Anisotropic intermolecular potentials and transport properties in polyatomic gases

Abstract

It is widely accepted that the ordinary bulk transport properties of polyatomic gases, such as the shear viscosity or the thermal conductivity, are predominantly determined by the isotropic part of the intermolecular interaction, so that it is difficult to utilize them directly as sources of or tests for intermolecular anisotropies. It is also widely known that the effects of external electric and magnetic fields on these same transport properties depend critically upon the anisotropies, e.g. they are nonzero only for anisotropic potentials. Thus, external field effects on transport properties, particularly their temperature dependence, provide an important source of data for testing and/or determining intermolecular anisotropies. Before such data can be utilized, however, it is necessary to have available exact relationships between the effective cross-sections determining these phenomena and the S-matrix elements obtained from scattering calculations, together with reliable numerical procedures for calculating the S-matrix elements. An illustration of Liouville space methods for carrying out the first step of this procedure is given for one of the cross-sections occurring in the thermal conductivity. The infinite-order sudden approximation is utilized to show the importance of taking into consideration the full potential surface when analysing ordinary bulk properties of systems. Results are given for binary mixtures of N2 and Ar. The results of a full close-coupled calculation of the thermal conductivity Senftleben–Beenakker effect (SBE) for the H2–He system are presented and discussed briefly.