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Microwave spectrum, structure, quadrupole coupling constant, and force constants of NSCl
JOURX
\I, OF MOLECUL.11~
SPIWTROSCOPY
36, 386-397 (1970)
Microwave Spectrum, Structure, Quadrupole Coupling Constant, and Force Constants of NSCI TATSURO BEPPU,~ EIZI HIROTA,~ AND YOKEZO ~.~ORINO~ Departmenl
of Chemistry,
Faculty of Science,
The I;niversiiy
of Tokyo, Hongo,
Tokyo, Japan
Microwave spectra of the NSCI molecule were observed by pumping the products of thermally decomposing N3S&13 continuously through the cell. The rotational constants were obtained for 14N32S35C1,14N32S37C1,14N~4S36C1, and 16N32S36C1,all in the ground vibrational states. The r8 structure calculated from these rotational constants is the configuration N=S-Cl with 0 0 r(NS) = 1.450 A, r(SC1) = 2.161 A and LNSCl = 117”42’. The nuclear quadrupole coupling constant of W!l in the 1sN32S36C1species is determined to be ~a6 = 23.51, and xec = 15.00 MHz, which corresponds to xbond Xaa = -38.51, of -43.36 MHz. In addition to the ground-state spectra, several sets of vibrational satellites were observed and assigned to the ~2 , vg , 2~2 , and 2~3 stat,es. The vibrational increments of the inert,ia defects, A2 and A3 , are combined with two known vibrational frequencies, ~1 and 02 , to calculate the force constants. The value of ~3 , 261 cm-l, calculated using the inertia defect increments is in agreement with 273 cm+, estimated by Miiller and others from the infrared spectra. Redundancy among the three inertia-defect increments is noted for triatomic molecules with the C, symmetry, and its consequence is discussed briefly.
The NSCI molecule was first detected by Glemser and Richert (1) through its infrared spectrum in the reaction of chlorine gas with NSF, though Meuwsen (2) reported long ago that NSCl seemed t,o be formed as an int,ermediate in the synthesis of N3S3C13 by passing chlorine gas into carbon tetrahcloride suspension of S3N2C12 prepared from N4S4 and S2C12. Glemser and Richert’ observed an infrared absorption band at 1322 cm-l, lower by 50 cm-l than the KS stretching band of NSF. Judging from the similarity in t,he band shape of t’hese two bands, t,hey presumed that, t,he band at 1322 cm-l was due to the NS stretching vibration of the KSCl molecule. It, x\-as discovered (5, 4) that S3NzC12 was conveniently prepared from am1Present Kawasaki. 2 Present
address:
Central
address:
Department
Fukuoka. 3 Present address:
Research
Laboratory,
of Chemistry,
Sagami Chemical
Research
gawa, Japa.n. 386
Tokyo
Faculty
Shibaura
of Science,
Electric Kyushu
Co.,
Ltd.,
TJniversity,
Cent,er, 3100, Ohnuma, Sagamihara,
Kana-
MICROWAVE
SPECTRUM OF NSCl
3%
monium chloride and sulfur chloride and that S3NzC12 was easily converted to S,K&l, , SJSkY, or S3N&13 . The 1322 cm-l absorption band was used to confirm the formation of the NSCl molecule when these sulfur nikogen chlorides were heated (3). NSCl and other sulfur nitrogen chlorides were also formed in the reaction of SK% vapor with active nitrogen, the formaGon of NSCl being identified by its infrared absorption band (4, 5). Information on the molecular structure of NSCl was first obtained by Mi.iller et a/. (6). They calculated force constants from three observed vibrational frequencies vl = 1325, v2 = 414, and v3 = 273 cm-‘, neglecting cross terms in the potential function. The force constants were found to be similar to those of NSF: for instance, the calculated force constant for NS stretching is very large and close to that of NSF. From this fact and bond-order calculation, they concluded that the arrangement of atoms in NSCl was not, S-N-Cl but N-S-Cl, similar to iSSF for which microwave spectroscopy clearly indicated the structure of N-S-F (7,). In t)he present study, the microwave spectrum of t,he NSCl molecule was observrd for precise determinat’ion of its molecular structure. EXPERIMENTAL
METHODS
The sample of NSCl was prepared by heating N3S3C13 to about 70°C under high vacuum and was led to an ordinary 3-m waveguide cell t,hrough a capillary tube. Rapid decay of the NSCl molecule in the cell made it, necessary to pump the sample continuously through t’he cell. The compound N3S&& was synthesized by the following process: ammonium chloride and sulfur were suspended in sulfur monochloride placed in a flask which was connected t,o a long tube terminated with a calcium chloride column. When heated, a red substance, presumably SJSJ& , was deposited on the wall of t,he tube. The tube was then connect,ed to the second flask with a side arm, through which chlorine gas was introduced to react wit’h the red deposits. The N$$13 thus formed fell down gradually with sulfur dichloride to the bottom of t’he flask After completion of t,he reaction sulfur dichloride \vas pumped off. The MC1 molecule was also formed by an electric discharge through a mixture of t,he N, and SZCIZ vapor. The microwave spectrum was observed using a 60-cm Pyres cell, which had been built for the detection of free radicals (8). Because the spectrum thus obtained was weak and the optimum condition of the reaction was difficult t’o maintain, all absorption lines used for the analysis were observed lyith the sample prepared by t,he first met,hod. The spectrum of 15N32S35C1n-as observed with t,he sample containing l5N enriched to 1.i at. %. After mixing 1.5.4 g of l5N-enriched ammonium sulfate wit,h 25 g of barium chloride and 100 ml of water, stirring and filtrating out the precipitates of barium sulfate, the aqueous solution of 15S-enriched ammonium chloride was evaporated. Then 11.5 g cf ammonium chloride thus c;btained was
BEPPU,
388
HIROTA,
AND
TABLE TRANSITION
FREQUENCIES OF NSCl
IN THE
MORINO
I GROUND VIRR~TI~N~L
ST.ITE
(MHz)
Obs ll,a~ln,I
37
983.1
0.1
21,1-20,?
38
361.72
0.27
38
340.96
31.?-3”.3
38
934.40
0.02
38
d83.7i
0.68
0.03 -0.26
36
883.0
0.2
36
706.72
37
264.42
-0.2’)
3i
079.88
0.17
37
842.35
-0.48
37
64l.i2
0.08
38
624.08
0.12
41,ado,r
39
iO6.7.3
39
617.1G
51.4-50.6
40
6:,0.41
-0.35
40
546.83
-0.39
39
Hii.
61.sr6a.s
41
833.52
-0.29
41
683.50
-0.55
40
5fi3.54
-0.14
71.6-70.7
43
32i.0
0.6
43
037.i
-0.8
42
282.5
-0.2
41
Y87.25
-0.85
81,7r80,8
45
005.0
44
620.9
-2.1
43
982.2
-0.6
44
283.33
-0.3
0.19
A”
O.OR -0.08
11.1-00.0
45
460.22
0.00
45
264.20
0.00
44
005.32
0.01)
21,2r10,1
52
93i.9
0.5
52
546.4
0.4
51
304.06
0.08
lI,Ir20.?
21
YO3.Y
0.5
22
349.7
0.1
21
001.94
0. x3
3W20.?
