Spectrochimica Acta, Vol. 278, pp. 1002 to 1018. Pergamon Pnw 1971. Printed In Northern Ireland

The VibMional spectra of (HC=C),CO anil (N=C),CO* FOIL A. MILLER and BRIAN M. HARNEY

Department of Chemistry, University of Pittsburgh Pittsburgh, Pa. 16213, U.S.A.

and JAMES T~ELL

Department of Chemistry, Southern Illinois University Carbondale, Illinois 62901, U.S.A.

(Received 7 July 1970)

AbstractInfrared and Raman spectra are reported for diethynyl ketone, (HC%C),CO and for carbony cyanide, (N=C),CO. Both are planar C,, molecules. Assignments are made for all 18 fundamentals of the former, and for all 12 of the latter. All but two or three for each molecule are established beyond any doubt.

!I’HB paper presents infrared and Raman data and vibrational assignments for diethynyl ketone, (HC%C),CO and for carbonyl cyanide, (N&Y&CO. The two substances were studied independently, diethynyl ketone at the University of Pittsburgh and carbonyl cyanide at Southern Illinois University. Because the mole- cules are isoelectronic, they resemble each other in many ways. In particular the frequencies of their skeletal modes are quite similar, so that the vibrational assign- ments for one molecule aid and support those for the other. Because of this it was decided to combine the results in a single joint publication. Each laboratory then made some contribution to the results for the other molecule. The compounds will be discussed separately.

I. DIETEYNYL KETONE

There is almost no prior work on the spectroscopy of this substance. A paper by WILLE and STRASSER [l], which deals with its synthesis and reactions, reports only the five strongest infrared bands. Our laboratory has worked with a number of acetylenic compounds in the past. Because so little has been done on this ene, we thought a study of it would be worthwhile. Another reason for undertaking the work was that our co-author, Dr. Tyrrell, expressed an interest several years ago in knowing the fundamental frequencies in the ground electronic state to help in a projected study of its electronic spectrum.

The ketone is a colorless liquid (m.p. about -2O’C) with a strong irritating odor. It decomposes quickly in the liquid state at room temperature, but it can be kept at -196°C for a number of months. When the infrared spectrum of the vapor was measured at room temperature and about 10 torr, there was no noticeable decom- position over a period of approximately 4 hr.

A. Preparatim of the sample Diethynyl ketone was prepared in about 2-g amounts by the method of WILLE

and SKRASSER [I], with minor modifications. To avoid one hazardous step, we

* A portion of this paper is taken from a thesis submitted by Brian M. Haney in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the University of Pittsburgh.

[l] F. WILLE and R. STRASSER, Chem. Ber. 94, 1606 (1961).

1003

1044 F. A. MILLER, B. M. HARNEY and J. TYRRELL

followed a recommendation by JONES et al. [2]. The reaction sequence was:

C,HSMgCl + H-C=C--H -Z+ H-C%CMgCI HCooCaH5 + (HC=C),CH-OMgCI 0°C

+ (HC=C),CHOH v (HC%&C=O.

Commercial C,H5MgCl was gradually added to dry tetrahydrofuran (THF) which was saturated with acetylene, while acetylene was simultaneously bubbled through the liquid. A solution of ethyl formate in THF was then added at 0°C and the mixture stirred for 24 hr. The resulting complex was decomposed with an aqueous saturated NH&I solution. The aqueous layer was separated and extracted with several portions of diethyl ether, and the extract was added to the organic layer. The latter was dried with NazSO, and evaporated until a dark syrup re- mained. This syrup was extracted continuously with petroleum ether (b.p. 33-60%) and the insoluble residue was discarded. The alcohol was then crystallized from the petroleum ether and purified by vacuum sublimation to a cold Snger at liquid nitro- gen temperature. It was oxidized with a solution of sulfuric acid and sodium chrom- ate. The ketone was carried from the reaction flask to a dry-ice trap by a stream of gaseous N,. Purification was effected by holding the product at -25’ and vacuum transferring impurities to another trap at -78°C. The process was then repeated holding the product at -78’ and transferring impurities to a trap at -196°C. This latter step was essential for removing propynal, HC=C-CHO, which is a by- product of the reaction.

WILLE and STRASSER [l] used only the second of these transfers. They state that diethynyl ketone is collected in the liquid nitrogen trap. It was our finding, however, that this trap contains mainly propynal and no diethynyl ketone, and that the latter remains in the -78’ trap. The propynal can be identified by its strong doublet infrared bands at 1697 and 945 cm-l in the gas [3].

Final identification of our product was made by nmr and mass spectrometry. Vapor phase chromatography indicated a purity of at least 99%.

