Thermal Diffusion Factor and Quantum Collision Integrals for the H2–4He System: The Effect of Inelastic Collisions

We have extended our measurements of the composition dependence of the thermal diffusion factor of the hydrogen-helium system to lower temperatures in search of the inelastic (rotational) collision effect reported by Ghosh et al. and Mathur and Watson. We measured αT as a function of composition in a seventube trennschaukel at an average temperature of 82°K and failed to find any maxima or minima greater than our average experimental scatter of approximately ± 10%. We have also determined the temperature dependence of the thermal diffusion factor for an equimolar mixture from 30 to 550°K which is characterized by a broad maximum at approximately 125°K. A sharp decrease in αT was observed on the low temperature side of the maximum while a gradual, almost linear decrease was obtained on the high temperature side. We have calculated quantum mechanical transport collision integrals for hydrogen-helium assuming an (exp-6) spherical interaction potential and have used them to evaluate [αT]3, the third order Chapman-Enskog approximation to the thermal diffusion factor. The theoretical calculations are in excellent agreement with the experimental determinations.