Using the surface-specific vibrational technique of vibrational sum-frequency generation, we reveal that the double-peaked structure in the vibrational spectrum of hydrogen-bonded interfacial water molecules originates from vibrational coupling between the stretch and bending overtone, rather than from structural effects. This is demonstrated by isotopic dilution experiments, which reveal a smooth transition from two peaks to one peak, as D2O is converted into HDO. Our results show that the water interface is structurally more homogeneous than previously thought.
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Phys. Rev. Lett.
Ultrafast Spectroscopy

Sovago, M, Campen, R.K, Wurpel, G.W.H, Müller, M, Bakker, H.J, & Bonn, M. (2008). Vibrational response of hydrogen-bonded interfacial water is dominated by intramolecular coupling. Phys.Rev.Lett., 100(Article number: 173901), 1–4. doi:10.1103/physrevlett.100.173901