Vibrational and Electronic Relaxation in Moderate Sized Systems

Abstract

When molecules interact with each other or with an environment it becomes more difficult to obtain information fundamental to a better understanding of molecular dynamics. In a sufficiently dilute gas or molecular beam the molecules can be arranged to be isolated for long enough to carry out an experiment. In high pressure gases or condensed phases there is some question as to whether isolated molecule effects can ever be exposed. Even though the intermolecular interactions will influence the pathways of chemical and physical transformations, the final states are still available for study providing that observations can be made soon enough after the occurrence of the process, yet before the energy distributions are destroyed by medium induced relaxations. A considerable effort has been put into learning about the medium induced relaxation by making direct measurements in condensed phases using subnanosecond laser pulses. It is necessary to make such measurements in time, rather in the frequency domain, because the fluctuations in the energies of the molecular states contribute to the linewidths and this effect can dominate the population relaxation at Sufficiently high temperatures. KAISER, LAUBEREAU and coworkers [1–3] have demonstrated this effect for vibrational levels of a number of liquids in showing that Raman linewidths are mainly determined by dephasing.