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 vibratio ns on the hydrogen bond lifetime (tau (H)) of the isolated water trimer is investigated by far-infrared laser spectroscopy. Single excitation of a lib rational vibration decreases tau (H) by 3 orders of magnitude to tau (H) = 1-6 ps, comparable to the time scale of a number of important bulk water dy namical relaxation processes. In contrast, excitation of translational or t orsional vibrations has no significant effect (tau (H) = 1-2 ns). Although such a dependence of tau (H) on intermolecular motions has also been propos ed for liquid water via computer simulations, these are the first experimen ts that provide a detailed molecular picture of the respective motions with out extensive interpretation.