The temperature dependence of the ultrafast depolarized Raman response of water and deuterium dioxide has been measured in a heterodyne-detected optical Kerr-effect geometry using 30-fs, 600-nm pump-pulses and 30-fs, 800-nm probe pulses. On ultrashort time scales below 1 ps, the Kerr-response reveals distinct underdamped coherent oscillations due to impulsively perturbed acoustic modes of the liquid. On longer time scales, the Kerr-response is dominated by a bi-exponential decay. The time constant, τ2, characterizing the slowly decaying exponential is in full agreement with orientational correlation times, τ(2), obtained from NMR spin lattice relaxation rates. The time constant, τ1, associated with the fast exponential is comparable in magnitude to inverse spectral line widths deduced from Rayleigh-wing scattering. However, a detailed Arrhenius analysis of the temperature dependence of τ1 is inconsistent with dynamics of hydrogen-bond breakage and formation as previously suggested by these frequency domain experiments. Our data suggest that the fast exponential is linked to delocalized restricted translational modes in the strongly hydrogen-bonded network.
© 2000 Optical Society of AmericaPDF Article