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Electric Field Fluctuations Drive Vibrational Dephasing in Water

Joel D. Eaves and Andrei Tokmakoff*

Department of Chemistry and George Harrison Spectroscopy Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Phillip L. Geissler

Department of Chemistry, University of California and Physical Biosciences Division and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720

J. Phys. Chem. A, 2005, 109 (42), pp 9424–9436

DOI: 10.1021/jp051364m

Publication Date (Web): September 30, 2005

Corresponding author. E-mail: tokmakof@mit.edu.

Abstract

We present a microscopic description of the vibrational spectroscopy of the OH stretch of HOD in liquid D₂O. Our model predicts that OH frequency correlations decay with a sharp and rapid (≈35 fs) decrease, followed by a beat at ≈125 fs from intermolecular oxygen vibrations. On a short time scale (≈200 fs), ultrafast infrared spectroscopy of the OH stretch is sensitive to localized intermolecular motions. For times longer than ≈200 fs, cooperative molecular rearrangements drive dephasing. The interplay of electric field fluctuations, both local and cooperative, dictate vibrational frequency shifts and destroy vibrational coherence in water.

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