Abstract
A numerical integration procedure to calculate the second virial coefficient of simple polyatomic molecules is proposed. The intermolecular pair potential is assumed to be a sum of a spherically symmetric contribution and an unsymmetric, angular dependent, contribution. The method is based on evaluating the possible different numerical values for this latter term. Quadrupolar and dipolar molecules are considered. Calculations for the virial coefficient for quadrupolar molecules are judged to be correct to within one part in 2500 or better, and to within one part in 300 or better for polar molecules. Results from the method are compared to corresponding results from the well-known Pople expansion procedure. It is shown that care must be taken to ensure this latter technique yields a convergent answer.