60
228.4
0.4
59
651.8
0.8
58
418.62
0. 62
il 4 = obs
-
0.00
talc.
employed for small-scale g, the overall yield being The spectrometer used kHz oscillator as a Stark perature.
synthesis of 151Y3S3C13. The N3S3C13 obt,ained was 1.1 about 5.8%. u-as of conventional Hughes-Wilson type Lvith a 110 modulat’or. The speckurn Teas observed at room t,em-
RESULTS
A. Rotational Spectrum XSCl is a bent triatomic molecule of a nearly prolate symmetric top. Since the dipole moment has components both along the a- and b-axes, t’he a- and b-type transitions are expected but all the observed transitions were of the b-type, because the u-component of the dipole moment is smaller than the b-component. In Table I are listed unsplit frequencies of t,he observed transitions nhen correct’ed for hyperfine structure. The assignment, was first made for the b-type Q-branch series, J1,.,-_-l+ Jo,, , then extended to R-branch transitions. The spins of nitrogen and chlorine nuclei (1 and 3/2, respectively) couple \\-ith the molecular rotation to give complicat,ed hyperfine struct,ures for the rotational spectrum of NSCl. The assignment was greatly facilitated by the use of the fact that the quadrupole hyperfine splitting due to chlorine nucleus is much larger t*han t,hat due to nitrogen nucleus. The b-type Q-branch series mentioned above gave the rotational constant A - C and the asymmetry parameter K, whereas A + C was determined by the b-type R-branch lines. Centrifugal distortion effect was ignored in the analysis, because the transitions observed were between levels with rather small quantum numbers. The spectra of the YV32S35C1,~4N3%37C1,and 14N34S35C1were observed with the
MICROWAVE
SPECTI:T’RI
OF NM’1
:w
Rotational constants, s;:~mple containing these species in natural abundance. asvmmetrv parameters K, and inertia defectjs of thca four spwies are given in T:ible II. U In thr course of searching, the spwtra in two recited \-ibrational st:ltw \vtw~ found. Hy comparing their intensi&s \yith thaw of the ground-statcb linrs, t II(~ S- 4‘1 bending nltdc~ stronger one \vas assigned to the first excited state of the S I’:: (281 cm--‘), md the weaker one to that of thtl S-C’1 stretching modts 1~~(11-k CI~--~). &Ycouple of lines in the second tlscittd statw of botll v:( mtl vL’ u t’rt’ :LIs) ohst!rved. l’hr center frequencies mtl tlw rot:ltioll:il cv)nst;mts tlrrived from I III~I~~ :IIY’ listctl itI Tables III and IT.
-
h
1, II 1.
,:,tIIII
0. %30”20 , _ 1%. llG(is
.\‘)I
122.873s
1:15.210,, 0.220.I .s
-!,
- o.!!812:j:i
- 0.979455
--IJ.‘l7OXL’4
12.14541:
lX.4(il., l:B.fw, 0
2:x$>
” (‘tbrlvprsitltl factor used is 505 531 nmu .\’ RlHz.
IL
0
It,,,
, L’,,,, 3, ” :3,,,.. 4, :< -I,#,I , 5, / 311, fi,,, fi,,,, ‘)-1
:ix
1 l:$. 5 :<8491 (8 39 OGi.51 39 83; ,42 40 817.81 11’ Oli.41
0.1
3X 710.1
0 .5
:
0.34 O.O(i 0.44 0. ti3 0.1:<
40 945.2 #2 144.G
3!1 li(i7.20 40 44ti. 2s 41 434. a5 4L’ 64’s .x:j
--o.:j1 - 0.07
-0.50 --1.74
LO 432. ;
-0.980311
K
1, (amu A2)~~
13.083lii, 123.371, 135.805y 1, A 0.3?k97 ~_____ ~~~~_~~ ~~~~ ibConversion factor used is 505 531 amu Ii2 MHz. Ib
- 0.980155 11.912’75, 123.155s 135.6577 0.589?
B. Stwctwe Analysis Since the struct’ure of NW1 is specified by three parameters, r(NS), $3~2) and the NSCl bond angle, it is necessary to observe the spectra of at, least t)no isotopic species, in order to det,ermine the 1’0 structure: for example, t\vo moment’s of inertia I, and Ib of the normal species must be combined either with 1, or I\-ith Ib of another isotopic species. Because the rot)ational constan& of three isot.opesubstituted species are available, three r0 structures \vere calculated, us list,ed in Table V. On the other hand, the ).S coordinates of the three atoms A\-ere calculated b> combining I, and Ib of the normal and isot.ope-substituted species. Table V sho\~s t,he comparison of the r8 Wucture t)hus obt,ained \vit,h the 1’”st,ructures. The 1) coordinate of t’he Cl atom is close to zero and might, therefore be in large error. However, the first-moment equat)ion gives bcl of 0.1220 8, only one thousandth smaller than t’he value by isotope substitjutjion. In fact, when the w, and b, coordinates are used, the first moment,s and the cross product Ltre all wry claw to zero as shown in Table V. The Y, structure is therefore probably accurate to fO.OO1 s for the bond lengths and t’o f3’ for the bond angle. The moments of are compared \\ith thr observed in inertia calculated using the I‘, coordinates Table V. C’. Quadrupole HyperJine Structure The chlorine nuclear quadrupole coupling const’ants were det,ermined by mensuring the hyperfine structure of four rot,at,ional transitions of 1sW32S35c’I\~hich has no hyperfine structure due t’o t)he nitrogen nucleus. For the species \~hich contains
a 1% nucleus, it was dificult~ to resolve the nitrogen hyperfine
completely.
Therefore,
neglecting
the splittings
due to the nitrogen
structur(b
nucleus, the
MICROWAVE
SPECTRUM
:i91
OF NSCl
cluadrupole coupling constants of the chlorine nucltwh \verc determined by tlw least-squares met’hod. By the lack of accidental degeneracy in the rotation:rl energy levels, only three diagonal components of the coupling constant, xua , xbb , :tnd xce \vere obtained, as shown in Table VI. The observed hyperfine splittings of the rotational spectrum and the comparison \\-ith the c:dculntrd \-alucs :tw shown in Table VII. Because only diagonal terms in the a, b, ant1 r axis system were determintvl, it is not, possible to calculate the principal valut 9 of the X-tensor directly front t hc observed data. Therefore, the angle bt%veen the S- (‘I bond and the a-:tsis i.s TABLE \: i%LIXIJLAR
-___.
STRUCTURE
0~
XXI
r.
structurea _____~ -. UN”4s”5C] 1C_V32S3SC1
14N”S3’CI 1.458 2.157 118”8’
T (NS) (8) r (XI)
(A)
N
1.3566 (8) -0.7356 -1.7101
1.448 2.164 lli”-!5’
1.450 2.161 llT”42’
b.
ua (:I s
1.450 2.1ti3 117”18’
0.1232 -0.4197 0.6535
(8)”
Zr,r,a, = -0.0292 am11 ..i Z,U,b, = 0.0414 amu J Z,n,n,h; = 0.0670 amu wz
I ca,c
14N%3YYI
I 0bs
12.1464 (amu AZ) IO 122.6462 Ib 134.7926 I, _ ~~~~.~~ ~-a Calculated by the combinat.ion of the rotational those of the isotopic species mentioned below. ‘1 The firsr-moment equation gives 0.1220 .“\.
15NYPCl:
Y,structure
12.11677 (amu Lis2) 122.8729 135.219,, cunst:tnta
a’.2 = 0.9656 assumed XIX = 15.00 (MHZ) xllU = 28.36
of the normal species
(R = 15”4’)
XZZ =
-43.36 7 = (xz7 - xl/U)/xz; = 0.3081 .-__
~_
~~_.
