Bulklike Vibrational Coupling of Surface Water Revealed by Sum-Frequency Generation Spectroscopy

Vibrational coupling between interfacial water molecules is important for energy dissipation after onwater chemistry, yet intensely debated. Here, we quantify the interfacial vibrational coupling strength through the linewidth of surface-specific vibrational spectra of the water's O-H (O- D) stretch region for neat H2O/D2O and their isotopic mixtures. The local-field-effect-corrected experimental SFG spectra reveal that the vibrational coupling between hydrogen-bonded interfacial water O-H groups is comparable to that in bulk water, despite the effective density reduction at the interface.