The rotational-vibrational spectra of HNCS and DNCS

JOURNAL OF MOLECULAR

SPECTROSCOPY

50,36!%-402 (1974)

The Rotational-Vibrational

Spectra of HNCS

and DNCS

An Analysis of the High Resolution Spectra G. Department

R. DRAPER

AND R. L. WERNER

of Chemistry, The Nem South Wales Institute of Technology, Broadway, Sydney, Australia. 2007

Ro-vibrational spectra of HNCS and DNCS have been obtained in the spectral range 3OfMOOLl cm-’ with a practical resolution limit of 0.06 cm-r in the region 350-1200 cm-r and 0.15 cm-i in the region 12OCMOOO cm-r. The observed fine structure permitted definitive assignments for some of the PQ~, QQK, and ~QK branches in both molecules, and yielded sets of rotational constants in substantial agreement with those obtained from recent microwave and far-infrared studies. Precise estimates of the band origins have been obtained and there is evidence of second-order Coriolis coupling between the three bending modes in each molecule. The isolation of the out-of-plane bending modes has lead to a re-assignment of Ye, Y+ ~6, and ~6 for each molecule. The band origins, uncorrected for Coriolis interaction, are for HNCS and DSCS, respectively. Y, : 3538.6 f 0: 1989.0 f “3 : 857.0 f Yq: 615.0 f “5: 469.2 f Ye: 539.2 f

0.3, 2644.5 + 0.3, 1944.3 f 0.6, 851.0 f 549.1 f 0.5, 0.1, 365.8 f 0.5, 481.0 f

0.5 0.1 1.0 0.5 0.2 1.0

cm-‘; cm-‘; cm-r; cm-‘; cm-‘; cm-i.

INTRODUCTION

The structural parameters of HNCS and DNCS have been determined from microwave spectra (1-3). These have also yielded precise estimates of the J-dependent rotational constants but relatively poor values for those that are K-dependent. Recent studies of the high resolution far-infrared spectra by Krakow et al. (4) and Neely (5) show that the K-dependent rotational constants of these pseudosymmetric top molecules are extremely sensitive to the energy of rotation about the spindle axis. Large centrifugal distortion effects produced by the relatively light off-axis atoms necessitate the inclusion of semiempirical higher order distortion terms in the Kivelson-Wilson energy expression, that is EQ =

[Ao - $(Bo + Co)]K2 - DKK~ + HKK~ - HKxK’ + HRK,~K”.

(1)

Although the structural and rotational parameters of HNCS and DNCS are now reliably established, a number of differing assignments have been made for the bands observed in their vibrational spectra (6-IO), particularly for the three bending modes (Table J). Consequently, the force constant analysis by Orville-Thomas (11-12) using 369 CopyrIght

All

0

1974 by Academic

rights of reproduction

Press, Inc.

in sny form reserved

370

DRAPER

AND

WERNER

TABLE I INFRARED BAND ASSIGNMENTS FOR HNCS AND DNCS BY VARIOUS AUTHORS

BAND POSITIONS (cm-l) Reid (6) (Gaseous)

HNCS

Morgan (L) (Gaseous)

Barakat (3, (CC14 Soln.)

Durig (9) (Gaseous)

Present Work (Gaseous)

v1

3536

3539

3469

3538

3539

\)2

1963

1980

1980

1979

1989

V)3

995

851

850

999

857

V4

817

542

583

615

615

V5

469

470

464

467

469

'6

600

615

600

834

539

2

-

2644

2601

2641

2645

v2

-

1944

1937

1941

1944

v3

-

854

845

851

DNCS v4

-

483

511

586

549

"5

-

374

377

369

366

'6

-

566

580

835

481

Reid’s assignments

(6) differs significantly

on the assignments

of Durig and Wertz

This analysis of the high resolution

from that by Ore1 et al. (13) which was based (9).

ro-vibrational

spectra of HNCS

and DNCS

was

undertaken to determine the origins of the fundamental bands more precisely and to settle their assignment. Force constant and normal coordinate analyses based on this new data will be presented

in a subsequent

paper.

EXPERIMENTAL a. The Preparation

and Purification of Gaseous HNCS and DNCS

Isothiocyanic acid (HNCS) was prepared in good yield by the dropwise addition of a saturated aqueous solution of potassium thiocycanate to 100% orthophosphoric acid while the total vapour pressure was maintained at 2 mm Hg. The gaseous HNCS evolved was dried over PZOs and collected in a trap at -80°C

as a crystalline

solid. Carbonyl

sulphide, sulphur dioxide and hydrogen cyanide were removed when the HNCS was polymerized by rapidly heating the condensate to 4072 under a pressure maintained at 4 mm Hg. The polymer was stored at -8O’C under a total pressure of 1 mm Hg for up to five days. Pure gaseous HNCS was collected in glass cells by partial depolymerization of the yellow solid at 40-50°C each time a sample was required.

RO-VIBRATIONAL

SPECTRA OF HNCS AND DNCS

371

FIG. 1. The infrared spectrum of HNCS: 400@300 cm-’ (2 cm Hg pressure, 10 cm path length).

Isothiocyanic acid -d (DNCS) was prepared in a similar manner to HNCS except that 100% DsP04 and D,O were used instead of H3P04 and HZO, respectively. In order to avoid hydrogen-deuterium exchange all glassware was treated with gaseous sulphonyl chloride to remove surface water, and labile hydrogen atoms on the glass were removed by exposure to dimethyldichlorosilane vapour. The DNCS so produced contained 95-98 atom percent deuterium. The high resolution spectra of both HNCS and DNCS were obtained with sample pressures below 20 mm Hg since both materials polymerize and decompose rapidly when this figure is exceeded. Gaseous samples were replaced every three hours with fresh material collected in cleaned cells.

b. Meastiyement of the Spectra A single beam high resolution spectrometer was built by us to a Littrow design using four kinematically mounted gratings for radiation dispersion in the range 350-4.500 cm-‘. A 6” off-axis paraboloid mirror of 66 cm focal length was used at an aperture of f/4.4 to collimate either singly or doubly passed radiation. The arrangement of the optics for the double-pass mode of operation was similar to that used previously by Walsh (16) and Lord (17). A zirconium oxide glower and a silicon carbide bar were used as energy sources above and below 600 cm-‘, respectively. Radiation below 3000 cm-’ was detected by a thermocouple which was replaced by a cooled lead sulphide cell for radiation above 3000 cm-l. Higher order radiation was removed by use of the filter-chopper technique of Firestone (18) and Lord (19). The spectrometer housing was continuously purged with air essentially free from carbon dioxide and water vapor to minimize spectral interference from these molecules. Frequency calibration was accomplished by an interpolative procedure using the spectra of standard gaseous calibrants (20) in the first and second orders supplemented by published high resolution spectra (21-23). A scanning rate of 2-3 cm-’ per hour ensured a photometric accuracy of f0.05 cm-1 for sharp unblended lines when the amplifier conditions were set for maximum resolution. Practical resolution limits of 0.06 cm-’ and 0.15 cm--l were achieved in the regions 3.50-1200 cm-’ and 1200-4000 cm-‘, respectively.

372

DRAPER HNCS

AND WERNER

%

p4K

K =7

6

4

5

2

3

1

% ,

IO

2

345

! I Q, 65

K=

'

4

3

2 1; I

II

u I 3200

I 3100

I

1 I 3400

I 3380

II

II 3 00

3500

FIG. 2. Positions of the perpendicular and parallel Q branches in VI of HNCS. ENERGY EXPRESSIONS

AND COMBINATION

RELATIONS

The inclusion of the tenth power distortion term HKKK is required in the K-W energy expression [Eq. (l)] to completely account for the extreme centrifugal distortion in HNCS and DNCS, however a reasonable representation of the data obtained for both molecules was achieved by using the general energy expression: F(J,

- DJ(J + 1)2J2- DmJ(J

K) = Z?J(J + 1) + (A - &K”

-DKK4

+ 1)K”

+ H&-P - L&C8

(‘2)

TAGLE II Q BEGCH

POSITIOSS (m-1) X:D COXBIXATIOS DIFFTRiZCES (m-1) FOR "1 OF

RQ R

QQK

K

RQ,-QQ,.+L

PQI<

KCS

QQ,-‘Q,,

RQ,_,-pQ,l

RQ,-PQ,

0

3538.60

3576.3 + O.Za

1

3533.25

3634.7 + O.Za

3495.3 + 0.2=

116.3 + 0.2

118.00

161.0 2 0.2

139.4 _ + 0.4

2

3518.45

3676.45

3415.25

177.00

178.15

294.35

261.20

3

3499.45

3708.55

3340.30

228.15

228.30

405.30

368.25

4

3490.40

3731.05

3271.15

274.15

274.10

502.25

459.90

5

3456.90

3750.50?

3206.30

313.40

587.55

544.20

6

3447.17?

3143.50

349.90?

64‘?.70?

7

3457.7?

3107.80?

