Hydrogen bond dynamics in water and ultrafast infrared spectroscopy

Molecular dynamics simulations are used to examine two key aspects of recent ultrafast infrared experiments on liquid water dynamics. It is found that the relation between the OH stretch frequency and the length of the hydrogen bond in which the OH is involved, currently assumed to be one-to-one, is instead characterized by considerable dispersion and that the time scale currently interpreted in terms of a stochastic modulation by the surrounding solvent of a highly frictionally damped hydrogen bond system is shown to be governed by hydrogen bond-breaking and -making dynamics, whereas the motion of an intact hydrogen-bonded complex is underdamped in character.