47
33 966.56
1.51
34 978.89
34 978.81
1.66 10.96
34 483.59
34 483.62
34 499.39
34 499.25
10.98
34 503.80
34 503.69
26.59
34 503.80
34 503.73
26.59
34 524.76
34 524.65
48.46 48.46
34 524.76
34 524.65
34 552.15
34 552.36
76.58
34 552.15
34 552.36
76.58
-12 099.21
-12 099.30
5.84
13 233.94
13 233.99
-15.77
'10,11-'01,1G
19 734.63
19 734.75
-23.85
'30 13-721 12 77 l'1b-162',5 . .
32 911.39
32 911.43
-43.76
-33 129.56
-33 129.70
-37.98
HOCKING AND GERRY
556
TABLE II Transition 35C114N12C'8D '81.17-'72,16
Unsplit lineC
(continued)
Calculated Frequencyd
Distortion Corre
Ground Vibrational State (cont'd) -25 957.86
-25 957.88
-76.23
-18 714.69
-18 714.68
-117.85
201'19-1g2'18 "1 18-"2 17
-11 401.51
-ii 401.43
-162.98
231:22-222:21
10 943.11
10 943.25
-320.81
241 23-232 22 25 "24-242'23
18 520.72
18 520.77
-381.33
26 159.78
26 159.76
-446.02
261:25-252:24
33 853.23
33 858.10
-514.96
241 24-232 21
-37 140.25
-37 140.17
-147.56
251'25-242'22
-34 582.99
-34 582.95
-163.39
261:26-252:23
-32 231.88
-32 231.90
-176.06
271 27-262 24
-30 093.48
-30 093.52
-184.94
28"28-272'25
-28 173.93
-28 173.99
-189.84
3ol:3D-2g2:27
-25 014.01
-25 0'3.98
181.95
50.5 - 40,4
28 839.44
28 839.56
51,s - 41,4
28 408.97
28 409.11
1.50
51.4 - 41.3
29 290.10
29 290.26
2.0' 10.03
First Excited Vibrational State V. = 1
.-
52,4 - 42,3 52,3 - 42.2 53.3 - 43,2 53.2 - 43,l 54,2 - 44,1 54,1 - 44,o 60.6 - 50,s ?,6
- 51,5
'2.5 - 52,4 62,4 - 52,3 63.4 - 53,3 63,3 - 53,2 64,3 - '4,2 64.2 - 54.1 65,2 - 55,1 65,l - 55,o 60,6 - 51.5 '00,10- 91,9 201 19-192 18 241:23-232:22
=
-1.02
28 858.98
28 858.98
28 868.28
28 868.42
10.06
28 875.54
28 875.45
23.84 23.84
28 875.54
28 875.46
28 894.29
28 894.20
43.lG
28 894.29
28 894.20
43.16
34 601.72
34 601.76
-1.76
34 098.11
34 089.20
1.35
34 629.36
34 629.38
11.51
34 645.97
34 645.89
11.55
34 650.84
34 650.64
28.08
34 650.84
34 650.69
28.08
34 673.12f
34 672.86
51.27
34 673.12f
34 672.86
51.27
34 701.96f
34 702.25
81.08
34 702.25
81.08
34 701.96f -13 501.09
-13 501.11
8.20
12 030.95
12 030.97
-14.44
-14 949.30
-14 949.30
-142.08
15 369.26
15 369.26
-371.23
aAll freqwncies are in megahertz (HHz). b Estimated uncertainty in transition frequencies is iO.10, except where otherwise indicated. c Hypothetical unsplit frequencies with hyperfine structure removed. dFrequency calculated using the rotational constants and centrifugal distortion constants obtained in the analysis. eOeviation between the calculated frequency of the adjacent column and that ca'culated using the derived rotational constants in a rigid rotor approximation. f Estimated uncertainty is 0.3 flHz (quadrupole strxture unresolved).
_MICROWAVE
SPECTRUM
OF ClNCO
557
where
do = Fl(Fl+
1) -
11(11f
1) -
J(J
+
I),
-41 = F(F + 1) -
I*(12 + 1) -
Fl(F, + l),
A2 = IlVl +
JV
Fl(K
1) -
+
1) -
+
1).
is the average value of the square of the angular momentum along the u-inertial axis, and W (b,) is the Wang reduced energy, with b, Wang’s asymmetry parameter; both (Pa2) and W (b,) were evaluated to sufficient accuracy in a rigid rotor basis. The quadrupole coupling constants of interest are xaa and xbb - xec for each nucleus. Using Eq. (I), a least-squares fit was made of the measured first-order splittings up to J = 30 for the quadrupole coupling constants of all isotopic species in all observed vibrational states. The results are collected in Table III. The nuclear quadrupole hyperfine structure could then be subtracted off the rotational transitions, and the resulting frequencies used in the subsequent analysis. (Pa2)
Rotational and Centrifugal Distortion Constants It was necessary to account for centrifugal distortion in order to obtain accurate rotational constants. To first order the energy expression for a semirigid asymmetric rotor may be written as (8) E
= E, + ED,
(2) TABLE
NUCLEBR QUADRUPOLE COUPLING Vibrational State Ground Xa.(lP X&(l) xm (2)
III
CONSTANTS
35C1’4N’2C’60
OF CHLORINE ISOCYANATE 3,tJMN”ZC’“G
(MHz)
36C1’4NBC’BG -
-71.13 -4L.59 3.99 1.96
f f f f
0.13” 0.07 0.09 0.04
-56.61 f -33.15 i 4.14 f 2.00 f
0.15 0.09 0.10 0.04
-69.82 f -43.81 * 4.02 f 2.00 f
0.18 0.10 0.11 0.06
First Excited (0, = 1) x0.W Xbb(l) - Xc*(l) x00 (2) Xbb(2) - x..(2)
-71.39 -43.06 4.12 2.10
f f f f
0.20 0.16 0.14 0.10
-56.57 -33.58 4.29 2.04
0.36 0.32 0.18 0.22
-69.56 -44.31 4.13 2.09
0.39 0.44 0.22 0.26
Second Excited (~5 = 2) xm(l) Xbb(1) - XW(1) x00 (2) Xbb(% X.42)
-70.99 zk 0.47 -43.52 f 0.35 3.78 f 0.23 2.10 f 0.24
Xab(2)
-
XWU) Xm(2)
a Chlorine is nucleus 1; nitrogen is nucleus 2. b Errors cited are twice the standard errors.
f f f f
f f f f
HOCKIXG
558
AND
GERRY
ER = %(B + C)J(J + 1) + M - ?Ji@ + C)W(b,), Eo =
?,65r&apo (Pa2Pp2 + PB”P~.“>.
(3) (4)
Here E, is the rigid rotor energy, and ED is the first-order centrifugal distort.ion c;)rrection. The 7&uaa are related to the centrifugal distortion constants by and ~&,ab = fi4(7aapB + 27u~c1~) ; a, /I can be a, b, or c. Expres~uaolo!= fi4 ~aCW2a sions for the average values of the angular momentum operators in the rigid rotor basis are given elsewhere (9, 20). It has been shown (10) that in general it is possible to determine at most only five combinations of the T’S from a rotational spectrum. The energy cxpresuion can be rewritten with Ex = >4(B + c)J(J Eu = -d.,J”(J
+
+ 1) + [A 1)” - dmJ(J
>;(B
+ l)(P,‘, -
+ C)]W(b,)
= Wo,
(5)
- &(P:) dw, WoJ (J + 1) -
rZwzcWo(P,2).
(6)
B, 8, 6, differ from A, B, C by a small centrifugal term. An attempt was made to fit by least squares all transitions with J 5 30 to the five distortion constants, with linear variations of the rotational constants being allowed. However, a stable fit could not be found, though apparently good values of the rotational constants were obtained. On the other hand, it was possible to make stable fits to four constants, wit’h either & or dwKneglected. The rotational constants thus obt.aincd were in excellent agreement with those of the first analysis, but c~onsistcnt, values of all the distortion constants were not found. An alternative treatment was also carried out. It is shown in the fOll(J\viIlg section that chlorine isocyanate is planar; in this case constraints exist which enable the number of determinable constants to be reduced from five to four (10, 11). The constraints are strictly applicable when the rotational constants are the equilibrium constants. Since these are not available a good approximation was made by using the ground state constants, and a lea&squares fit \vas made to the four centrifugal distort.ion constants T,,,,,, , ~i,bb~, , 7,bab, 7,&b, vi&h linctar variations of the rotational constants again being allowed. The results are collected in Table IV. Once again rotational csonstants ivere obtained -c\-hicall were in excellent agreement with those determined in the previous analyses. Four determinate 7’s were also obtained; in particular 7naa(ln-as found to bc very large. r\‘o attempt was made to include higher order or P” t,erms in the analysis. As a check the analysis was carried out, wi-ithJ 5 25; the results agreed with thosct of Table IV to within experimental error. A varia,tion of the latter procedure n-as alno used in which t’he relations linking the 7’s included the ground state values of A and B and a value for C adjustSed to make the inertial defect zero. The results of this analysis are also given in Table IV; the rotat’ional constants and two of the distortion constants agree well with
MICROWAVE
SPECTRUM TABLE
559
OF ClNCO
IV
ROTATIONAL CONSTANTS AND CENTRIFUGAL DISTORTION CONSTANTS OF 36C1i~NWi60 IN THE GROUND VIBRATIONAL STATE USING DIFFERENT METHODS OF ANALYSIS (ALL VALUES IN MHz) Analysis A
B
c 7...a Tbbbb Toabb T.bab
1s 51 576.21 3 130.588 2 945.171 -59.138 -0.01075 0.6923 -0.0101
f f f f f f f
IIb 0.130 0.006 0.005 0.094 0.00005 0.0016 0.0012
8 In the relations reducing the number of determinable rotational constants were ground state constants. b In the relations reducing the number of determinable ground state values of A and B were used, with C adjusted c Errors cited are twice the standard errors.
