Water inertial reorientation: hydrogen bond strength and the angular potential

Moilanen, David E. ; Fenn, Emily E. ; Lin, Yu-Shan ; Skinner, J. L. ; Bagchi, B. ; Fayer, Michael D. (2008) Water inertial reorientation: hydrogen bond strength and the angular potential Proceedings of the National Academy of Sciences of the United States of America, 105 (14). pp. 5295-5300. ISSN 0027-8424

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Official URL: http://www.pnas.org/content/105/14/5295.abstract

Related URL: http://dx.doi.org/10.1073/pnas.0801554105


The short-time orientational relaxation of water is studied by ultrafast infrared pump-probe spectroscopy of the hydroxyl stretching mode (OD of dilute HOD in H2O). The anisotropy decay displays a sharp drop at very short times caused by inertial orientational motion, followed by a much slower decay that fully randomizes the orientation. Investigation of temperatures from 1°C to 65°C shows that the amplitude of the inertial component (extent of inertial angular displacement) depends strongly on the stretching frequency of the OD oscillator at higher temperatures, although the slow component is frequency-independent. The inertial component becomes frequency-independent at low temperatures. At high temperatures there is a correlation between the amplitude of the inertial decay and the strength of the O-D—O hydrogen bond, but at low temperatures the correlation disappears, showing that a single hydrogen bond (OD—O) is no longer a significant determinant of the inertial angular motion. It is suggested that the loss of correlation at lower temperatures is caused by the increased importance of collective effects of the extended hydrogen bonding network. By using a new harmonic cone model, the experimentally measured amplitudes of the inertial decays yield estimates of the characteristic frequencies of the intermolecular angular potential for various strengths of hydrogen bonds. The frequencies are in the range of ≈400 cm-1. A comparison with recent molecular dynamics simulations employing the simple point charge-extended water model at room temperature shows that the simulations qualitatively reflect the correlation between the inertial decay and the OD stretching frequency.

Item Type:Article
Source:Copyright of this article belongs to National Academy of Sciences, USA.
Keywords:Ultrafast IR Experiments; Dynamics Motion; MD Simulations; Harmonic Model
ID Code:3986
Deposited On:13 Oct 2010 07:06
Last Modified:16 May 2016 14:40

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