Effect of Hydrogen-Bond Strength on the Vibrational Relaxation of Interfacial Water

Time-resolved sum frequency generation (tr-SFG) reveals that the vibrational energy relaxation rate of O-H stretching of dilute HDO in D2O at the silica interface is markedly different from that of bulk water. As compared to the bulk liquid, the vibrational lifetime (T-1) of HDO is shorter at the charged surface than in the bulk, but longer at the neutral surface. The vibrational decoupling of the O-H of the HDO species leads to the observation of a frequency-dependent T-1 of the O-H stretch, which is shorter at the red than the blue side of the hydrogen-bonded OH spectral region. This correlates with the red-shift of the SFG spectra with increasing surface charge and is consistent with a theoretical model that relates the vibrational lifetime to the strength of the hydrogen-bond network.