April, 1951
SPECTRA AND FORCE CONSTANTS OF CHLOROFORM AND TRICHLOROSILANE Id31 [CONTRIBUTION FROM THE
DEPARTMENT O F CHEMISTRY,
CARNEGIE INSTITUTE OF TECHNOLOGY ]
Infrared Spectra and Force Constants of Chloroform and
Trichlorosilane’”,“
Ru T. C,. G I R I A N ’AND ~ . ~D. S. LICKINNEY The infrared spectra of chloroform and trichlorosilane were obtained with a rock salt spectrometer in the range of 1-15p in both the liquid and vapor states. The C-H stretching bond of chloroform vapor was resolved into the PQR branch with a high resolution grating spectrometer. A complete assignment of observed bands was made. A simplified potential function is proposed on basis of which the force constants of chloroform and trichlorosilane are obtained. Using these force constants fundamental frequencies are calculated which agree to within 1.5% with the experimental ones.
This paper presents infrared absorption spectra of chloroform and trichlorosilane in the liquid and vapor skates from 1 to 15 p obtained by means of a rock salt spectrometer. The nature of the chloroform spectrum in the 3 ,u region has also been investigated under high resolution with the aid of a grating spectrometer, The hitherto published infrared spectra of chloroform were limited mostly to the liquid or dissolved chloroform in the regions of the fundamentals ~ n l y , whilst ~ , ~ the Raman spectrum was obtained by numerous investigators in the I i q ~ i d ~as~ well as in the vapor states.6 In the case of trichlorosilane, only the Raman spectrum of the liquid has been reported so far’s8 with no infrared data published prior to this investigation. Consideration of the published Raman and infrared data, together with the data given here, permitted a complete assignment of the observed spectral bands as well as the calculation of the force constants for these compounds on the basis of a simplified potential function. This potential function is particularly suited to the analysis of the spectra of pentaatomic tetrahedral molecules of the type HXYI, where X = C, Si, Ge and Y = C1, B, I, utilizing the F and G Matrix method of Wilson.s
fied by shaking with concentrated sulfuric acid three times, washing with water, and after drying with CaC12 redistilling from a ground glass equipment using a Widmer column. The middle fraction was taken and stored in a dark bottle. Only small amounts were kept a t a time and more chloroform purified as needed. The trichlorosilane was obtained from the Anderson Laboratories, Adrian, Michigan, and was used without further purification. The manufacturer’s analysis for the pure grade was SiHC13 > ~ 99.5%, J Sic14 < 0.5%. Amalgamated lead washers12were used as spacers for the liquid cells. They also served to provide a gas tight joint between the rock salt window and the glass body of the vapor absorption cell. In the cell for the liquid chloroform investigation a narrow strip of lead was drawn tightly over the outside surface and sealed with a film of polyvinyl alcohol from a methyl alcohol solution. This seal remained gas-tight for periods of 24 to 48 hours. Due to the rapid decomposition of trichlorosilane in air, both the liquid and vapor cells were filled in a dry-box filled with drierite. To ensure perfect sealing, a layer of silicone putty was placed on the outside of the amalgamated lead washer, and the cell brought slowly to 180’ and kept a t this temperature for 8 hours. The hardened putty was then coated with silicone varnish and further cured