-

43.12

0.2

-

43.3 + 0.2

ROTATIOSAL CONSTANTS:'

A" - 2' = 44.15 cm-1

(A' - %') - (A" - 3') = 75.77

-1 cm

"f

=

1.04 cm-1

D' K - D'! k

= -0.18

-1 cm

El;

=

0.045 cm-1

H; - El;

= -0.002

-1 =pl

1-f

=

0.0006

L;: -

= -5.0 x 10-5 cm-l

cm

-1

L;

a : The error estimate is due to the broad contour of the branch. b

:

Centrifugal distortion terms taken to K8.

RO-VIBRATIONAL

1

SPECTR.4

373

OF HNCS AND DNCS

HNCS K=

3

4

2

1% I I I I I I I I

I

I 19Go

I

I 1980

I 2000

CM-’

FIG. 3. Positions of the parallel Q branches in YZof HSCS.

where l? = $(B + C). It follows that (RQK_l -

PQK1,)/4K

= (A”

- I?” -

4HK”)

-

(A? + 1)[2&”

+ (K* + 1)z(3HK”

-

16&“)

-

16LK” -

MK”]

(R2 + 1)34L~”

(3)

and (RQh- -

pQK),‘4K = (A’ - B’ -

4HK) -

(k’” + 1)[2D&

+ W

1Y (3Hix’ -

+

~'CABLEIII I.) BRANCH POSITIONS (cm-') FOR v2 OF HNCS.

0

1989.0

+

0.3

1

1987.4

+

G.3

1

1983.8

+

0.1

1

1977.3

+

0.1

4

1963.5

+

0.1

ROTATIONAL

CONSTANTS":

cm1

(A' - z') - (A" - 2') =

-1.28

tl;- u;;

=

-1 -0.028 cm

II;; - 13;:

=

-0.ob3

-1 cm

2: Centrifugal distortion terms taken to K

6.

-

16x&’ -

16LK’) -

~HK’]

(XI* + 1)34LK’.

(4)

DRAPER

374

FIG. 4. High resolution spectrum of HNCS:

AND WERNER

1018-985 cm-l (1.6 cm Hg pressure 50 cm path length).

For parallel bands, the subband centers are related by V$ = vg + [(A’

- B’)

-

(A” - B”)]K2

-

(DK’ -

DK”)P

+ (HK’ -

HK”)P

-

(LK’ -

LK”)IP

(5)

and the following relations apply: R(J

-

1, K) -

P(J

+ 1, K) = (4B”

-

6DJ”

-

4D&‘K2)

(J + $)

-SD=“(J R(J

-

1,K)

+ P(J,

K) = 2~0”+ 2J2[(B’ - B”) + (D&

For hybrid bands, the following combination

relations

apply

+ +)3,

- D.m”)K21.

(6) (7)

:

(RQ~ - QQ~+~) = (&QK - PQ~+~) = (K + 3){ 2 (A” - B”) - Dg” + QHK’l - +LIc” - (4DK” - SHK” + $LR”) x (K + a,2 + (6Hd’

-

14L~“) (K + 3)” -

SLK”(K

TABLE IV Q BRANCH POSITIONS (cm-l) FOR TIIII 997 cm-l BAND OF IINCS.

K

QQ,

Assigned

Estimated

(IQK

0

996.59

0.05

996.6

1

996.89 +

0.05

996.8 +

0.3

2

997.75 t

0.05

997.7 +

0.3

3

998.93 +

0.05

998.9 +

0.2

4

1001.90 _ +

+

O-05?

5

0.3

+ $)6},

(8)

RO-VIBRATIONAL

SPECTRA

OF HNCS

AND

37.5

DNCS

HNCS

I

I

FIG. 5. Detail length).

in the infrared

(“QK - QQK)= = (E; +

GO0

500

400

+){ 2(A’

(Q&+1

-

I

spectrum

of HNCS:

CM-’

I

3.5&700

cm-’

(2.5 cm Hg pressure,

10 cm path

PQK+l)

-

B’)

700

-

DK’ + #H,’

x (K + 4)’ +

-

(~HK’ -

$LK’ -

(40~’

~~LK’)(K

-

5He’ + ZLg’)

+ a)” -

~LK’(K

+ ;)6),

(9)

(“QK +

&QK pQ~+~- '9~+1)/(2K -I-1) =2(.~"- jj")- DK" + QHK" - ;LK” - (4DK” - 5Hx” + ;LK”)(K

+ (6HK”

ANALYSIS

OF THE

-

~~LK”)(K

SPECTRUM

+ +)” -

8Ljy”(K

+ 4)” + 3)“.

(10)

OF HNCS’

HNCS has six fundamental vibrational modes, five of a’ species and one of u” species. The bands arising from these modes (Fig. 1) should all be strong except that for the symmetric stretching mode, ~3, which should appear as a strong band in the Raman spectrum (IO, 24). The justification for the band assignments will be given in subsequent discussion. The Region 3100-3750

~rn-~: vI

The hybrid band in this region has a relatively strong parallel component branches of which were identified in the high resolution spectrum. An intensity 1 The published .Wditional spectra

high resolution spectrum has been restricted to those regions may he obtained hy communication with the authors.

of particular

the Q ‘well’ interest.

DRAPER AND WERNER

376

ROTATIONAL COXSTANTS FOR THE 997 cm-1 Rotational Constant n" - "2Dj,

K=l

I<=2

0.1953 _ + 0.0008 cm-1 -O.OrlOl rJ.0001cm-1 5

li'-B"

Utl,WOF HNCS.

D;

K=3

0.1958 + 0.0008 cm-1 -0.0003


+

0.0001 m-1

0.1959 _ + 0.0005 m-1 -1 -rl.o002+ 0.0001 cm



Mean Value of :" (assimin;;D&. negligible) 0.1957 + 0.0008 CI-1 \ -6 -1 " (A' -ii') - (A' - 2,) = 0.32 cm-1 , II’. - D" = 0 0064 cm-l cm , DJK = -10 h I( ’ TABLE VI -1 LINE POSITIONS (cm-l) IX THE 997 cm DMD

J 0 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

OF IINCS

IL=1

:;=2

1<=3

996.89

997.75

998.93

‘R (J)

QPl(J)

QR2 (J)

QP2 (J)

QR3(J)

Qpp

99Y.62”

998.06" 998.45" 998.85" a 999.25 999.65= 1000.03 1000.41 1000.77 1001.15 1001.50 1001.88" 1002.35a 1002.Y5a 1003.13a 1003.48 1003.87 1004.28 1004.68 1005.03 1005.43 1005.79 1006.17 1006.53 1006.93 1007.31 1007.68 1008.07 1008.44 1008.84 1009.23 1009.63a 1009.98" 1010.38" 1010.7? 1011.22= -

996. OOa

995.60= 99s.27a 994.85 994.45 994.05 993.63 993.23 992.83 992.42 992.04" 9Y1.64a 991.23" 990.85a 990.45 990.06 989.69 989.32 988.92 988.56 988.15 987.76 987.38 987.02 986.64 986.26 985.84 985.44 985.04a 984.60a 984.22= 983.86a 983.42" 983.04 982.65 982.18" 981.82" 981.45n 981.05= 980.68"

998.88”

999.32= 999.6Ea 1000.07 1000.48 1000.84 1001.24 1001.59 1001.95 1002.35 1002.73 1003.09 1003.43 1003.84 1004.28 1004.68 1005.05 1005.43 1005.81 1006.17 1006.54 1006.93 1007.29 1007.66 1008.08 1008.42 1008.83 1009.18 1009.50 1009.93 1010.30 1010.70 1011.10 1011.4ea 1011.84 1012.23" 1012.60 1012.95 1013.40a 1013.74

996.57

996.71 995.76 995.36 994.93 994.54 994.12 993.708 993.35 992.93 992.52 991.67 991.23 990.81 990.43a 989.69 989.32 988.92 988.54 988.12 987.68 987.26 986.83 985.97 985.55 985.14 984.39 984.00 953.60 983.15

a : Doubtful accuracy due to overlapping hands.

