Abstract

▪ Abstract Experimental and theoretical studies of polar solvation dynamics and spectral line broadening are described. Photon echo and fluorescence Stokes shift experiments are discussed, and the relationship between the information content of the two techniques clarified. The interaction of the chromophore with its solvent bath is described by a spectral density, and the connection of this spectral density with the liquid's instantaneous normal modes discussed. The ubiquity of the ultrafast phase of solvation dynamics is demonstrated, and a discussion of its physical origin given. The slower phases of solvation vary strongly from solvent to solvent. Molecular theories of liquid dynamics are able to rationalize such variations over at least a 2000-fold range of time scale. The review concludes with a brief discussion of the relevance of ultrafast solvation to chemical dynamics.