Abstract

Vibrational energy transfer in condensed phases is a process which occurs on the picosecond time scale. In our lab, we are studying this process in complex molecules in the well-defined environment of a single molecular crystal. We have measured the lifetime of several vibrons in the model system naphthalene, and then extended these studies to several partially deuterated naphthalenes [1,2]. Vibrations in pure crystals form delocalized vibron bands which relax by emission of optical phonons. In disordered or mixed crystals, excited vibrations scatter off impurities and transfer energy to adjacent molecules. Our mixed crystal studies identified these processes. An important question which was raised was the relative importance of two types of relaxation processes. In a one site process, an excited vibration on one molecule decays to a lower vibration in the same molecule by emitting a phonon. In a two site process, the excited vibration decays to a mode on an adjacent molecule. In the naphthalene system, both processes seem to be important.

© 1986 Optical Society of America