Theory of surface tension for molecular liquids. II. Perturbation theory calculations

Abstract

A general perturbation expansion for the surface tension of a molecular liquid is considered, and the first order term is evaluated. For the special case of a Pople reference potential, perturbation terms up to the third are evaluated for both the general interface and for the Fowler model (abrupt vapor–liquid transition). A Padé approximant to this latter series, similar to that used by Stell, Rasaiah, and Narang for the free energy, is proposed and is used to calculate the effects of dipolar and quadrupolar intermolecular forces on the surface tension. The effects of anisotropic overlap and dispersion forces are also computed, using the series terminated at the second order term. The Padé approximant is also compared with experimental data for hydrogen bromide; using the Fowler approximation, good results are obtained for the low temperature liquid.