S. Woutersen et al., FEMTOSECOND MID-IR PUMP-PROBE SPECTROSCOPY OF LIQUID WATER - EVIDENCEFOR A 2-COMPONENT STRUCTURE, Science, 278(5338), 1997, pp. 658-660
A femtosecond mid-infrared pump-probe study of the vibrational and ori
entational dynamics of the OH-stretching mode of HDO dissolved in D2O
is presented. The orientational relaxation of the HDO molecules was ob
served to occur on either a very slow or a very fast time scale, with
associated time constants of tau(R) = 13 picoseconds and tau(R) = 0.7
picosecond. It was observed that strongly hydrogen-bonded water molecu
les only relax through the slow orientational relaxation process, wher
eas the fast process dominates for weakly hydrogen-bonded molecules. T
his suggests that, with respect to orientional dynamics, two distinct
molecular species exist in liquid water.