-’

1001.01" 1001.40= 1001.80a 1002.19a 1002.89

1004.06 1004.44 1004.84 1005.11 lCO5.99 1006.38 1006.77 1007.19 1007.60a 1007.95 lCO8.33 1008.73 1009.18 1009.53 1009.93 1010.24 1010.70 1011.10 1011.50 1011.90 1012.18 1012.67 1013.04 1013.43 1013.80 1014.20 1014.59 1014.95 1015.34

Y97.2Ba

996.95= 996.59" Y96.1ga 995.76 995.36 994.95 994.54 994.16 993.76 993.35 992.96 992.54 992.11 991.74 991.35 990.97 990.56 990.15 989.76 989.36 988.97 988.62" 988.27" 987.90a 987.52"

RO-VIBRATIONAL

FIG. 6. Detail in the infrared

spectrum

SPECTRA

of HNCS:

OF HKCS

700-1050

AND

377

DNCS

cm-’ (2.5 cm Hg pressure,

10 cm path length).

cm-1 was assigned as the band origin and this is within 0.2 cm-l of its position calculated using the appropriate combination relation. The assignment of the Q branches was straight forward (Fig. 2, Table II). “QO and ‘Qr are degraded to high and low wavenumbers respectively, due to the asymmetry splitting of the K = 1 rotational energy level : The positions of the Q-branch lines in RQOof a pseudosymmetric top molecule are given by

at 3538.6

,Q = vg + @’ - B’ - DK’) + J(J

+ l)(B’&d - P

- DJK’) -_P(J + 1)2(D.r’ - DJ”)

(11)

and in ‘Qr by vQ = rO -

(,I” - B” - DK”) + J(J + l)@

- B”c,d + DJ~“) -_P(J

+ ~)*(DJ’ - DJ”)

(12)

where B = +(B+ C), B, = 4(3C+ B) and Bd = $(3B + C). B, and Bd are the effective B values arising from the ‘c’ and ‘d’ asymmetry doublets in the K = 1 level. For u” +- a’ and a’ +- a’ transitions the ‘c’ and ‘d’ sublevels are involved respectively (25, 26). The line like Q branches observed for transitions where K > 2 indicates negligable degrading due to the difference B’ - B”, that is B’ ‘v B”. Since Bd” > l?’ >B,“, it follows from Eqs. (11) and (12) that RQOwill be degraded to higher and PQr to lower wavenumbers for transitions of a’ species, and in the reverse directions for transitions of u” species. “Q1 and ‘Q 2 will be shaded in both directions because each arises from transitions involving both ‘c’ and ‘d’ levels. It is therefore apparent that this band is of a’ species. A number of the perpendicular Q branches have what appear to be associated Q branches, their positions are indicated in Fig. 2. No reasonable explanation could be found for their presence.

378

DRAPER AND WERNER

HNCS

726.5

713.6

i:

706.5

66.1

CM-'-

FIG. 7. High resolution spectrum of HNCS: 726-688 cm’ (7 mm Hg pressure, 50 cm path length).

The Region 1940-2020

cm-r: vp

The band in this region is five times more intense than any other in the infrared spectrum of HNCS that A’ amongst

(Fig. 1). Its irregular profile is degraded to low wavenumbers

A” is negative. the overlapping

It was possible to identify the Q branches fine structure

and a significant

intensity

indicating

(Fig. 3, Table III)

‘well’ at 1989.0 cm-l

was assigned as the band origin. Although all bands in HNCS of a’ species should be hybrid in character, lar component

a perpendicu-

of this band system could not be found. The parallel component

is SO

TABLE VII Q BRANCN POSITIONS (cm-')AND COllBINATION DIFFCUZNCES(cm-l)FOR U4 OF BNCS

K

0

QQK

“QK

PQ,

RQ~-QQ~+r qQ,-PQ,l

RQ,;_,-PQ,l

RQ,-PQ,

1

615.0 + 0.5 646.20

689.76 S30.25

573 + la

43.56 116.63

42 + 1.5 116.6+ 0.2

160.2 + 0.2

257 + 1

2

713.62

948.52

529.6 + 0.2a

176.87

177.09

293.72

418.9 + 0.2

3

771.65

1042.37

536.53

228.29

228.32

405.19

505.84

4

814.08

543.33

274.63

502.92

5

834.20

539.45

6

841.93?

a : The error estimateis due to the broad contourof the branch.

RO-VIBRATIONAL

@WI&.

SPECTRA

OF HNCS

AND

HNCS

5’6.6

Frc. 8. High resolution

379

DNCS

56i.t

spectrum

of HNCS:

608-562

cm-’

(7 mm Hg pressure,

50 cm path

length).

intense that it probably conceals the weaker perpendicular subbands and this suggests that the relevant normal coordinltte is almost parallel to the prolate axis. The Regiolz Y6U-1OsK)cm]:

vj + vg

The relatively weak parallel band centered near 997 cm-’ has a symmetric profile indicating that (A’ - Z?‘) - (A” - B”) is relatively small (Fig. 1). It is also evident from the high resolution spectrum (Fig. 4) that the parallel subbands are almost superimposed on each other, and since the inertia ratio ZA/Zn is exceedingly small, it follows that the QQK branches will be weak and are likely to appear as abnormally broad or intense J lines close to the band origin. They were, in fact, assigned on this basis (Table IV). The fine structure of the P and R branches of the parallel subbands for K = 1, 2 and 3 were assigned up to _Zv 40 (Table VI). Values for the J-dependent rotational constants (Table V) were estimated using Eqs. (6) and (7). Since the value of B” - DJK”K2 increases slightly with increasing K, DJ~” must be both negative and very small, in accord with the millimetre wave K-patterns observed by Kewley et al. (3). The Region 300-900 cm-‘:

~3, vq, vj, vg

Four hybrid band systems were found in this region, each with its rotational fine structure overlapped by that from one or more other band systems. An analysis of the high resolution spectra permitted their disentanglement and each band will be considered separately in an order which simplifies discussion. v,. The key to the analysis of this band is the very intense Q branch at 689.76 cm-’ which is degraded to high wavenumbers, indicating that it is either an R branch of an

DRAPER

380 TABLE

AND

WERNER

“III

I:OTATlONAL CONSTANTS

FOR

\)‘

OF UNCS

Rotational CORStXlt

K=O

K=l

0.1958

+0.0008 cm-1

K=2

0.1958

-1 +0.0008 cnl

0.1958cln -1 +0.0003

0.1959

_1

+0.0003 cm us

_

-

2:’

-0.0001

cn,-1

ZlO-7

cm-1

-1 -0.0001 cm

-0.0001 cm-l

K=5

K=4

K=3

0.1960 _1 +0.0002 cm

0.1965 _1 +0.0007 cm

Neg.

(approx.) D;


cm-1


c,-1


-7

-1 cm

(ilpprox.)

-1

?K =

-10-5 cm

Mean Value of 2"

(K:O + 3, neglectingD;IK):0.1958 + 0.0008 cm-1

(A’ - B’) - (1\”- 21) = 33.88

cm -1

A" -pa

= 44. 26

D;;"

=

1.049 cm-1

wa K

=

0.042 cm-1

f

1; L"a

=

0.0007 cm-1

Li': - L;;

D; - D;; - H;

= = =

cm-l

2.76

-1 cm

0.12

-1 cm

0.002

cm-1

a : Centrifugaldistortionterms taken to K8.

a’ + a’ transition or P branch of an u” * a’ transition. It was assigned RQo and this was confirmed by the presence of a linelike Q branch at 646.20 cm-r which must be QQr since one line is missing from its associated P and R branches. A second intense Q branch at 830.25 cm-l, assigned as RQ1, has a profile consistent with that expected for Q branches involving K (2 +-- 1) or K (1 + 2) transitions except that it is slightly skewed to high wavenumbers. ‘Q1 is strongly degraded to low wavenumbers and its center was placed in the range 573 f 1 cm+ (Fig. 8). The other pQK branches are grouped near 535 cm-’ and in general

HNCS

FIG. 9. High resolution spectrum of HNCS: 62&608 cm-’ (7 mm Hg pressure, 50 cm path length).

RO-VIBRATIOS.U,

are degraded band

origin

to low wavenumbers could

not be precisel!.

of the lines each side of the intensity Measurements

made

for this band

SPECTRA

Ok’ HNCS

consistent fised

with

from

ASD

u’ +- a’ transitions

‘01 but was positioned

‘well’ at 615.0 cm-i are presented

381

DNCS

(Fig.

10). The

b!. the doubling

(Fig. 9).

in Tables

VII and IX and the rota-

tional constants calculated therefrom are given in Table VIII. Q-branch positions shown in relation to those in other bands by the line diagrams in Figs. 5 and 6. L4synlmetry

splitting

was observed

for .I > 10 but an accurate structure

with other

The differences

estimate

in the fine structure

of the K = 1 parallel

of R” and C” was prevented

by overlap

the upper

and lower state

i:=o

rotational

constants

0 1

c%$,IJ)

-

1

;

616.46 616.03

4 5 ii 7 n 'i 10 11 1" 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 18 29 30 31 32 3J '14 i: Ih

616.80" h17.203 b17.58 1117.86 618.27 b18.58 618.93 619.33 619.70 b20.08 620.50 620.91 621.27 611.75 622.21 622.61 623.02 623.43 623.81 624.25 624.bX 625.3X 626.25 626.70 627.11 627.52 627.94 62R.32 628.68 b29.117 blci.48

i;= 2

i;=L

615.0 + 0.5 --I_----

‘1~

J

subband of the fine

subbands.

between

1‘,,1:1.1: Ix

0 ‘0

are

I%U (.I)

h46.2ll '%(.I)

h14.63

64h.92”

614.30a (113.98"

647.24 647.b') 648.Iih (148.44 b4ii.YL 1149.18 h49 .h4 65U.04 651J.44 65lJ.S? 651.21 65l.il4 b51.01 (152.37 652.75 65 1.17 653.53 643.Y4 654.35 654.73 613.14 h55.47 655.89 656.28 h56.68 657.0X 657.4X 657.85 hjS.?h 658.65 b5,,.')h hjCi.!,,l

613.WJ" bl.'.h9n b12.153 611.75n 611.3? 61U.95' 610.52 hlU.UB 6OY.7? 6OY.3.? 608.Y? 60X.5? 608.11 607.3~ 606.b5 hUh.3U hil5.91 605.47 605.05 604.65 604.17 603.82 603.43 603.08 6Ul.70 (~02.31 601.97 bUl.hlI hill.24 i,OO.Xi