51 576.22 3 130.591 2 945.166 -59.141 -0.01075 0.6992 -0.0175 distortion
f f f f f f f
0.13 0.006 0.005 0.096 0.00005 0.0016 0.0012
constants
to four the
distortion constants to four the to make the inertial defect zero.
those of the previous calculation, but the others do not; indeed T&b is different by a factor of nearly two, well outside experimental error. Table V contains the rotational and centrifugal distortion constants of each isotopic species studied in each vibrational state. The values given were obtained by analysis for three rotational constants and four distortion constants, in which the rotational constants for the particular vibrational state being studied were used in the relations reducing the number of determinable distortion constants to four. Some care must be taken in interpreting the results in Tables IV and V. It is clear, for a start, that the distortion analyses have yielded accurate rotational constants, which can be used for determination of the internuclear parameters. A similar phenomenon has been observed previously (12’). The meaning of the distortion is less clear. Evidently, the correct order of magnitude was obtained, though the variations noted above suggest that our fits to four constants have not given values entirely meaningful physically, and that these can be obtained only through a full fit to five constants using further branches. Unfortunately, insufficient transitions were observable in the frequency range of our spectrometer to enable such a fit, and we must be content with the reliable values of the rotational constants. MOLECULAR
STRUCTURE
It was originally anticipated that chlorine cyanate might exist in one or both of two forms, having formulas ClOCN or ClNCO, with the latter being more probable, analogous to HNCO, CH3NC0 and SiHsNCO. Both these forms were expected to be planar.
560
HOCKING
AND
TABLE
GERRY V
ROTATIONAL CONSTANTS AND CENTRIF~JUL DISTORTION CO~VST.~NTS~ Vibrational State
3sC1’4N’2C’60
s7C,I4NrJC’60
Ground -4
51 576.21 3 130.588 C 2 945.171 7.004 -59.138 7bbtd -0.01075 zaabb 0.6923 Tab& -0.0101 First Excited (0, = 1) 11 53 261.08 B 3 147.363 c 2 953.772 7o.ao -70.308 76bbb -0.01116 7aabb 0.7572 Tabd -0.0242 Second Excited (2~5= 2) A 55 137.02 B 3 163.210 c 2 961.743 7.(10(1 -84.24 7bbbb -0.01217 S,.bb 0.760
B
lsCt”N’2Cy)
_
.___ f f f * f f i
0.13~ 0.006 0.005 0.094 0.00005 0.0016 0.0012
51 256.45 3 057.596 2 879.465 -58.428 -0.01027 0.6718 -0.0093
f zt f f f zt f
0.13 0.005 0.005 0.094 0.00005 0.0019 0.0016
50 689.75 2 957.234 2 788.544 -57.524 -0.00957 0.6460 -0.0098
f zt * f f rt f
0.22 0.009 0.009 0.155 0.00007 0.0941 0.0034
52 912.96 f 3 073.943 f 2 887.988 f -69.29 zk -0.01118 f 0.673 f (1
0.48 0.021 0.050 0.30 0.00089 0.105
52 305.62 f 0.61 2 973.065 f 0.032 2 796.934 zt 0.069 -68.13 f 0.45 -0.01046 I!Z 0.60112 0.649 zk 0.140 r/
f zk f f zk f
0.67 0.036 0.075 0.51 0.00120 0.153
constants
to four used the rotational
zt f zk f It zk &
0.15 0.006 0.006 0.113 0.00005 0.0018 0.0013
Cl
rczb(ib _
8 The relations reducing the number of distortion constants for the appropriate vibrational state. h All frequencies are in MHz. 0 Errors cited are twice the standard errors. ClValues indet,erminate.
In Table VI are given the principal moments of inertia and inertial defects of all isotopic species studied. The inertial defects in the ground vibrational state are all small positive numbers, which change little with isotopic substitution, and arc thus consistent with a planar structure. Furthermore, the changes in principal moments of inertia on isotopic substitution of oxygen are all large; for the structure ClOCN the oxygen atom is very near the b-inertial axis and subst’itution of oxygen wou!d thus cause only a very small change in IBo. The isocyanate structure, ClNCO, is thus confirmed. The isocyanate configuration is consistent with the quadrupolc coupling of nitrogen. In the structure ClOCN, the CN bond can be assumed to be a principal axis of the quadrupole tensor, and the nitrogen coupling constant along this axis should be about -4 MHz (13). Consequently, if this bond mere symmetric
MICROWAVE
SPECTRUM TABLE
OF ClNCO
561
VI
MOMENTSOF INERTIAAND INERTIALDEFECTS*OF CHLORINEISOCYANATE Vibrational State
3bCl14N12Cl60
Ground zAb
ZB
ZC AC First Excited (~5 = 1) IA IS
9.798 915
161.436 4 171.599 9 0.364 5 9.488 935 160.576 0
IC 171.100 2 A 1.035 2 Second Excited (115= 2) IA 9.166 090 IB 159.771 5 zc 170.639 7 A 1.702 1
9.860 165.290 175.515 0.365
044 3 6 3
9.970 170.899 181.238 0.368
277 9 3 1
9.551 164.411 174.997 1.034
363 3 6 9
9.662 169.989 180.694 1.042
268 9 6 4
a In amu bz.
b Calculated from rotational constants of Table VI using conversion factor 505391 amu bz MHz. eA = 1~ - 1~ - IA
xcc should be +2 MHz, in sharp contrast to the observed value of in molecules, such (CNh and CH1 SCN (15), this bond has found quite asymmetric, even a similar large asymmetry ClOCN a positive value of xcc would found in the present molecule has a small positive value (+3.99 thus of the order that found HNCO (+2.0 MHz) (16) and CHSNCO MHz) (15). This than the value xcc, however, because the ainertial axes three molecules. Both constants, however, tend rule out the structure With the planarity order of atoms established, the internuclear parameters were (17) was to locate the atoms which isotopic substitutions were In method one isotopic species (here the abundant, 35C114N12C160) is as a basis; the substituted atoms are located basis molecule using Rraitchman’s (18) for a rigid both chlorine were easily obtained this To determine four remaining coordinates five equations were available, namely, mass conditions product of inertia condition CiTn
HOCKING
562
AN11 GERRY
Three combinations of these five relations were used to locate these atoms. In all of them the center of mass conditions were used, along with two of the romaining three relations. The resulting structures are given in Table VII. Of these three the one preferred is that calculated by method I, which used the product of inertia condition and reproduced IBo. Since both chlorine and oxygen are near the u-principal inertial axis, the magnitudes of their b-coordinates arch small and rather inaccurate (17); thus the coordinates of nitrogen and carbon, when obtained by reproducing I.,‘, are similarly inaccurate. On the ot1~c.r hand, the u-coordinates of chlorine and oxygen are large in magnitude, and thus more reliable; consequently, a better det’ermination of the coordinates of carbon and Furthermore, only tllc n-. nitrogen can be expected when I Bo is reproduced. coordinate of carbon is in practice obtained from Ieo, since nitrogen, being Neal the b-axis, contributes effectively nothing to this principal moment. Thr: a-coordinate of nitrogen is determined almost exclusively by the center of mass condition, which is the most accurat’e equation for locating atoms near a principal plane (17). The principal axis system of chlorine isocyanate is shown in Fig. 1. It is seen from Table VIII that the derived internuclear distanccbs are vcrj reasonable. The CliK length is very near, though slight,ly less than, the sum of the single bond radii (l.T3A) (19). The NC and CO distances are very nt’ar t,hosct of other isocyanates. The most surprising feature cJf the structure is the bend in the NC0 chain of about S” away from chlorine. This is to the authors knowledge the first case where such a bend has been observed in an isocyanate, though R similar bend was found in isoelectjronic chlorine azid(t (J). Our internuclear parametcbr:i TABLE
VII
COMPARISONOF MOLECUL~~~STRUCTURES OF CHLORINE ISOCT.\N.~TE OBT.UIUIW USING DIFFERENT CAI,CUL,YTION METHODS
__
Method Ia r(C1-N)d r(N-C)d r(C-0) < GINC) < (NCO)’ ____
1.703 1.218 1.165 119” 22’ 171” 24’
f + i f f
0.011~ 0.012 0.008 1” 1” 30’
Method 11”
Method IIIc
1.714 1.206 1.173 118” 26’ 169” 59’
1.706 1.2“4 1. 163 118” 45’ 170” 38’
a Nitrogen and carbon located using the center of mass and product tions, and reproducing ZBO. b Nitrogen and carbon located using the center of mass and product tions, and reproducing lao. 0 Nitrogen and carbon located using t.hr center of mass ronditions, IAO and IBO. d All distances in Angstroms. B Error limits are outside limits of error obtainrd by comparing t,he calculation. f Cl and 0 are trans in all cases.
of inertia
wndi-
of inertia
condi-
and reproducitlg
three met hods of
MICROWAVE
SPECTRUM
OF ClNCO
563
are in excellent agreement with the electron diffraction results of Oberhammer (SO). Here the structure with a bent NC0 chain was strongly suggested, but the data could not distinguish between it and one with a linear NC0 chain, though the former was preferred in the light of the known bond lengths of other isocyanates. From our resu1t.s we concur with this deduction. To confirm further whether the bend is real the posit.ions of carbon and
FIG.1.Positions
of the atoms in the principal TABLE
axis system of chlorine isocyanate. VIII
STRUCTURAL PARAMETERS OF CHLORINE ISOCYANATE COMPARED WITH THOSE OF SIMILAR MOLECULES
-
Molecule
r(Cl-N
ClNCO* HNCO (6) F3SiNC0 (3) H $iNCO (3) C13SiNCOb H&NCOc
1.703
CINI (4) ClNOd CINOze
1.745 1.975 1.840
)
r(N-C)
r(C-0)
< (NCO)
1.218 1.207 1.190 1.216 1.219 (1.190’ (1.207’
1.165 1.171 1.168 1.164 1.139 1.18’ 1.171’
171” 24’ 180”’ 180”’ 180°’ 180”’ 180”
< (XNC) 119” 22’ 128” 5’ 160.7” 151.7” 138.0” 140.1”) 140.0”)
(X (X (X ;$
Cl) H) Si) ;; i (X = C)
* This work. b R. L. Hilderbrandt and S. H. Bauer, J. Mol. Slructure 3, 325 (1969). c Reference (16). d D. J. Millen and J. Pannell, J. Chem. Sot. 1322 (1961). e D. J. Millen and It. M. Sinnott, J. Chem. SOC. 350 (1958). f Assumed. g Microwave spectroscopy. h Electron diffraction.
= = = 1
Method M.W.g M.W. E.D.h E.D. E.D. M.W. M.W. M.W. M.W.
