Multipolar polarizabilities isotropic molecules

In summary, since the early 1980s or so, collision-induced light scattering experiments on molecular fluids have demonstrated that the study of the collision-induced absolute-unit spectra (depolarized and/or isotropic ones) is an useful tool, and up to now the only one, to measure multipolar polarizabilities of molecules. 

The influence of multipolar polarizabilities has been examined subsequently in several optically isotropic molecules such as CH4, CD4, neopentane, CF4, or SF6 [4,7-14,17,18]. In this review, our attention is focused on CF4 for which both Rayleigh [8,13] and Vi Raman [17,18] depolarized and isotropic bands have been studied and published by us. In the Rayleigh studies, we measured the /j (v) and / (v) intensities that are scattered by gaseous CF4 up to 340 cm-1, in... 

The profiles of the rototranslational absorption of CH4-CH4 in the far infrared have been reported [56] see Fig. 3.22 for an example. The treatment of the spectra is based on the multipolar induction model and an advanced isotropic potential empirical overlap-induced dipole components have also been included for fitting the experimental data at several temperatures (126 through 300 K). At the lower temperatures, satisfactory fits of the measurements are possible. The analysis seems to suggest that at temperatures near room temperature a significant rotation-induced distortion of the tetrahedral frames occurs which affects the properties of the individual molecules (multipole strengths, molecular symmetry, polarizabilities, and perhaps the interaction). 

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