B. Spectroscopic procedures and results

Raman spectra. The source of exciting radiation was a Carson Laboratories model 300 rare gas ion laser which can be fllled with either argon or krypton. For this work Ar+ 4880 L! was used. Because the output power of approximately 1 W at 4880 L% is too intense for condensed phases, it was reduced to about 180 mW with a filter. The laser radiation was plane polarized. The remainder of the equip- ment was the Spex “Ramalog” system consisting of: (1) a Spex model 1401 double monochromator, using two 1200 line/mm gratings blazed at 5000 A and scanning linearly in wavenumbers, (2) an ITT FW 130 detector with S-20 spectral response, which can be cooled to -20°C by a thermoelectric cooler, (3) both d.c. amplification and photon counting. (Only the former was used in this work.) The system employs 90’ viewing. There is a spike transmission filter in the exciting beam to remove weak emission lines coming from the laser discharge, and a wedged crystal quartz

[2] E. R. H. JONES, H. H. LEE md M. C. WHITING, J. Chem. Sm. 3486 (1960). [3] 5. C. D. BRAND and J. K. G. WATSON, Tmw. I%mzday Sot. 56, 1682 (1960).

The vibrational spectra of (HCkC),CO and (N=C),CO 1006

polarization scrambler plate in front of the entrance slit. Depolarization ratios are measured by keeping the plane of polarization of the exciting radiation fixed and rotating a Polaroid analyzer in the scattered beam. We find depolarized lines to have p = 0.75 f 0.03. Liquid and solid samples are conveniently held in a small melting point tube oriented parallel to the plane of the slit jaws and perpendicular to the long axis of the slit [a].

The spectrum of diethynyl ketone was obtained in the liquid and solid states. Because the liquid decomposes in a few minutes at room temperature, a low tem- perature Raman cell was used which has been described elsewhere [a]. The sample was vacuum transferred from a storage ampoule into the melting point tube, sealed off and placed in the cell. Since the sample melts near -2O”C, its temperature was held near -10’ for the liquid and near -40’ for the solid state measurements. Spectral slit widths were 4 cm-l for frequency measurements and 10 cm-l or more for polarizations.

Infrared spectra. Infrared spectra were obtained from 33 to 4000 cm-l with Beck- man IR-11 and IR-12 spectrophotometers. The spectral slit width was about 1 cm-l everywhere. For the gas a lo-cm cell with CsI windows was used above 300 cm-l; below 300 cm-l an 8.2-m cell with polyethylene windows was employed. The vapor pressure was varied between 5 and 20 torr. The spectrum of the liquid was obtained at about -15% with a Beckman variable temperature cell (model VLT-2) of 0.025-mm sample thickness. Since the inner windows were AgCl and the outer ones KBr, the lower frequency limit was 400 cm-l. The cell was fllled manually at room temperature and then quickly cooled to -15’. There was no evidence of decomposition. This cell was much too thick for several of the strongest bands, so for them we used a capillary film between two CsI plates at room temperature. The sample gradually turned brown and then black. Only the peaks of the five strongest bands were scanned. Two samples were used, and for each sample the bands were run at least twice and in a different sequence. The results agree so we believe they are valid.

This experiment had a startling consequence. The two salt plates were cemented together by the black decomposition product. A number of organic solvents failed to have any effect, so a razor blade was carefully forced between the plates to separate them. This was eminently successful. There was a bang, a flash of blue flame and a deposition of soot over the otherwise-unharmed plates. We presume that the decomposition had formed a polymer containing many acetylenic groups, and that this exploded on contact with air or under the mechanical tension. It was the only explosion we had while working with diethynyl ketone, but it suggests that there are hazards and that care should be exercised. Only small quantities should be handled and decomposition products should be avoided.

The infrared spectrum of the solid was obtained at about -173’C with a con- ventional low temperature infrared cell fitted with KBr or polyethylene windows. The appropriate amount of vapor was isolated and then deposited slowly onto a CsI or polethylene plate cooled with liquid nitrogen.

Results. The results for (HCrC)&O are given in Table 1 and Figs. 1 and 2.

[4] S. K. FREEMAN and D. 0. LANDON, Anal. Ch.em. 41, 398 (1969). [5] F. A. MILLER and B. M. HUNEY, AppZ. Spectry. 24, 291 (1970).

Ta

b10

1.