564
HOCKING AIW GERRY
nitrogen were obtained by using the center-of-mass conditions and the product of inertia equation, and constraining the NOCO chain to be linear. The resulting NC and CO lengths were 1.309 and 1.111 A, respectively. Since both bonds are multiple bonds, these lengths are unreasonable in comparison with those of othw isocyanatcts. Also this structure predicts a value for lee differing from t(hc c,xpcrimental one by 2 amu p. It thus seems certain that the bend in the NC0 chain in real. 1) ISCUSHIOPU‘ The deduced planarity of t’hc molecule is COnSiStent with several other features of its microwave spectrum. In the first place, the out-of-plane components IJ~ the nuclear quadrupole coupling tensor, xcc , are the same for both species cont,aining 3”C1. Furthermore, thr ratio xcc (3”C1)/~ec (37C1) = 1.267; this agrws well with the ratio of the quadrupole moments of the two isotopes [Q (“%1)/Q (“‘Cl) = 1.86883. Secondly, it has been shown (21) t,hat for a planar molecule a good approximation to the ground vibrational state inertial defect A is given by A = 4K/wl , where K = 16.863 amu k cm-’ and ~2 is the frcqurncy of th(J lowest in-plane vibration. Using our rxperiment’al value of A, wi is found to bc IS.5 cm-‘. This is in very good agreement with the frequencies measured in t,he Raman spectrum [WI = w5 = 199 cm-l in the solid and 174 cm-’ in the liquid (.B)], as well as with t,hat deduced from the relative intensities of molecules in excited vibrational states [< 200cm-‘]. This low vibration frequency is also conskt’cnt with the large centrifugal distortion. The irkrnuclcar parameters of chlorine isocyanate are shown in Table VIII, along with those of related molecules. Since the ClN bond length is near the sum of the chlorine and nitrogen single bond radii (19), and since the NC0 chain is near linear, thr following resonance form is probably the major one:
Cl \
N=C=O
To determine the degree of any possible double bond character of the ClN bond the principal values of the chlorine nuclear quadrupole coupling tensor were determined for 35C1’4N’2C’60 in its ground vibrational state. With the assumption that one principal axis of the quadrupole coupling tensor coincides with the ClN bond the coupling const’ants were transformed from the inertial axis system to the principal axis system (z parallel to t’hc Cl?; bond, y perpendicular to the molecular plane). The principal values obtained were xzz = 64.20 MHz, xVzl = XCC= 56.86 MHz, xz. = - 121.06 ;\IHz. The difference xz2 - xyU gives a measure of the double bond character of the ClN bond (23, 24); this value is 4YX.
MICROWAVE
SPECTRUM
56:’
OF ClNCO
likely
, parallel to the ClN bond, is very near that of the chlorine atom. Since chlorine and nitrogen have essentially the same electronegativity, such a value is to be expected if the ClN bond is essentially covalent (7) ; similar values have been observed previously (25-27). Indeed [ xzt 1 = 121.06 MHz is larger than 1xc1 ato,n/ = 109.7 MHz. Now, the double bond character of the ClN bond should decrease / xzz / from 1xc1 atorn1, but the effect of ionic character is to increase it if the positive pole of the ClN bond is on chlorine. Possible resonance forms in which this occurs are: cl+
N=C=O
cl+ NZC-o-
(III)
(IV)
Any shortening of the ClN bond by double bond character should be counterbalanced by this ionic character, and therefore a ClN length close to the sum of the single bond radii is not inconsistent. With the assumption that hybridization of chlorine can be neglected, and with application of the charge-screening correction (7), the ionic character is found to be 9 %; as a result, the single bond character is 87 %. These figures must be viewed with caution, however, because of the neglect of overlap and hybridization, both of which can have a significant effect on ionic character calculations (28, 29). ACKNOWLEDGMENTS We acknowledge gratefully the support of the National Research Council the form of research grants and a scholarship to one of us. (W. H. H.). RECEIVED:
of Canada
October 12, 1971 REFERENCES
1. E. NACHBAUR AND W. GOTTARDI, Monatsh. 97, 115 (1966). 2. M. C. L. GERRY, J. C. THOMPSONAND T. M. SUGDEN,Nature 211,846
(1966).
in
HOCKING
561i
ANI)
GERBY
3. W. AII~EY, C. GLIDE~~ELL, A. G. K~UIETTE END G. M. SHELDRICK, J. Mol. Struclnre 6, 435 (1971). Q. IL. L. Coors AND M. C. L. GERRY, J. Chem. Phys. 63,2525 (1970). .5. 1~. H. JONES, J. N. SHOOLERY, R. G. SHUIX\Z~ ANU D. M. YOST, J. Chem. Phys. 18,990 (1950). 0. J. BARDEEN AND C. H. TOJ~NES, Phys. Rev. 73, 97 (1948j. Spectroscopy,” Mc(;raw-Hill, New 7. C. H. TO\%-iXES AND A. I~. ~EI.\\I.LOW, “Micrownve York,
1955.
8. 11. KIVELSON _~NDE. B. WILSOX, JH., J. Chew. Phyr. 20, 1575 (1952). 9. R. L. Cook;, J. Chem. Phys. 42, 2927 (1965). f0. J. K. G. W.~TSON, J. Chem. Phys. 46, 1935 (1967). 11. L. PIERCE, N. DICIBXNI .\NDR. H. JXBSON, J. Cham. Phys. 38, 730 (1963). 12. G. E. HERBEHICH, R. H. J.~cKso~; ibid D. J. MILLEN, J. Chem. Sot. A336, (1966). 13. W. B. Molv~z AND H. S. GUTO~SKY, J. Chem. Phys. 38, 1155 (1963). 14. L. PIERCE, IL. NELSON BND C. THOMAS, J. Chem. Phys. 43,3423 (1965). 15. l<. G. LETT AND W. H. FLYG.II
24. 25. 26. 27. 28. 29.
L. PAULING, “The Chemical Bond,” Cornell University Press, Ithaca, NY, H. ORERH.\MMER,2. Natnrforsch. d26, 280 (1971). I>. 1~. HEKSCHBICH xw V. W. L.~URIE, J. Chem. Phys. 40, 31Q (1964). E. H. KYSEI, -\NDl+J.NxHB~~I~, 2. Anorg. illlgewt. Chem. 381, 71 (1971). R. BEKSOHN, J. Chem. Phys. 22, 2078 (1954). J. H. GOLDSTEIN, J. Chem. Phys. 24, 106 (1956). H. 0. HOOPER AND P. J. BRAY, J. Chem. Phys. 33, 334 (1960). II. K~sHI\%T~\GI, I). NAKAMURI END M. Kuno, Tetrahedron 21, 1095 (1965). It. M. HART AND M. A. WHITEHEIU, Trans. Faraday Sot. 67,1569 (1971). W. (;ORDY, Discuss. Faraday Sot. 19, 14 (1955). 1:. H. JXKSOX AND D. J. MILLEN, Advan. Spectrosc. 3, 1157 (1962).
1960.
OF
The
MOLECUL.LR
SPECTROSCOPY
Microwave
&?,
of Chemistry,
(1972)
Spectrum and Structure lsocyanate
W. H. HOCKING Depadment
547-566
University
of Chlorine
and M. C. L. GERRY
of British
Colwnbia,
Vancouver
8, B.C.,
Cartada
The microwave spectra of three isotopic species of chlorine isocyanate, ClNCO, have been measured in the frequency region 8-37 GHz. Spectra have been observed for molecules in both the ground and excited vibrational states, and have yielded values for the rotational const.ants, inertial defects, centrifugal distortion constants, and nuclear quadrupole coupling constants for both chlorine and nitrogen. The molecule has been shown to be planar, with the following internuclear parameters: r(ClN) = 1.703 f 0.0114, = 1.218 f 0.012 B, r(NC) r(C0) = 1.165 f 0.008 A, < (ClNC) = 119” 22’ z!z l”, < (NCO) = 171” 24’ f 1” 30’, with Cl and 0 trans. The principal values of the chlorine nuclear quadrupole coupling tensor were calculated, and were found to be consistent with the derived struct,ure. INTRODUCTION
The preparation of chlorine isocyanatc, CINCO, has been reported recently (1). This molecule is isoelectronic with two others whose structures have unusual features. For one, silyl isocyanate, SiH&CO, the microwave spectrum is consist,ent with a linear heavy atdm chain (.2), but electron diffraction results suggest it to be bent (5’). In the ot’her, chlorine azide, ClIY3 , the azide chain, which is usually linear, has been recently shown to be bent (4). Accordingly we have measured the rotational speckurn of several isotopic species of chlorine isocyanate to determine its structural parameters, and particularly to discover whether these too show unusual features. This article gives a full account of this st.udy’, which has yielded, besides rotational constants and internuclear parameters, inertial defects, centrifugal distortion constants and nuclear quadrupole coupling constants. EXPERIMENTAL Chlorine isocyar1at.c was prepared by the pyrolysis of t.richloroisocyanuric acid according to the method of Nachbaur and Gottardi (1). Commercial trichloroisocyanuric acid (Baker Chemical) was placed in a Pyrex tube and heated slowly over eight hours from 150 to 200°C. A portion of the sample was sublimed and pyrolgsed at 310°C further along the tube. The pyrolysis products were collected
1A preliminary
account
has appeared in Chen~. Gown. 448 (1970). 547
Copyright
@ 1972 by Academic
Press,
Inc.
