MOLECULAR MECHANISMS OF DIELECTRIC-RELAXATION OF HIGHLY POLAR LIQUIDS

The dielectric spectra of highly absorbing simple liquids CH3F, CH3CI, CH3I and CHF3 caused by reorientations of polar molecules have been computed. The calculations were performed over a wide temperature range for the confined rotator (CR) model and for the hybrid confined rotator/extended diffusion model (HM). The mechanisms of absorption and dielectric losses result from periodic librations of molecules and from their orientation in the alternating local electric field E(c)(t), respectively. The calculated dielectric spectra agree with experiment over the frequency range 0 < nu/cm-1 < 200, covering the Debye relaxation and Poley absorption regions of the spectra. With increasing temperature T, the libration amplitude beta increases while the libration time tau-(the correlation time of the angular velocity \OMEGA\) and the barrier height U-OMEGA decrease. The maximum discrepancy between theory and experiment occurs at temperatures close to the critical value; in this case the HM gives a better description of the Debye frequency spectrum than the CR model. Estimates based on application of the resonance condition, the liquid cell model and the hard sphere model are proposed. The self-diffusion coefficient D(T) has been calculated; in this case the collision frequency of molecules 1/tau-v(v) was estimated for the hard-sphere model and it was assumed that the self-diffusion is caused by molecules whose translational velocity v is sufficient to surmount the barrier U(v) which is dependent on T. It was shown that the barrier U(v) is essentially less than U-OMEGA and for a first approximation, is proportional to U-OMEGA.