Assignment of the Vinyl Fluoride Wagging ModesJ. R. Scherer and W. J. Potts Citation: The Journal of Chemical Physics 31, 1691 (1959); doi: 10.1063/1.1730690 View online: http://dx.doi.org/10.1063/1.1730690 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/31/6?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Theoretical and experimental structures of vinyl fluoride and vinyl alcohol J. Chem. Phys. 97, 6113 (1992); 10.1063/1.463721 Infrared absorption measurement of the overtone of the wagging mode of hydrogen on W(100) J. Vac. Sci. Technol. A 4, 1324 (1986); 10.1116/1.573602 Direct observation and assignment of the bending vibrations of vinyl fluoride J. Chem. Phys. 63, 1311 (1975); 10.1063/1.431426 Microwave Spectrum and Molecular Structure of Vinyl Fluoride J. Chem. Phys. 30, 1025 (1959); 10.1063/1.1730077 The Assignment of the Vibrational Spectra of the C4 Hydrocarbons Butyne−1, Butene−1, and VinylAcetylene, to the Normal Modes of Vibration of These Molecules J. Chem. Phys. 17, 74 (1949); 10.1063/1.1747056

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LETTERS TO THE EDITOR 1691

TABLE II. Frequency shifts as in Table I, for various concentra­tions of p-CI.c/> in p-xylene, at -78°C.

Concentration of p-CI2cf> in mole percent

13.4 37.5 47.4 66.7 86.6 90.9 98.7

Frequency shift in kc

-95±25 +200±25 -55±15

0±15 0±15 0±15 0±15

+440±15

chosen for these samples. A self-quenched superregener­ative spectrometer2 was used, with magnetic field modu­lation and conventional recording techniques.

The samples were melted, stirred, or shaken, and solidified. It was not established that each was a homogeneous solid solution, but the resonance widths and shifts indicated that enough were sufficient approxi­mations to verify the utility of the technique. Para­substituted benzenes were chosen to minimize geomet­ric incompatibility as a factor contributing to their possible immiscibility with p-dichlorobenzene. The zero shifts in Table I may indicate a separation into two components, one of which is predominantly p­dichlorobenzene, although the case of terephthaloni­trile suggests caution in such an interpretation. Earlier work has shown, however, that with a sequence of sam­ples of a binary system with various concentration ratios one may obtain enough such indications to deduce a clear picture of at least part of its phase diagram.l,3,4

The span of the frequency shifts of Table I is small relative to the range of about 530 kc found in the xylene samples (Table II). It should be compared with the small span of about 35 kc encompassed by the cases with known structures, the,8 phase of p-dichlorobenzene5

which has features of marked similarity to the a phase,6,7 and the solid solution with p-dibromobenzene which is isomorphous to a phase p-dichlorobenzene.8 Since these frequency shifts are determined by the nature of the intermolecular bonds and by the freedom for torsional oscillations that is permitted the probe molecules,9 and since these known cases show considerable simi­larity in their packing of the molecules, it is not un­reasonable to suspect that the restricted span of fre­quency shifts in Table I may indicate some aspects of similarity in the intermolecular force systems for those samples. The xylene samples were unusual not only for the large range of frequency shifts but also because there were some indications that the frequency, and thus the state of the solid sample, may depend on the temperature reached while liquid, suggesting possibly some state of aggregation being maintained in the liquid at the lower temperatures.

A complicated spectrum was recorded for the hydro­quinone sample at O°e. Although not fully interpre­table it appeared to be a multiplet, suggesting either more than one nonequivalent unit cell site for the

impurity or a separation into more than one component containing p-dichlorobenzene. Some of the other data suggest that a search should be made in the interven­ing temperature region for possible frequency-tempera­ture discontinuities which would mark solid-solid phase transitions. However sharper signals are needed for bet­ter frequency precision. For this reason, as well as for data more nearly representing the pure host material, one should seek the minimum detectable probe con­centration. Since the random distribution of probe molecules in the sample produces the usual impurity broadening,10-12 the decrease in total signal will be compensated to some extent by decreased line widths as the probe concentration is reduced.

* This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command.

t Based on a thesis submitted by R. Baer for the degree of Master of Science in Physics, University of Pittsburgh, 1959.

:j: Now at Emory University, Atlanta, Georgia. 1 C. Dean, J. Chern. Phys. 23, 1734 (1955). 2 C. Dean and M. Pollak, Rev. Sci. Instr. 29, 630 (1958). 3 C. Dean and E. Lindstrand, J. Chern. Phys. 24, 1114 (1956). 4 E. Lindstrand, unpublished work in this laboratory with

p-chloroiodobenzene in p-dichlorobenzene. 5 C. Dean and R. V. Pound, J. Chern. Phys. 20, 195 (1952). 6 G. A. Jeffrey and W. J. McVeagh, J. Chern. Phys. 23, 1165

(1955) . 7 Housty and Clastre, Acta Cryst. 10, 695 (1957). 8 S. B. Hendricks, Z. Krist. 84, 85 (1932). 9 Kushida, Benedek, and Bloembergen, Phys. Rev. 104, 1364

(1956) . 10 A. Monfils and D. Grosjean, Physica 22, 541 (1956). 11 D. E. Woessner and H. S. Gutowsky, J. Chern. Phys. 27,

1072 (1957). 12 Kojima, Ogawa, Minematsu, and Tonaka, J. Phys. Soc.

Japan 13, 446 (1958).

