Preaveraged potential and the third virial coefficient of polar gases

Abstract

The third virial coefficient of polar gases has been calculated on a preaveraged 12-6-6 potential model. The nonadditive corrections due to dipole, dispersion and repulsion three body interactions have also been computed. It has been found that while the dipole and dispersion nonadditive corrections are always positive, the repulsion nonadditive correction is negative. The net effect of these corrections is sizeable in the temperature range of our interest. The theoretical results have been compared with the experimental data of ammonia and methyl fluoride. The agreement between theory and experiment is reasonable in view of the large uncertainties in the experimental data. The overall agreement between experimental values and those obtained on the preaveraged potential for polar gases is comparable to that of the Lennard-Jones (12-6) model for nonpolar gases.