~ .._
_..__._~~~
with
BEPPU,
392
HIROTA, TABLE
AND
MOKINO
VII
HYPERFINE STRUCTURE DUE TO CHLORINE NUCLEUS IN THK 15N3W~C1Sr~xr~:s (MHz)
J’ - J
F’ - F
A=
Obs
IL-00.0
3/2-3/2 5/2-3/2 l/2%3/2
4.78 -1.17 -5.96
0.05 0.01 -0.06
ll,o-lo,l
3/2-3/2 5/2-3/2 l/2-3/2 3/2-5/2
10.77 6.88 4.18 1.08
0.01 -0.11 0.21 0.00
5/2-5/2 3/2-l/2 l/2-1/2
-2.72 -6.97 -13.38
J’ - J
F’ - F
31,2-30,3
g/2-7/2 3/2-5/2 5/2-7/2 7/2-712 5/2-5/2 g/2-9/2 3/2-3/2 7/2-5/2 T/2-9/2 5/2-3/2
-0.03 -0.13 0.07 21,2-lo.1
21,1-20.2
&A = obs -
7/2-5/2 31%5/2 l/2-3/2 5/2-5/2 3/2-3/2 7/2-7/2 5/2-3/2 5/2-7/2 3/2-l/2
8.67 6.97 5.89 2.71 0.02 -1.05 -4.05 -6.96 -9.56
talc; calculated
0.07 0.06 -0.02 0.02 0.02 0.03 0.17 0.02 0.10
31,3-20,Q
values were obtained
3/2-3/2 5/2-3/2 7/2-5/2 5/2-5/2 3/2-l/2 5/2-5/2 7/2-5/2 g/2-7/2 3/2-l/2
with the constants
Obs 9.18 8.57 4.72 0.89 0.29 -0.48 -1.06 -3.63 -8.69 -9.32
A& -0.03 -0.02 -0.05 0.00 0.02 -0.04 0.00 -0.01 0.07 0.06
-9.36
0.04 -0.01 -0.00 -0.03 0.32
5.46 2.78 -0.92 -4.62
-0.21 -0.00 -0.22 0.10
7.78 5.04 -0.86 -4.66
listed in Table VI
calculated using the struct,ure obt)ained in Sect,. B. The angle is 14” 33’ for t,he 14N32S35C1species, which corresponds to 15” 4’ for the W32S35C1 species, if the structure is assumed not affected by isotope subst,itution. If the direction cosine is denoted by aa, , the two component’s, xaa and xcc , are given by Xaa = K3&
-
I)/:!
+ M2
rl>Plx*z
,
-
l)/~lx,z )
(1)
and X cc =
K-
1 +
0)
where rl = (xzz -
XYY)IXZZ ’
The principal values and asymmetry parameter are shown for 15N32S35C1in Table VI.
(3) of the x-tensor
thus det’ermined
D. Inertia Defects The inertia the rotational were obtained
defects in the first excited states of ~2 and v3 were calculated from constants listed in Table IV. Inertia defect increments AZ and A3 by taking differences bet,ween the inert,ia defects of the first, excited
MICltOWAVE
states
of
v2
and
v3
and that
SPECTRUM OF NSCI
of the ground
state,
393
respectively:
A, = A(v2 = 1) -
A0 = 0.1204 amu AZ,
(4?
A3 = A(u3 = 1) -
A0 = 0.35g9 amu H2,
(5)
where the inertia defect in t,he ground st,ate A0 was taken as 0.22g3 amu w2, as was already given in Table II. The inertia defect, can be calculated from the vibrational frequencies and Coriolis coupling constants, wit#h small correction terms due to the effects of centrifugal distortion and electronic motion (9) : A(u)
=
cc
A&i
+
%)
+
Acent +
(6)
Ae~ec,
\\here A1
=
k
w22
7r2c
A, =
k fC
wz(w22 a2 [ wq(w12 -
A3 = k 7r2c
w22)
W12 WS(W12-
(7)
u,2)
w32)
w2
+
,,,32uc
(ha2
+
w3(w22wc w32) (I:;))2].
w22) (W’]
,
(S)
(9)
It might be expected that the Coriolis coupling constants would be obtained from the observed inertia defect increments. Unfortunately, hhis is not feasible for the triatomic molecules with C, symmetry, for which three coupling constants, and there exists a relation rk’, &’ and &‘, are all nonvanishing (I$‘)”
+
({‘“Q2 + 23
(p’c’)2 = 1. 13
(IO)
It is
easily shown that Eqs. (7)-(10) are not independent: the determinant composed of the coefficients is zero for any three of t’he four equations. From Eqs. (7)-(10) a sum rule is derived: w13A, + w$A2 +
ws3As = 0,
(11)
and three relations
among
( WI2 -
W~~)WZAZ +
(w12 -
( wz2 -
w12)w1A, + (wz2 -
h wz2, wa2)w3Az = ?rYJ
(13)
(ws2 -
W&IA,
wz2)wzAz = -&
(14)
+ (ws2 -
three Ai and three wi . By inserting
WS~)WS& =
the observed
&
w12,
ws’,
values
(1’)
of A2 , As , WI and
BEPPU,
394
HIROTA, TABLE
AND
MORINO
VIII
OBSERVEDVALUES OF INERTIA DEFECTS FOR 14N3%W1 Inertiadefectof vibrational state 0.2293 (0.2225)” 0.3497 0.5892
A0 A(LQstate) A& state) A(Q state)
Inertiadefectincrement
Ala A2 A3
(-0.006@ 0.1204 0.3599
& A; = A(Vi state) - Ao. b Calculated from A, (obs) + A,. 0 Calculated using Eq. (11). TABLE
IX
FORCE CONSTANTS OF SIMPLE VALENCE FORCE FIELD FOR NSCl INCREMENTSCALCULATEDBY THEIR USE
F,r (NS stretching) md/A F22 (SC1 stretching) md/W D Fs3 (NSCl deformation) mdA
A1 A, A3
AND INERTI,\ DEFECT
Present work
Miiller et al. (6)
10.021 1.581 0.72,
10.03 1.67 0.64
Calc
Obs
-0.0058 0.0903 0.4031
-0.006s 0.1204 0.3599
Obs -
Calc
-0.001, 0.0301 -0.0432
w2in Eq. (la), wg is calculated to be 261 cm-‘, which is in rough agreement with the frequency 273 cm-’ estimated from the infrared spectrum by Miiller et al. (6). Then, Eq. (11) provides the value of Al by the use of A, , Aa and the three vibrational frequencies. The results are shown in Table VIII. E. Force Constants When one uses the three vibrational frequencies, 1325, 414, and 261 cm-l, and the structure obtained above, three diagonal force constants are easily obtained in t,he same way as was done by Miiller et al. (t;), on the assumption that the cross terms in the F matrix are all zero. Small frequency corrections to be added to the observed frequencies were all ignored either for the anharmonicity factors or for the frequency differences (probably 1 cm-l or less) between the mother molecule 14N32S35C1 and the isotope mixture really observed. The results are listed in Table IX, which are in good agreement with those by Mtiller et al. (6). The inertia defect increments for this set of force constants were calculated through the Coriolis coupling constants. The calculation was done by the use of the programs registered in the Computer Center of the University of Tokyo. Table IX reveals that the force field must be somewhat revised, because the
MICROWAVE
F M.\TIIIXELEMENTS
OF
SPECTRUM OF NSCI
TABLE X NSCl OBTAINED
BY
THE
USE OF
395
f_di l~~~
ai
-
-F11
F22
F33
Fijs
Valence fowe field
10.027
1.581
0.72,
0
set, IL
10.031 9.22, 9.540
1 .-l(is 2.064 1.532
0.76, 0.72~ 0.971
Fza = -0.067 F,, = -1.842 Frz = -1.362
Set
II III
= Terms unspecified are all assumed to be zero. h Coriolis coupling constants for the set I are: r12= 0.6283, (-,3 = 0.6815, and cp3= 0.3752. and wt = 259 cm-l and A, = -0.0064. calculated values indicated discrepancies with the observed over the experimental uncertainties. Rigorously speaking, the general force field for the KSCl molecule involves three cross terms, F,, , FL3 , and F23 , in addition to t,hree diagonal force constant,s. Since the inertia defects provide two observed quantit,ies, AZ and A3 , four indeof the pendent data, WI , w:! , A, , and A3 , are now available for the determination force field. Therefore, one more parameter can be added to the simple valence force field. Table X shows the final se& of force constants, in which only one cross term among the three is assumed to be finite. The set I wit,h a finite value of Fz3 may be t,he most preferable, because in other sets the cross terms must be enormously large and even comparable t’o the diagonal terms in order to account for the observed four data.
