ANISOTROPY AS AN ULTRAFAST PROBE OF ELECTRONIC COHERENCE IN DEGENERATE SYSTEMS EXHIBITING RAMAN-SCATTERING, FLUORESCENCE, TRANSIENT ABSORPTION AND CHEMICAL-REACTIONS

The effects of electronic coherence of doubly or triply degenerate lev els are discussed, This coherence will show up in the anisotropy of a pump-probe experiment in which a pump pulse creates the coherence and a probe pulse connects the degenerate levels to a non-degenerate final state, Simple stochastic models for the decay of the anisotropy as a function of pump-probe delay are given, both for molecules with a high symmetry and for symmetric dimers and trimers, The possible role that degenerate level coherence may play in chemical reactions is also dis cussed, Finally, the stochastic models used to calculate the anisotrop y decay are applied towards the calculation of absorption line shapes, Raman scattering and fluorescence.