Theoretical results for aqueous electrolytes. Ion–ion potentials of mean force and the solute-dependent dielectric constant

The linearized hypernetted-chain theory is applied to solutions of hard spherical ions immersed in a dipole-tetrahedral quadrupole solvent with waterlike parameters. Temperatures ranging from 25 to 300 °C are considered and the ion–ion potentials of mean force and the solute-dependent dielectric constant are examined in the infinite dilution limit. For this model electrolyte the ion–ion potentials of mean force are shown to be less structured and to approach the continuum limit more rapidly than those previously obtained for simple dipolar solvents. The limiting slope which determines the behavior of the solute-dependent dielectric constant at low ionic concentrations is negative and much smaller in magnitude than that found for comparable dipolar hard sphere solvents. Finally, the theoretical limiting slope is shown to be consistent with experimental results for aqueous solutions at 25 °C and low ionic concentrations.