DISCUSSION It is first mentioned that t,he Pu’SCl molecule has the arrangement of K-S-Cl, in accord with the structure of NSF. This is in great contrast to the arrangement, of O-N-X for ONC1(10), ONBr(ll), and Or\;F(1s). It presumably corresponds to the valence formula of N=S-Cl; really the sum of Pauling’s covalent, radii (IS) for 1J=S, 0.55 8 (N=) + 0.82 & (=S) = 1.42 8, is close to the observed value 1.450 A; whereas the sum for S=N, 0.94 d (S==) + 0.60 B (=K) = 1.54 w is far from the observed. Thus the skucture must be K=S-Cl, but, not S--R_----Cl. The above statement, does not imply t.hat the electronic structure is COIIfined simply to the electronic distribution expressed by the single formulas of r\’ = S--Cl. It would be more natural to include a number of other configuration, such as K = S+Cl- or others, as stated below. It was found t’hat, t’he N-S bond lengths in NSF and NSCl are identical within 0.004 A and the bond angles LNSX are equal within 50’. It suggests t,hat t,he nature of t.he NS bond seems t.o be similar in both molecules. It should also be noted that the S-Cl bond length of NSCl is definitely larger than the sum of Pauling’s covalent, radii, 1.04 + 0.99 = 2.03 A. It is 0.16 A
BEPPU,
396
HIROTA,
AND
TABLE COMPARISON
MORINO
XI
OF THE BOND LENGTHS IN VARIOUS MOLECULES
NSCl” r(NS) r(SC1)
NSFb
= 1.450 B = 2.161 A = 117”41’
r(NS) r(SF)
= 1.446 i = 1.846 ii = 116”52’
Molecule
r(SC1)
molecule
r(SF)
SZClZ SClz SOClZ so*c12
2.07 (b)c 2.00sd 2.07” 1.99’
&F, SFf, SOFZ
1.598, 1.635 (8)f 1.589g 1.585h 1.530’
SOzFz
8 This work. b Ref. (7). c E. Hirota, Bull. Chem. Sot. Jap. 31, 130 (1958). d D. P. Stevenson and J. Y. Beach, J. Amer. Chem. Sot. 60,2872 (1938). e K. J. Palmer, J. Amer. Chem. Sot. 60, 2360 (1938). f R. L. Kuczkowski, J. Amer. Chem. Sot. 66,3617 (1964). g D. 12. Johnson and F. S. Powell, Science 164,950 (1969). h R. C. Ferguson, J. Amer. Chem. Sot. 76,850 (1954). i D. It. Lide, Jr., D. E. Mann, and R. E. Fristrom, J. Chem. Phys. 26,734
(1957).
longer than that in SC12 . It corresponds to t,he fact t’hat the SF bond length of NSF is 0.06-0.12 L%longer than that of SF6 , SOF2 or SOzFz , as shown in Table XI. This anomaly in the bond length seems consistent with the fact that the quadrupole coupling constant of the Cl nucleus is smaller than the average value for many ordinary molecules. The latt’er evidence makes it possible to estimate the bond nature in this molecule. If the fractions of three resonance forms, N==S-Cl, N-=S=Cl+, and N=S+Cl-, are designated by fi , f2 , and f3 , the formulas developed by Dailey and Townes (14) provide the following three relations to t.he principal values of the x-tensor: xzz = 1-f,
-
%(l
xzz = Mfi - ?a XL/j/ = Mfi + (1 +
+ ~)hlml
,
+ ~)hlq31” I ~lf21Q310,
(15) (16) (l’i)
where j-1 +jz+j3
= 1.
(18)
Assuming the ant,ishielding constant c to be 0.15 and q310to be 109.6 MHz, the observed coupling constants listed in Table VI give f, = 0.355, _fi = 0.071, and ,fa = 0..%‘4. It indicates that, the SC1 bond is appreciably ionic and weak in the XSCl molecule. Finally, the lifetime of the NSCl molecule should be mentioned. The micro-
MICROWAVE
SPECTRUM OF NSCI
397
wave spectrum was observed under the flow of gas, t,o maintain constant supply of monomer molecules from N&S&l,. When t,he flow of t,he gas was stopped, the signals faded out’ in several ten seconds. The rate of decay of t,he microwave lines n-as measured for the transit,ions 2”,:! + 11,I and 41,3 +- 40,4 of the normal species, with the microwave speckometer fixed at the peak frequency of the signals. The decay was found to obey the first-order law with the half-life of about, 20 sec. It seems most, likely that the extinction of the NSCl molecules in the waveguide cell is attributable to the polymerization of the molecules on t,he wall of the naveguide. Note added in. proof: Guarnieri [Z. Naturfomch. 26a, 18 (1970)] has recently reported for CH#Cl that S-Cl = 2.014 f 0.01 8, xzz = -80.69 f 0.8 MHz, and 77 = 0.0784 k 0.013. It affords a substantial support to the above statement t,ltat the ionic as well as double-bonded forms are indispensable for NSCl. ACKNOWLEDGMENT The authors acknowledge the help of Masaaki Sugie in carrying out the calculation of the force constants. Thanks are also due to the Computer Center of the University of Tokyo for the use of their facilities.
RECEIVED: March
2.3, 1970 REFERENCES
1. 0. GLEMSRR .IND H. BICHI’:K~‘, Z. Anorg. Allg. Chew. 307, 313 (1961); 0.
2. 3. 4. 5. 6.
GLEMSER
.AND
H. PERL, A~alurwissenschaften 48, 620 (1961). .4. MIDX~SEN, Chem. Ber. 66, 1724 (1932). W. L. JOLLY, K. Il. Mt\~ul~s, .~NDL). B\UINOVIC!H,Inorg. Chew. 2, 1304 (1963). K. I>. MBGUIRE, J. J. SMITH, .\NDW. L. JOLLY, Chem. Ind. 28, 1589 (1963). J. J. SMITH >\NDW. L. JOLLY, 1norg. Chenl. 4, 1006 (1965). A. MILLER, 6. NAG.~RAJAN, 0. CI,F;MSER, 8. F. CYVIN, .\NDJ. WEGENER,Spectrochittc.
Ada, Part d, 23, 2083 (1967). 7. W. H. KIRCHHOFF :\NI) E. B. WILSON, JR., J. Amer. Chem. Sot. 86, 1726 (1963); 11. I,. CooR .~XD W. H. KIRCHHORF, J. Ch.m. Phys. 47, 4521 (1967). 8. T. AM.%NO,E. HIR(JT.\, .\NDY. MORINO, J. Phys. Ser. Jap. 22, 499 (1969). 9. T. Ox;\ .ZND Y. MORINO, J. Mol. Speclrosc. 6, 472 (1961). 10. R. L. COOK. .I. Chem. Phyx. 42, 2927 (1965). 11. T. L. WE~~HRRI,Y .\ND &. WILLI.\MS, J. Chem. Phys. 26, 717 (1956). 12. D. J. MILLEN .\ND J. P.\NNF,LL,J. Chem. Sot. 1961, 1322. 19. L. P.\TJLINO,“The Nature of the Chemical Bond,” p. 154. Cornell Univ. Press, Ithaca, N. Y. 1939. 14. B. P. I),\ILEY .\ND C. H. TO\VNES, J. Chem. Ph?ys. 23, 118 (1955).
