Advanced continuum approaches for treating time correlation functions. Therole of solute shape and solvent structure

Time correlation functions describing the solvent relaxation around a molec ule of coumarin-153 and a benzophenone anion in acetonitrile are calculated using dynamical continuum theories of solvation with an experimental diele ctric function epsilon(omega) including the resonance absorption region of the solvent. Apart from the local model with a single molecular-shaped solu te cavity of the solute studied previously, a new dynamic local model with a double molecular-shaped cavity and a dynamic nonlocal theory with a spher ical cavity are presented, both of which introduce elements of solvent stru cture. It is shown that both local models, one- and two-cavity, exhibit exp erimentally unobserved oscillations in the shorter time region t < 1 ps, al though the experimental asymptote for t > 1 ps for coumarin is obtained. Th e dynamics of the two-cavity model are not seen to differ from those of the one-cavity model. The nonlocal dynamic theory is shown to be able to suppr ess these oscillations, but the long-time asymptote differs markedly from t hat of the local theories. The nature of this asymptote is studied analytic ally.