Ra

ma

n a

nd

in

fra

red

spec

tra

of

(HC

hC

),C

O

Rem

an

Infm

red

Sol

id

Liqu

id

Sol

id

Liqu

id

Gas

cm

-’ In

tal.

cm-l

rn

ten

. Po

hn

.*

cm-l

X

x&en

. cm

-1

Inte

n.

on+

I&E

$L

‘Jbe

A

ssig

nm

ent

14s

204

238

269

668

669

716

733

768

(I w

7m

m

w

YW

ow

uw

m

142

e 0.

78

200

w

dP7

200

239

m

0.73

23

8

268

m

0.73

661

671

w

0.70

NE

WW

N

E

w

NE

NE

667

669

W

670

712

w

dP

704

737

w

w.

ah

BB

S

734

74s

n

0.10

74

6 *

989

1036

m

8 e * w

VW

116

(122

) 12

s I

179

190

202

1 22

3 22

9 23

8 1

642

648

667

1

642

(646)

662

I 67

6 62

2 (~

688)

I

686

694

720

729

739

t 73

2 73

9 88

0 99

4

1073

VW

ah

VW

8 vvw

V

W

WJ

ow

VW

x.3 u A

A B

A?

c c

V? VlS

671

f 12

2 =

6B3

VS

VlO

vlO

+vk-

-vkt

V

4 688

f 19

0 3

876

729

-+ 2

68 -

987

? ?

The vibrational spectra of (H~----C)~CO and (N-~=C),CO 1007

+++

x x ~

<

o~

qq Q ~

-H

O

II

U

fl

o

~o

S ®

1008

XT -

I

t

B A

Raman (liquid,- 10°C )

Signal t

F. A. MILLER, B. M. HARNEY and J. TYRIXELL

3400 3000 2600 2200 1600 1400 1000 600 200 I

1

1600 1400 Wave Numberrkrf’)

Fig. 1. Infrared and Raman survey spectra of (HCkC),CO. A. Infrared spectrum of the gas at room temperature. lo-cm path, 10 torr. B. Infrared spectrum of the

solid near - 173°C. C. Raman spectrum of the liquid at - 10%.

1292 1669 3325

v \:i

v Fig. 2. (HC=zC),CO. Contours of some of the infrared bands of the vapor. The 548,1144 and 3326 om-1 bands are examples of Type A, 1292 and 1669 of Type B,

and 729 of Type C. Wavenumbers increase to the left.

The vibrational spectra of (HC%C),CO and (N=C),CO 1009

Raman frequencies are believed to be accurate to f2 cm-l and infrared ones to f 1 cm-l unless marked broad or shoulder. Consequently we regard band8 whose frequencies differ by more than 4 cm-l when measured in the same non-crystalline state as due to different vibrations.*

It is therefore very helpful to have both infrared and Reman frequencies measured on the same non-crystalline physical state, because one can then attach significance to differences of 6-20 cm-l in their values. If the result8 were for differ- ent physical states such discrepancies might be due to that, but if the (non- crystalline) physical state is the same it is certain that the frequencies must then be due to different vibrations. For this reason we went to considerable effort to make both infrared and Raman measurements on the liquid as well a8 the solid. These data were of great help in sorting out the bands and making some of the assignments. For example they establish that the following infrared vapor band8 and Raman liquid one8 are due to different vibrations: (a) 648 and 671, (b) 729 and 749 and (c) 2116 and 2097 cm-r. On the other hand the following are due to the same vibration: (d) 1669 and 1636 (in spite of the 6 cm-r discrepancy for the liquid) and (e) 3326 and 3276 cm-l.

One interesting feature of the result8 is that more than half of the bands increase in frequency upon condensation from the vapor to the liquid or solid. We have no explanation for this unusual behavior. The same behavior is even more pronounced for carbonyl cyanide, which shows that it is not connected with weak hydrogen bond8 in diethynyl ketone.

C. Assignments for diethynyl ketone

C,, symmetry was assumed. It is completely satisfactory, as will be seen, and there is no need to consider any other. Table 2 classifies the fundamental vibrations and summarizes our assignments for both diethynyl ketone and carbonyl cyanide. BEEZBERQ’B convention8 [6] are used throughout. The z-axis is the two-fold axis of symmetry, and the x-axis is perpendicular to the plane of the molecule as recom- mended by MULLJKEN [7].

Separations of the P and R branches of the infrared band8 were estimated by the method of SETH-PAUL and DIJKSTRA [S]. (BADGER and ZUMWALT’S results [9] could not be used because the values of p (1.89) and S( -0.71) fall far outside the range of their plots.) Table 3 gives the assumed dimensions and describes the deduced contours. Agreement between calculated and observed P-R separations was very

* In a cr@allime sample splittings due to coupling between two or more molecules in a unit cell may be larger than 4 cm-r. If one of the resulting frequencies were only infrared active and the other only Rsman active, the 4 cm-l criterion would no longer hold. Examples of this seem to occur in the solid for the Ramsn-infrared pairs 755-748 and 2096-N2103. Alternatively, these larger discrepancies may be due to the fact that the Raman spectrum of the solid was obtained at about -40% and the infrared spectrum at about -173°C. There may have been different crystalline forms in the two experiments.