0 ‘rl(.J)

645.43 6>45.03 h44.6Ci 644.22 io43.8j hS3.43 043.U4 1142.63 642.24 1041.81 641.48 (141.08 640.66 640.27 639.88 639.50 h39.13 638.74 638.39

637.98 617.55 637.15 636.77 Ib3b.35" (135.96 635.58 (135.17 634.77 634.31 h33.90 633.12 632.74 6??.38 h?l.'Id

713.hL QR., (J)

(1 ‘I', (.J)

714.743 a 7I5.?0 71i.hO' 715.95" 7u>.3?c1 716.78 717.10 717.45 717.90 718.30 718.69 719.08 719.49 719.95" 7X.15 72U.65 721.03 72X.39 721.77 722.18 722.54 7?.!.YE 723.32 72J.70 7?4.08 724.50 724.x9 72i.29 725.68 i?f*.IIX 7.!(>.47 7.!0.87 iI!;'.? i';.hi ;>i.o7

712.54 712.12 711.70 711.14 71U.92 710.58 710.12 709.73 709.32 708.89 708.43 708.00 707.66 707.10 706.Y5 706.60 706.19 705.78 705.38 705.01 704.60 704.20 701.81 703.45 703.04 702.66 702.28 701.87 7U1.48 701.06 7UU.bH 7GU.I!i (199.84 0I,9 .4 5a

are abnormally

382

DRAPER TABLE IX -

continued

LINE POSITIONS (cm-l) IW "

9

Q,

J

0 1 2 3 4 5 6 7

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 15 20 27

28 29 30 31 32 33 34 35 36

AND WERNER

K=3 771.65

"I; (.J)

773.1S8 713.x+' 773.94" 714.35 774.74 775.15 775.54 775.93 776.73 777.15 777.45 777.84 779.19 778.60 77Y.03 779.41 779.73 780.17 JEO.60 780.97 781.38 781.7h 781.17 782.54 782.91 783.32 783.72 784.07 784.45 754.79 785.18 785.58 JS5.96

%'3 (.J)

769.28

768.88 768.47 768.08 767.72 767.35 766.97 766.55 766.16 765.78 765.41 765.00 764.64 764.25 763.84 763.45 763.04 162.66 762.23 761.64 761.48 761.10 760.70 760.30 759.85 759.45 759.07 758.67 758.30 757.92 757.55

4

OF HSCS

K=4 814.08

K=5 834.20

%C5 (3)

'k (.I) il

816.42" 816.82" 817.2Zn 817.61 818.00 818.35 818.77 819.14 S19.62a 819.99 820.37 820.70 X21.08 821.55 521.97 822.35 822.70 823.10 823.50 823.92 824.29 524.69 825.09 S25.49 825.85 826.24 826.63 827.02 821.44 827.85 628.23 824.63

large, as is the degrading of the perpendicular

--

811.61' 811.23a 310.89a 810.48" 810.10" 809.72 809.31 808.92 808.5!, 808.211 807.78 807.35 806.95 806.57 806.23 805.86 505.43 805.05 804.65 so4.30 803.88 803.48 803.12 SO2.70 802.32 801.96 801.56 801.18 800.73 800.32 799.95

836.54 837.00 837.38 837.79 838.25 838.61 839.03 x39.44 839.80 840.17 840.68 841.94

Q branches,

QP(J)

L

831.72 831.34 830.94 830.48 829.85 829.45 829.02 828.63 828.23 X27.85

and the “QK branches

are

more intense than the corresponding pQK branches. These features indicate that the upper state rotational energy levels of this vibrational mode are perturbed. A similar phenomenon has been observed in the bending modes of H(D)NCO (14, 15) and H(D)N, (27), and was attributed in these cases to second-order Coriolis coupling between the three bending modes in the excited vibrational states. yr,. This hybrid band system spreads across the region 500-900 cm-’ and has a relatively strong parallel component pulled out to high wavenumbers mixing with structure from ~4 (Fig. 5). The RQK branches diverge to high wavenumbers with a consequent packing of the ‘QK branches into the region 430-500 cm-‘. A linelike Q branch at 555.37 cm-r has one line missing from its associated P and R branches

and was assigned as QQ1 (Fig. 10). RQO and PQp are in the expected positions

RO-VIBRATIONAL

TABLE IS

-

383

SPECTRA OF HNCS AND DNCS

continued

LINE POSITIONS (cm-l) IX \)&OF :(idCS

ki=I

J

‘!Pl(.J)

"l<,(J)

37 38 39 40 41 42 43 44 45 46 47 48

631.52" 631.16" 63U.75a 63O.378 629.97" 679.49" 629.12" 62X.& 62X.32 h27.94 627.52 627.11 626.70

728.47 728.83 729.20 729.63 730.00 730.39 730.77 731.17 731.55 731.92 732.30 732.70 733.07 733.47 733.86 734.25 734.611 735.00 735.39 735.R2 736.23 736.62 737.10" 737.43n 737.52 738.26 778.64 739.04 739.43

49

511 51 52 53 54 55 56 57 58 59 60 61 62 63 64 6:

K=4

6=3

I:=2

G99.10a 698.74" 698.35" G97.97a 697.55a G97.17 696.78 695.97 695.56 695.15 694.75" G94.373 643.96

%3(J)

',3(J)

%4(J)

'P4(J)

766.35 786.75 787.08 787.50 787.92 788.30 788.68 789.10 783.53 789.88 790.27 790.68 791.08 791.51" 791.87 792.33 792.70~ 793.05" 79j.44;1 7')3.79 7Y4.15

757.18 756.79 756.37 755.98 755.58 755.16 754.77 754.40 753.89 753.50:' 753.13" 752.79" 752.38 751.95" 751.55 751.15 7517.7;; 750.37 750.00

829.02

799.54 799.16 798.80 798.38 798.00 797.64 797.23 796.85 796.48 796.10 795.70 795.30 794.91 794.53 794.13 793.78 793.44

829.45 829.85 830.54a 830.92 831.34 831.72 832.12 632.53 832.95 633.37 633.77 S34.57 834.97 635.0's 835.77 835.20 836.55"

a : Doubtful accurncy due to overlapping bands.

(Figs. 8, 11) and have profiles consistent with an a” +- a’ transitions involving the K = 1 rotational energy level. ‘Qr has been assigned to a very broad, strongly degraded Q branch whose origin can only be approximately tised at 495.7 A 0.5 cm-l, thus placing QQOnear 539.2 cm-*. There is no parallel subband centered near this position and this is to be expected when the parity selection rule operates for an u” +- a’ transition. The other Q branches for this band system have been assigned using appropriate ground state combination difference relations, intensity characteristics and band profiles (Figs. 5,6, 11; Tables X, XII). Relevant rotational constants (Table XI) must be regarded as less reliable than those obtained from other band systems where more data is available. The calculated differences between the ground and excited state rotational constants are usually large and, like Y,, it is apparent that the excited state rotational energy. levels are perturbed. It is pertinent to state here that the profiles of the perpendicular ‘QK and “QK branches, and the absence of the K = 0 parallel subband specify the normal coordinate responsible for this band system.

384

DRAPER

AND

I

WERNER

CM-’L__

FIG. 10. High

resolution

spectrum

of HNCS:

562-522

cm-l

(12 mm Hg pressure,

50 cm path

length).

vg. The hybrid band system evident in the interval 350-550 cm-l is of medium intensity and is strongly distorted to low wavenumbers (Fig. 1). Perpendicular Q branches complicate the profile but the P and R branches of two parallel subbands centered near 470 cm-’ and 42.5 cm-’ are clearly discernible (Fig. 5). The very strong Q branch at 425.6 cm+ (Fig. 11) was assigned as ‘Q1 since its profile differs from nearby perpendicular Q branches of v6 and the assignment is consistent with the absence of a line associated with QQo at 469.15 cm-‘. QQI was confidently assigned TABLE X

Q URANCI!POSITIONS (cm-l) AND COMBINATION DIFFERENCES (cm-l) FOR V6 OF HNCS

K

QQ,

RQK

pQK

“QK-QQK+I

QQK-pQK+l

RQK_,-PQ,,

-

0

Missing

598.85

-

43.48

1

555.37

723.70 495.7 5 O.Sn

115.85

116.7 + 0.2

160.2 + 0.2

2

607.85

874.93 4%.7 + 0.2"

178.59

177.19

293.04

3

696.34

22ii.99

405.50

4

776.13

5

849.46?

6

904.0?

-

430.66 469.43

U. (estimated from the position of

1’

Q~):

“QK-‘QK

539.2 _ + 0.5

-1 cm

a : The error estimate is due to the broad contour of the branch.

