Third Virial Coefficients for Mixtures of Nonspherical Molecules

The influence of a large number of tensor interactions on the third virial coefficient, in some cases through the third order of perturbation theory, is evaluated for gas mixtures. The spherically symmetric components of the potential functions are assumed to be either of the Lennard-Jones 12–6 or 18–6 form. Molecular asymmetries of very general types are described in this work by permanent electric multipole moments, induced dipole moments, and anisotropic dispersion forces. Permanent moment interactions involving dipoles and quadrupoles are considered through the third order. Other asymmetric interactions involving permanent multipole moment tensors up to and including the hexadecapole moment are considered through the second order of perturbation. Pairwise potential nonadditivity due to three-body induced moment interactions occur in the second-order results and are studied for molecules with permanent dipole and quadrupole moments. Numerical examples of the effects of tensor interactions are given for CO2, N2, and C6H6.