Hydrogen Bond Breaking Dynamics of the Water Trimer in the Translational and Librational Band Region of Liquid Water

The effect of exciting each of the three classes of intermolecular vibrations on the hydrogen bond lifetime (τH) of the isolated water trimer is investigated by far-infrared laser spectroscopy. Single excitation of a librational vibration decreases τH by 3 orders of magnitude to τH = 1−6 ps, comparable to the time scale of a number of important bulk water dynamical relaxation processes. In contrast, excitation of translational or torsional vibrations has no significant effect (τH = 1−2 ns). Although such a dependence of τH on intermolecular motions has also been proposed for liquid water via computer simulations, these are the first experiments that provide a detailed molecular picture of the respective motions without extensive interpretation.