Dephasing processes of molecular vibrations in liquids

A model based on semiclassical collision theory is presented to describe the dephasing of vibrationally excited molecules in a liquid. It is shown that fluctuations of the vibrational frequencies, which are caused by the intermolecular interaction, lead to phase relaxation of a coherently excited state. The theoretical results compare favorably with data of the vibrational dephasing time measured with picosecond probing techniques. The relationship between the dephasing time and the linewidths observed in IR and Raman spectroscopy is discussed.