Toward a simple molecular understanding of sum frequency generation at air-water interfaces [electronic resource].

Published:: Berkeley, Calif. : Lawrence Berkeley National Laboratory, 2009.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description:: 28 : digital, PDF file
Additional Creators:: Lawrence Berkeley National Laboratory and United States. Department of Energy. Office of Scientific and Technical Information

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Summary:

Second-order vibrational spectroscopies successfully isolate signals from interfaces, but they report on intermolecular structure in a complicated and indirect way. Here we adapt a perspective on vibrational response developed for bulk spectroscopies to explore the microscopic fluctuations to which sum frequency generation (SFG), a popular surface-specific measurement, is most sensitive. We focus exclusively on inhomogeneous broadening of spectral susceptibilities for OH stretching of HOD as a dilute solute in D₂O. Exploiting a simple connection between vibrational frequency shifts and an electric field variable, we identify several functions of molecular orientation whose averages govern SFG. The frequency-dependence of these quantities is well captured by a pair of averages, involving alignment of OH and OD bonds with the surface normal at corresponding values of the electric field. The approximate form we obtain for SFG susceptibility highlights a dramatic sensitivity to the way a simulated liquid slab is partitioned for calculating second-order response.

Report Numbers:

E 1.99:lbnl-1513e
lbnl-1513e

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Note:

Published through SciTech Connect.
01/13/2009.
"lbnl-1513e"
Journal of Physical Chemistry B FT
Geissler, Phillip L.; Smith, Jared D.; Noah-Vanhoucke, Joyce.
Chemical Sciences Division

Funding Information:

DE-AC02-05CH11231

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