Reorientational motion and hydrogen-bond stretching dynamics in liquid water
نویسنده
چکیده
The reorientational motion of the molecules in liquid water is investigated by measuring the anisotropy decay of the O±H stretching mode of HDO dissolved in D2O using femtosecond mid-infrared pump±probe spectroscopy. We observe that the anisotropy shows a non-exponential decay with an initial fast component of which the amplitude increases with increasing lengths of the O±H O hydrogen bond. The experimental results can be accurately described with a model in which the dependence of the reorientation rate on the hydrogen-bond length and the stochastic modulation of this length are accounted for. It is found that the O±H group of a water molecule can only reorient after the O±H O hydrogen bond has suciently lengthened. As a result, the eective rate of reorientation of the molecules in liquid water is determined by the rate at which the length of the hydrogen bonds is modulated. Ó 2000 Elsevier Science B.V. All rights reserved. PACS: 77.22.-d; 78.20.-e; 03.65.-w
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