On the sensitivity of thermal diffusion to the anisotropy of intermolecular interaction potentials

Abstract

Using pairs of potential energy surfaces with common isotropic components for a series of nitrogen-rare gas mixtures, the sensitivity of thermal diffusion to changes in the anisotropy of intermolecular interaction potentials has been examined. The thermal diffusion factor has been shown to be sensitive to variations in the anisotropy of the repulsive wall; however each system has been found to exhibit a temperature range over which α T is relatively insensitive to details of the potential energy surface. Additionally, the contribution of angular momentum polarizations, rotational-translational coupling and the transport of rotational energy to the thermal diffusion factor have been examined for each of the nitrogen-rare gas systems. The relative importance of each of these contributions has been found to depend upon the mass ratio of the components of the binary mixture. It is seen that in general none of these terms can be neglected, and that for most systems, higher-order Chapman-Cowling approximations will be required in order that meaningful comparisons can be made with experiment.