228.0 t 0.5 '436.2+ 0.2

RO-VIBRATIONAL

SPECTRA OF HSCS AND DNCS

FIG. It. High resolution spectra of HNCS: 508-488 cm-l, 474-461 cm-l, and W23 pressure, 50 cm path length).

since the two adjacent Q branch assign

this Q branch

RQo and

J-lines

at 307.7 cm-’ “Q1 have

profiles

assignments

(Table

However,

and it has the correct

was assigned

to a pure rotational

level and their XIII).

are absent

which

consistent

QQ2 is more

combination

as PQ2; (Krakow a’ +-- a’ transitions

by the positions

intense

than

would

involving

be expected

from

ROTATIONN. CONSTANTS FOR ~6 OF HNCS

p

K=l 0.1957

- ,p?D;;

K=2 0.001 cm-1

0.0004 i 0.0001 cm-1

Bs - 2,

xean

+

of "

Value

1:=3

-

-1 0.1959 i_ 0.0009 C",

-

0.0002 + 0.0001 c"l-1

(D& nssumed negligible) U.1958 & 0.001 cm-I

A" - i?'a = 44.36

a-'

D; a

=

0.90

-1 cm

,,'! ii :\

=

0.02

-1 cm

to a to

(A' - A") - (li'- 1:") = 13.76

cm-'

1,;- 1);;

= -1.14

-1 C",

111- 11;; "I:

= -0.10

cm-1

";(- I$

= -0.002

m-1

3 : Centrifugal distortion trrms taken to Kb.

the h

= 1

of QQ1 and QQ,, respectivelh-

TABLE XI

Rotational Constant

relation

et aZ. (4) were unable

transition). with

are supported

cm-’ (6-9 mm Hg

the overall

386

DRAPER AND WERNER

J ..0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1G 17 18 19 20 2L 22 23 24 25 2G 27 28 29 30 31 32 33 34 35 36 37 3s 39 40

“1: (J)

_A-.. _ ._ 550 15 556:40” 556.77 557.15 557.55” 55S.3JJ 555.82 559.57 560.04 560.50” 560.90 5Gl. 29

562. 50J 562.80 5G3.20 5G3.60 564.00 564.42 564.85 565.28 565.72 566.13 566.55 567.03 567.44 567.85 568.22 568.62 568.03

II ‘I’,

(.I)

i54.59” 554.20” 357 ii”’ . -,I 553.42 5S3.0En 552.60 552.18 551.75 351.411 551.01 550.20. 549. 3in 549.00 548.62 548.30 547.92 547.55” 547.X” 546. RO 546.4j 545.65 541.28 544.92 544.54” 544.15 543.83 543.39

I!!:,(J)

hW.Y7 6LlS. 35” 69X.74 69il.07 hY9.45 C>YY. 54 700.27 7l10, 69 701 .04 701.45 Jfll.S7 702.26 702. hh 703.114 701.45 7U3.Sl 704.211 704. 6(1 705.01 705.39 705. 7:s 7116.1’) 706. GO

‘!I’

(.J)

694.75” 694.39’ 693.96” 693.57 693.17 692.80 692.42 592.00 691.65

691.25 690.88 hY0.48

658.84 hS8.50 688.13 687.77

706.Y7 707.30 707.70 703.08 708.52 708.89 709.32 709.73 710.12 710.55 710.94 ill.34 711.70 712.12 712.54

a : Doubtful accuracy due to overlapping bands.

band profile and this branch may also be attributed

to the RQS ground state pure rota-

tional transition (4). RQ2 could only be tentatively assigned to a Q branch at 349.5 cm-’ since this is the expected position for “Q8 from the pure rotational spectrum. Apart from the K = 0 parallel subband (Table XIV) the fine structure was not resolved due to the accumulation of perpendicular Q branches from both ~6 and v5 in the region 425475 cm-1 (Fig. 5). The spectrum was further complicated by very weak Q branches which were thought to come from a hot band, the origin of which could not be determined. The most striking feature of this band system is its gross distortion. All the RQ~ branches

are on the same side of the band origin as the pQ~ branches,

a

phenomenon

387

SPECTRA OF HNCS AND DNCS

RO-VIBRATIONAL 'T.\I;Ll! SILL '1 BRANCH

POSITIONS(c.m~l) ANND COMBINATION DIFFERENCES

(cm-l)FOK "5

"Q,<-(!Q,l

ROTATIUNAL

-1

y

44cm

1:"

=

-1 0.1956 _t 0.0002 cm

=

-4 -1 0.5 x 10 cm

B'_ F'

(A' - A") - (C' - 2') =

RQ,_,-PQ,l

-1

II'- q

= -2.41 cm

H; - 5

= -0.095 cm-l

-1 -47.02 cm

a : The error estimate is due to the broad contour of the :

QQr-"Q,.+l , \

b CONSTANTS:

,\\"

b

OF IINCS.

‘vrandl.

Centrifugal distortion terms taken to Ii'. TliELGXIV ______ LI:X 1'USITIOSS(cm-') IN "5 OF HNCS. K=O

469.15

-

9,

L--469.40a 469.82' 470.20" 470.58" 4i0.9zn 471.30 Ail.72 472.15 472.55 ii'.92 473.30 47:.03 I, ;'i . i,5 47i.8U :75.15"

46X.55 468.18 467.80 467.40 4fi6.YV 466.65 466.25 46j.,?i 465.45 465.f15.! 4h4.7U'1 4lA.W' 463.W' SRJ.51 iih1.11

(J)

478.67 47Y.K 479.49 179.88 48U.30 480.78 481.13 481.53 481.90

iR5. !+Si.92

2.’

QIJnLJ) 459.60 459.20 458.80 458 45n 458:OO" 457.59" 457.22 456.80 456.46 456.n3 455.66 455.27 45+.86 454.50

RQK-PQ,

388

DRAPER

I

AND

WERNER

l

CM-'---

851.4

82 8.4

FJG. 12. High resolution spectrum of HNCS: 916-828 cm-’

(2 cm Hg pressure, 50 cm path length)

without precedent in the literature. This distortion is reflected by the highly negative values obtained for A’ - A”, DK’ - DK” and Hg’ - HK” (Table XIII), and indicates a perturbation of the upper state rotational energy levels similar to that observed for v4 and vg. VS.Two prominent Q branches at 897.67 cm-’ and 813.63 cm-i do not belong to ~4, ~5, or ~6, nor can they be assigned to hot bands. The fact that they are both approximately 43 cm-i removed from 856 cm-‘, and are equally intense, strongly suggests that they are “Qo and ‘Qi, respectively, of a band centered near this position. An intensity ‘well’ at 857 & 0.6 cm-r is considered to be the band origin and several relatively weak QQK branches nearby are thought to be part of the band system (Fig. 12, Table XV). ANALYSIS

There is general agreement arising from the fundamental

33GO

OF THE SPECTRUM

OF DNCS’

in the literature that the regions containing the bands vibrational modes are 2800-2400, 2000-1900 and 950-

2000

3 so0

I

I

FIG. 13. The infrared spectrum of DNCS: 4000-300 cm-’

1 ODO

I

500

CM-’

I

(2 cm Hg pressure, 10 cm path length).

RO-VIBRATIONAL

SPECTRA

OF HNCS

AND

389

DNCS

DNCS

Psr K=

4

5

FIG. 14. Positions

9%

‘30 3

2

of the parallel

1

IO

1

and perpendicular

Q branches

23-l

in YI of DNCS.

ONCS

3.

/

I

I

I i ‘I

I )

I

I

I

1920

1930

! j

I ,I

I

(

1940

TM-1

FIG. 1.5. Positions

of the parallel

Q branches

in the ~2 of DNCS.

c!Q,;-~‘!!,;+l il

857.0 +

1

854.57

813.63

1

847.14

735.63

3

835.38

WIATIOShL ___-

0.6

897.67

43.10

CUiiSTANlS: a

(A' - is') - (.\" -c")

= -2.56

U: - D'I I\ i\

= -0.016

a : Centrifugal

distortion

cm -1

cm -1

terns

taken

to K4.

I’,

!I;_l-“I’i, ,

43.4 _i.0.6 118.94

162.04

_I’

.‘,,

K

390

DRAPER

FIG. 16. Detail in the infrared

spectrum

AND

of DNCS:

300 cm-l. The latter region contains bending modes (Fig. 13).

WERNER

30&500

cm-l (2.8 cm Hg pressure,

10 cm path length).

four band systems, three of which should arise from

Q IXUXCIIPOSITIOSS (cm-l) AXD COMBINATION DIFFERENCES (cm-') FOR v1 UF DNCS

RQgQQ,l

K

QQK-pQK+l

KQK_l-PQK+I RQK-PQ,

0

2644.5 _ + 0.5

2665.9 _ + 0.2a

1

2642.54

2701.7 + 0.P

2620.9 2 O.Za

2

2636.30

2.730.45

2577.10

102.37

102.73

168.13

80.8 _ + 0.4 153.35

-

23.4 + 0.2

23.6 + 0.7

65.4 + 0.2

65.44

88.8 + 0.2

3

2628.08

2736.80

2533.57

134.52

134.68

237.05

203.23

4

2602.28

2742.45

2493.40

160.301

162.83

297.30

249.05

5

2682.15?

