RELATIONSHIP BETWEEN MICROSCOPIC AND MACROSCOPIC ORIENTATIONAL RELAXATION-TIMES IN POLAR LIQUIDS

Microscopic relations between single-particle orientational relaxation time (τu), dielectric relaxation time (τD), and many-body orientational relaxation time (τM) of a dipolar liquid are derived. We show that both τD and τM are influenced significantly by many-body effects. In the present theory, these many-body effects enter through the anisotropic part of the two-particle direct correlation function of the polar liquid. We use mean-spherical approximation (MSA) for dipolar hard spheres for explicit numerical evaluation of the relaxation times. We find that, although the dipolar correlation function is biexponential, the frequency-dependent dielectric constant is of simple Debye form, with τD equal to the transverse polarization relaxation time. The microscopic τD falls in between Debye and Onsager-Glarum expressions at large values of the static dielectric constant. © 1990 American Chemical Society.