Hyper‐Raman investigation of intermolecular vibrations of water and ice

Abstract We have constructed a hyper‐Raman optimized spectrometer using a high repetition rate (200 kHz) picosecond‐pulsed Nd:YAG laser. This system has been applied to measure liquid water and ice (H 2 O and D 2 O) to obtain their hyper‐Raman spectra with high signal‐to‐noise ratios. Unique vibrational spectra of water and ice, distinct either from infrared absorption and Raman scattering, have been obtained. The intermolecular bands in the low‐wavenumber region are observed in the hyper‐Raman spectra with intensities higher than those of the intramolecular ones. They show H/D isotope shifts fully consistent with their assignments to the librational and translational motions of assembled water. The librational bands are found to shift to higher wavenumber on going from liquid water to ice, indicating a more confining environment in ice than in water. Hyper‐Raman spectroscopy will shed new light, complementary to the traditional infrared and Raman vibrational spectroscopies, on intermolecular interactions in liquid water and ice.