HOCKING
AND
GERRY
in vacua at 77°K; they were then fractionally distilled from the collection trap, with the middle portion being retained for spectroscopic study. Samples prepared in this way were essentially free of interfering impurities. The sample was stored at 77”K, at which temperature it was indefinitely stable. To obtain the sample enriched with 1*0, alkaline hydrolysis of cyanuric chloride with H2180 was first carried out; on acidification, labeled cyanuric acid was deposited and then isolated. The product was then converted to trichloroisocyanuric acid as follows: chlorine gas was bubbled t’hrough a 0.40 ICI suspension of the cyanuric acid in a 1.25 M sodium acetate solution initially at pH 6.5, until the pH dropped to 2. The labeled trichloroisocyanuric acid which precipitated was isolated, dried, and pyrolysed as described above. The microwave spectrum was obtained in the frequency region 5-37 GHz using a 100 kHz Stark modulated spectrometer having a 7-foot X-band cell. This spectrometer was of conventional design, except that in the frequency region 818 GHz the source was a phase-stabilized Hewlett-Packard 84OOB Microwave Spectroscopy Source. Above 18 GHz an appropriate OK1 klystron was used as the source; its frequencies were measured by comparison with the output of a Micro-Now 1OlC Frequency i\lultiplier Chain whose fundamental was continuously monitored with a Hewlett-Packard .524.5LFrequency Counter. Gaseous samples of chlorine isocyanate for microwave spectroscopic study wore taken from the vapor above the bulk liquid sample held at approximately -80°C. At this temperat.ure liquid chlorine isocyanate polymerizes very slowly, but still has a significant vapor pressure. The micromavc cell was cooled with dry ice; the samples were stable in the cell for about five minutes. Pressures of .‘,-2.5 p were used, depending on t)he intensity of t.he lines being studied. OBSERVED
SPECTRA
a7(3’4N’2C16() :tnd The spectra of three isotopic species, 35C1’4N12C’80,were observed in both the ground and excited vibrational st!ates. Transitions of molecules in two excited vibrational stat,es were measured for 3sC114N’2C160, and in one excit’ed state for the other isotopic species. From the relative intensities and frequencies these were found to be excited states of the same vibration, with a frequency of less than ZOO cm-‘. Numerous a- and b-type transit’ions were assigned and measured for all isotopic species in all vibrational state*. The u-type transitions were fairly easily assigned as R-branches of a slightly asymmetric near-prolate rotor; rpsolut,ion of transitions with different values of E1 , which is often difficult for such a molecule, was easy in this case and provided evidence of large centrifugal distortion. Three series of b-type P- and R-branches were observable, and were measured up to J = 30; these had the forms Jo,_, - (J - ~)L.T-I , JLM - (J - 1)s-2 , and J,,., - (J - 1)2,5--3 . These transit,ions also showed evidence of large centrifugal distort’ion. Both the a- and b-type transitions were of comparable intensity. All transitions showed considerable hyperfine structure due to nuclear quad35C114N12~16~,
MICROWAVE
SPECTRUM
OF ClNCO
549
rupole coupling of the molecular rotation with the nuclear spins of chlorine and nitrogen. The structure due to chlorine was large and easily resolved; that of nitrogen was smaller, and resolution was more difficult. The quadruple coupling was used to confirm all rotational assignments. The entire measured spectrum was analysed, first for the nuclear quadrupole coupling constants, and then for the rotational and centrifugal distortion constants using the methods described in the following section. Some representative observed transitions of 35Cl’4N12C’60, along with their assignments and the splittings calculated using the derived quadrupole coupling constants are given in Table I. In Table II are given the frequencies of all the observed rotational transitions with nuclear quadrupole hyperfine structure removed, along with t,he calculated frequencies and centrifugal distortion corrections. ANALYSIS ;lTuclear
Quadrupole
OF THE
SPECTRA
Coupling
Nuclear quadrupole coupling was observed for both chlorine and nitrogen. The theory of such coupling by two nuclei has been treated by Bardeen and Townes (6). In chlorine isocyanate the coupling of nitrogen is very much less than that of chlorine, and the following coupling scheme is approximated very closely : II + J = F1 ; I2 + F, = F. Here 11 and 12 are the nuclear spins of chlorine and nitrogen, respectively. In general, the well-known quadrupole Hamiltonian is diagonal in II, IZ and F, but can have elements both diagonal and off -diagonal in J and F1 (7). However, in chlorine isocyanate the quadrupole couplings of both nuclei are sufficiently small so that elements off -diagonal in J can be ignored. Preliminary coupling constants obtained from the spectrum using first-order perturbation theory (i.e., ignoring elements off-diagonal in F1) were used in the full matrix scheme to predict the quadrupole hyperfine patterns. In virtually all cases the elements off-diagonal in Fl gave negligible contributions to the patterns, and could therefore be ignored. The analysis thus used the following expression for the quadrupole energy of a given rotational level: E
= 3AdAo Q
M&21~
-
+ 1) l)J(2J
Pa’> -
4I1(I1 + ljJ(J + 1) - l)(J + 1>(2J + 3)
1
cc
,3(P “) _ ’
J(J
W(b,) [X&(l) - x (l)] b, [3Al(Al + 1) - 4IdIz + lP0’~ + 111 +[3Az(Az + 1) - 4J(J + W’dF1 + 111
+ .‘* + 1612(2I2 - l>J(2J - l)(J + 1) . (25 + 3)F1(2Fl - l)(K + 1) (2F1 + 3) x . . x
[3(P,2) - J(J + 1)1x.&>
+
(“)
+
l>jx
aa(1)
(1)
7 - xccc91 P 1[Xbzm
; W(bp)
550
HOCKING TABLE I
AND GERRY
SOME REPRESENTATIVE TRPNSITIONS OF 35C114N12C160 IN THE GROUND VIWATIONAL
F,'
F'
F,"
F"
Unsplit line:
313 + 212
STATEaTb
Observed Frequency Ohs 17 950.00'
ouadrupole Correction Observed Calculatede Calc
17 950.1Zd
512 512 512 7/z
712 512 512 512
3/2 312 312 312 312 512
;;; 312 312 3/2 912 312 ;;g
;;; l/2 l/2 512 712 312 ;;;
512 l/2 l/2 l/2 712 II2 712 l/2
712 512 l/2 312 312 712 312 5/2 l/2
17 17 17 17 17 17 17
947.52 948.08 949.90 949.90 950.59 951.03 951.38 951.98 951.3&
-2.48 -1.92 -0.10 -0.10 0.59 1.03 1.38 1.98 1.38
-2.43 -1.90 -0.08 -0.08 0.56 0.95 1.35 2.01 1.35
9/2 11/2 912 912 912 912
712 712 712
9/2 712 912
17 951.98 17 952.42 17 953.28
1.98 2.42 3.28
2.04 2.44 3.26
'4,3 + 54,2
3/z l/2 512 512 312 3/2
17 17 17 17 17 17
945.84 945.84 946.15 946.80 946.80 947.52
-4.16 -4.16 -3.85 -3.20 -3.20 -2.48
-4.17 -4.17 -3.89 -3.23 -3.23 -2.55
Unsplit line:
Obs 36 507.9GC
cak
36 507.a6d
64,2 + 54,1 1312 13/Z 1312 1112 1112 11/2 15/Z 15/2 1512 9/2 912 912
1112 15/2 1312 912 1312 11/z 13/2 17/Z 15/2 712 1112 9/2
1112 11/2 11/2 912 912 912 13/2 13/Z 1312 712 712 l/2
120,12 + 11, ,, 2112 2112 2112 2712 27/2 2712 2312 2312 2312 25/2 2512 2512
21/2 2312 1912 2712 2912 2512 2312 2512 2112 2512 2712 2312
1912 1912 1912 2512 2512 2512 2112 2112 2112 2312 2312 2312
221,21t212,20
912 13/2 11/2 712 11/z 9/2 11/i 15/2 13/2 512 q/2 772 Unsplit line: 1912 2112 1712 2572 27/2 2312 21/2 2312 19/2 23/2 2572 2112 Unsplit line-
36 36 36 36 36 36 36 36 36 36 36 36
502.77 502.77 503.25 505.15 505.15 505.6C' 510.89 510.89 511.51 513.36 513.38 513.0')
Obs 30 011.62‘ 30 30 30 30 30 30 30 30 30 30 30 30
008.85 009.14 009.14 009.59 009.89 009.89 013.14 013.43 013.43 013.94 014.20 014.20
Obs 10 485.40' 10 lo 10 10 10 10 10 10 10 10 10 10
482.70 4e3.03 483.03 483.03 483.37 483.37 487.30 487.63 487.63 487.63 488.02 488.02
-5.19 -5.19 -4.71 -2.81 -2.81 -2.36 2.93 2.93 3.55 5.42 5.42 5.93 C?llC Y.77 -2.48 -2.48 -2.03 -1.73 -1.73 1.52 1.81 1.81 2.32 2.50 2.58 C
-5.28 -5.19 -4.66 -2.88 -2.76 -2.27 2.81 2.91 3.51 5.18 5.35 5.e9 30 011.6gd -2.76 -2.50 -2.46 -2.00 -1.73 -1.70 1.55 l.El 1.84 2.31 2.57 2.60 10 485.53d -2.73
2.25 2.27 2.60 2.62
MICROWAVE
SPECTRUM
OF ClNCO
551
TABLE I (continued)
aAll transition frequencies are in MHz. bEstimated uncertainty in transition frequencies is t 0.10 MHz. 'Hypothetical unsplit frequencies with hyperfine structure removed. dFrequency calculated using the rotational constants and centrifugal distortion constants obtained in the analysis. eFrequency shift due to quadrupale coupling calculated using the constants in Table 111.
