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Dielectric relaxation in symmetric-top molecules Clark, Robert Bernard

Abstract

Dielectric dispersion has been observed in the symmetric-top molecules CHF₃ and CH₃­F in the gas phase over a density range from 10­³ to 40 amagats at a temperature of 309°K and a frequency of 30 MHz. The absorption (related to the dispersion by the Kramers-Kronig relations) has been expressed in terms of a simple correlation function of the permanent electric dipole moment which is the product of the correlation function for free motion and an exponentially decaying "reduced" correlation function. The effects of molecular collisions were described by a single correlation time which measures the apparent molecular diameter. The results were compared with microwave nonresonant absorption and nuclear spin relaxation experiments done on the same molecules. At low densities (1 amagat) the dependence of the dielectric susceptibility on density deviated from that expected from the Clausius-Mossotti equation. The origin of this effect is not understood at present.

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