[S] G. HERZJSERG, Infrared and Ramn Spectra of Polyatomic Molec&ee, pp. 106, 271. Van Nostrand, New York (1946).

[7] R. 5. MULLIKEN, J. Chem. Phys. 98, 1997 (1955). [8] W. A. SETH-PAUL and G. DIJK~TRA, Spectrochim. Acta 28,2861 (1967). [9] R. M. BADQER and L. R. ZUM~ALT, J. Chem. Phy8.6, 711 (1938).

1010 F. A. MILLER, B.M. ELmmy and J. TYRRELL

Table 2. Fundamental vibrations of (HCk&)sCO and (NGC),CO

Assignmenta C

Spezas (HW),CO (Nd),CO

Activity Sohematio description No. Liq. Uas No. Liq. Gas

4 R(P) ix. (Type B)

as Wp)

-

4 WW

i.r. (Type C)

bs Wp) i.r. (Type A)

C-H stretah CzX stretch C=O stretch C-C stretch H-CGC bend C-C-C s&soring x=a bend H--Cd bend, out of

plane s-c bend, out of

plan0 H-G& bend, out of

phUL.3 c=o wag, out of plme X.E.= bend, out of

plane C-H stretoh &X stretoh C-C stretch H-C=C bend c=o wag K=c--C bend

3276 2097 1639 749

3326

1669 739 648

- 1 2 3

- - 2240 2230 1712 1711

712 712

671 142 122

- -

4 663 6 141

-

663 127.6

8 712 - - -

9 268 6 307 294.6;

10 734 729 - 11 696 688 7 (112)

- 712*

12 200 190 8 13 (3276) (3326) -

14 2107 2116 9 16 1164 1144 10 16 670 682 -

17 667 648 11 18 239 229 12

218 208.2

(2240) (2230) 1136 1124 - -

-640 ~660 256 246.2

( ) Used twice. + From malyGs of the ultraviolet spectrum.

Table 3. Calculated moments of inertia and band contours for (HCkC),CO

A. Assumed dimensions: C-H 1.065A kc 1.20 A C-C 1.45 c=o 1.216 LC-C-C 120° Planar molecule

B. Calculated moments of inertia (amu-A*). I, = 256.1 Iv = 70.92 I8 = 186.2

c. p = 1.888 9 = -0.707

Calcd. P-R Band separation

D. Species We (300’K) Description

a1 B 11.3 cm-r Doublet

bl C 21.0 Strong central Q branch; ill-defmed P t R branches.

be A 14.0 All 3 branches well developed.

good in nearly all cases. The separa,tions and the contours were of great help in making the assignments. Figure 2 shows the envelopes of six of the bands.

zC-H and CzC stretches. There are two of each of these. In our earlier work on molecules such as Si(CrCH)4 [IO], H&!--%(C&H), [ll] and P(CGCH)~ [12],

[lo] R.E. SACHER,D. H. LEMMON andF. A. ~~~,S~ect~ochirn.ActaaSA, 1169 (1967). [ll] R. E. SA~EER, W. DAVIDSOHN and F. A. MILLJER, Spectmchim. Acta MA, 1011 (1970). [12] F. A. &bLLJER and D. H. LEMMON, Spectrochim. Acta S!i, 1099 (1967).

The vibrational spectra of (HCkC),CO and (NEC),CO 1011

it was found that the several &H stretches do not couple, nor do the Cd! stretches. Only a single band is observed for each of these two types of vibration. The same result is found for the two &H stretches of (HC=C),CO. There is only a single band (at 3325 cm-l in the vapor, 3275 in the liquid and 3236 in the solid) which we assign to both y1 and r19.

