Statistical Mechanics of Linear Molecules. IV. Nonspherical Polar Molecules

A modified form of the Stockmayer potential for polar molecules is utilized to calculate: pair correlation functions in the limit of zero density, ordinary second virial coefficients, and dielectric second virial coefficients. The potential function is modified by allowing the dispersion–repulsion part of the energy to be that for a linear symmetric molecule whose potential energy is represented by Lennard-Jones functions for the two “atoms” in the molecule interacting with the two “atoms” in neighboring molecules. This is combined with an ideal dipole–dipole energy to give the over-all potential function. Changes in the statistical properties are calculated as a function of the molecular length, and results are presented which indicate that the ordinary second virial coefficients change by moderate amounts, but that the dielectric second virial coefficient is strikingly affected by the introduction of nonspherical molecular shapes.