Angular Correlation Functions: Application to Dielectric Absorption in Polar Fluids

In recent work on the theory of dielectric absorption, the complex dielectric constant has been expressed as a function of the correlation function of the electric moments of the system. Here, the equations are written down which relate this correlation function to the time-dependent distribution functions for molecular orientation. Two model calculations of the singlet angular distribution function are discussed; and the pair-wise distribution function is related to the singlet motion by an extension of the convolution approximation to rotational motion. The correlation function of the permanent dipole moments is obtained from these distribution functions, and the contribution of induced dipoles to the correlation function of the moments is briefly discussed. Finally, the theoretical expressions developed here are applied in a partial analysis of the dielectric absorption properties of liquid water.