Experimental a t 150’. Both these silicone materials were special The spectrometers have been described by samples obtained through the courtesy of the The spectra were taken by the usual Westinghouse Electric Corporation. With these cell-in, cell-out method, using a rock salt dummy. precautions no decomposition of SiHC13took place, Readings were usually taken every slit width; and the cells remained gas-tight for several days. sometimes, two per slit width when it seemed The equilibrium vapor pressure method was used advisable. to obtain the desired concentrations of chloroform The chloroform was Merck C.P., further puri- and trichlorosilane in the vapor cells. The liquid was placed in a small (10 cc.) glass bulb connected (1) (a) Abstracted from a thesis submitted by T. G. Gibian to the Committee on Graduate Degrees, Carnegie Institute of Technology, in to the body of the vapor cell through a groundpartial fulfillment of the requirements for the DSc. degree, December, glass joint. To obtain chloroform vapor pressures 1948. (b) Presented before the Division of Physical and Inorganic a t higher than room temperature, the whole cell Chemistry a t the Meeting of the American Chemical Society, Septemassembly was heated electrically, with the tember, 1950, Chicago, Ill. ( c ) American Chemical Society pre-doctoral fellow, 1946-1948. (d) Atlantic Refining Company, Philadelphia, perature of the cell being kept higher than that Pa. of the liquid bulb to prevent condensation on the (2) G. Herzberg, “Infrared and Raman Spectra of Polyatomic rock salt windows. To reduce the vapor pressure hlolecules,” D. Van Nostrand Co., New York, N. Y., 1945. of trichlorosilane (b.p. 31S0), cooling mixtures (3) G. L. Jenkins and J. W. Straley, Phys. Rcu., 68, 99 (1945). (ice/water, Dry Ice, COz/acetone) were placed (4) K. W. F. Kohlrausch, “Der Smekal-Raman Effect,” J. Springer, Berlin, 1931. around the liquid container. ( 5 ) J. H. Hibben, “The Raman Effect and Chemical Applications,” The cell thicknesses and vapor concentrations Reinhold Publishing Corp., New York, N. Y., 1939. are indicated on the spectra. (6) J. R. Nielsen and N. E. Ward, J . Chcn. Phys., 10, 81 (1942). (7) C. A. Bradley, Phys. Reu., 40, 908 (1932). Results (8) M. de Hemptienne, Nalurc, 138, 884 (1936). (9) E. Bright Wilson, Jr., J. Chcm. Phys., 7, 1047 (1939); ibid., 9, The infrared spectra of chloroform and trichloro76 (1941). silane in the liquid and vapor are shown in Figs. (10) D. S. McKinney, C. E. Leberknight and J. C. Warner, THIS 1, 2. The observed bands are given in Table I JOURNAL, 69, 481 (1937). (11) C. E. Leberknight and J. H. Ord, Phys. Rcv., 61, 430 (1937).
(12) L. Gildart and N. Wright, Rev. Sci. Ins;., 12, 204 (1941).
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Fig. 2.--Infrared spectrum of trichlorosilane.
together with the complete assignment of the fundamentals, overtones and combination frequencies. The convention used for designating and ordering the frequencies is that adopted by
HerzbergS2 Best values of the fundamental frequencies as determined by Raman spectroscopy are compared with those of the present investigation in Table 11.
SPECTRA AND FORCE CONSTANTS OF CHLOROE'ORM AND TRICHLOROSILANE1433
April, 1951
bond bendings equal to zero. This is necessary TABLE I THEOBSERVED FREQUENCIES AND ASSIGNMENTS OF CHLORO- to keep the number of force constants used to six, which is the number of the observed fundamentals. FORM AND TRICHLOROSILANE Assignment Ut
2UP us UI
.