For the two C--rC stretches, however, there is a small splitting. The Reman band at 2097 cm-l is polarized and must therefore be Y*. In the infrared spectrum of the liquid this is a shoulder on a stronger band at 2107 cm-l, so the latter is taken

as 1114. Remaining a1 fundamentals. Polarizations and type B infrared contours identify

these bands. The CL0 stretch is certainly at 1669 cm-l. There is a 6 cm-l difference between the Raman and infrared values for the liquid. This discrepancy disturbs us because it is outside our stated limit of 4 cm-l for the sum of errors. The polarized band at 749 cm-l is assigned to the C-C stretch. The strong infrared band at 648 cm-l exhibits a typical B contour, and is assigned to the C-H bend v,. Its Raman counterpart is completely missing, which is unusual for a totally symmetric mode. The Raman band at 671 cm-l seems to be polarized (p = 0.70), and the frequency is reasonable for the C-C-C scissoring mode vs. The last of the a1 vibrations, the C%C-C bending, is identified as the 122 cm-l band in the far infrared by its clear type B contour.

aa fundamentals. These are out-of-plane modes and are infrared forbidden. The Raman band at 712 cm-i is assigned to the C-H bend vs, and the one at 268 cm-l to the C&C bend vg.

b, fundamentals. These also are out-of-plane modes, and the type C contour is helpful. We assign 729 cm-i to the C-H bend. The next lower type C band is at 688 cm-i. This is close enough to 729 to make one suspect Fermi resonance, but there is no acceptable combination tone which could participate in it. We therefore attribute 688 to vrr, the out-of-plane carbonyl wag. The value seems high, especially since it will turn out to be 140 cm-l higher than the in-plane wag vl,. We had expected vlr to be lower than vr, rather than higher. However there is no apparent alternative for vrr. The band at 190 cm-l is clearly the last b, fundamental, the C=C-C bend via.

b, fundamentals. Values for vra and vr4 have already been assigned. The remain- ing b, fundamentals can be identified by their type A contours. The C-C stretch, vr6, is 1144 cm-l and the C-H bend, vrB, is assigned to 682 cm-l. At first the latter band was thought to have a type B contour, but the PR separation would then be only 7 (tm-l rather than the expected 11 cm -l. We now believe that 682 is a type A band with the R branch buried under the strong band at 688 cm-l. Finally, band contours identify vi, at 548 and vrs at 229 cm-l.

Reca@tulation. This completes consideration of the fundamentals. Values have been chosen for all 18 of them, and all of these seem certain except three : V~ at 57 1, vll at 688 and vlB at 682 cm-l. Even these are probably correct.

Remaining bad. Most of the other bands can be explained as shown in Table 1. Only binary combinations were used because almost any frequency above 1000 cm-l can be explained by ternary combinations.

1012 F. A. MILLER, B. M. HARNEY and J. TYRRELL

II. CARB~NYL CYANIDE

The first reported spectral investigation of carbonyl cyanide was that of the Raman spectrum in diethyl ether solution by KEMULA and TRAMER [13] in which a total of seven bands were found. Of these the ones at 605 cm-l and 793 cm-l have “zero” intensity and are probably spurious. The bands at 253 cm-l and 306 cm-l were unassigned, and those at 702-720 cm- l, 1720 cm-l and 2238 cm-l were attri- buted to the C-C stretch, the C--O stretch and the C--hT stretch respectively. The infrared spectrum has been reported by TRAMER and WJXRZCHOWSKI [la] and by PROCHOROW, TRAMER and WIERZCHOWSKI [15], the assignments almost being identical in the two papers. The microwave spectrum has been analyzed by LEES and TYRELL [IS] to give the ground state rotational constants A = 6761.3 MC, B = 2924.6 MC, C = 2038.0 MC and K = -0.6246 and a dipole moment of 0.703 debye.

Very recently a paper by BATES and SMITH [17] has appeared which gives the infrared spectrum for gas and solid and the Raman spectrum for liquid and solid. Our data are considerably more complete than theirs although we do not have results for the solid. For example they list only five Raman bands and no polarizations for the liquid, whereas we have eighteen bands and polarizations for eleven of them. Our infrared spectrum for the gas is much richer than theirs, and we also report it for the liquid for the first time. Frequency agreement with BATES and SMITH is poor for several bands in both the infrared and Raman spectra, with discrepancies of 7 cm-l or more appearing in five cases. Finally we differ in the assignments for three fundamentals (or 1/4th of them). (Table 4 compares the various earlier assignments of the fundamentals with ours.) For these reasons we believe it is worthwhile to present our results.

A. Experimental

Carbonyl cyanide was prepared from tetracyanoethylene oxide by the method of LINN, WEBSTER and BENSON [18], giving a slightly yellow liquid with a boiling point of 65”-66°C. The samples always contained a small amount of hydrogen cyanide. The infrared spectrum of the gas was obtained at Southern Illinois Uni- versity. For the 200-5000 cm-l region a Perk&Elmer model 226 spectrometer was used with both a lo-cm cell and a 10-m multiple reflection gas cell equipped with cesium iodide windows. The far-infrared spectrum was obtained on a Perkin- Elmer 301 spectrometer using a lo-cm gas cell with polyethylene windows.