TABLE II
Transition 35C114N12C160 31,3 - 21,2
ASSIGNED TRANSITIONS OF CHLORINE ISOCYANATEa'b
Unsplit lineC
Calculated Frequencyd
Distortion corrd
Ground Vibrational State 5.0
17 950.12
1.30
-30 022.23
13.36
24 297.16
24 297.21
-0.51
23 932.54
23 932.69
1.55
30.3 - 21.2
-30 022.24
40,4 - 30,3 4 1,4 - 31,3 41,3 - 31,2
24 674.65
24 674.68
1.87
42,3 - 32,2 4 2,2 - 32,1
24 311.04
24 310.98
8.36
24 316.32
24 316.30
8.37
43,2 - 33,1
24 323.65
24 323.54
19.45
43.1 - 33,0 4 0,4 - 31,3 5 0,5 - 40.4
24 323.65
24 323.55
19.45
-23 675.00
-23 675.14
11.55
30 367.18
30 367.17
-1.00
51,5 - 41.4
29 914.38
29 914.58
1.64
51,4 - 41,3
30 841.96
30 841.92
1.92 10.10
52,4 - 42,3
30 387.76
30 387.71
52,3 - 42,2
30 398.34
30 398.35
10.11
53,3 - 43,2
30 404.68
30 404.57
23.96
53,2 - 43,1
30 404.68
30 404.59
23.96
54,2 - 44,1
30 423.42
30 423.33
43.36 43.36
54.1 - 44.0
30 423.42
30 423.33
50,5 - 41,4
-17 240.58
-17 240.66
9.00
60,6 - 50,5
36 434.24
36 434.24
-1.72
61,6 - 51,5
35 895.56
35 895.62
1.54
61,5 - 51.4
37 008.23
37 008.21
1.69
36 463.78
36 463.75
11.59
36 482.46
36 482.36
11.61
36 485.05
36 485.67
28.22
36 485.85
36 485.72
28.22
36 507.96
36 507.86
51.50
64,2 - 54,1
36 507.96
36 507.86
51.50
65,2 - 55,1
36 537.04
36 537.31
El.43 81.43
62,5 - 52,4 62,4 - 52,3 63,4
53,3
63,3 - 53,2 64,3 - 54,2
65.1 - 55.0
36 537.04
36 537.31
60,6 - 51,5
-10 720.92
-10 720.99
5.64
90,9 - El.8
9 320.90
9 320.96
-10.22
'00,10- 91,9
16 151.15
16 151.23
-17.72
"0,11-'01,10
23 049.59
23 049.66
-26.49
'20.12-"1,ll
30 011.62
30 011.69
-36.59
HOCKING
AND
TABLE II Transition
Unsplit line‘
35C,14N12C160
GkXKY
(continued)
Calculated Frequencyd
Distortion Come
Ground Vibrational State (cont'd)
'30 13-121 12
37 032.40
37 032.41
-48.10
16,:15-l52:14
-36 021.94
-36 022.04
-13.84
'71 M-162
15
-28 462.68
-28 462.75
-51.79
181:17-172:16
-20 824.51
-20 824.51
-93.29
'91,w'82,17
-13 108.93
-13 108.85
-138.48
221,21-2'2,20
10 485.40
10 485.54
-297.78
231,22-222,Zl
18 492.95
18 493.02
-359.27
241,23-232,22
26 568.23
26 568.24
-425.17
251,24-242,23
34 708.94
34 708.78
-495.61
241,24-232,21
-35 027.80
-35 027.70
-151.37
251,25-242,22
-32 536.70
-32 536.67
-164.64
261,26_252.23
-30 279.58
-30 279.60
-173.89
271,2J-262.24
-28 263.55
-28 263.56
-178.38
281,28-2J2,25
-26 495.0‘
-26 495.13
-177.34
2g1,29-282,26
-24 980.30
-24 980.33
-169.96
301,30-2g2,27
-23 724.62
-23 724.58
-155.43
35C,14N12C160 40,4 - 30,3 41,4 - 31,3 41,3 - 31.2 42,3
32,2
42,2 - 32,l 43,2 - 33,1 43.1 - 33.0 40,4
31,3
50,5 - 50,4 51,5 - 41,,4 51,4 - 41,3 52,4 - 42,3 52,3 - 42,2 53,3 - 43,2 53,2
43,l
54,2 - 44.1
24 017.91
1.66
24 792.51
24 792.59
1.99
24 413.00
24 412.99
8.89
24 418.54
24 418.60
8.90
24 426.33
24 426.32
20.66
-0.53
24 426.33
24 426.32
20.66
-25 219.04
-25 219.10
14.14
30 493.34
30 493.44
-1.04
30 020.88
30 021.03
1.77
30 959.21
30 989.25
2.05
30 515.17
30 515.17
10.74
30 526.36
30 526.38
10.76
30 533.70
30 533.05
25.45
30 533.20
30 533.05
25.45
30 553.09
30 552.97
46.05
30 553.09
30 552.97
46.05
-18 743.56
11.44
36 585.40
36 585.44
-1.79
51,5
36 023.12
36 023.27
1.68
- 51,4
37 184.92
37 184.90
1.83
44,0
50,5
41,4
60,6 - 50,5 Y,5
24 398.41
24 017.75
-18 743.52
54,l
61.6
First Excited Vibrational State vz = 1 24 398.20
6235
52,4
‘2,4
52,3
63,4 - 53,3 63,3
53,2
64,3
54,2
64,2
54,1
65,2
55,l
‘5.1 - 55,o
36 616.64
36 616.64
12.35
36 636.46
36 636.25
12.37
36 640.18
36 ‘39.87
30.00
36 640.18
36 639.92
30.00
36 663.64
36 6‘3.43
54.72
36 663.64
36 6‘3.43
54.72
3‘ ‘94.33
36 694.70
86.49
36 ‘94.33
36 694.70
86.49
MICROWAVE
SPECTRUM TABLE II
Transition
Unsplit lineC
35C1'4N12C'6D
OF ClNCO
(continued)
Calculated Frequencyd
Distortion Car?
First Excited Vibrational State v5 = 1 (cont'd)
-12179.19 60,6 - 51,5
.Ba 14 905.62
14 905.70
-16.80
21 864.70
21 864.76
-26.04
28 889.99
28 889.94
-36.68
'30,13-'21,lZ
35 976.10
35 976.09
-48.80
171 16-162 15
-32 410.85
-32 410.91
-25.51
181'17-172'16
-24 679.52
-24 679.55
-69.27
1gl:18-182:17
-16 867.55
-16 867.50
-116.90
'00,10- 91,9 "0.11-'01.10
231 22-222 21 241'23-232'22
15 150.41
15 150.51
-349.37
23 336.83
23 336.83
-418.69
31 591.21
31 591.11
-492.75
24
-34 728.54
-34 728.52
-161.22
2g1:29-282:26
-31 813.55
-31 813.57
-152.95
-30 760.17
-30 760.17
-137.98
251:24-242:23 271 27-'%
,
,
3ol 30-2g2 27
-
Second Excited Vibrational State v5 = 2
50.5 - 40,4
30 611.68
30 611.89
51,5 - 41,4
30 119.98
30 120.22
1.67
51,4 - 41.3
31 127.90
31 128.15
2.28
52;4 - $2.3
30 635.02
30 634.87
11.40
52,3 - 42.2
30 646.40
30 646.59
11.43
53.3 - 43,2
30 654.10
30 653.88
27.12
-1.18
53,2 - 43,1
30 654.10
30 653.91
27.12
54,2 - 44,1
30 675.22
30 fi75.17
49.11
54,) - 44,0
30 675.22
30 675.17
49.11
60,6 - 50.5
36 727.15
36 727.23
-2.04
61,6 - +,5
36 142.09
36 142.16
1.49
62,5 - 52,4
36 760.16
36 760.15
13.06
62,4 - 52,3
36 780.85
36 780.66
13.12
63,4 - 53,3
36 785.10
36 784.83
31.93
63,3 - 53,2
36 785.10
36 784.89
31.93
64,3 - !j4,2
36 E10.08f
36 810.02
58.32
64,2 - 54,l
36 810.0Bf
36 810.02
58.32
65,2 - 55,l
36 B43.21f
36 843.42
92.24
65.1 - 55,0
36 B43.21f
36 843.42
92.24
60,6 - 51,5
-13 839.62
-13 839.64
11.02
'00 lo- 91 9
13 448.62
13 448.64
-14.87
-13 259.17
-13 259.17
-139.08
11 172.71
11 172.71
-329.15
201'19‘~92'1B 23 1'22-222'*, . . 37C,14N12C160 31,3 - 21.2
Ground Vibrational State 17 544.92 17 544.95
40,4 - 30,3
23 742.74
23 742.82
-0.49 1.62
1.30
41,4 - 31,3
23 392.41
23 392.51
41.3 - 31,2
24 105.30
24 105.35
1.83
42,3 - 32,2
23 756.10
23 756.02
8.16
42,2 - 32,l
23 760.94
23 760.95
8.17
43,2 - 33,1
23 768.30
23 768.19
18.97
43.1 - 33,0
23 768.30
23 768.20
18.97
TABLE II Transition 37C,14N12C160 -____ +I,4 50,5
- 31,3 40,4
51,5 - 41,4 51,4 - 41,3 52,4
42,3
52,3
42,2
53.3 - 43,2 53,2
43,1
54,2
44,l
54.1 - 44.0 50.5
41,4
60.6 - 50,5 b1,6 - 51,5 61,s - 51,4 '2,5 - 52,4 62,4
52,3
63,4 - 53,3 b3,3 - '3,2
Unsplit lineC
(continued)
Calculated Freq"encyd
Distortion Corre
Ground Yibrational State [cont'd) -24 000.85
-24 000.91
11.46
29 674.45
29 674.43
-0.96
29 239.31
29 239.44
1.61
30 130.30
30 130.36
1.89
29 695.09
29 694.06
9.86
29 703.9%
29 703.93
9.87
29 710.4%
29 710.36
23.37
29 710.48
29 710.37
23.37
29 723.81
29 728.68
42.28 42.2%
29 728.81
29 728.6%
-17 718.83
-17 718.93
8.98
35 603.42
35 603.46
-1.65 1.52
35 085.53
35 085.57
36 154.52
36 154.47
1.67
35 631.45
35 631.47
11.32 11.34
35 648.83
35 648.73
35 652.68
35 652.59
27.54
35 652.68
35 652.64
27.54
35 674.39
35 674.27
50.23
'4,2 - 54.1
35 674.39
35 674.27
50.23
65,2 - 55,1
35 702.75
35 703.00
79.41
35 702.75
35 703.00
79.41
-11 354.87
-11 354.91
5.71
% 203.30
8 203.34
-9.66
14 867.56
14 867.60
-16.93
21 598.03
21 598.0%
-25.41
b4,3
54,2
65.1 - 55,o 60,b - 51,5 90,9 - *I,.¶ '00,10- 91,9 11 0,11-'01,lO 120 12-1'1 1,
28 390.55
2% 390.57
-35.19
130:13-121:12
35 240.44
35 240.49
-46.33
171,16-'62,15
-30 601.00
-30 601.37
-46.18
-23 160.82
-23 160.32
-86.32
-15 645.78
-15 645.73
-130.03
15 130.62
15 130.71
-343.39
22 994.61
22 994.63
-407.06
30 922.38
30 922.27
-475.10
-31 169.95
-31 169.89
