The corresponding states principle for radial distribution functions of homonuclear diatomic liquids

Abstract

A new method of applying the corresponding states principle to the radial distribution functions of molecular liquids is presented. The molecular dynamics technique is employed to model liquid argon, nitrogen, chlorine and iodine at about the same corresponding state. The introduction of disjoint classes of dimer geometries (configurations Γ) appears to be a powerful tool for describing orientational correlations in liquids. By exploiting and extending previous models of correlations it is shown that each configuration has a specific orientational correlation length which extends up to the first coordination shell and that the derivation of the atom-atom distribution function g _aa(r) from the centre-centre distribution function g _aa(r) becomes possible for each configuration Γ. A complete set of disjoint configurations covering all angular space of a pair has been obtained for each liquid. It is shown that the total centre-centre distribution functions for I₂, Cl₂ and N₂ reproduce g(r) for Ar if suitable scaling parameters are applied to the distribution functions g ^Γ _cc(r) predicted by each configuration, thus demonstrating the validity of the corresponding states principle for g(r) of liquids. The centre-centre and atom-atom distribution functions of molecular liquids derived from g(r) for argon are compared with those obtained from molecular dynamics. The differences are attributable to the orientational correlations which rearrange the populations of each configuration in the first coordination shell, the total population being the same for all liquids. The role played by specific configurations is analysed and discussed and a method for ‘measuring’ orientational correlations in molecular liquids is suggested.