FLUIDS OF THE KIHARA MOLECULES .1. PAIR POTENTIAL PARAMETERS OF N-ALKANES FROM THE VAPOR-LIQUID COEXISTENCE DATA

The full second-order perturbation expansion of the convex molecule fl uid, involving new approximations for the radial distribution function of hard spheres and for the surface-to-surface correlation function o f the hard convex bodies, has been developed. Parameters of the Kihara generalized pair potential have been determined for n-alkanes in a se ries from methane up to hexadecane (modeled as hard rods) by fitting t he expressions for the residual thermodynamic functions obtained withi n the theory to the phase equilibrium-data of the individual real comp ounds along their vapor-liquid coexistence curve. All the Kihara pair potential parameters, i.e., the particle size parameter, the potential depth, the rod length, characterizing the hard core of the model conv ex molecule, and (for the lower alkanes) also the parallel hard body t hickness, were expressed in a general and simple way as functions of t he number of carbon atoms in a molecule over the entire range of n-alk anes investigated. The results represent a successful correlation sche me making it possible to represent the bulk thermodynamic data of pure real. substances on the basis of molecular parameters.