Close-coupled calculations of transport cross-sections for a highly quantal system

Essentially exact calculations of the transport collision integrals for the interaction of argon and hydrogen through an intermolecular pair potential with enhanced anisotropy are reported. The close-coupled formalism of Arthurs and Dalgarno has been employed to treat the collision dynamics, and the collision integrals have been evaluated without approximation. The enhanced anisotropy of the model potential surface employed ensures that in all respects the molecular system is at the opposite extreme from the He-N2 system studied earlier. The ‘benchmark’ values of the collision integrals have been used to examine the accuracy of the Mason-Monchick procedure for their evaluation. Despite the fact that the assumptions of the approximate procedure are inappropriate for Ar-H2, the approximate collision integrals reproduce the exact values within a few per cent. As was found for He-N2 the viscosity is rather more accurately evaluated than the diffusion coefficient. It is concluded that the Mason-Monchick approximation has an essentially uniform error for two extreme molecular systems although it is inadequate for work of the highest accuracy.