A theoretical study of transport coefficients in benzene vapour

Abstract

The shear and bulk viscosities, and thermal conductivity, of benzene vapour have been calculated using a realistic interaction potential. Results are reported for the Taxman and Wang Chang-Uhlenbeck theories under the assumptions that internal vibrational states do not contribute to the transport coefficients and that the rotational motion of the molecules can be treated using classical mechanics. Apart from these assumptions the calculations are rigorous, and in particular the solution to the two-particle trajectory problem has not been simplified either by neglecting out-of-plane scattering or by holding the relative orientations of the molecules fixed during a collision. A small, but systematic, difference between results from the Taxman and Wang Chang-Uhlenbeck theories was found and it is suggested that the former theory is more accurate. Good agreement between theory and experiment is readily obtained for the shear viscosity but the corresponding results for the thermal conductivity are in poor agreement. After a correction term is included to allow for energy transfer between rotational and translational states, and the internal vibrational states, the thermal conductivity is also in good agreement with experiment. The results are used to develop an effective pair potential for benzene that is in agreement with experimental values of the shear viscosity, thermal conductivity, and second virial coefficient of the vapour and with the static lattice energy and structure of the solid.