Mixture virial coefficients for the Hamann-Lambert model for globular molecules

Abstract

The Hamann-Lambert model for globular molecules using Lennard-Jones 12- 6 potential functions for the atomic interactions has been used to obtain second virial coefficients for CH₄, CF₄, SF₆, SiF₄, CMe₄, SiMe₄, and the mixtures CH₄-CF₄, CH₄-SF₆, CH₄-CMe₄, CH₄-SiMe₄, and CF₄-SF₆. Additive third virial coefficients have been computed where experimental data are available. Of the 18 parameter sets needed for the 12-6 interactions in the above molecules and their combinations ten were obtained by a least-squares fitting process using experimental values of second virial coefficients, five were obtained from combining rules, and the remaining three from sources independent of virial coefficient data. The computed values of the virial coefficients agree well with the experimental data although in the case of the third virial coefficients improved agreement would be obtained if some form of non-additivity could be allowed for.