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The vibrational dephasing of polyatomic moleucles in condensed phases by intermolecular vibrational energy exchange is treated theoretically. In the exchange model, dephasing arises from random modulation of the vibrational frequency caused by intramoleuclar anharmonic coupling to low frequency modes which are undergoing intermolecular energy exchange with the bath. The exchange rates are temperature dependent and as a consequence manifest themselves experimentally as a temperature dependent broadening and shift of the Raman spectral lineshape. Using a reduced density matrix technique within the constraints of a Markoff approximation, the theory allows the time dependence introduced by the exchange process to be propertly accounted for, and allows explicit expressions for the vibrational correlation '. u J. ' 'J ..) 0 J J } This report was done with support from the Department of Energy. Any conclusions or opinions expressed in this report represent solely those of the author(s) and not necessarily those of The Regents of the University of California, the Lawrence Berkeley Laboratory or the Department of Energy.

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