Analytical approach to molecular liquids. II. Solvation of ions in molecular fluids

Analytical equations are obtained for the pair correlation functions in the mean spherical approximation (MSA) for two charged hard-sphere ions in a model molecular solvent. Model solvents of dipolar dumbbells (which may be partially dissociative) or charged hard-spheres fused in a tetrahedral configuration are treated in an extended MSA. The resulting expressions for the Born solvation free energy of an ion are very similar to that obtained earlier by Chan et al. for a charged hard-sphere ion in a dipolar hard-sphere solvent. The solvent averaged ion–ion potentials are obtained in the hypernetted chain approximation. Comparisons among results of various solvents are also made. In order of increasing oscillation amplitudes of the solvent averaged ion–ion potential for given molecular density and dipole moment we have continuum ≪dumbbell≤tetrahedral<dipolar hard sphere.