Intermolecular Potential Function and the Second Virial Coefficients of Simple Polar Gases

A modified form of the Stockmayer potential function is used to represent the pair interactions of axially symmetric polar molecules. The potential function is modified by assuming that the dispersion–repulsion part of the potential energy is the sum of all the pair interactions between constituent atomic groups on adjacent molecules and that the molecules are polarizable. The second virial coefficient is then calculated by treating the directional part of the potential energy as a perturbation on the central force part. With two adjustable potential parameters, this model closely reproduces the experimental second virial coefficients for methyl fluoride and fluoroform.