Laser spectroscopic visualization of hydrogen bond motions in liquid water

Ultrafast pump-probe experiments are described permitting a visualization of molecular motions in diluted HDO/D ₂O solutions. The experiments were realized in the mid-infrared spectral region with a time resolution of 150 fs. They were interpreted by a careful theoretical analysis, based on the correlation function approach of statistical mechanics. Combining experiment and theory, stretching motions of the OH⋯O bonds as well as HDO rotations were 'filmed' in real time. It was found that molecular rotations are the principal agent of hydrogen bond breaking and making in water. Recent literatures covering the subject, including molecular dynamics simulations, are reviewed in detail.