The Dielectric Polarization of Polar Liquids

An extension of the Onsager theory of dielectric polarization is presented. The local dielectric constant is approximated by the macroscopic dielectric constant of the fluid in a region outside a molecule and its first shell of neighbors rather than in the entire region exterior to the molecule. In addition to the molecular dipole moment, the average value $〈\cos {\mathrm{\gamma 〉}}_{\mathrm{Av}}$ of the cosine of the angle between neighbor dipoles is a determining factor. Hindered relative rotation of neighboring molecules produces a correlation between their orientations and prevents $〈\cos {\mathrm{\gamma 〉}}_{\mathrm{Av}}$ from vanishing. The theory is applied to liquid water under the assumption of tetrahedral coordination and directed bonds between neighboring molecules.