Abstract

Water is the most commonly used solvent for chemical reactions. Water molecules are believed to play an important role in the reaction dynamics by rearranging around the reactants and by lowering the energy barrier for the reaction. Detailed knowledge of the energy dynamics of liquid water can help us in understanding the role of water in reactions. In the past few years, extensive studies were performed on a dilute solution of HDO molecules in D₂O [1,2,3]. It was found that the lifetime of the OH-stretch vibration T₁ was 740 ± 20 fs [4]. Energy was shown to be transferred to a high overtone of the hydrogen bond stretch vibration [5]. Not much is known about the energy dynamics of “real” liquid water, i.e. H₂O. Deàk et al. found that after excitation of the OH-stretch band of H₂O population is transferred to the bending mode [3]. However, the time resolution of their experiment was not sufficient to determine the time constant of the relaxation. Here we present the first measurement of the timescale of the energy relaxation of H₂O. We measured this time constant as a function of temperature. From the temperature dependence we conclude that the hydrogen bond strongly influences the relaxation behavior.

© 2002 Optical Society of America