\I, OF MOLECUL.11~
SPIWTROSCOPY
36, 386-397 (1970)
Microwave Spectrum, Structure, Quadrupole Coupling Constant, and Force Constants of NSCI TATSURO BEPPU,~ EIZI HIROTA,~ AND YOKEZO ~.~ORINO~ Departmenl
of Chemistry,
Faculty of Science,
The I;niversiiy
of Tokyo, Hongo,
Tokyo, Japan
Microwave spectra of the NSCI molecule were observed by pumping the products of thermally decomposing N3S&13 continuously through the cell. The rotational constants were obtained for 14N32S35C1,14N32S37C1,14N~4S36C1, and 16N32S36C1,all in the ground vibrational states. The r8 structure calculated from these rotational constants is the configuration N=S-Cl with 0 0 r(NS) = 1.450 A, r(SC1) = 2.161 A and LNSCl = 117”42’. The nuclear quadrupole coupling constant of W!l in the 1sN32S36C1species is determined to be ~a6 = 23.51, and xec = 15.00 MHz, which corresponds to xbond Xaa = -38.51, of -43.36 MHz. In addition to the ground-state spectra, several sets of vibrational satellites were observed and assigned to the ~2 , vg , 2~2 , and 2~3 stat,es. The vibrational increments of the inert,ia defects, A2 and A3 , are combined with two known vibrational frequencies, ~1 and 02 , to calculate the force constants. The value of ~3 , 261 cm-l, calculated using the inertia defect increments is in agreement with 273 cm+, estimated by Miiller and others from the infrared spectra. Redundancy among the three inertia-defect increments is noted for triatomic molecules with the C, symmetry, and its consequence is discussed briefly.
The NSCI molecule was first detected by Glemser and Richert (1) through its infrared spectrum in the reaction of chlorine gas with NSF, though Meuwsen (2) reported long ago that NSCl seemed t,o be formed as an int,ermediate in the synthesis of N3S3C13 by passing chlorine gas into carbon tetrahcloride suspension of S3N2C12 prepared from N4S4 and S2C12. Glemser and Richert’ observed an infrared absorption band at 1322 cm-l, lower by 50 cm-l than the KS stretching band of NSF. Judging from the similarity in t,he band shape of t’hese two bands, t,hey presumed that, t,he band at 1322 cm-l was due to the NS stretching vibration of the KSCl molecule. It, x\-as discovered (5, 4) that S3NzC12 was conveniently prepared from am1Present Kawasaki. 2 Present
address:
Central
address:
Department
Fukuoka. 3 Present address:
Research
Laboratory,
of Chemistry,
Sagami Chemical
Research
gawa, Japa.n. 386
Tokyo
Faculty
Shibaura
of Science,
Electric Kyushu
Co.,
Ltd.,
TJniversity,
Cent,er, 3100, Ohnuma, Sagamihara,
Kana-
MICROWAVE
SPECTRUM OF NSCl
3%
monium chloride and sulfur chloride and that S3NzC12 was easily converted to S,K&l, , SJSkY, or S3N&13 . The 1322 cm-l absorption band was used to confirm the formation of the NSCl molecule when these sulfur nikogen chlorides were heated (3). NSCl and other sulfur nitrogen chlorides were also formed in the reaction of SK% vapor with active nitrogen, the formaGon of NSCl being identified by its infrared absorption band (4, 5). Information on the molecular structure of NSCl was first obtained by Mi.iller et a/. (6). They calculated force constants from three observed vibrational frequencies vl = 1325, v2 = 414, and v3 = 273 cm-‘, neglecting cross terms in the potential function. The force constants were found to be similar to those of NSF: for instance, the calculated force constant for NS stretching is very large and close to that of NSF. From this fact and bond-order calculation, they concluded that the arrangement of atoms in NSCl was not, S-N-Cl but N-S-Cl, similar to iSSF for which microwave spectroscopy clearly indicated the structure of N-S-F (7,). In t)he present study, the microwave spectrum of t,he NSCl molecule was observrd for precise determinat’ion of its molecular structure. EXPERIMENTAL
METHODS
The sample of NSCl was prepared by heating N3S3C13 to about 70°C under high vacuum and was led to an ordinary 3-m waveguide cell t,hrough a capillary tube. Rapid decay of the NSCl molecule in the cell made it, necessary to pump the sample continuously through t’he cell. The compound N3S&& was synthesized by the following process: ammonium chloride and sulfur were suspended in sulfur monochloride placed in a flask which was connected t,o a long tube terminated with a calcium chloride column. When heated, a red substance, presumably SJSJ& , was deposited on the wall of t,he tube. The tube was then connect,ed to the second flask with a side arm, through which chlorine gas was introduced to react wit’h the red deposits. The N$$13 thus formed fell down gradually with sulfur dichloride to the bottom of t’he flask After completion of t,he reaction sulfur dichloride \vas pumped off. The MC1 molecule was also formed by an electric discharge through a mixture of t,he N, and SZCIZ vapor. The microwave spectrum was observed using a 60-cm Pyres cell, which had been built for the detection of free radicals (8). Because the spectrum thus obtained was weak and the optimum condition of the reaction was difficult t’o maintain, all absorption lines used for the analysis were observed lyith the sample prepared by t,he first met,hod. The spectrum of 15N32S35C1n-as observed with t,he sample containing l5N enriched to 1.i at. %. After mixing 1.5.4 g of l5N-enriched ammonium sulfate wit,h 25 g of barium chloride and 100 ml of water, stirring and filtrating out the precipitates of barium sulfate, the aqueous solution of 15S-enriched ammonium chloride was evaporated. Then 11.5 g cf ammonium chloride thus c;btained was
BEPPU,
388
HIROTA,
AND
TABLE TRANSITION
FREQUENCIES OF NSCl
IN THE
MORINO
I GROUND VIRR~TI~N~L
ST.ITE
(MHz)
Obs ll,a~ln,I
37
983.1
0.1
21,1-20,?
38
361.72
0.27
38
340.96
31.?-3”.3
38
934.40
0.02
38
d83.7i
0.68
0.03 -0.26
36
883.0
0.2
36
706.72
37
264.42
-0.2’)
3i
079.88
0.17
37
842.35
-0.48
37
64l.i2
0.08
38
624.08
0.12
41,ado,r
39
iO6.7.3
39
617.1G
51.4-50.6
40
6:,0.41
-0.35
40
546.83
-0.39
39
Hii.
61.sr6a.s
41
833.52
-0.29
41
683.50
-0.55
40
5fi3.54
-0.14
71.6-70.7
43
32i.0
0.6
43
037.i
-0.8
42
282.5
-0.2
41
Y87.25
-0.85
81,7r80,8
45
005.0
44
620.9
-2.1
43
982.2
-0.6
44
283.33
-0.3
0.19
A”
O.OR -0.08
11.1-00.0
45
460.22
0.00
45
264.20
0.00
44
005.32
0.01)
21,2r10,1
52
93i.9
0.5
52
546.4
0.4
51
304.06
0.08
lI,Ir20.?
21
YO3.Y
0.5
22
349.7
0.1
21
001.94
0. x3
3W20.?
