Calculation of Raman scattering parameters for methane and halomethanes from an atom dipole interaction model

Abstract
Derivatives of molecular polarizability tensors with respect to vibrational normal coordinates are calculated using an atom dipole interaction model for CH4, CD4, CF4, CCl4, CHF3, CH3Cl, CHCl3, CF3Cl, CFCl3, CH3Br, CF3Br, and CH2Cl2. Isotropic atom polarizabilities obtained from previous studies of molecular polarizability are used. Derivatives of atom polarizabilities with respect to bond lengths are adjusted to give a best fit to the mean polarizability derivative ?′ for 29 totally symmetric modes as found from published gas phase Raman scattering intensities and depolarization ratios. A satisfactory fit to ?′ is obtained, but the calculated anisotropies γ′ correlate only roughly with the experimental values. The signs of the calculated ?′ values are consistent with the view that the mean molecular polarizability increases with increasing bond length for all normal modes in which bond stretching motions predominate.

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