-176.67
271,27-262,24
-29 092.76
-29 092.75
-183.29
2%7,2%-272,25
-27 250.54
-27 250.54
-184.86
2gl,29-282,26
-25 649.13
-25 649.18
-180.63
3ol>30-"2 ,27
-24 294.07
-24 294.06
-169.81
1*1,17-172,16 1g1,1%-182,17 231,22‘222,21 241,23-232,22 251,24-242,23 261,2b-252,23
37C114,,12C160
First Excited Vibrational State v
=
1
50,5 - 40,4 ---2n9fi7--
29 798.1% --
51,5 - ?,4
29 343.95
29 344.02
1.52
52,4
29 818.90
29 818.92
10.42
42,3
-1.09
52,3 - 42,2
29 829.25
29 829.34
10.45
53,3 - 43,2
29 636.26
29 836.24
24.80
53.2
43,l
29 836.26
29 836.25
24.80
54,2 - 44,l
29 055.73
29 855.73
44.92
54,1
29 855.73
29 855.73
44.92
44,o
MICROWAVE
SPECTRUM TABLE II
Transition 37C114N'2C160
Unsplit line‘
OF CINCO
555
(Continued)
Calculated Frequencyd
Distortion Came
First Excited Vibrational State v5 = 1 (cont'd)
60.6 - 50,s
35 751.51
35 751.54
$.6
- 51.5
35 210.90
35 210.94
1.35
%5
- 52,4
35 781.17
35 781.19
11.94
62,4 - 52,3 63,4 - 53.3
-1.87
35 799.44
35 799.41
11.98
35 803.74
35 803.62
29.20
35 803.74
35 803.67
29.20
64,3 - 54,2
35 826.90f
35 826.69
53.34
64,2 - 54,l
35 826.90f
35 826.69
53.34
65.2 - 55.1
35 857.lOf
35 857.27
84.38
35 857.27
84.38
63.3 - 53.2
65.1 - 55,o
35 857.10f -12 790.32
-12 790.34
8.13
13 638.49
13 638.51
-15.57
201 19‘192 18
-11 675.07
-11 675.07
-156.57
231:22-222:21
11 819.00
11 819.00
-330.63
60,6 - 51,5 '%,1a-
91,9
35C,14N12C180 31,3 - 21.2
16 Ground 985.16 Vibrational16 State 985.25 1.23
30,3 - 21,2
-30 315.61
-30 315.69
13.04
41.4 - 31.3
22 646.03
22 646.32
1.48
23 321.56
23 321.37
1.78
22 990.62
22 990.64
7.86
41,3 - 31.2 42,3 - 32,2 42.2 - 32,1
22 995.08
22 995.11
7.00
43,2 - 33,1
23 002.38
23 002.30
18.30
23 002.38
23 002.30
18.30
28 719.10
28 719.06
-0.90
28 306.64
28 306.80
1.58
29 150.56
29 150.50
1.85
20 737.47
28 737.42
9.53
43.1 - 33,o 50,5 - 40,4 51,5 - 41,4 51,4 - 41,3 52,4 - 42,3 52,3 - 42,2
28 746.39
28 746.36
9.54
53,3 - 43,2
28 753.05
28 752.97
22.55
53,2 - 43,l
28 753.05
28 752.98
22.55
28 770.71
28 770.66
40.78 40.78
54,2 - 44,l 54,l - 44,o
28 770.71
28 770.66
50,5 - 41,4
-18 249.96
-18 250.00
8.97
34 457.48
34 457.50
-1.55
'0,6 - 50,5 61.6 - 51,5 61,5 - 51,4 62,5 - 52,4 '294 - 52,3 63,4 - 53,3 63.3 - 53,2 64,3 - 54,2 '4,2 - 54.1 65.2 - 55,l 65,l - 55,0 60,6 - 51,5 '00,10- 91,9
33 966.47
33 966.56
1.51
34 978.89
34 978.81
1.66 10.96
34 483.59
34 483.62
34 499.39
34 499.25
10.98
34 503.80
34 503.69
26.59
34 503.80
34 503.73
26.59
34 524.76
34 524.65
48.46 48.46
34 524.76
34 524.65
34 552.15
34 552.36
76.58
34 552.15
34 552.36
76.58
-12 099.21
-12 099.30
5.84
13 233.94
13 233.99
-15.77
'10,11-'01,1G
19 734.63
19 734.75
-23.85
'30 13-721 12 77 l'1b-162',5 . .
32 911.39
32 911.43
-43.76
-33 129.56
-33 129.70
-37.98
HOCKING AND GERRY
556
TABLE II Transition 35C114N12C'8D '81.17-'72,16
Unsplit lineC
(continued)
Calculated Frequencyd
Distortion Corre
Ground Vibrational State (cont'd) -25 957.86
-25 957.88
-76.23
-18 714.69
-18 714.68
-117.85
201'19-1g2'18 "1 18-"2 17
-11 401.51
-ii 401.43
-162.98
231:22-222:21
10 943.11
10 943.25
-320.81
241 23-232 22 25 "24-242'23
18 520.72
18 520.77
-381.33
26 159.78
26 159.76
-446.02
261:25-252:24
33 853.23
33 858.10
-514.96
241 24-232 21
-37 140.25
-37 140.17
-147.56
251'25-242'22
-34 582.99
-34 582.95
-163.39
261:26-252:23
-32 231.88
-32 231.90
-176.06
271 27-262 24
-30 093.48
-30 093.52
-184.94
28"28-272'25
-28 173.93
-28 173.99
-189.84
3ol:3D-2g2:27
-25 014.01
-25 0'3.98
181.95
50.5 - 40,4
28 839.44
28 839.56
51,s - 41,4
28 408.97
28 409.11
1.50
51.4 - 41.3
29 290.10
29 290.26
2.0' 10.03
First Excited Vibrational State V. = 1
.-
52,4 - 42,3 52,3 - 42.2 53.3 - 43,2 53.2 - 43,l 54,2 - 44,1 54,1 - 44,o 60.6 - 50,s ?,6
- 51,5
'2.5 - 52,4 62,4 - 52,3 63.4 - 53,3 63,3 - 53,2 64,3 - '4,2 64.2 - 54.1 65,2 - 55,1 65,l - 55,o 60,6 - 51.5 '00,10- 91,9 201 19-192 18 241:23-232:22
=
-1.02
28 858.98
28 858.98
28 868.28
28 868.42
10.06
28 875.54
28 875.45
23.84 23.84
28 875.54
28 875.46
28 894.29
28 894.20
43.lG
28 894.29
28 894.20
43.16
34 601.72
34 601.76
-1.76
34 098.11
34 089.20
1.35
34 629.36
34 629.38
11.51
34 645.97
34 645.89
11.55
34 650.84
34 650.64
28.08
34 650.84
34 650.69
28.08
34 673.12f
34 672.86
51.27
34 673.12f
34 672.86
51.27
34 701.96f
34 702.25
81.08
34 702.25
81.08
34 701.96f -13 501.09
-13 501.11
8.20
12 030.95
12 030.97
-14.44
-14 949.30
-14 949.30
-142.08
15 369.26
15 369.26
-371.23
aAll freqwncies are in megahertz (HHz). b Estimated uncertainty in transition frequencies is iO.10, except where otherwise indicated. c Hypothetical unsplit frequencies with hyperfine structure removed. dFrequency calculated using the rotational constants and centrifugal distortion constants obtained in the analysis. eOeviation between the calculated frequency of the adjacent column and that ca'culated using the derived rotational constants in a rigid rotor approximation. f Estimated uncertainty is 0.3 flHz (quadrupole strxture unresolved).
_MICROWAVE
SPECTRUM
OF ClNCO
557
where
do = Fl(Fl+
1) -
11(11f
1) -
J(J
+
I),
-41 = F(F + 1) -
I*(12 + 1) -
Fl(F, + l),
A2 = IlVl +
JV
Fl(K
1) -
+
1) -
+
1).
is the average value of the square of the angular momentum along the u-inertial axis, and W (b,) is the Wang reduced energy, with b, Wang’s asymmetry parameter; both (Pa2) and W (b,) were evaluated to sufficient accuracy in a rigid rotor basis. The quadrupole coupling constants of interest are xaa and xbb - xec for each nucleus. Using Eq. (I), a least-squares fit was made of the measured first-order splittings up to J = 30 for the quadrupole coupling constants of all isotopic species in all observed vibrational states. The results are collected in Table III. The nuclear quadrupole hyperfine structure could then be subtracted off the rotational transitions, and the resulting frequencies used in the subsequent analysis. (Pa2)
Rotational and Centrifugal Distortion Constants It was necessary to account for centrifugal distortion in order to obtain accurate rotational constants. To first order the energy expression for a semirigid asymmetric rotor may be written as (8) E
= E, + ED,
(2) TABLE
NUCLEBR QUADRUPOLE COUPLING Vibrational State Ground Xa.(lP X&(l) xm (2)
III
CONSTANTS
35C1’4N’2C’60
OF CHLORINE ISOCYANATE 3,tJMN”ZC’“G
(MHz)
36C1’4NBC’BG -
-71.13 -4L.59 3.99 1.96
f f f f
0.13” 0.07 0.09 0.04
-56.61 f -33.15 i 4.14 f 2.00 f
0.15 0.09 0.10 0.04
-69.82 f -43.81 * 4.02 f 2.00 f
0.18 0.10 0.11 0.06
First Excited (0, = 1) x0.W Xbb(l) - Xc*(l) x00 (2) Xbb(2) - x..(2)
-71.39 -43.06 4.12 2.10
f f f f
0.20 0.16 0.14 0.10
-56.57 -33.58 4.29 2.04
0.36 0.32 0.18 0.22
-69.56 -44.31 4.13 2.09
0.39 0.44 0.22 0.26
Second Excited (~5 = 2) xm(l) Xbb(1) - XW(1) x00 (2) Xbb(% X.42)
-70.99 zk 0.47 -43.52 f 0.35 3.78 f 0.23 2.10 f 0.24
Xab(2)
-
XWU) Xm(2)
a Chlorine is nucleus 1; nitrogen is nucleus 2. b Errors cited are twice the standard errors.
f f f f
f f f f
HOCKIXG
558
AND
GERRY
ER = %(B + C)J(J + 1) + M - ?Ji@ + C)W(b,), Eo =
?,65r&apo (Pa2Pp2 + PB”P~.“>.
