FLOW OF VIBRATIONAL ENERGY IN POLYATOMIC MOLECULES: USING ACETYLENIC ANHARMONIC COUPLINGS TO FOLLOW VIBRATIONAL DYNAMICS
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Date
2007
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Ohio State University
Abstract
Vibrational lifetimes of a variety of C--H stretches in butyne, methylbutyne, and methylbutenyne have been measured in the gas and dilute solution phases with ultrafast mid-IR transient absorption spectroscopy. In all of these molecules, we monitor dynamics beyond the first stage of intramolecular vibrational relaxation (IVR) by exploiting the significant anharmonic coupling of the acetylenic C--H stretching and bending modes ($\sim-20 \textrm{cm}^{-1}$). Due to this coupling, the absorption frequency of the acetylenic C--H fundamental redshifts as population eventually arrives in the low frequency ($\sim600 \textrm{cm}^{-1}$) bending mode after leaving the initially prepared bright state. By monitoring the redshifted acetylenic absorption as a function of time after the excitation pulse, we are effectively using the molecule's inherent anharmonic couplings to ``up-convert'' signals arising from the final stages of IVR, providing us with a sensitive probe of vibrational dynamics in a convenient spectral region.
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Author Institution: Department of Chemistry, University of Virginia, McCormick Rd., P.O. Box 400319, Charlottesville, VA 22904