Second Virial Coefficients Calculated from Atom‐Atom Intermolecular Potentials

Abstract

Atom‐atom intermolecular potentials derived from studies of crystal properties are used to calculate the second virial coefficients of a number of polyatomic gases: carbon dioxide, methane, ethane, cyclopropane, benzene, and ethylene. Calculated virial coefficients are in moderate agreement with observed data and could be brought into excellent agreement with changes in attractive potential parameters of a few percent. Effective intermolecular central potentials—averages including rotational correlation—for methane, ethane, and benzene are compared with previous averaged potentials. It is possible to obtain good fits to the data with potentials of greatly differing well depths and ``molecular volumes.'' The effective potential is temperature dependent and in the case of benzene clearly reflects the anisotropy of the molecule at lower temperatures.