Effects of solvent viscoelasticity in the solvation dynamics of an ion in a dense dipolar liquid

Abstract

For ultrafast solvation of an ion in a liquid which is in the underdamped limit of momentum relaxation, the initial inertial response of the solvent to the newly created ion can be controlled largely by the viscoelastic properties of the solvent. This viscoelasticity can give rise to long-lived oscillations in the solvation energy which arise primarily from the dipolar excitations (or dipolarons). A non-markovian theory of solvent dynamics with the inertial and the viscoelastic effects included is used to study the solvation dynamics of an ion. Numerical studies reveal rich relaxation behavior, such as pronounced short-time oscillations followed by a slow long-time decay. It is argued that in the recent computer simulations of soivation in acetonitrile this long wavelength colleciive excitation is essentially observed; the molecular length scale contributions appear as a slow long-time decay. In the presence of a sizeable translational contribution, excitations with wavelengths comparable to the molecular diameter can also be long lived because of the viscoelasticity in the solvent response.