60
228.4
0.4
59
651.8
0.8
58
418.62
0. 62
il 4 = obs
-
0.00
talc.
employed for small-scale g, the overall yield being The spectrometer used kHz oscillator as a Stark perature.
synthesis of 151Y3S3C13. The N3S3C13 obt,ained was 1.1 about 5.8%. u-as of conventional Hughes-Wilson type Lvith a 110 modulat’or. The speckurn Teas observed at room t,em-
RESULTS
A. Rotational Spectrum XSCl is a bent triatomic molecule of a nearly prolate symmetric top. Since the dipole moment has components both along the a- and b-axes, t’he a- and b-type transitions are expected but all the observed transitions were of the b-type, because the u-component of the dipole moment is smaller than the b-component. In Table I are listed unsplit frequencies of t,he observed transitions nhen correct’ed for hyperfine structure. The assignment, was first made for the b-type Q-branch series, J1,.,-_-l+ Jo,, , then extended to R-branch transitions. The spins of nitrogen and chlorine nuclei (1 and 3/2, respectively) couple \\-ith the molecular rotation to give complicat,ed hyperfine struct,ures for the rotational spectrum of NSCl. The assignment was greatly facilitated by the use of the fact that the quadrupole hyperfine splitting due to chlorine nucleus is much larger t*han t,hat due to nitrogen nucleus. The b-type Q-branch series mentioned above gave the rotational constant A - C and the asymmetry parameter K, whereas A + C was determined by the b-type R-branch lines. Centrifugal distortion effect was ignored in the analysis, because the transitions observed were between levels with rather small quantum numbers. The spectra of the YV32S35C1,~4N3%37C1,and 14N34S35C1were observed with the
MICROWAVE
SPECTI:T’RI
OF NM’1
:w
Rotational constants, s;:~mple containing these species in natural abundance. asvmmetrv parameters K, and inertia defectjs of thca four spwies are given in T:ible II. U In thr course of searching, the spwtra in two recited \-ibrational st:ltw \vtw~ found. Hy comparing their intensi&s \yith thaw of the ground-statcb linrs, t II(~ S- 4‘1 bending nltdc~ stronger one \vas assigned to the first excited state of the S I’:: (281 cm--‘), md the weaker one to that of thtl S-C’1 stretching modts 1~~(11-k CI~--~). &Ycouple of lines in the second tlscittd statw of botll v:( mtl vL’ u t’rt’ :LIs) ohst!rved. l’hr center frequencies mtl tlw rot:ltioll:il cv)nst;mts tlrrived from I III~I~~ :IIY’ listctl itI Tables III and IT.
-
h
1, II 1.
,:,tIIII
0. %30”20 , _ 1%. llG(is
.\‘)I
122.873s
1:15.210,, 0.220.I .s
-!,
- o.!!812:j:i
- 0.979455
--IJ.‘l7OXL’4
12.14541:
lX.4(il., l:B.fw, 0
2:x$>
” (‘tbrlvprsitltl factor used is 505 531 nmu .\’ RlHz.
IL
0
It,,,
, L’,,,, 3, ” :3,,,.. 4, :< -I,#,I , 5, / 311, fi,,, fi,,,, ‘)-1
:ix
1 l:$. 5 :<8491 (8 39 OGi.51 39 83; ,42 40 817.81 11’ Oli.41
0.1
3X 710.1
0 .5
:
0.34 O.O(i 0.44 0. ti3 0.1:<
40 945.2 #2 144.G
3!1 li(i7.20 40 44ti. 2s 41 434. a5 4L’ 64’s .x:j
--o.:j1 - 0.07
-0.50 --1.74
LO 432. ;
-0.980311
K
1, (amu A2)~~
13.083lii, 123.371, 135.805y 1, A 0.3?k97 ~_____ ~~~~_~~ ~~~~ ibConversion factor used is 505 531 amu Ii2 MHz. Ib
- 0.980155 11.912’75, 123.155s 135.6577 0.589?
B. Stwctwe Analysis Since the struct’ure of NW1 is specified by three parameters, r(NS), $3~2) and the NSCl bond angle, it is necessary to observe the spectra of at, least t)no isotopic species, in order to det,ermine the 1’0 structure: for example, t\vo moment’s of inertia I, and Ib of the normal species must be combined either with 1, or I\-ith Ib of another isotopic species. Because the rot)ational constan& of three isot.opesubstituted species are available, three r0 structures \vere calculated, us list,ed in Table V. On the other hand, the ).S coordinates of the three atoms A\-ere calculated b> combining I, and Ib of the normal and isot.ope-substituted species. Table V sho\~s t,he comparison of the r8 Wucture t)hus obt,ained \vit,h the 1’”st,ructures. The 1) coordinate of t’he Cl atom is close to zero and might, therefore be in large error. However, the first-moment equat)ion gives bcl of 0.1220 8, only one thousandth smaller than t’he value by isotope substitjutjion. In fact, when the w, and b, coordinates are used, the first moment,s and the cross product Ltre all wry claw to zero as shown in Table V. The Y, structure is therefore probably accurate to fO.OO1 s for the bond lengths and t’o f3’ for the bond angle. The moments of are compared \\ith thr observed in inertia calculated using the I‘, coordinates Table V. C’. Quadrupole HyperJine Structure The chlorine nuclear quadrupole coupling const’ants were det,ermined by mensuring the hyperfine structure of four rot,at,ional transitions of 1sW32S35c’I\~hich has no hyperfine structure due t’o t)he nitrogen nucleus. For the species \~hich contains
a 1% nucleus, it was dificult~ to resolve the nitrogen hyperfine
completely.
Therefore,
neglecting
the splittings
due to the nitrogen
structur(b
nucleus, the
MICROWAVE
SPECTRUM
:i91
OF NSCl
cluadrupole coupling constants of the chlorine nucltwh \verc determined by tlw least-squares met’hod. By the lack of accidental degeneracy in the rotation:rl energy levels, only three diagonal components of the coupling constant, xua , xbb , :tnd xce \vere obtained, as shown in Table VI. The observed hyperfine splittings of the rotational spectrum and the comparison \\-ith the c:dculntrd \-alucs :tw shown in Table VII. Because only diagonal terms in the a, b, ant1 r axis system were determintvl, it is not, possible to calculate the principal valut 9 of the X-tensor directly front t hc observed data. Therefore, the angle bt%veen the S- (‘I bond and the a-:tsis i.s TABLE \: i%LIXIJLAR
-___.
STRUCTURE
0~
XXI
r.
structurea _____~ -. UN”4s”5C] 1C_V32S3SC1
14N”S3’CI 1.458 2.157 118”8’
T (NS) (8) r (XI)
(A)
N
1.3566 (8) -0.7356 -1.7101
1.448 2.164 lli”-!5’
1.450 2.161 llT”42’
b.
ua (:I s
1.450 2.1ti3 117”18’
0.1232 -0.4197 0.6535
(8)”
Zr,r,a, = -0.0292 am11 ..i Z,U,b, = 0.0414 amu J Z,n,n,h; = 0.0670 amu wz
I ca,c
14N%3YYI
I 0bs
12.1464 (amu AZ) IO 122.6462 Ib 134.7926 I, _ ~~~~.~~ ~-a Calculated by the combinat.ion of the rotational those of the isotopic species mentioned below. ‘1 The firsr-moment equation gives 0.1220 .“\.
15NYPCl:
Y,structure
12.11677 (amu Lis2) 122.8729 135.219,, cunst:tnta
a’.2 = 0.9656 assumed XIX = 15.00 (MHZ) xllU = 28.36
of the normal species
(R = 15”4’)
XZZ =
-43.36 7 = (xz7 - xl/U)/xz; = 0.3081 .-__
~_
~~_.
