Vibrational sum-frequency generation (SFG) spectroscopy of aqueous interfaces has focused on the fundamental transitions of hydroxyl stretches (v=0?1) in the 3000-3800 cm-1 range.  However, higher frequency (~4000�7000 cm-1), low cross-section vibrational modes, e.g. combination bands and overtones of OH modes, have not been explored with SFG spectroscopy.  We report, what we believe to be, the first surface-specific vibrational SFG spectroscopic measurements of the stretch+bend combination band, ?comb=? OH+dHOH  of liquid water at silica surfaces near 5200-5300 cm-1.  To complement SFG measurements, FTIR and Raman spectroscopic investigations of ?comb  in liquid water were performed.  Combining bulk and interface spectroscopy, an assignment of ?comb  observed in SFG spectra was developed.  SFG of these high frequency vibrations can provide access to previously unobserved  modes, e.g., surface water bend, as well as coupling between modes and the dissociation energy of surface hydroxyls.

Sum-frequency generation spectroscopy of the combination band vibrations of water molecules at silica surfaces

244th National Meeting (2012)

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