Accurate effective potentials and virial coefficients in real fluids Part IV. Heterodiatomic and polyatomic substances with permanent multipoles and their mixtures with noble gases

Abstract

The approximate nonconformal (ANC) theory recently proposed has been very successful for determining effective interaction parameters from the measured gas imperfection B(T) for a variety of substances, from the noble gases to perfluoro-n-alkanes. Here we report the application of the ANC treatment to the polar substances: NO, CO, HCl, CO₂, H₂O, D₂O, NH₃, CH₂:CH₂ and SF₆ and predict the cross interactions in the mixtures of these substances with noble gases. The theory is successful in describing B(T). It also permits us to extract atom–atom potential parameters for CO. The resulting C–C interaction follows the simple dependence on atomic number already found for other atoms. For NO, which is partially dimerised in the gas phase, and using the approach pioneered by Guggenheim and Scott, the ANC theory gives a very good account of the observed B(T) for partially dimerised NO. Lastly, the ANC prediction of the cross virial coefficient is in excellent agreement with experiment in all but one of the binary mixtures considered.