Structural correlation in water probed by hyper-Rayleigh scattering.

Abstract

Second-harmonic or hyper-Rayleigh scattering (HRS) is sensitive to molecular interactions and correlations, and there is a large coherent HRS contribution for water. This work shows that the distinctive angle and polarization dependence observed for HRS from water is due to the long-range orientation correlation of the molecules. The results of HRS experiments for water are analyzed in combination with a molecular dynamics simulation to determine the molecular hyperpolarizability and the short-range and long-range orientation correlation functions for the molecules. At long range, the longitudinal and transverse dipole-dipole orientation correlation functions are BL(r) = -2BT(r) = a3/r3 with a = 0.166 nm. Molecular correlation at distances r > 100 nm must be included to account for the HRS observations.