RAYLEIGH DEPOLARIZATION RATIOS AND PRINCIPAL POLARIZABILITY COMPONENTS OF FLUOROMETHANES

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1979

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Ohio State University

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Conventionally, Rayleigh depolarization ration measurements of gases have entailed the polarization analysis o all scattered light, without spectral $dispersion.^{1,2}$ For this method vibrational Raman scattering makes a contribution to the observed depolarization ratio which can be significant for highly polarized Rayleigh $scattering.^{2}$ Recently, a method was developed which involves measurements of the spectrum of the scattered light, and determination of the weak anisotropic intensity by fitting the calculated spectrum to the observed rotational $contour.^{3}$ The major advantage of this method is that it is not affected by stray light and other sources of experimental errors which contribute to the measured intensity at the incident frequency; however, in addition, it avoids contributions from vibrational bands since the measurement is made from the spectrum of the scattered light. This method has been used to remeasure the depolarization ratios of the partially fluorinated methanes. For the symmetric top molecules, fluoroform and methyl fluoride, the depolarization ratio results may be combined with the mean polarizability available from refractivity data to obtain values for the two unique principal components of the molecular polarizability tensor. For the asymmetric top difluoromethane, the relation between the rotational contour and the relative value of the principal components is the third quantity needed to determine the three unique principal polarizability components. A direct measurement of the possible contribution of vibrational bands to the previous results has also been made.

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$^{1}$M.P. Bognard, A.D. Buckingham, R.K. Picrens and A.H. White, J.C.S. Faraday I 74 3008 (1978) and references therein. $^{2}$N.J. Bridge and A.D. Buckingham, Proc. R. Soc. A. 295, 334 (1966). $^{3}$W.F. Murphy, J. Chem. Phys. 67, 5877 (1977).
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