~ .._
_..__._~~~
with
BEPPU,
392
HIROTA, TABLE
AND
MOKINO
VII
HYPERFINE STRUCTURE DUE TO CHLORINE NUCLEUS IN THK 15N3W~C1Sr~xr~:s (MHz)
J’ - J
F’ - F
A=
Obs
IL-00.0
3/2-3/2 5/2-3/2 l/2%3/2
4.78 -1.17 -5.96
0.05 0.01 -0.06
ll,o-lo,l
3/2-3/2 5/2-3/2 l/2-3/2 3/2-5/2
10.77 6.88 4.18 1.08
0.01 -0.11 0.21 0.00
5/2-5/2 3/2-l/2 l/2-1/2
-2.72 -6.97 -13.38
J’ - J
F’ - F
31,2-30,3
g/2-7/2 3/2-5/2 5/2-7/2 7/2-712 5/2-5/2 g/2-9/2 3/2-3/2 7/2-5/2 T/2-9/2 5/2-3/2
-0.03 -0.13 0.07 21,2-lo.1
21,1-20.2
&A = obs -
7/2-5/2 31%5/2 l/2-3/2 5/2-5/2 3/2-3/2 7/2-7/2 5/2-3/2 5/2-7/2 3/2-l/2
8.67 6.97 5.89 2.71 0.02 -1.05 -4.05 -6.96 -9.56
talc; calculated
0.07 0.06 -0.02 0.02 0.02 0.03 0.17 0.02 0.10
31,3-20,Q
values were obtained
3/2-3/2 5/2-3/2 7/2-5/2 5/2-5/2 3/2-l/2 5/2-5/2 7/2-5/2 g/2-7/2 3/2-l/2
with the constants
Obs 9.18 8.57 4.72 0.89 0.29 -0.48 -1.06 -3.63 -8.69 -9.32
A& -0.03 -0.02 -0.05 0.00 0.02 -0.04 0.00 -0.01 0.07 0.06
-9.36
0.04 -0.01 -0.00 -0.03 0.32
5.46 2.78 -0.92 -4.62
-0.21 -0.00 -0.22 0.10
7.78 5.04 -0.86 -4.66
listed in Table VI
calculated using the struct,ure obt)ained in Sect,. B. The angle is 14” 33’ for t,he 14N32S35C1species, which corresponds to 15” 4’ for the W32S35C1 species, if the structure is assumed not affected by isotope subst,itution. If the direction cosine is denoted by aa, , the two component’s, xaa and xcc , are given by Xaa = K3&
-
I)/:!
+ M2
rl>Plx*z
,
-
l)/~lx,z )
(1)
and X cc =
K-
1 +
0)
where rl = (xzz -
XYY)IXZZ ’
The principal values and asymmetry parameter are shown for 15N32S35C1in Table VI.
(3) of the x-tensor
thus det’ermined
D. Inertia Defects The inertia the rotational were obtained
defects in the first excited states of ~2 and v3 were calculated from constants listed in Table IV. Inertia defect increments AZ and A3 by taking differences bet,ween the inert,ia defects of the first, excited
MICltOWAVE
states
of
v2
and
v3
and that
SPECTRUM OF NSCI
of the ground
state,
393
respectively:
A, = A(v2 = 1) -
A0 = 0.1204 amu AZ,
(4?
A3 = A(u3 = 1) -
A0 = 0.35g9 amu H2,
(5)
where the inertia defect in t,he ground st,ate A0 was taken as 0.22g3 amu w2, as was already given in Table II. The inertia defect, can be calculated from the vibrational frequencies and Coriolis coupling constants, wit#h small correction terms due to the effects of centrifugal distortion and electronic motion (9) : A(u)
=
cc
A&i
+
%)
+
Acent +
(6)
Ae~ec,
\\here A1
=
k
w22
7r2c
A, =
k fC
wz(w22 a2 [ wq(w12 -
A3 = k 7r2c
w22)
W12 WS(W12-
(7)
u,2)
w32)
w2
+
,,,32uc
(ha2
+
w3(w22wc w32) (I:;))2].
w22) (W’]
,
(S)
(9)
It might be expected that the Coriolis coupling constants would be obtained from the observed inertia defect increments. Unfortunately, hhis is not feasible for the triatomic molecules with C, symmetry, for which three coupling constants, and there exists a relation rk’, &’ and &‘, are all nonvanishing (I$‘)”
+
({‘“Q2 + 23
(p’c’)2 = 1. 13
(IO)
It is
easily shown that Eqs. (7)-(10) are not independent: the determinant composed of the coefficients is zero for any three of t’he four equations. From Eqs. (7)-(10) a sum rule is derived: w13A, + w$A2 +
ws3As = 0,
(11)
and three relations
among
( WI2 -
W~~)WZAZ +
(w12 -
( wz2 -
w12)w1A, + (wz2 -
h wz2, wa2)w3Az = ?rYJ
(13)
(ws2 -
W&IA,
wz2)wzAz = -&
(14)
+ (ws2 -
three Ai and three wi . By inserting
WS~)WS& =
the observed
&
w12,
ws’,
values
(1’)
of A2 , As , WI and
BEPPU,
394
HIROTA, TABLE
AND
MORINO
VIII
OBSERVEDVALUES OF INERTIA DEFECTS FOR 14N3%W1 Inertiadefectof vibrational state 0.2293 (0.2225)” 0.3497 0.5892
A0 A(LQstate) A& state) A(Q state)
Inertiadefectincrement
Ala A2 A3
(-0.006@ 0.1204 0.3599
& A; = A(Vi state) - Ao. b Calculated from A, (obs) + A,. 0 Calculated using Eq. (11). TABLE
IX
FORCE CONSTANTS OF SIMPLE VALENCE FORCE FIELD FOR NSCl INCREMENTSCALCULATEDBY THEIR USE
F,r (NS stretching) md/A F22 (SC1 stretching) md/W D Fs3 (NSCl deformation) mdA
A1 A, A3
AND INERTI,\ DEFECT
Present work
Miiller et al. (6)
10.021 1.581 0.72,
10.03 1.67 0.64
Calc
Obs
-0.0058 0.0903 0.4031
-0.006s 0.1204 0.3599
Obs -
Calc
-0.001, 0.0301 -0.0432
w2in Eq. (la), wg is calculated to be 261 cm-‘, which is in rough agreement with the frequency 273 cm-’ estimated from the infrared spectrum by Miiller et al. (6). Then, Eq. (11) provides the value of Al by the use of A, , Aa and the three vibrational frequencies. The results are shown in Table VIII. E. Force Constants When one uses the three vibrational frequencies, 1325, 414, and 261 cm-l, and the structure obtained above, three diagonal force constants are easily obtained in t,he same way as was done by Miiller et al. (t;), on the assumption that the cross terms in the F matrix are all zero. Small frequency corrections to be added to the observed frequencies were all ignored either for the anharmonicity factors or for the frequency differences (probably 1 cm-l or less) between the mother molecule 14N32S35C1 and the isotope mixture really observed. The results are listed in Table IX, which are in good agreement with those by Mtiller et al. (6). The inertia defect increments for this set of force constants were calculated through the Coriolis coupling constants. The calculation was done by the use of the programs registered in the Computer Center of the University of Tokyo. Table IX reveals that the force field must be somewhat revised, because the
MICROWAVE
F M.\TIIIXELEMENTS
OF
SPECTRUM OF NSCI
TABLE X NSCl OBTAINED
BY
THE
USE OF
395
f_di l~~~
ai
-
-F11
F22
F33
Fijs
Valence fowe field
10.027
1.581
0.72,
0
set, IL
10.031 9.22, 9.540
1 .-l(is 2.064 1.532
0.76, 0.72~ 0.971
Fza = -0.067 F,, = -1.842 Frz = -1.362
Set
II III
= Terms unspecified are all assumed to be zero. h Coriolis coupling constants for the set I are: r12= 0.6283, (-,3 = 0.6815, and cp3= 0.3752. and wt = 259 cm-l and A, = -0.0064. calculated values indicated discrepancies with the observed over the experimental uncertainties. Rigorously speaking, the general force field for the KSCl molecule involves three cross terms, F,, , FL3 , and F23 , in addition to t,hree diagonal force constant,s. Since the inertia defects provide two observed quantit,ies, AZ and A3 , four indeof the pendent data, WI , w:! , A, , and A3 , are now available for the determination force field. Therefore, one more parameter can be added to the simple valence force field. Table X shows the final se& of force constants, in which only one cross term among the three is assumed to be finite. The set I wit,h a finite value of Fz3 may be t,he most preferable, because in other sets the cross terms must be enormously large and even comparable t’o the diagonal terms in order to account for the observed four data.
