IVR and VER at high state densities: Ultrafast transient absorption spectroscopy of vibrational overtones

PHYS 389

Steven T. Shipman, sts5x@virginia.edu, Pamela L. Crum, pc4z@virginia.edu, Ellen L. Mierzejewski, and Brooks H. Pate, bp2k@virginia.edu. Department of Chemistry, University of Virginia, McCormick Road, PO Box 400319, Charlottesville, VA 22904
Ultrafast transient absorption spectroscopy has been used to study the vibrational dynamics of a series of terminal acetylenes in gas and dilute solution (0.05 M in CCl4) excited to the v=2 level of the acetylenic C-H stretch.  Excitation to this vibrational overtone provides the molecules with a significant amount of internal energy which rapidly redistributes itself out of the localized C-H stretch and into the rest of the molecule.  The resulting timescales for intramolecular vibrational redistribution (IVR) and vibrational energy relaxation (VER) are compared to those obtained when the initial excitation is to the v=1 level, where the vibrational state densities are much lower.  For molecules such as propargyl chloride that do not possess the threshold state density for IVR (10 states/cm-1) at energies corresponding to the fundamental excitation, IVR is effectively "turned on" with the overtone excitation, reflected in a 6-fold decrease in the lifetime of the excited state.
 

Poster Session
7:30 PM-10:00 PM, Wednesday, 13 September 2006 Moscone Center -- Hall D, Poster

Sci-Mix
8:00 PM-10:00 PM, Monday, 11 September 2006 Moscone Center -- Hall D, Sci-Mix

Division of Physical Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006