-
"3
+
932(m)
ud
+ ua + us UI
UL
CHCla Liquid Vapor 6Ws) 680(s) 709(sh) 720(sh) 759(s) 774(s) 85l(w) 843 852(m) 858
UI
1017(m) 1118(w) 1218(s)
924(sh) 932(w) 944 1029(w) 1125(w) 1221(s)
Assignment YZ
us u4 Y3
+ + +
SiHCla Liquid Vapor 654(m) 667(m) 739(sh) 752(sh) 798(s) 808(s) 829(sh)
UI
VI Y5
2ui
978(m)
+ + 2vs + ua
v4
v2
YL
u4
2ur
1048(sh) 1090(m) llll(sh) 1182(m)
971 985(m) 99 1
1441(w) 1594(m) 2258(s) 2734(w)
1061(w) 1096(m) 1124(w) 1196 1204(m) 1306(m) 1386(w) 1454(w) 1610(m) 2274(s) 2751(w)
3059(w) 4514(w)
3090(w) 4526(w)
The assumption that the omitted terms are quite small is reasonable on physical grounds, and is supported by the work of Decius14on the systematic halomethane force constants. Further data of Simanouti, published after the completion of the present work, also agree with this postulate. The potential function was written as
+
+
+
2 V = f d [ Adi2 Ad?2 Ada2] f a d 2 [ Ao1z2 A.(~23* Aa312] f i ~ [ A D 2 ] fpd2[AP12 APz2 f A/3s21 2fdjd [( A&) ( AdJ ( A&) ( Adz) 4- ( M a ) (Ad31 1 2fdud[Adi(Aoiz A d Adz(Aai2 ALY?~) Ada( Aaz3
+
+
+
+
+ +
+ + + + + I
~~
2vl I2 VI
2ua 'I u1
Yt
+ ur +
+ + +
vn us Y.
v4
2rr
2w
+
u3
vl
1686 (wl 2420(m) 2480(sh) 2870(w) 3032(s)
VI
+
+ 2Vl + 2v: 2n
1338(w) 1428(m) 1480(m) l527(m) 1582(sh)
VI YI
us
4260(m) 4420(sh) 5920(w) 7049(w)
COMPARISON
1356(w) 1447(m) 1481(w) 1549(m) 1 580( w) 1634 1840(m) 1891(w) 2424(m)
3028(a) 3034(s) 3041 4273(m)
v4
2vz 2 Y4 VI
VI
YL
f u4
+ +
+ +
2Ul
1301(m)
u5 YI
YZ
u4
a-with grating spectrometer (sh)-shoulder (s)-strong (m)-moderate (w)-weak
5934(w)
..
..
..
680 774 1221 3034
668 759 1218 3032
261 363 672 760 1217 3030
where d = equilibrium distance of C-C1 (or Si-C1) bond; fi = force constant associated with change in i's internal coordinate. In HYCl3 molecules the coordinates used are. bond length, H-Y = D; Y-Cl = dl, dz, & ; bond angles, HYCl = P I , PZ, 0 3 ; ClYCl = a 1 2 , a31, a23. The F matrices of Wilson's methodg were then calculated from this potential function. F Matrix for A1 Type Vibrations / F11 FIZF13 ! f ~ 0 ~
I
Iafrared 2
260 364 667 760 1205 3033
Trichlorosilane This work Vapor Liquid Raman'
.. .. .. ..
.. , . .. ..
808 2274
798 2258
179 250 489 587 799 2258
With the aid of the grating spectrometer the C-H stretching band in CHCl3 was resolved into the PQR components in the vapor, but not in the liquid. Calculation of Force Constants.-The chloroform and trichlorosilane molecules belong to the CSvpoint g r o ~ p , ~ with J ~ three non-degenerate symmetrical fundamental vibrations A, and three doubly degenerate, anti-symmetrical fundamentals E, active both in the infrared and the Raman. A simplified potential function with six force constants was set up, containing force constants associated with changes in bond length and bond angle, as well as force constants related to the changes in the distances between the non-bonded atoms. The proposed potential function takes into account the interactions between the C-C1 (or Si-Cl) stretching and the various bond bendings, but sets the interactions of the C-H (or Si-H) bond stretchings with the various bendings as well as the interactions between the different (13) J, E. Rosenthal and G M. Murphy, Rev. M o d . Phys., 8, 317 (193fi).
( )
j FZIFZZF23 j = 0 ,, '' ,
j
TABLE I1 O F FUNDAMENTAL FREQUENCIES O F CHLOROFORM AND TRICHLOROSILANE
Chloroform This work Raman Vapor liquid vapor*
..
uz
F31 F 3 2 F 3 3
j
!
I
i0
I
f
