APPROXIMATE CALCULATIONS OF TRANSPORT-PROPERTIES FOR THE HE-CH4 SYSTEM

The infinite order sudden (IOS) treatment of the dynamics that yields the necessary collision integrals for the calculation of transport coe fficients is tested for a gaseous mixture that includes a nonlinear po lyatomic partner, the methane molecule, interacting with He. The use o f a fully anisotropic potential obtained before from crossed beam expe riments is shown to provide rather good agreement with the available e xperiments for diffusion and viscosity coefficients over a broad range of temperatures. The comparison with more accurate calculations alrea dy carried out by us also shows extremely good agreement between the I OS calculations and the earlier, much more costly, evaluation through a quantum coupled states dynamics. The present calculations therefore indicate that, even for a more complicated nonlinear molecular partner in the mixture, IOS results for diffusion and viscosity coefficients can provide a way of further improving the chosen form for the full po tential energy surface of the system.