The potential of mean force between two ions in a dipolar solvent

Publisher Website
Google Scholar
Abstract
The potential of mean force Wij between two solute ions in a dipolar solution at infinite solute dilution is investigated using a potential analysis. The ions are taken to be charged hard spheres of radii ai and aj with point charges ei and ej at their centres while the solvent molecules are represented by point dipoles fixed at the centre of hard spheres of diameter d. For the separation r of the two ions greater than ai + aj + 2d with 1/2dˇ-ai and aj we find that where gij 0 is the radial distribution function for the two uncharged ions in the dipolar solution, ε is Onsager's dielectric constant, b = ai + 1/2d, c = aj + 1/2d, An i and An j are constants independent of the ionic charge, while zn are the complex roots with positive real parts of the equation z + (ε - 1) sinh z = 0. Further cavity terms involving d and terms of order r -2 exp (- znrtd) exist but were not calculated. For d ≠ 0, the theory is restricted to those dipole parameters for which ε < 5·603. When d → 0, the continuum limit, the expression for Wij reduces to the correct classical form with the bulk dielectric constant being replaced by Onsager's dielectric constant. For small r the last teTF029189rm gives rise to a damped oscillatory behaviour depending critically upon the solvent structure.