Test of intermolecular potentials for the noble gases by comparison with experimental thermal diffusion factors

The description of the equilibrium and transport properties of dilute gases follows from a knowledge of the pair interaction energy of the gas particles. We have used a second order effect, the thermal diffusion factor, which is extremely sensitive to the intermolecular potential, as a test of various potentials which have been proposed for the noble gases. Measurements of the thermal diffusion factor were made over a wide range of temperatures in the trennschaukel; and these results, along with other values reported in the literature, were fitted to empirical equations within the experimental uncertainties. Many proposed intermolecular potentials, including some recently obtained from solid state properties and molecular beam scattering, were used to calculate transport collision integrals and thence theoretical thermal diffusion factors which were compared to the empirical equations. In the case of helium, quantum mechanical calculations were made. The ''best'' potentials for each noble gas were then used to evaluate other macroscopic properties of the homologues.