15min:

PAM L. CRUM, BRIAN C. DIAN, HYUN S. YOO, CHARLOTTE E. HINKLE AND BROOKS H. PATE, Department of Chemistry, University of Virginia, McCormick Rd., P.O. Box 400319, Charlottesville, VA 22904..

Ultrafast time-domain transient absorption spectroscopy is used to study the vibrational dynamics of the cyclic hydrogen bonded dimers of trifluoroacetic acid and formic acid in both the gas- and solution-phase. Deposition of energy into the broad dimer bands of these acid dimers in the gas-phase provides the means to break open the dimer, as evidenced by the growth of a \` \` free O-H\' \' absorbance at 3580cm^-1 on the time scales of energy flow out of the initially excited dimer region. In trifluoroacetic acid there is no change in the rate of \` \` free O-H\' \' growth with varying pump frequency between 2596cm^-1 and 3131cm^-1. Spectrally resolved pump-probe experiments are performed to reveal the evolution of a broad range of the spectra in time, which facilitates interpretation of the dynamics behind the time scales provided by single frequency measurements. When the acid dimers are solvated (0.05M CCl₄ solution), energy pumped into the broad dimer band can be cooled out by the solvent, making it unavailable to the process of dimer opening.