ULTRAFAST ELECTRONIC FLUCTUATION AND SOLVATION IN LIQUIDS

Solvation and optical dephasing of electronic transitions in molecular liquids are studied over a large range of time scales. It is shown that these optical effects, which are due to coupling of the electronic degrees of freedom with the nuclear motion in the liquid, are closely connected. The rapidly changing nuclear configurations are modelled by Brownian motion in harmonic potential wells. From photon echo decays, that occur on a timescale of 20 femtoseconds or faster, optical properties such as the chirped four-wave mixing response (timescale 50-200 fs) and the absorption and emission spectra (steady state) can be calculated in a straightforward manner. The magnitude of the Stokes shift is also predicted accurately. The physical significance of this approach to optical dynamics in liquids is discussed in the context of molecular dynamics simulations.