NONLINEAR EFFECTS IN DIPOLE SOLVATION .1. THERMODYNAMICS

The method of Pade truncation of perturbation expansions for thermodyn amic potentials of molecular liquids is extended to the calculation of the solvation chemical potential of an infinitely dilute dipolar solu te in a dipolar liquid. The Padi form is constructed to include nonlin ear solvation effects of dipolar saturation at large and the linear re sponse quadratic solute dipole dependence at small solute dipoles. The theory can accommodate polarizable solvents. The limiting case of ele ctronically rigid solvent molecules is tested on the nonlinear referen ce hypernetted chain (RHNC) approximation for dipolar liquids. At high solvent polarities the Padi solvation chemical potential exceeds that of the RHNC. For both treatments, the nonlinear solvation contributio n is found to pass through a maximum as a function of solvent polarity indicating that orientational saturation created by the solute breaks down with increasing solvent-solvent dipolar coupling. The Padi form of the chemical potential provides an analytical solution applicable t o spectroscopic and electron transfer calculations involving solvation of fictitious complex-valued dipoles. (C) 1997 American Institute of Physics.