DISCUSSION It is first mentioned that t,he Pu’SCl molecule has the arrangement of K-S-Cl, in accord with the structure of NSF. This is in great contrast to the arrangement, of O-N-X for ONC1(10), ONBr(ll), and Or\;F(1s). It presumably corresponds to the valence formula of N=S-Cl; really the sum of Pauling’s covalent, radii (IS) for 1J=S, 0.55 8 (N=) + 0.82 & (=S) = 1.42 8, is close to the observed value 1.450 A; whereas the sum for S=N, 0.94 d (S==) + 0.60 B (=K) = 1.54 w is far from the observed. Thus the skucture must be K=S-Cl, but, not S--R_----Cl. The above statement, does not imply t.hat the electronic structure is COIIfined simply to the electronic distribution expressed by the single formulas of r\’ = S--Cl. It would be more natural to include a number of other configuration, such as K = S+Cl- or others, as stated below. It was found t’hat, t’he N-S bond lengths in NSF and NSCl are identical within 0.004 A and the bond angles LNSX are equal within 50’. It suggests t,hat t,he nature of t.he NS bond seems t.o be similar in both molecules. It should also be noted that the S-Cl bond length of NSCl is definitely larger than the sum of Pauling’s covalent, radii, 1.04 + 0.99 = 2.03 A. It is 0.16 A
BEPPU,
396
HIROTA,
AND
TABLE COMPARISON
MORINO
XI
OF THE BOND LENGTHS IN VARIOUS MOLECULES
NSCl” r(NS) r(SC1)
NSFb
= 1.450 B = 2.161 A = 117”41’
r(NS) r(SF)
= 1.446 i = 1.846 ii = 116”52’
Molecule
r(SC1)
molecule
r(SF)
SZClZ SClz SOClZ so*c12
2.07 (b)c 2.00sd 2.07” 1.99’
&F, SFf, SOFZ
1.598, 1.635 (8)f 1.589g 1.585h 1.530’
SOzFz
8 This work. b Ref. (7). c E. Hirota, Bull. Chem. Sot. Jap. 31, 130 (1958). d D. P. Stevenson and J. Y. Beach, J. Amer. Chem. Sot. 60,2872 (1938). e K. J. Palmer, J. Amer. Chem. Sot. 60, 2360 (1938). f R. L. Kuczkowski, J. Amer. Chem. Sot. 66,3617 (1964). g D. 12. Johnson and F. S. Powell, Science 164,950 (1969). h R. C. Ferguson, J. Amer. Chem. Sot. 76,850 (1954). i D. It. Lide, Jr., D. E. Mann, and R. E. Fristrom, J. Chem. Phys. 26,734
(1957).
longer than that in SC12 . It corresponds to t,he fact t’hat the SF bond length of NSF is 0.06-0.12 L%longer than that of SF6 , SOF2 or SOzFz , as shown in Table XI. This anomaly in the bond length seems consistent with the fact that the quadrupole coupling constant of the Cl nucleus is smaller than the average value for many ordinary molecules. The latt’er evidence makes it possible to estimate the bond nature in this molecule. If the fractions of three resonance forms, N==S-Cl, N-=S=Cl+, and N=S+Cl-, are designated by fi , f2 , and f3 , the formulas developed by Dailey and Townes (14) provide the following three relations to t.he principal values of the x-tensor: xzz = 1-f,
-
%(l
xzz = Mfi - ?a XL/j/ = Mfi + (1 +
+ ~)hlml
,
+ ~)hlq31” I ~lf21Q310,
(15) (16) (l’i)
where j-1 +jz+j3
= 1.
(18)
Assuming the ant,ishielding constant c to be 0.15 and q310to be 109.6 MHz, the observed coupling constants listed in Table VI give f, = 0.355, _fi = 0.071, and ,fa = 0..%‘4. It indicates that, the SC1 bond is appreciably ionic and weak in the XSCl molecule. Finally, the lifetime of the NSCl molecule should be mentioned. The micro-
MICROWAVE
SPECTRUM OF NSCI
397
wave spectrum was observed under the flow of gas, t,o maintain constant supply of monomer molecules from N&S&l,. When t,he flow of t,he gas was stopped, the signals faded out’ in several ten seconds. The rate of decay of t,he microwave lines n-as measured for the transit,ions 2”,:! + 11,I and 41,3 +- 40,4 of the normal species, with the microwave speckometer fixed at the peak frequency of the signals. The decay was found to obey the first-order law with the half-life of about, 20 sec. It seems most, likely that the extinction of the NSCl molecules in the waveguide cell is attributable to the polymerization of the molecules on t,he wall of the naveguide. Note added in. proof: Guarnieri [Z. Naturfomch. 26a, 18 (1970)] has recently reported for CH#Cl that S-Cl = 2.014 f 0.01 8, xzz = -80.69 f 0.8 MHz, and 77 = 0.0784 k 0.013. It affords a substantial support to the above statement t,ltat the ionic as well as double-bonded forms are indispensable for NSCl. ACKNOWLEDGMENT The authors acknowledge the help of Masaaki Sugie in carrying out the calculation of the force constants. Thanks are also due to the Computer Center of the University of Tokyo for the use of their facilities.
RECEIVED: March
2.3, 1970 REFERENCES
1. 0. GLEMSRR .IND H. BICHI’:K~‘, Z. Anorg. Allg. Chew. 307, 313 (1961); 0.
2. 3. 4. 5. 6.
GLEMSER
.AND
H. PERL, A~alurwissenschaften 48, 620 (1961). .4. MIDX~SEN, Chem. Ber. 66, 1724 (1932). W. L. JOLLY, K. Il. Mt\~ul~s, .~NDL). B\UINOVIC!H,Inorg. Chew. 2, 1304 (1963). K. I>. MBGUIRE, J. J. SMITH, .\NDW. L. JOLLY, Chem. Ind. 28, 1589 (1963). J. J. SMITH >\NDW. L. JOLLY, 1norg. Chenl. 4, 1006 (1965). A. MILLER, 6. NAG.~RAJAN, 0. CI,F;MSER, 8. F. CYVIN, .\NDJ. WEGENER,Spectrochittc.
Ada, Part d, 23, 2083 (1967). 7. W. H. KIRCHHOFF :\NI) E. B. WILSON, JR., J. Amer. Chem. Sot. 86, 1726 (1963); 11. I,. CooR .~XD W. H. KIRCHHORF, J. Ch.m. Phys. 47, 4521 (1967). 8. T. AM.%NO,E. HIR(JT.\, .\NDY. MORINO, J. Phys. Ser. Jap. 22, 499 (1969). 9. T. Ox;\ .ZND Y. MORINO, J. Mol. Speclrosc. 6, 472 (1961). 10. R. L. COOK. .I. Chem. Phyx. 42, 2927 (1965). 11. T. L. WE~~HRRI,Y .\ND &. WILLI.\MS, J. Chem. Phys. 26, 717 (1956). 12. D. J. MILLEN .\ND J. P.\NNF,LL,J. Chem. Sot. 1961, 1322. 19. L. P.\TJLINO,“The Nature of the Chemical Bond,” p. 154. Cornell Univ. Press, Ithaca, N. Y. 1939. 14. B. P. I),\ILEY .\ND C. H. TO\VNES, J. Chem. Ph?ys. 23, 118 (1955).