Slow polarization relaxation in water observed by hyper-Rayleigh scattering

Polar fluctuations due to reorientation of the dipolar molecules in liquid water are central to its properties. Here we report a high resolution hyper-Rayleigh light-scattering spectrum for liquid water which shows collective dipole orientation fluctuations on two very different time scales: 100.3em0exps and >500.3em0exns. The 100.3em0exps relaxation time for the transverse fluctuations matches the macroscopic dielectric relaxation time, but the >500.3em0exns relaxation time for the longitudinal fluctuations has not been previously observed and is dramatically (10⁵×) slower than expected.