Effect of Surface Charge on the Vibrational Dynamics of Interfacial Water

The effect of the structuring of interfacial water, induced by surface charge, on the ultrafast vibrational dynamics of the O-H stretch in the hydrogen bonded spectral. region was studied at the H2O/fused silica interface. At high pH, where the electric field resulting from deprotonation of silanol groups polarizes several layers of water molecules, fast vibrational dynamics similar to the dynamics of bulk water is observed. At the neutral surface, where the structural ordering of interfacial water and the thickness of interfacial water are smaller than those at the charged surface, the vibrational lifetime of the O-H stretch becomes more than two times longer (T-1 similar or equal to 570 fs). The longer vibrational lifetime is a result of reduced intermolecular coupling resulting from incomplete solvation of the interfacial water species.