Abstract

The outcome of a photochemical reaction in the condensed phase depends on the nature of the reacting chromophore and its environment, which may for instance be a liquid, glass or a protein. In liquids, solvation dynamics has been well characterized, primarily through the use of time-resolved fluorescence and photon echo techniques, combined with molecular dynamics (MD) simulations [1]. Two solvation components are often observed: a fast inertial response, occurring on a timescale less than 100 fs, followed by a slower, diffusive component on a picosecond timescale. The inertial response often accounts for half the total reorganization energy or more, and entails independent, underdamped motion of the solvent molecules in their native potential wells. The diffusive component represents the reorientation of the solvent molecules into a new equilibrium, whereby the nuclei may hop between different potential wells. It involves collective motions of the solvent molecules, like librations and large rotations. It is thought that the diffusive solvent rearrangement plays an important role in chemical reactivity, as it may reduce reaction barriers and stabilize reaction intermediates [2].

© 2002 Optical Society of America