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 (T1) 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 T1 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.