(3) (4)
Here E, is the rigid rotor energy, and ED is the first-order centrifugal distort.ion c;)rrection. The 7&uaa are related to the centrifugal distortion constants by and ~&,ab = fi4(7aapB + 27u~c1~) ; a, /I can be a, b, or c. Expres~uaolo!= fi4 ~aCW2a sions for the average values of the angular momentum operators in the rigid rotor basis are given elsewhere (9, 20). It has been shown (10) that in general it is possible to determine at most only five combinations of the T’S from a rotational spectrum. The energy cxpresuion can be rewritten with Ex = >4(B + c)J(J Eu = -d.,J”(J
+
+ 1) + [A 1)” - dmJ(J
>;(B
+ l)(P,‘, -
+ C)]W(b,)
= Wo,
(5)
- &(P:) dw, WoJ (J + 1) -
rZwzcWo(P,2).
(6)
B, 8, 6, differ from A, B, C by a small centrifugal term. An attempt was made to fit by least squares all transitions with J 5 30 to the five distortion constants, with linear variations of the rotational constants being allowed. However, a stable fit could not be found, though apparently good values of the rotational constants were obtained. On the other hand, it was possible to make stable fits to four constants, wit’h either & or dwKneglected. The rotational constants thus obt.aincd were in excellent agreement with those of the first analysis, but c~onsistcnt, values of all the distortion constants were not found. An alternative treatment was also carried out. It is shown in the fOll(J\viIlg section that chlorine isocyanate is planar; in this case constraints exist which enable the number of determinable constants to be reduced from five to four (10, 11). The constraints are strictly applicable when the rotational constants are the equilibrium constants. Since these are not available a good approximation was made by using the ground state constants, and a lea&squares fit \vas made to the four centrifugal distort.ion constants T,,,,,, , ~i,bb~, , 7,bab, 7,&b, vi&h linctar variations of the rotational constants again being allowed. The results are collected in Table IV. Once again rotational csonstants ivere obtained -c\-hicall were in excellent agreement with those determined in the previous analyses. Four determinate 7’s were also obtained; in particular 7naa(ln-as found to bc very large. r\‘o attempt was made to include higher order or P” t,erms in the analysis. As a check the analysis was carried out, wi-ithJ 5 25; the results agreed with thosct of Table IV to within experimental error. A varia,tion of the latter procedure n-as alno used in which t’he relations linking the 7’s included the ground state values of A and B and a value for C adjustSed to make the inertial defect zero. The results of this analysis are also given in Table IV; the rotat’ional constants and two of the distortion constants agree well with
MICROWAVE
SPECTRUM TABLE
559
OF ClNCO
IV
ROTATIONAL CONSTANTS AND CENTRIFUGAL DISTORTION CONSTANTS OF 36C1i~NWi60 IN THE GROUND VIBRATIONAL STATE USING DIFFERENT METHODS OF ANALYSIS (ALL VALUES IN MHz) Analysis A
B
c 7...a Tbbbb Toabb T.bab
1s 51 576.21 3 130.588 2 945.171 -59.138 -0.01075 0.6923 -0.0101
f f f f f f f
IIb 0.130 0.006 0.005 0.094 0.00005 0.0016 0.0012
8 In the relations reducing the number of determinable rotational constants were ground state constants. b In the relations reducing the number of determinable ground state values of A and B were used, with C adjusted c Errors cited are twice the standard errors.
51 576.22 3 130.591 2 945.166 -59.141 -0.01075 0.6992 -0.0175 distortion
f f f f f f f
0.13 0.006 0.005 0.096 0.00005 0.0016 0.0012
constants
to four the
distortion constants to four the to make the inertial defect zero.
those of the previous calculation, but the others do not; indeed T&b is different by a factor of nearly two, well outside experimental error. Table V contains the rotational and centrifugal distortion constants of each isotopic species studied in each vibrational state. The values given were obtained by analysis for three rotational constants and four distortion constants, in which the rotational constants for the particular vibrational state being studied were used in the relations reducing the number of determinable distortion constants to four. Some care must be taken in interpreting the results in Tables IV and V. It is clear, for a start, that the distortion analyses have yielded accurate rotational constants, which can be used for determination of the internuclear parameters. A similar phenomenon has been observed previously (12’). The meaning of the distortion is less clear. Evidently, the correct order of magnitude was obtained, though the variations noted above suggest that our fits to four constants have not given values entirely meaningful physically, and that these can be obtained only through a full fit to five constants using further branches. Unfortunately, insufficient transitions were observable in the frequency range of our spectrometer to enable such a fit, and we must be content with the reliable values of the rotational constants. MOLECULAR
STRUCTURE
It was originally anticipated that chlorine cyanate might exist in one or both of two forms, having formulas ClOCN or ClNCO, with the latter being more probable, analogous to HNCO, CH3NC0 and SiHsNCO. Both these forms were expected to be planar.
560
HOCKING
AND
TABLE
GERRY V
ROTATIONAL CONSTANTS AND CENTRIF~JUL DISTORTION CO~VST.~NTS~ Vibrational State
3sC1’4N’2C’60
s7C,I4NrJC’60
Ground -4
51 576.21 3 130.588 C 2 945.171 7.004 -59.138 7bbtd -0.01075 zaabb 0.6923 Tab& -0.0101 First Excited (0, = 1) 11 53 261.08 B 3 147.363 c 2 953.772 7o.ao -70.308 76bbb -0.01116 7aabb 0.7572 Tabd -0.0242 Second Excited (2~5= 2) A 55 137.02 B 3 163.210 c 2 961.743 7.(10(1 -84.24 7bbbb -0.01217 S,.bb 0.760
B
lsCt”N’2Cy)
_
.___ f f f * f f i
0.13~ 0.006 0.005 0.094 0.00005 0.0016 0.0012
51 256.45 3 057.596 2 879.465 -58.428 -0.01027 0.6718 -0.0093
f zt f f f zt f
0.13 0.005 0.005 0.094 0.00005 0.0019 0.0016
50 689.75 2 957.234 2 788.544 -57.524 -0.00957 0.6460 -0.0098
f zt * f f rt f
0.22 0.009 0.009 0.155 0.00007 0.0941 0.0034
52 912.96 f 3 073.943 f 2 887.988 f -69.29 zk -0.01118 f 0.673 f (1
0.48 0.021 0.050 0.30 0.00089 0.105
52 305.62 f 0.61 2 973.065 f 0.032 2 796.934 zt 0.069 -68.13 f 0.45 -0.01046 I!Z 0.60112 0.649 zk 0.140 r/
f zk f f zk f
0.67 0.036 0.075 0.51 0.00120 0.153
constants
to four used the rotational
zt f zk f It zk &
0.15 0.006 0.006 0.113 0.00005 0.0018 0.0013
Cl
rczb(ib _
8 The relations reducing the number of distortion constants for the appropriate vibrational state. h All frequencies are in MHz. 0 Errors cited are twice the standard errors. ClValues indet,erminate.
In Table VI are given the principal moments of inertia and inertial defects of all isotopic species studied. The inertial defects in the ground vibrational state are all small positive numbers, which change little with isotopic substitution, and arc thus consistent with a planar structure. Furthermore, the changes in principal moments of inertia on isotopic substitution of oxygen are all large; for the structure ClOCN the oxygen atom is very near the b-inertial axis and subst’itution of oxygen wou!d thus cause only a very small change in IBo. The isocyanate structure, ClNCO, is thus confirmed. The isocyanate configuration is consistent with the quadrupolc coupling of nitrogen. In the structure ClOCN, the CN bond can be assumed to be a principal axis of the quadrupole tensor, and the nitrogen coupling constant along this axis should be about -4 MHz (13). Consequently, if this bond mere symmetric
MICROWAVE
SPECTRUM TABLE
OF ClNCO
561
VI
MOMENTSOF INERTIAAND INERTIALDEFECTS*OF CHLORINEISOCYANATE Vibrational State
3bCl14N12Cl60
Ground zAb
ZB
ZC AC First Excited (~5 = 1) IA IS
9.798 915
161.436 4 171.599 9 0.364 5 9.488 935 160.576 0
IC 171.100 2 A 1.035 2 Second Excited (115= 2) IA 9.166 090 IB 159.771 5 zc 170.639 7 A 1.702 1
9.860 165.290 175.515 0.365
044 3 6 3
9.970 170.899 181.238 0.368
277 9 3 1
9.551 164.411 174.997 1.034
363 3 6 9
9.662 169.989 180.694 1.042
268 9 6 4
a In amu bz.
b Calculated from rotational constants of Table VI using conversion factor 505391 amu bz MHz. eA = 1~ - 1~ - IA
xcc should be +2 MHz, in sharp contrast to the observed value of in molecules, such (CNh and CH1 SCN (15), this bond has found quite asymmetric, even a similar large asymmetry ClOCN a positive value of xcc would found in the present molecule has a small positive value (+3.99 thus of the order that found HNCO (+2.0 MHz) (16) and CHSNCO MHz) (15). This than the value xcc, however, because the ainertial axes three molecules. Both constants, however, tend rule out the structure With the planarity order of atoms established, the internuclear parameters were (17) was to locate the atoms which isotopic substitutions were In method one isotopic species (here the abundant, 35C114N12C160) is as a basis; the substituted atoms are located basis molecule using Rraitchman’s (18) for a rigid both chlorine were easily obtained this To determine four remaining coordinates five equations were available, namely, mass conditions product of inertia condition CiTn
HOCKING
562
AN11 GERRY
Three combinations of these five relations were used to locate these atoms. In all of them the center of mass conditions were used, along with two of the romaining three relations. The resulting structures are given in Table VII. Of these three the one preferred is that calculated by method I, which used the product of inertia condition and reproduced IBo. Since both chlorine and oxygen are near the u-principal inertial axis, the magnitudes of their b-coordinates arch small and rather inaccurate (17); thus the coordinates of nitrogen and carbon, when obtained by reproducing I.,‘, are similarly inaccurate. On the ot1~c.r hand, the u-coordinates of chlorine and oxygen are large in magnitude, and thus more reliable; consequently, a better det’ermination of the coordinates of carbon and Furthermore, only tllc n-. nitrogen can be expected when I Bo is reproduced. coordinate of carbon is in practice obtained from Ieo, since nitrogen, being Neal the b-axis, contributes effectively nothing to this principal moment. Thr: a-coordinate of nitrogen is determined almost exclusively by the center of mass condition, which is the most accurat’e equation for locating atoms near a principal plane (17). The principal axis system of chlorine isocyanate is shown in Fig. 1. It is seen from Table VIII that the derived internuclear distanccbs are vcrj reasonable. The CliK length is very near, though slight,ly less than, the sum of the single bond radii (l.T3A) (19). The NC and CO distances are very nt’ar t,hosct of other isocyanates. The most surprising feature cJf the structure is the bend in the NC0 chain of about S” away from chlorine. This is to the authors knowledge the first case where such a bend has been observed in an isocyanate, though R similar bend was found in isoelectjronic chlorine azid(t (J). Our internuclear parametcbr:i TABLE
VII
COMPARISONOF MOLECUL~~~STRUCTURES OF CHLORINE ISOCT.\N.~TE OBT.UIUIW USING DIFFERENT CAI,CUL,YTION METHODS
__
Method Ia r(C1-N)d r(N-C)d r(C-0) < GINC) < (NCO)’ ____
1.703 1.218 1.165 119” 22’ 171” 24’
f + i f f
0.011~ 0.012 0.008 1” 1” 30’
Method 11”
Method IIIc
1.714 1.206 1.173 118” 26’ 169” 59’
1.706 1.2“4 1. 163 118” 45’ 170” 38’
a Nitrogen and carbon located using the center of mass and product tions, and reproducing ZBO. b Nitrogen and carbon located using the center of mass and product tions, and reproducing lao. 0 Nitrogen and carbon located using t.hr center of mass ronditions, IAO and IBO. d All distances in Angstroms. B Error limits are outside limits of error obtainrd by comparing t,he calculation. f Cl and 0 are trans in all cases.
