Picosecond Processes in Chemical Systems: Vibrational Relaxation

A review is presented of our recent studies of vibrational energy relaxation of moderatelysized molecules in a variety of media and of the effect of vibrational relaxation onprocesses such as molecular rearrangements. Data are presented on intramolecular dynamical processes involving p-difluorobenzeneand an experiment is described which allows the study of spectral evolution on thepicosecond timescale under collision-free conditions. The vibrational (T 1 ) relaxation of the apparently simple system consisting of adiatomic CN − ion in aqueous solution was studied and found to be in the range of a fewpicoseconds and to be concentration dependent. These results, and the effects ofcounterions, are suggested to be the result of aggregation of the ions. A discussion ofthe Raman lineshapes is given in relation to the measured T 1 times.