Ultrafast depolarized Raman-response of water

摘要

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, τ_2, 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, τ_1, associated with the fast exponential is comparable in magnitude to inverse spectral line widths deduced from Rayleigh-wing scattering. However, a detailed Axrhenius analysis of the temperature dependence of τ_1 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.