of inertia
wndi-
of inertia
condi-
and reproducitlg
three met hods of
MICROWAVE
SPECTRUM
OF ClNCO
563
are in excellent agreement with the electron diffraction results of Oberhammer (SO). Here the structure with a bent NC0 chain was strongly suggested, but the data could not distinguish between it and one with a linear NC0 chain, though the former was preferred in the light of the known bond lengths of other isocyanates. From our resu1t.s we concur with this deduction. To confirm further whether the bend is real the posit.ions of carbon and
FIG.1.Positions
of the atoms in the principal TABLE
axis system of chlorine isocyanate. VIII
STRUCTURAL PARAMETERS OF CHLORINE ISOCYANATE COMPARED WITH THOSE OF SIMILAR MOLECULES
-
Molecule
r(Cl-N
ClNCO* HNCO (6) F3SiNC0 (3) H $iNCO (3) C13SiNCOb H&NCOc
1.703
CINI (4) ClNOd CINOze
1.745 1.975 1.840
)
r(N-C)
r(C-0)
< (NCO)
1.218 1.207 1.190 1.216 1.219 (1.190’ (1.207’
1.165 1.171 1.168 1.164 1.139 1.18’ 1.171’
171” 24’ 180”’ 180”’ 180°’ 180”’ 180”
< (XNC) 119” 22’ 128” 5’ 160.7” 151.7” 138.0” 140.1”) 140.0”)
(X (X (X ;$
Cl) H) Si) ;; i (X = C)
* This work. b R. L. Hilderbrandt and S. H. Bauer, J. Mol. Slructure 3, 325 (1969). c Reference (16). d D. J. Millen and J. Pannell, J. Chem. Sot. 1322 (1961). e D. J. Millen and It. M. Sinnott, J. Chem. SOC. 350 (1958). f Assumed. g Microwave spectroscopy. h Electron diffraction.
= = = 1
Method M.W.g M.W. E.D.h E.D. E.D. M.W. M.W. M.W. M.W.
564
HOCKING AIW GERRY
nitrogen were obtained by using the center-of-mass conditions and the product of inertia equation, and constraining the NOCO chain to be linear. The resulting NC and CO lengths were 1.309 and 1.111 A, respectively. Since both bonds are multiple bonds, these lengths are unreasonable in comparison with those of othw isocyanatcts. Also this structure predicts a value for lee differing from t(hc c,xpcrimental one by 2 amu p. It thus seems certain that the bend in the NC0 chain in real. 1) ISCUSHIOPU‘ The deduced planarity of t’hc molecule is COnSiStent with several other features of its microwave spectrum. In the first place, the out-of-plane components IJ~ the nuclear quadrupole coupling tensor, xcc , are the same for both species cont,aining 3”C1. Furthermore, thr ratio xcc (3”C1)/~ec (37C1) = 1.267; this agrws well with the ratio of the quadrupole moments of the two isotopes [Q (“%1)/Q (“‘Cl) = 1.86883. Secondly, it has been shown (21) t,hat for a planar molecule a good approximation to the ground vibrational state inertial defect A is given by A = 4K/wl , where K = 16.863 amu k cm-’ and ~2 is the frcqurncy of th(J lowest in-plane vibration. Using our rxperiment’al value of A, wi is found to bc IS.5 cm-‘. This is in very good agreement with the frequencies measured in t,he Raman spectrum [WI = w5 = 199 cm-l in the solid and 174 cm-’ in the liquid (.B)], as well as with t,hat deduced from the relative intensities of molecules in excited vibrational states [< 200cm-‘]. This low vibration frequency is also conskt’cnt with the large centrifugal distortion. The irkrnuclcar parameters of chlorine isocyanate are shown in Table VIII, along with those of related molecules. Since the ClN bond length is near the sum of the chlorine and nitrogen single bond radii (19), and since the NC0 chain is near linear, thr following resonance form is probably the major one:
Cl \
N=C=O
To determine the degree of any possible double bond character of the ClN bond the principal values of the chlorine nuclear quadrupole coupling tensor were determined for 35C1’4N’2C’60 in its ground vibrational state. With the assumption that one principal axis of the quadrupole coupling tensor coincides with the ClN bond the coupling const’ants were transformed from the inertial axis system to the principal axis system (z parallel to t’hc Cl?; bond, y perpendicular to the molecular plane). The principal values obtained were xzz = 64.20 MHz, xVzl = XCC= 56.86 MHz, xz. = - 121.06 ;\IHz. The difference xz2 - xyU gives a measure of the double bond character of the ClN bond (23, 24); this value is 4YX.
MICROWAVE
SPECTRUM
56:’
OF ClNCO
likely
, parallel to the ClN bond, is very near that of the chlorine atom. Since chlorine and nitrogen have essentially the same electronegativity, such a value is to be expected if the ClN bond is essentially covalent (7) ; similar values have been observed previously (25-27). Indeed [ xzt 1 = 121.06 MHz is larger than 1xc1 ato,n/ = 109.7 MHz. Now, the double bond character of the ClN bond should decrease / xzz / from 1xc1 atorn1, but the effect of ionic character is to increase it if the positive pole of the ClN bond is on chlorine. Possible resonance forms in which this occurs are: cl+
N=C=O
cl+ NZC-o-
(III)
(IV)
Any shortening of the ClN bond by double bond character should be counterbalanced by this ionic character, and therefore a ClN length close to the sum of the single bond radii is not inconsistent. With the assumption that hybridization of chlorine can be neglected, and with application of the charge-screening correction (7), the ionic character is found to be 9 %; as a result, the single bond character is 87 %. These figures must be viewed with caution, however, because of the neglect of overlap and hybridization, both of which can have a significant effect on ionic character calculations (28, 29). ACKNOWLEDGMENTS We acknowledge gratefully the support of the National Research Council the form of research grants and a scholarship to one of us. (W. H. H.). RECEIVED:
of Canada
October 12, 1971 REFERENCES
1. E. NACHBAUR AND W. GOTTARDI, Monatsh. 97, 115 (1966). 2. M. C. L. GERRY, J. C. THOMPSONAND T. M. SUGDEN,Nature 211,846
(1966).
in
HOCKING
561i
ANI)
GERBY
3. W. AII~EY, C. GLIDE~~ELL, A. G. K~UIETTE END G. M. SHELDRICK, J. Mol. Struclnre 6, 435 (1971). Q. IL. L. Coors AND M. C. L. GERRY, J. Chem. Phys. 63,2525 (1970). .5. 1~. H. JONES, J. N. SHOOLERY, R. G. SHUIX\Z~ ANU D. M. YOST, J. Chem. Phys. 18,990 (1950). 0. J. BARDEEN AND C. H. TOJ~NES, Phys. Rev. 73, 97 (1948j. Spectroscopy,” Mc(;raw-Hill, New 7. C. H. TO\%-iXES AND A. I~. ~EI.\\I.LOW, “Micrownve York,
1955.
8. 11. KIVELSON _~NDE. B. WILSOX, JH., J. Chew. Phyr. 20, 1575 (1952). 9. R. L. Cook;, J. Chem. Phys. 42, 2927 (1965). f0. J. K. G. W.~TSON, J. Chem. Phys. 46, 1935 (1967). 11. L. PIERCE, N. DICIBXNI .\NDR. H. JXBSON, J. Cham. Phys. 38, 730 (1963). 12. G. E. HERBEHICH, R. H. J.~cKso~; ibid D. J. MILLEN, J. Chem. Sot. A336, (1966). 13. W. B. Molv~z AND H. S. GUTO~SKY, J. Chem. Phys. 38, 1155 (1963). 14. L. PIERCE, IL. NELSON BND C. THOMAS, J. Chem. Phys. 43,3423 (1965). 15. l<. G. LETT AND W. H. FLYG.II
24. 25. 26. 27. 28. 29.
L. PAULING, “The Chemical Bond,” Cornell University Press, Ithaca, NY, H. ORERH.\MMER,2. Natnrforsch. d26, 280 (1971). I>. 1~. HEKSCHBICH xw V. W. L.~URIE, J. Chem. Phys. 40, 31Q (1964). E. H. KYSEI, -\NDl+J.NxHB~~I~, 2. Anorg. illlgewt. Chem. 381, 71 (1971). R. BEKSOHN, J. Chem. Phys. 22, 2078 (1954). J. H. GOLDSTEIN, J. Chem. Phys. 24, 106 (1956). H. 0. HOOPER AND P. J. BRAY, J. Chem. Phys. 33, 334 (1960). II. K~sHI\%T~\GI, I). NAKAMURI END M. Kuno, Tetrahedron 21, 1095 (1965). It. M. HART AND M. A. WHITEHEIU, Trans. Faraday Sot. 67,1569 (1971). W. (;ORDY, Discuss. Faraday Sot. 19, 14 (1955). 1:. H. JXKSOX AND D. J. MILLEN, Advan. Spectrosc. 3, 1157 (1962).
1960.