Dielectric Constant and Interactions of Polar Molecules

Abstract

The theory of the dielectric constant previously developed by Van Vleck and others for permanent dipoles is extended to third‐order interactions with inclusion of induced polarization represented by harmonic oscillators. This is carried out by a high‐temperature expansion of the partition function in powers of dipole coupling energy. Third‐order interaction terms are of the triangle and shuttle forms found by Rosenberg and Lax for permanent dipoles, but for induced moment contributions only the triangle interaction sum is involved. For neither type of term can agreement with Onsager's model be secured in any reasonable way. Kirkwood's treatment of long‐range interactions is shown to be consistent with the series expansion results if short‐range correlations are properly evaluated, but the results of this evaluation depend on molecular distributions.