Collective molecular rotation in D2O

Abstract

The hyper-Rayleigh scattering (HRS) spectrum of liquid D2O was measured at 90° scattering angle with linearly polarized light (VV, HV, VH, and HH polarization geometries). The VV and HV spectral profiles are similar, but the HV and VH spectral profiles are very different. This can be accounted for by scattering from nonlocal modes of molecular reorientation. The local mode and the transverse nonlocal mode both result in Lorentzian spectral components with width increasing from 1.1 cm−1 at T=23 °C to 3.3 cm−1 at 80 °C. The spectrum due to the longitudinal nonlocal mode has width <0.3 cm−1. A relatively weak and very broad collision-induced spectral component is also observed. The relative integrated intensities of the local, transverse and longitudinal components of the VH HRS spectrum are 21%, 45%, and 34%, indicating that molecular reorientation in water is predominantly a collective effect.