Relaxation Dynamics of Water and HCl Aqueous Solutions Measured by Time-Resolved Optical Kerr Effect

Fast relaxation processes in water and HCl−water solutions are measured by time-resolved heterodyne detected optical kerr effect. The decay of the signal, observed after 500 fs, is well fitted by a biexponential. The temperature dependence of the two decay time constants and the relative weights of the two exponentials, for water and for samples of different HCl concentration, are consistent with a picture in which the hydrogen bonds dominate the dynamics and the optical response of the system: the fast decay time is closely related to the mean lifetime of individual H bonds, while the slow time constant is attributed to collective relaxation of structured regions of the liquid.