2439.45

ROTATIONAL COSSTILUTS:b A" - 5' = 13.54

3)

c",-I

(
D’ - 1,': K h 1::- II"

D'I 1,

=

0.36

cni-'

IL'! !\

=

0.013

cn-1

1:;

=

0.0002

a-1

-

ii

-

(A”

-

21)

2

-2.5

,“p,-l

- -0.1.

cm-1

2 -0.01

cm-1

1:

a : The error estimate is due to the broad contour of the branch. b

:

Centrifugal distortion terms t&en

to K8,

RO-VIBRATIONAL

600

OF HNCS

FIG. 17. Detail in the infrared

AND

900

I

spectrum

of DNCS 600-900

391

DNCS

00

700

I

I

The Region 2400-2800

SPECTRA

CM-’

I

cm-1 (2.8 cm

Hg pressure, 10 cm path length).

cm-‘: VI

The major band in this region is hybrid in character ponent. A relatively strong combination combination

and has an intense parallel comband centered near 2794 cm-’

TAELE XVII Q BRANCH POSITIONS (cm-l) FOR "2 OF DSCS.

0

1

1944.2 _ + 1943.1 _ +

0.1

2

1940.5 2. 0.2

ti.1

3

1935.8 +

0.1

4

1922.0 +

0.1

ROTATIONAL CUXSTANTS:"

(A' - x') - (A" - 2") = -1.14 .N-~ D' _ D" K K

-1 = -0.07 cm

11;: - El;;

= -0.005 cm-1

a : Centrifugal distortion terms taken to K6.

392

DRAPER

FIG. 18. High resolution

spectrum

of DNCS:

AND

697-650

WERKER

cm-1 (7 mm Hg pressure,

50 cm path

length).

blends with the perpendicular R branches but, apart from this, the assignment of the Q branches was straightforward (Table XVI, Fig. 14). Some perpendicular Q branches appear to possess ‘satellites’, a feature observed in vi of HNCS. The QQx branches are more prominent than their counterparts in HNCS reflecting an approximate twofold increase in the value of IA/Ju. The significant negative value of A’ - A” suggests that the normal coordinate associated with this band system involves an appreciable change in molecular geometry upon vibrational excitation. The Region 1900-2000

cm-‘:

uz

Relatively poor resolution capabilities the disentanglement of the fine structure

0

549.7

I

578.54

‘?

05l.HO

+ I.0

w11.75 716.15

515.s5

of the spectrometer in this region prevented associated with the very intense parallel band

ZJ.11

2i.x

04. 45

64.57

513.97

l(13.10 135. 82

3

713.12

548.70

4

085.40

577.Y

+ 1.0

87.78 Lb7. 55

90.40

KO-VIBRATIONAL

SPECTK-1

OF HNCS

AND

393

DKCS

DNCS

J:IG. 19. High resolution

centered sufficientI!.

near

1944 cm-‘.

prominent

HNC’S, the absence of the associated

spectrum

of DNCS:

However,

to permit

cm-’

a number

contident

of a perpendicular

vibrational

552-514

(12 mm Hg pressure,

of parallel

assignments

component

mode lies almost

indicates

parallel

subband

(Table

XVII,

that

50 cm path

Q branches

length).

were

Fig. 15). As with

the normal

to the figure axis.

coordinate

DRAPER

394

AND

WERNER

TABLE XX

LIi:EPOSITIOSS (cm-l) IN '$4OF I)SCS

0 'Q1 \

1:=1 578.54

1:=2 651.80

I<=3 713.12

R=4 685.40

_ J __-

(%
0 1

579.27=

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1.7 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

579.64 580.04

580.$3 580.72 581.10 581.17 581.87 582.15 582.63 582.97 583.40 583.75 5x4.10 584.47 584.85 585.21 585.58 585.95 586.34 586.75 587.12 537.46 587.85 588.20 588.62 589.00 589.39 589.79 590.12 590.50 590.92 591.32 591.68 592.05 592.40 592.79 593.14 593.54 593.80 594.20 594.55

'R2(J)

577.83a 577.40= 577.04 576.65 576.39 576.05 576.76 575.41 575.04 574.62 574.25 573.89 573.54a 573.23" 572.85 572.44 572.03=

570.83" 570.39= 570.00" 569.35" 568.98" 568.67" 568.19 567.77 567.38 566.90 566.55 566.09 565.77 565.40 565.06 564.68 565.30 563.93 563.49 563.15

652.803 653.17n 653.63 653.98 654.37 654.71 655.09 655.47 655.83 656.24 656.62 657.09 657.47 657.8G 658.19 658.51 658.84 659.20 659.57 659.93 660.30 660.70 661.10 661.54" 661.90" 662.27" 6G2.GGa GG3.058 663.458 663.85" 664.24; 664.65 665.06"

%2(J)

650.64' 650.28" G49.88a 649.5&? 649.27 648.93 648.55 648.17 647.78 647.40 647.06 646.67a 646.34a 646.05" 645.67" 645.30 645.00 644.62 644.28 643.81 643.39 643.00 642.60 642.23 641.40 641.50 641.04 640.67 640.25 639.89 639.51 639.15 638.74 638.57 637.91 637.52 637.10 636.72 636.39 636.00

'%3(J)

714.SY3 715.22" 715.633 716.10 716.45 716.80 717.17 717.55 717.90 718.20 718.56 718.90 719.32 719.70 7?0.(17 720.39 720.80 721.13 721.55 721.91 722.27 722.65 723.04 723.40 723.70 724.04 724.42 724.79 725.12 725.50 725.85 726.20 725.57 726.44 727.27" 727.56

QR4 (J)

711.89’

711.50" 711.00" 710.61 710.28 709.88 709.48 709.12 708.69 708.27 707.91 707.52 707.15 7OG.77 70b.42 706.09 705.77 705.42 705.09 704.73 704.36 703.96 703.54 703.20 702.85 702.50 702.18 701.77 701.40 700.98 700.58 700.22

687.21 687.58 687.Y5U 698.35= 688.64 689.00 6X9.35 689.97 690.36 690.72 691.06 691.38 691.70 692.00 692.34 692.69 693.05a 693.71 693.96 694.30 694.66 695.00 695.29 695.58 695.90 696.23 696.64 696.95 697.28 697.57 697.88 698.19 698.58

'!P,(J)

683.57 683.22 682.85" 682.45 682.05 681.71 681.31 680.90 680.52 680.13 679.75 679.34 678.98 678.57 678.17 677.75 677.35a 677.00 676.57 676.18 675.77 675.42 575.03 674.62 674.25 673.87 673.44 673.02 672.62 672.27 671.77 671.38 676.97

D : Doubtful nccurncy due to overlapping bands.

The Region

300-950

cm-‘:

~3, ~4, 15, vg

The presence of a fundamental band near 370 cm-r means that the other three fundamental band systems are in the spectral range 400-900 cm-’ and the complexity of the spectral profile in this region arises from gross overlapping of their fine structure (Fig. 13). ~4. The spectral profile between 500 and 750 cm-l (Figs. 16, 17) is characteristic of a band system which originates near 550 cm-l and which has widely separated parallel subbands.

RO-VIBRATIONAL

Q GRANCH POSITIONS

(co-l)

AND

SPECTRA

OF HSCS

AND DNCS

39.5

COCIIIINATION DIFFERENCES (m-1) FOR ‘J6OF DNCS

1’

Qi. \

I:(] _-QQ ‘I\

I’‘(?,:-T’QIc+l RQ,l-l'Q,,l

1\+1

KUs-PQ,;

_.___ 0

23.54

511.03

64.34

457.61)

1

487.46

2

516.73

3

567.58

413.37

4

616.27

433.00

5

665.04

6

738.65?

669.68!

423.12

246.56?

134.58

(estimated from the position ofl'ql):

‘.I~

87.88

103.36

102.10?

236.88?

-1 481.1 Cn

cm-l

(A' - u') - (A" - 13")= a.52 cm-1

1)': h

=

0.33

cm-1

"; - D;

=

:I;;

=

0.05

cn, -1

11:- 11': i, li

= -0.02 cm-1

,A"- 1:"=

23.7

r;" - 16D"P = .Jh

-1 -0.33 cm

0.1823 + 0.0004 cm-1

Centrifugal distortion terms taken to i;'.

‘1

:

b

: Fromtllc R=4sub-band.

A broad Q branch

at 601.75 cm-r is typical of “Q. for an a’ +- a’ transition

of an u” +- a’ transition, is unequivocally

but must be the former since the Q branch

QQr of the same band system.

With

or ‘Q1

at 578.54 cm-’

these assignments

established,

those for the other Q branches follow readily (Tables XVIII, XX; Figs. 1619). It is possible however, to assign the Q branch at 685.40 cm-r as QQa of I+,and its position in relation to QQz and QQ3would tend to support this. Its nomination as part of band system of vJ is based on two factors : The sharp drop in intensity of the band profile on the high wavenumber side of the K = 3 parallel subband (Fig. 17) indicates that centrifugal distortion effects may override the effect of the positive value of A’ - A”; the value of 8’ - B” determined from the fine structure of the K = 4 subband fits the pattern established for the other parallel subbands of vq (Table XIX).

