Selfhyphen;diffusion and mutual diffusion coefficients in the range 195deg; to 373deg;K have been measured for the isostere systems, COsngbnd;CO and COsngbnd;N2. The selfhyphen;diffusion coefficients are consistently higher than the mutual diffusion coefficients, with differences twohyphen; to fourfold greater than the experimental error. On the assumption that the classical Chapmanmdash;Enskog transport relations are applicable, parameters have been obtained for intermolecular potentials of the Lennardhyphen;Jones (12ndash;6) and the exphyphen;six types.Parameters derived from diffusion measurements have been compared with those obtained from measurements of viscosity, compressibility and crystal properties. It was not possible, for either system, to reproduce both the transport and equilibrium properties with a single set of parameters. It is concluded that the failure may be attributed mainly to the use of average spherically symmetric potentials instead of potentials which are functions of both relative molecular orientation and internuclear separation.
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