The Raman and infrared spectra of the liquid were measured at the University of Pittsburgh with the instruments already described. The Raman spectrum was obtained at room temperature, and there was no evidence of decomposition. The -- [13] W. KENLA and A. T-R, Rocz. Chem. 27, 622 (1963). [la] A. TRY and K. L. WIICRZCHOWSKZ, Bdl. Accd. Polon. Sci., Clame III, 5,411 (1967). [15] J. PROCHOROW, A. TRAMER and K. L. WIERZCHOWSKI, J. Mol. Spectq. 19,45 (1906). [IS] R. M. LEES md J. TYRRELI, Symp. MoZecdw &wture and Spectroscopy, Paper GlO. Ohio

State University (1967). [17] J. B. BATJZS md W. H. S~H, Spectroehim. Acta 26A, 456 (1970). [lS] W. J. LINN, 0. W. WEBSTER and R. E. BENSON, J. Am. Chem. Sot. 87, 3661 (1966).

The vibrational specks of (HCkC),CO end (N&&CO

Table 4. Compsrison of the assignments for (NzC),CO

1013

Species No. Mode

Assignments (cm-l) TRAMRR et al. BATIZS & SIUITE

114, 151 i271 This WOrK

a1 1 2 3 4 6

%4 6 4 7

8 b, 9

10 11 12

C=N stretch C=C stretch C-C stretch C-C-C scissoring NEC-C bend N&--C bend c=C wag NzC-C bend C=N stretch C-C stretch c=o wag NEC-C bend

2242 1714

712 520* 142*

[3701 475 255*

2222 (.TI&) 1116 667 306*

2242 2230 1712 1711

715 712 495 553 127 127.6 298* 307* 567 712 208 208.2

2234 (2230) 1131 1124

? -550 244 245.2

( ) Used twice. [ ] Deduced from combination tones. * Liquid vrtlues. All others sre for the vapor. & = shoulder.

infrared cells were filled in an inert atmosphere and the spectrum was obtained at slightly above room temperature. In this case there was some decomposition as evidenced by weak impurity bands which developed at 661 (VW), -875 (VW), 1674 (mw, A), 1796 (VW), 1858 (vww), 2347 (VW) and 2364 (VW, sh) cm-l.

The results are given in Table 6 and Figs. 3 and 4. It is noteworthy that in car- bony1 cyanide the great majority of the observed frequencies shift upward on con- densation from vapor to liquid. This is similar to the behavior in diethynyl ketone but even more pronounced.

B . Discussion

Csrbonyl cyanide is a planar C,, molecule with linear CCN groups. fundamental vibrations are distributed among the various symmetry follows :

r = lia, + aa + 2b, + 4b,

The axes are labeled in the same way as for (HCSC),CO.

Its twelve species as

Table 2 summarizes the fundamentals and our assignments. Band contours and Reman polarizations were the main aids in making the latter, but snalogy with diethynyl ketone strongly supports the conclusions. The assignments for diethynyl ketone were made without any reference whatsoever to carbony cyanide, so the former compound serves as a completely independent analog whose fundamentals are, in the main, reliably established.

a1 fundanzetiab. Most of the totally symmetric fundamentals are strong in both spectra and are easily identified. The C--hT symmetric stretch appears to coincide

1014 I?. A. MILIJW, B. M. ~NEY and J. TYRRELL

Table 6. Raman and infrared spectra of (N6$$0

Raman (liquid) Infrared (liquid) Inframd (ges)

om-1 Inten. PO&m. * am-l Inten. am-l Intal. Type Assignment

141 218 266 307 431

611

662

622 712

v* VW

m w vv2D

vvw

VUI

1103 YptpD 1137 ¶ww

1382 VWJJ

1418 vvw

1873 vvw, eh 1712 d

2098 VW

2186 vvw. ah 2242 v*

0.72 NE NE

0.76 NE 0.76 NE

dp 608 vnu

0.66 664 nr

0.16 709 d 749 VW

823 FW

926 VW

971 w

1013 *

1101 S.9 1136 4 1230 w

1263 VW

1366 VW

1419 a0 1466 C’UJ 1461 VP0

058 1712 fk?

p 0.57

2099 ww 2186 2238 vvw, d d

2417 ww

2488 vuw

2804 tn.w

2861 uuw 2923 VW 2964 cxwa 3264 w 3402 m

127.6 208.2 245.2 - -

494

663 686 617.4 712

808

839 926

966

1004

1102 1124 1213

1249

1711 1838 1968 2094

2230 2340 2420

2460

2612

2793

2930

3401 3690 3618 3708

B c A

A/B

AIB

2!

