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SPONTANEOUS AND STIMULATED RAMAN STUDIES OF VIBRATIONAL DEPHASING IN CONDENSED PHASES Paul Arthur Cornelius ABSTRACT Vibrational dephasing in condensed phases is studied here from both a theoretical and experimental standpoint. A theory is presented which describes the dynamics of motional or exchange processes in weakly perturbed systems. This general formalism, which has been previously used to describe motional narrowing in magnetic resonance, is here applied to vibrational spectroscopy. The model treats the case of a high frequency vibration anharmonically coupled to a low-frequency vibration. Intermolecular exchange of low frequency vibrational quanta results in a temperature dependent broadening and frequency shift of the high frequency vibration. Analysis of experimental data by this model yields both the exchange rates and the anharmonic couplings. The Raman spectra of 1,2,4,5 - tetramethyl benzene (h ,-durene) and the deuterated analog (d.,-durene) exhibit the predicted broadenings and frequency shifts. The C-H and C-D stretch spectra of these molecules have been taken as a function of temperature and analyzed using the exchange model. This analysis, combined with other spectral evidence, has confirmed the applicability of the model and resulted in a detailed understanding of the dephasing mechanisms which operate in this molecule. Evidence has been obtained pertaining both to the physical origins of the anharmonic couplings, and to the nature of the energy transfer in the low-fri4UMicy modes. — DISCLAIMER . Th* boo* m i oreatfra J I «n acrouni nt UAL i n wwca product, m x n cr wn.it* i™ . ~ * . ™>«™nw nereln IQ Y USTSIBUTiON UF TiiiS bGCUMENT IS UNUNiTfil

Spontaneous and stimulated Raman studies of vibrational dephasing in condensed phases