396

DRAPER

I

3

CM-’

491 .l

FIG. 20. High resolution

The differences

spectrum

of DNCS:

514-480

-4

cm-’

(6 mm Hg pressure,

between upper and lower state rotational

large and signify rotational Ye. Absorption

in the region 403-750

constants

cm-r must be partly

near 475 cm-r since the band at 370 cm-r

and its subbands

20 cm path

length).

are abnormally

energy level perturbations.

and ~4 is pulled to high wavenumbers. Strong

WERNER

DNCS

I

centered

AND

due to a band system

(YJ is not significantly

The band is predominantly

distorted,

parallel in character

mix with those of vh.

absorption

near 47.5 cm-r

follows that QQr should be relatively

(Fi,.0 16) is indicative

of subband

close to QQz. Their respective

packing

positions

19) were fixed by the presence of ‘Qz at 423.12 cm-r and PQ3 at 413.37 cm-‘. these pQ~ branches are skewed to high wavenumbers

and it

(Figs. 20, Both of

signifying that a perturbed u” +

a’

transition is involved. The assignment of RQO at 511.0 cm-’ (Fig. 20) presented some difficulty as the region is crowded with other Q branches and it is unexpectedly weak. Unfortunately parallel

this crowding

sub-band

is centered

also made it impossible near the estimated

to determine

position

whether

ONCS

FIG. 21. Profiles of the perpendicular

Q branches

or not a

of the band origin, that

in vg of DNCS.

is

RO-VIBKATIONAL

SPECTR~i OF HNCS .WD

30 7

DNCS

TABLE XXII LINE POSITIONS (cm-') IN v6 OF DNCS. i;=4 616.27

QQL7 J

‘R4(J)

'iP4(J)

0 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

617.96a 618.36" 618.8Za 619.20a 619.58 619.97 620.33 620.75' 621.08" 621.42 621.72 622.10 622.53

613.91a 613.65a 613.27 612.97 612.63 612.23 611.97 611.58 611.25 610.90 610.53 610.13 609.89 609.50 609.16 608.81 608.45 608.10 607.73 607.33 607.00 606.67 606.34 605.97= 605.65 605.27 604.95 604.61 604.23 603.85" 603.48 603.14" 602.77a 602.42" 602.0Sa

622.93

623.33 623.73 624.13 624.50 614.82 625.20a 625.60" 625.99

626.35a 626.77 627.09 627.48 627.89

628.30 628.65 629.05 629.43

629.83 630.20 630.60 630.96 631.34a 631.70a 632.12a

a : Doubtful accuracy due to overlapping bands.

481.1 cm-‘. However, the band the K = 0 parallel subband.

profile

A summary of the measurements XXI and XXII.

in this region made

for this

(Fig. band

16) suggests system

the absence

are given

of

in Tables

Kewley et al. (3) have shown from millimeter-wave data for DN-CS that the value of +(BO + Co) is 0.1824 cm-l. This fi gure almost equals the value of B” - K2DJK" obtained for the K = 4 parallel subband and it follows that DJK" must be very small. vs. This band is distinctly hybrid in character. Relatively strong perpendicular Q branches distributed almost symmetrically either side of the intense parallel component and the characteristic central Q branch (Fig. 16) indicate a near equality between upper

DRAPER

AND

WERNER

ONCS

382.0

360.2

CM-' 0

FJG. 22. High resolution

spectrum

of DNCS:

395-360

cm-1 (7 mm Hg pressure,

20 cm path

length).

TAGLC XXIII

(1BRANCIIPOSITIOBS (cm-l) AND CO1IEINATIONDIFFERENCES (cm-l) FOR "5 OF D"CS

QQ,

K

a

RQK

0

395.3

PQK +

0.3b

RQ,-QQ,l

-

23.5 + 0.3

1

371.83

436.43

342.3 2 0.3b

64.60

2

371.83

474.39

306.9 i O.Zb

102.56

3

371.83

506.42

269.1?

134.59

4

371.83

Q QK-",I

102.7?

-1 365.75 cm

ROTATIONAL CONSTANTS:' ii"-??'=

23.7

cm-1

D;;

=

0.34

cm-1

1%

=

0.05

co1 -1

a : All assumed centred at position of the line peak. b : The error estimate is due to the broad contour of the branch. c

:

Centrifugal distortion terms taken to K6.

'QK-'QK

64.9 + 0.2

-

u. (estimated from the position of '9,) :

RQ,l-PQ,l

88.4 + 0.5 167.3?

94.1+ 0.3 167.5 + 0.2 237.3?

RO-VIBRATIOXAL

SPECTRA

OF HNCS

AND

399

DNCS

DNCS

FIG. 23. High resolution

and lower state

spectrum

rotational

of DNCS:

constants.

875-826

cm9

(2 cm Hg pressure,

This is entirely

unexpected

SO cm path

because

of the values

the .I’ constants The assignment

in ud and ~6, and the analogy that can be made with HKCS. of the perpendicular Q branches presented no difficulty- (Table

and their profiles

indicate

to high wavenumbers features

which

molecular in both

directions

branches

to be of considerable

RQi is slightly

skewed

significance

in what it provides

appears

to be an unperturbed

at 371.83 cm-’ correct

ground

band

system.

CONBINATION AND OVERTONE BAXDS IN HNCS AND DXCS

HNCS

DSCS

Hand Type

3960 _ + 2636 _ + 2595 _ +

10

m-1

5

1224 + 1149 +

2

cm-l -1 cm -I cm

5

0.5

1078 _ + 997

0.5

3860 +

10

3226 +

5

3112 -. + 3011 &

5

2796 _ +

5

5

?

Relative Intensity

Assignment

1senli

2\12

Parallel

Medium

"* +

Parallel

Very weak

"2 t

PXallFZl

IJ‘xk

Mybrid

weal;

m-1 -1 cm -1 c"

Hybrid

Weak

Parallel

Xedium

cm-1 cm-1

Parallel

cm-1 -1 cm -1 cm

of the degraded

(Fi g. 22) must be due to superimposed @Qk. state combination relations with the appro-

TABLE XXIV

lhxl Position

XXIII) degraded

to low wavenumbers,

in the interpretation

since one would expect both RQi and ‘Qt to be significantly

Q structure

since

is involved.

and ‘Qz (Fig. 21) is more strongly

will prove

dynamics

The intense

that an a’ +- a’ transition

length).

2v4 v4 +

-1 = 3978 cm 113= 2846 cm-1 \J4= 2604 cm-1 -1 = 1230 cm -1 \' = 1154 cln 6 -1 = 1078 cm

2V6 'J6+ 1' = 1006 cm-i 5

Pnmllel

1Zeak

-1 = 3888 cm 2v2 v1 + u4 = 3194 lx-1 v1 + \)6= 3126 cm-1

Parallel

Medium

"1 f \

Parallel

strong

Pnriillel leak ideah

5

\I2+ \8 3

-1 = 3011 cm -1 = 1795 cm

400

DRAPER AXD WERNER

priate perpendicular Q branches for K = 0 to 3. The position of ‘Q1 fixes the band origin at 365.8 cm-l, that is 6 cm-’ lower than the other QQK branches. There is no doubt concerning the assignment of ‘Q1 and there is ample evidence to support the value of 23.5 cm-r for QQo - ‘Q1 SO the position of the band origin is confidently given. It is apparent then that the K-dependent rotational constants are highly irregular. There are a number of anomalous features apparent in this band when compared with the corresponding band in HNCS and an attempt will be made to rationalize these when the dynamics of both molecules are considered. Ye. The contour of the high resolution spectrum in the region 865-830 cm-’ (Fig. 23) is suggestive of a weak band centered near 855 cm-r which has not been reported previously. Unfortunately fine structure from v4 and ~6 and of some residual HNCS hides the band origin. Very weak Q branches at 869.80 cm-’ and 827.55 cm-r, were assigned as RQo and ‘Q1 respectively, the former fixing QQ1 at 846.50 cm-‘, and the position of ‘Q1 places the band origin at 850.9 cm-r. It follows that A’ - A” approsimates -4.4 cm-‘, which is not unreasonable for this type of molecule. Some support for placing the band origin at 851 cm-l is provided by the presence of a combination band at 2796 cm-r, only 1 cm-l removed from the estimated position for v2 + v3 (Table XXIV). This relatively intense combination band could not be reasonably assigned to any other simple combination. DISCUSSION*

The analysis of the high resolution spectra of HKCS and DNCS has permitted a reevaluation of the band assignments as follows. vl. There is no doubt that the bands centered at 3639 cm-l (HNCS) and 2645 cm-’ (DNCS) arise from the N-H and N-D stretching modes respectively. That the bands are of a’ species is confirmed by the profiles of the RQo and ‘Qt branches, and their obvious hybrid character indicates that the transition moment has a component both parallel and perpendicular to the spindle axis. The negative values of A’ - A” in both bands are to be expected since excitation of the N-H(D) stretching vibration must decrease the A value, more so in HNCS than in DNCS. It is significant that the perpendicular component of v1 in DNCS is less intense than in HNCS and the normal coordinate representing vl in each molecule should reflect this. y2. The bands at 1989 cm-’ (HNCS) and 1944 cm-l (DNCS) involve a’ + a’ transitions in which the transition moment is almost parallel to the unique axis. This is confirmed by the lack of dependence of the rotational constants on the vibrational state. The relevant normal coordinate must be dominated by the v,, (NCS) mode since the positions of the bands are similar to those found for asymmetric stretching vibrations in similar allenic type molecules (28-31), but must be sufficiently different in each molecule to produce the isotopic shift of 45 cm-l and difference in band intensities. v3. This band should arise from the NCS symmetric stretching vibration [vs(NCS)] in both molec*;les as the remaining modes are bending vibrations. The structural similarity and relative positions of the 857 cm-’ (HNCS) and 851 cm-’ (DNCS) bands are consistent with this mode and have been so assigned in preference to the 997 cm-r band seen only in HNCS. Further, the strong band near 2828 cm-l in HNCS cannot be * Normal coordinate and force constant analyses the molecular dynamics of these molecules.

will be included

in a subsequent

paper

concerning

RO-VIBRATIONAL

reasonably

assigned

band

IJ~if v3 is at 857 cm-l.

v2 +

(Table

XXIV).

