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Updated: Aug 5, 2026

Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy
Published on: May 27, 2018
Structure and vibrational spectroscopy of salt water/air interfaces: predictions from classical molecular dynamics
Eric C Brown1, Martin Mucha, Pavel Jungwirth
1Department of Chemistry and Environmental Molecular Sciences Institute, University of California, Irvine, Irvine, California 92697-2025, USA.
Abstract:
We report the sum frequency generation (SFG) spectra of aqueous sodium iodide interfaces computed with the methodology outlined by Morita and Hynes (J. Phys. Chem. B 2002, 106, 673), which is based on molecular dynamics simulations. The calculated spectra are in qualitative agreement with experiment. Our simulations show that the addition of sodium iodide to water leads to an increase in SFG intensity in the region of 3400 cm(-1), which is correlated with an increase in ordering of hydrogen-bonded water molecules. Depth-resolved orientational distribution functions suggest that the ion double layer orders water molecules that are approximately one water layer below the Gibbs dividing surface. We attribute the increase in SFG intensity to these ordered subsurface water molecules that are present in the aqueous sodium iodide/air interfaces but are absent in the neat water/air interface.
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