A/B

?

A/B A/B

A/B

A/B

$B

B B

;,ES

A/B A/B C

AIB

C

?

A/B

B A/B A/B A/B

us VI VlS Vb 2 X 218 = 436

( GM: 2 x 246 = 490(B) Liq: 2 x 266 = 612

vb* Vll 712 - 127 = 686 Real? see text. vat v, (Also HCN in gssf ? ? 663 + 266 = 819(?) 712 f 127 = 839(B)

( &as: 712 + 246 = 967 Liq: 712 -(- 266 = 968

( Gas: 712(v,) + 294 = 1008(A) Liq: 712(v,) + 307 = 1019

(* 663 f f~=i60] = 1103 m F.R. with vxe

( k: 1124 + 127 = 1261 Liq: 1136 + 141 = 1277(T)

:I36 + 266 = 1392(f) 2 x 712 = 1424 ? P ?

VP 1711+ 127 = 1838(B) 1711 f 246 = 1966(A) HCN 1

% % 2230 + 127 = 2367(B)(t) 1711 + 712(v,) = 2423(C)

(

Gas: 2230 + 246 = 2476 (A/B) Liq.: 2240 + 266 = 2498

ip &a: 2240 + 663 = 2793 Liq.: 2240 + 663 = 2803 2 ? 2240 $ 712 = 2962

; x 1711= 3422(B) ? ? P

ts, 0s. 6 = weak, medium, strong v=valy ah = shoulder NE = not exsmined A/B=- AorB.

+ p, dp = polarised, depolarirad. For de@&zed bcuxis, p = 0.76 f 0.03. [ ] Dedwed from oombbmtion tones. F.R. = Fermi resonance.

too-

80

20

0.

L 0 3000 2000 ’ lJ/- crc’

1600

Fig. 3a. I&&red sps~trum of (Z%sC),CO vapor, 4000-1600 cm-l. 1O-om path. Pressure 86 or 20 torr. The band at 2094 IX& ia due to ECN.

too-

80

20

O-

1r 60

CdCN)Z

f I i I I I f I I

0 1400 1200 1000 800 600 4 If- CM-

-l

10

Fig. 3b. Infrared 8pec;tru.m of (NsC),CO vapor, 1600--400cm-1. lo-cm path. Pressure 85 or 20 torr, The tie structure near 700 cm-1 is due to ECCN.

1016

1016 F. A. MILLER, B. M. HARNEY md J. TYRRELL

with the asymmetric stretch at 2230 cm-l, indicating little coupling between the two C?=_N vibrations. There is a trace of a shoulder on the lower frequency side of the band which may be due to rg, but it may also be due to an upper stage band v1 + rk - vk. The C=O stretching mode at 1’711 cm-1 is a clear type B band as expected. Its overtone, which is also type B, is evident at 3401 cm-l. The C-C symmetric stretch is partially obscured in the infrared spectrum of the vapor by the HCN bending vibration at 711.9 cm-l, which is responsible for the tie structure evident in Fig. 3. However it is identified with certainty at 712 cm-l in the Raman spectrum by its strong polarization. (The bending mode of HCN is not polarized.)

t 1 (N=C), C*O

RAMAN (LIQUID 1

;: I

A /

5 cn

I I I I I I I I I I I 2200 1600 1400 fOO0 600 200

CM-’

Fig. 4. Raman spectrum of liquid (N=C),CO. The dashed portions were run at lower gain, and segment B at higher gain.

The C-C-C scissoring mode is not clearly resolved from a complex band envelope centered at 553 cm-l. From evidence to be discussed later, having to do with Fermi resonance between the antisymmetric C-C stretch at 1124 cm-1 and a combination tone, it seems that the 663 cm-l band envelope includes two fundamentals. One has symmetry a, and the other b,. We therefore assign 563 to vp. The lowest band, at 127.5 cm-l, has a definite type B contour. It is therefore assigned to the N&J-C bend v5, and compares with a value of 122 cm-l for the equivalent vibration in di- ethynyl ketone and 167 cm-l in malononitrile [19]. This vibration is very active in combining with many other fundamentals as indicated in Table 5. It should be mentioned that the C-C-C scissoring and the NzC-C bend are probably mixed as they are in malononitrile [19], and these terms are convenient but inexact de- scriptions for va and vs.

a* fundamental. The only a2 fundamental in carbonyl cyanide is an NEC-C out-of-plane bend. It is allowedin the Raman but forbidden in the infrared spectrum. The only band which conforms to this requirement is that at 307 cm-l. This can be compared with a value of 268 cm-l in diethynyl ketone and 371 cm-l in malo- no&rile. The gas phase value of 294.5 cm-l comes from the electronic spectrum. (See later.)

