Energy redistribution in molecules on the femtosecond timescale

Liquid phase energy transfer has been studied in a range of molecules of varying complexity, providing a unique opportunity to compare various systems in solution. These systems include the recombination and relaxation of molecular iodine, the effect of solvent on the vibrational cooling of azulene, and the partitioning of energy in metal carbonyl fragments upon photodissociation. The iodine and azulene work, although performed in identical conditions, displays startling differences. The vibrational relaxation of molecular iodine is strongly dependent on solvent density and temperature, as predicted by isolated binary collision theories.1 The azulene relaxation rate is not strongly solvent dependent, yet it vibrationally relaxes much faster than molecular iodine.2 The vibrational cooling of Mn2(CO)10 photofragments occurs along two different pathways.3 Mn2(CO)9 relaxes through the CO stretch as well as through low frequency vibrational modes, while Mn(CO)5 relaxes only through low frequency modes, on a time scale similar to that seen in azulene. Thus IVR does not rapidly redistribute the excess energy in Mn2(CO)9 as it does in Mn(CO)5 and azulene.