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 measure d by time-resolved heterodyne detected optical kerr effect. The decay of the signal, observed after 500 fs, is well fitted by a biexponentia l. 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 t he hydrogen bonds dominate the dynamics and the optical response of th e system: the fast decay time is closely related to the mean lifetime of individual H bonds, while the slow time constant is attributed to c ollective relaxation of structured regions of the liquid.