SPECTRA OF HNCS AND DSCS

if the 997 cm-’ band is ~3 but it can be assigned combination

band

as the combination

can be assigned

in DNCS

Got’t (24) have observed a strong band at 848 cm-’ in the Raman spectrum of HNCS (in CU.) , and Durig et al. (IO) report strong bands at 851 cm-’ and 843 cm-r in the Raman spectrum of solid HKCS and DNCS, respectively. The intensity

Goubeau

A-similar

401

and

of these bands

v,? (NC‘S) mode. The normal coordinate

and since HNCS

is regarded

as a single

namely

mode

NCS bending (s’(NH))

between

these

in the “QK and

NH(D)

rotational

observed bending

DNCO

but

to be different at 615 cm-l

that

of Y,\

however

belong

the intensity

is somewhat

by

to the

distribution

irregular

and cannot

Nor can the unespected

vibrational

excitation.

between

the

magnitude

high variation These

of the

features

bending

modes

are

similar

(14, 15) and HN3, DN3 (28). (HNCS/DK’CS)

the positions

is of the order

are considerably features

lower

similar

and arises from the out-of-plane

(DNCS)

to this mode,

normal.

for a Their

to those described

bending

contrary

expected

than

The correct isolation of this species is imperative A number of factors substantiate the assignment

and 481 cm-l

greatI>. bending

in the two molecules

and 549 cm-l

and the abnormally

interaction

469/366

V6.This band is of a” species

539 cm-l (HNC‘S) (‘Table I) :

approximate not be influenced

hybrid character is expected but they have anomalous for VJ which also indicate Coriolis interaction. NCS group (6”(NCS)). force constant analysis.

should

due to the other

geometry.

with

Coriolis

ratio

mode

of the

should

components

‘QK branches

constants

in HNCO,

wavenumber

by the stretching

of the bands

in character,

of the molecular

of a second-order

I’:. The

for the

respectively.

and perpendicular

of degrading

to that

the bands

are hybrid

in terms

indicative

be expected

that

and DNCS

be esplained K-dependent

(V(NCS))

the positions

would

bands

their parallel

is expected

with OCS when the HN group

of v, (NCS)

vibration

whereas

mode in HNCS

As expected,

be dominated

and isoelectronic

the position

of 1.2 to 1.4. It follows

6’ (NCS)

counterparts

(Lo).

substitution,

of a’ species

a factor

should

is isosteric

atom,

859 cm+

vq. The in-plane by isotopic

to their infrared

for Y, (KCS)

(‘m-S bond, ((KS),

compared

vibration

of the

to an accurate of the bands at

to former

assignments

The “QK and ‘QK branches are degraded to low and high wavenumbers respectively, contrary. to all other perpendicular branches in these molecules but in accord with the parity

requirements

for an u” +- u’ transition.

in HNCS (probably in DNCS) operates for a” +- a’ transitions. These

bands

are very

((I) as are the bands second-order

Coriolis

and

weak or absent

of a“ species

this

The K = 0 parallel

occurs

only

in the argon

when matrix

subband

the parity spectra

in HiY, and DK3 (18, 32) which

is missing

selection

of both

rule

molecules

are also involved

in

interaction.

For both molecules, the QQK branches in these bands are more intense for high K values than those in the two associated bending fundamentals indicating that their intensities may be dependent upon K4 rather than K*. The parallel component in a band arising from an u” + a’ transition in the C, symmetry class must be borrowed from other transitions via dynamic coupling, in such cases the intensity of the QQK branches are dependent on K4.

DRAPER AND WERNER

402

For a linear NCS group the product rule predicts that Y6 (HNCS) and Y6 (DNCS) should be equal. The observed deviation may be explained by the fact that the band origins will be perturbed by Coriolis interactions and will only conform to the product rule when an harmonic oscillator approximation is made. Overtone and Combination

Bands

The settling of the assignment of ~3 in HNCS and DNCS and the more reliable estimation of the band centers, especially for the three bending modes, permit a more reasonable interpretation of the combination and overtone bands than those given previously (9, 33). These are given in Table XXIV. RECEIVED:

July 13,1973 REFERENCES

1. C. I. BEARD ANDB. P. DAILEY, J. Chem. Phys. 18, 1437 (1950). 2. 3. 3. 5. 6. 7. 8. 9.

10. 11.

12. 13. 14.

15. 16. 17. 18. 19. 20.

21. 22.

23. 24. 25. 26. 27. 28. 29. 30. 31.

32. 33.

G. C. DOUS~~ANIS, T. M. SANDERS,C. H. TOWNES,ANDH. J. ZEIGER; J. Chem. Phys. 21,1416 (1953). R. KEWLEY, K. V. L. N. SASTRY,ANDM. WINNEWISSER,J. Mol. Spectrosc. 10,418 (1963). B. KRAKOW, R. C. LORD, AND G. 0. NEELY, J. Mol. Spectrosc. 27, 148 (1968). G. 0. NEELY, J. Mol. Spectrosc. 27, 177 (1968). C. REID, J. Chem. Phys. 18, 1512 (1950). H. W. MORGAN, Oak-Ridge National Laboratory, U.S.A., private communication. T. M. BARAKAT, N. LEGGE, AND A. D. E. PULLIN, Trans. Faraday Sot. 59, 1773 (1963). J. R. DURIG AND D. W. WERTZ, J. Chem. Phys. 46, 3069 (1967). J. R. DURIG, C. M. PLAYER, J. BRAGIN,ANDW. C. HARRIS, Mol. Cryst. Liql&d Cryst. 13,97 (1971f. W. J. ORVILLE-THOMAS,J. Chem. Sot. 2383 (1952). W. J. ORVILLE-THOMAS,Trans. Faraday Sot. 49, 855 (1953). B. OREL, B. PETERYAN, M. OBRADOVIC,D. HADZI, AND A. AZMAN, Spectrosc. Lett. 4, 39 (1971). R. A. ASHB~ AND R. L. WERNER, J. Mol. Spectrosc. 18, 184 (1965). R. A, ASHBY ANDR. L. WERNER, Spectrochim. Acta 22, 134.5 (1966). A. WALSH, J. Opt. Sot. Am. 42, 94 (1952). R. C. LORD ANDT. K. MCCUBBIN, J. Opt. Sot. Am. 45,441 (1955). F. A. FIRESTONE,Rev. Sci. Instr. 3, 186 (1932). R. C. LORD ANDT. K. MCCUBBIN, J. Opt. Sot. Am. 47, 689 (1957). “Tables of Wavenumbers for the Calibration of Infrared Spectrometers” (W. H. Thompson, Ed.), Butterworths, London, 1961. E. K. PLIER ANDE. D. TIDWELL, Mem. Sot. Roy. Sci. Liege 18, 426 (1956). J. S. GARING,H. H. NIELSEN, AND K. NARAHARIRAO, J. Mol. Spectrosc. 3, 496 (1959). F. W. DALLEY ANDH. H. NIELSEN,J. Clzem. PIzys. 25, 934 (1956). J. GOUBEAUAND0. GOTT, Chem. Ber. 73, 127 (1940). G. HERZBERGAND P. A. WARSOP, Can. J. Phys. 41, 286 (1963). G. HERZBERGANDR. D. VER~[A, Culz. J. Phys. 42, 39.5 (1964). D. M. LEVINE AND D. A. Dows, J. Chem. Phys. 46, 1168 (1967). C. B. MOORE AND K. ROSENGREN,J. Chem. Phys. 44,4108 (1966). C. R. BAILEY AND A. B. CASSIE, Proc. Roy. Sot. London 140, 60.5 (1933). R. N. KNISELEY, R. P. HIRSCHMANN,AND V. A. FASSEL,Spectrochim. Acta 23A, 109 (1967). N. S. HAM ANDJ. B. WILLIS, Spectrochim. Acta 16, 279 (1960). G. C. PIMENTEL,S. W. CHARLES,ANDK. ROSENGREN,J. C&m. Phys. 44,3029 (1966). C. REID, J. Chem. Phys. 18, 1544 (1950).