Laser spectroscopic visualization of molecular rotations in liquid water

An infrared laser spectroscopic experiment is described permitting a visualization of molecular rotations in liquid water. One first selects hydrogen bonds of a given OH..O length by pumping the system with an appropriate infrared frequency; the rotational dynamics are analyzed next by measuring its rotational anisotropy. The procedure requires a careful theoretical analysis, realized by adopting the correlation function approach. This experiment also permits to visualize the passage from the inertial rotation to the rotational diffusion. The lifetime of OH..O bonds in water is rotation-limited.