Solvation energy of ions and dipoles in a finite number of solvent shells

The contribution of a polar solvent in solvent in thermodynamic equilibriuum to the solvation free energy of a dipole and of an ion are estimated anarytically as funtion of distance within the framework of the mean-sphereical approximation theory and compared to the analogous results derived from simple electroatical arguments. For equal-sized solute and solvent molecules. accumulanting 90% of the total enrgy in media of moderate polarity involves ∼1 and ∼7 solvent shells for dipole and ion solvation, respectively. For solvents characterized by high values of ε only upper bounds for the energy relevant to the solvent range can be stated. Relative to the continuum picture, the MSA calculation predicts an increase of the coupling range by ∼50%, without a significant dependence on the dielectric constant ε.