[19] T. FUJIYAMA and T. Sm OUCHI, Spectrochim. Acta 20, 829 (1964). (Especially pp. 836 and 842.)

The vibrational spectra of (HCkC),CO and (NzC),CO 1017

b, fundamentals. The two fundamental frequencies of this species are the car- bony1 out-of-plane wag (Y,) and an N=C-C out-of-plane bend (us). In diethynyl ketone the analogous modes are at 688 and 190 cm-l respectively. The strong type C band at 208 cm-l is clearly vs. The only other type C band below 1000 cm-l, even with a path of 10 m, is 617 om- l. It is very weak and not reproducible in the infra- red, and we fear that it is spurious. It therefore seems that the type C band we are looking for is buried in the complex absorption at either 553 or 712 cm-l. Analogy with diethynyl ketone suggests the latter. One of us (JT) has strong evidence from an analysis of the high-resolution ultraviolet spectrum that Y, is at 712 cm-l (and also that Ye in the gas is at 294.5 cm-l). This receives support from the sum tone at 1004 cm-l. This is too intense to ignore and yet it cannot be explained as a binary combination of any of the other fundamentals. It might be 712 (Y,) + 294 (Q) = 1006. The shift to the liquid value also fits well: 712 (Y,) + 307 (YJ = 1019,

observed 1013. The value of 712 for va cannot be used in this way because the sum is then infrared-forbidden. Additional support for a value of 712 for v7 comes from the type C combination tone at 2420 cm- l. It may be explained as 1711 + 712 = 2423. If the a, fundamental at 712 is used, the combination would have symmetry A, and be a type B band. If the 712 is vri, the contour will be type C as observed. Although several arguments support a value of 712 for v?, none of them is by itself convincing, and this is the weakest assignment of the entire set.

b, fudamentab. The C?=_N antisymmetric stretch is probably at 2230 cm-l as previously noted. The C-C antisymmetric stretch vi,, is either 1102 or 1124 cm-l. These two bands are in strong Fermi resonance. It is difficult to say which is closer to the unperturbed fundamental. In the gas the higher one is more intense and has a more definite type A contour. In the liquid the lower one is more intense in the infrared, but the higher one is slightly stronger in the Raman spectrum. We take vl,, as the higher one, at 1124 cm-l in the gas and 1136 cm-l in the liquid. Because the two interacting states must have the same symmetry, the second band (at 1102 cm-l) must also be of species b,. Its most reasonable explanation is as a sum of two bands in the 553 cm-l complex, one of which is of symmetry a1 and the other of b,. This places the b, member at about 550 cm-l in the gas, and about 540 in the liquid

(1102 - 553 = 549). This is a reasonable value for the carbonyl in-plane wag vlr. Thus in carbonyl cyanide the carbonyl wags Y, and vi1 are 712 and ~550. In di- ethynyl ketone the corresponding frequencies are 688 and 548 cm-l. In both com- pounds the out-of-plane wag is the higher of the two by roughly 150 cm-l. The last b, fundamental is an NsC-C in-plane bend which certainly is the type A band at 245 cm-l.

Remaining bands. Explanations for many of the remaining bands are given in Table 5, using only binary combinations.

Recqitulation. ‘Assignments for ten of the twelve fundamentals are well estab- lished. The two uncertain ones are v, and Q, which appear to be nearly coincident with al fundamentals at 712 and 553 cm-l respectively. The close similarity of the frequencies in carbonyl cyanide and diethynyl ketone shown in Table 2 is powerful support for the assignments.

It is noteworthy that the carbonyl stretch in the vapor is 42 cm-l higher in

6

1018 F. A. -, B. M. HARNEY and J. TyaRELL

carbonyl cyanide than in diethynyl ketone. In the liquid ketone it has the ab- normally low value of 1639 cm- l, due to the combined lowering effects of con- jugation and weak hydrogen bonding.

Acknowledgtwnents-The work at the University of Pittsburgh was supported by the U.S. Army Research Office-Durham under Grant DA-ARO-D-31-124-G960. The purchase of the spectro- scopic equipment there was aided by National Science Foundation Instrumentation Grant GP-8287. The support of the National Science Foundation, Chemical Instrumentation Section, in the purchase of the Perk&-Elmer 226 instrnment used at Southern Illinois University is also gratefully acknowledged.