Calculation of the binary diffusion coefficient and interaction viscosity of the H–H 2 system

Abstract

It has been argued that the Mason–Monchick approximation (MMA) and infinite order sudden approximation (IOSA) are not suitable for the calculation of the transport property coefficients of light polyatomic systems. It is proposed, on physical grounds, that a new approximation, the hybrid-MMA, is more appropriate. Although the hybrid-MMA belongs to the MMA/IOSA type methods, its accuracy is expected to decrease with increasing temperature. The hybrid-MMA was used to calculate the cross-sections that govern the binary diffusion coefficient and the interaction viscosity of the H–H 2 system. The results were compared with the existing quantum IOSA calculations. The agreement is excellent for temperatures above 500 K. The present results were also compared with the ‘exact’ CC calculations. The agreement is very good below 1000 K, but progressively fails at elevated temperatures. The differences observed, with increasing temperature, can be attributed to a combination of the decreasing accuracy of a particular CC calculation and the expected failure of the MMA/IOSA family of methods when applied to light systems at high temperature.