Assignment of the Vinyl Fluoride Wagging Modes

J. R. SCHERER AND W. J. POTTS

Spectroscopy Laboratory, The Dow Chemical Company, Midland, Michigan

(Received August 4, 1959)

THE correct assignment of the out-of-plane funda­mentals of vinyl fluoride has in the past been the

subject of considerable controversy. Thompson and Torkington1 originally assigned these modes to three prominent type C infrared bands at 860, 732, and 715 cm-1 whereas Pitzer and Freeman2 preferred to take 924, 860, and 715 cm-1 since these were more in line with their approximate potential function. Cole and Thompson,3 however, took issue with Pitzer and Free­man by showing the strong band at 924 cm-1 to be an in-plane. mode of AlB hybrid structure and therefore adopted the early assignment as the correct one. Re­cently Bak and Cristensen4 have obtained spectra for the deutero isotopes of vinyl fluoride. On the basis of the product and sum rules they conclude that there must be an out-of-plane fundamental near the 928-cm-1

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1692 LETTERS TO THE EDITOR

Table I. Observed and calculated frequencies for vinyl fluoride.

Calc. p obs. p

Molecule Weight (cm-I ) (cm-I ). D.p

{~ 931.5 (940) +8.5

CH2CHF 864.5 864 -0.5 714.7 714 -0.7

{: 866.4 867 +0.6 CH2CDF 790.5 791 +0.5

682.9 683 +0.1

{: 910.3 910 -0.3 cisCHDCHF 785.6 785 -0.6

642.2 642 -0.2

fb 926.4 926 -0.4 trans CHDCHF t: 814.4 815 +0.6

575.5 576 +0.5

trans CHDCDF {~ 825.4 844 +18.6 695.0 695 0.0 640.2 639 -1.2

{~ 844.2 844 -0.2

cis CHDCDF 724.6 726 +1.4 575.3 575 -0.3

{~ 887.9 888 +0.1

CD2CHF 692.2 693 +0.8 563.6 564 +0.4

fh 727.9 728 +0.1 CD,CDF t: 674.2 675 +0.8

562.8 563 +0.2

a From reference 4. b Weight factor=l/Aobs.

(924-cm-1 in the older work) in-plane mode. Although they could not determine its exact location, they favored placing it at 940 cm-l by analogy with vinyl bromide and chloride. Correlative data obtained by Potts and Nyquist6 seems, however, to place this fundamental closer to Pitzer and Freemans value.

Bak and Christensens' elegant analysis of the vinyl fluoride isotopic spectra now provides data to fix absolutely the position of the elusive CH2CHF twisting fundamental by a normal coordinate analysis identical to that used on vinyl bromide. 6 G matrices were numeri­cally computed with the Datatron 204 from cartesian coordinate input,7 the geometry being taken from re­cent microwave work of Bak et at.s

Having many more observed frequencies than force constants we excluded the doubtful ones from the force constant calculation by giving them zero weight. The converged results of this calculation are given in Table I. Because Bak and Christensen did not have pure cis and trans CHDCDF but a mixture, they were unable

TABLE II. F matrix for vinyl fluoride. (Coordinates same as in reference 6.)

F(mdIA) R, R, R, -~----~~~---

0.2161 0.1753 -0.1793 0.3989 -0.2526

Sym. 0.3014

TABLE III. Cartesian coordinate displacements out-of-plane CH2CHF modes in A/unit change in normal coordinate. Num­bering of the atoms follows the scheme used in Fig. 1 of reference 6.

Atom No. 931 cm-I 864 cm-I 714 cm-I

l(F) 0.00 0.00 -0.06 2(C) -0.08 +0.06 +0.15 3(H) +0.78 -0.10 -0.24 4(C) 0.00 -0.14 -0.02 5(H) +0.49 +0.58 +0.40 6(H) -0.23 +0.60 -0.67

to sort out entirely the corresponding out-of-plane bands. Consequently they have assigned an absorption

at 844 cm-l as a superposition of 116 of the cis and trans molecules. They do, however, observe an absorption maximum at 824 cm-l and in view of our calculations it would seem better to call this 116 of trans CHDCDF. * judging from the accuracy of the calculation of the remaining fundamentals we see that the disputed twisting frequency in CH2CHF is not at 940 cm-1 but at 931 ±2 cm-l . Unfortunately this mode occurs so close to the band center of the 929-cm-1 in-plane fun­damental that chances of detecting it in the gas phase are slim indeed. The converged F matrix in the co­ordinates of reference 6 is given in Table II and the cartesian displacements for CH2CHF are given in Table III.

1 H. W. Thompson and P. Torkington, J. Chern. Soc. 1944, 303.

2 Kenneth S. Pitzer and N. K. Freeman, J. Chern. Phys. 14, 586 (1946) .

3 A. R. H. Cole and H. W. Thompson, Proc. Roy. Soc. (London) A200, 10 (1949).

4 B. Bak and D. Christensen, Spectrochim. Acta 12, 355 (1958). 5 W. J. Potts and R. A. Nyquist, Spectrochim. Acta (to be

published) . 6 J. R. Scherer and W. J. Potts, J. Chern. Phys. 30,1527 (1959). 7 J. Overend and J. R. Scherer, J. Chern. Phys. (to be pub­

lished. 8 Bak, Christensen, Hansen Mygaard, and Rastrup-Andersen,

Spectrochim. Acta 13, 120 (1958). * In a private communication Professor Bak has indicated no

objection to this minor revision in the out-of-plane assignment.

Fundamental Vibration Frequencies of DZOl8 Vapor

S. PINCHAS AND M. HALMANN,

The Weizmann Institute of Science, ReTzovoth, Israel

AND

B. P. STOICHEFF, Division of Pure Physics,

National Research Council, Ottawa, Canada

(Received June 12, 1(59)

THE vibrational spectrum of D2018, although interesting in many respects, has not yet been

described in the literature. Since D2018 recently has

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