Surface Effect of Alumina on the First Electronic Transition of Liquid Water Studied by Far-Ultraviolet Spectroscopy.

The first electronic transition (à ← X̃) of liquid water (H2O and D2O) on an α-alumina substrate was studied using variable angle attenuated total reflection far-ultraviolet (VA-ATR-FUV) spectroscopy in the wavelength region 140-180 nm (8.86-6.89 eV). A variation in the penetration depth of the evanescent wave of a probe light (25-19 nm) directly determined individual FUV spectra associated with bulk water (distance from the alumina surface >2 nm) and interfacial water (<2 nm). We found that the à ← X̃ band of the interfacial water was markedly blue-shifted and red-tailed relative to the bulk water. The electronic state difference of the interfacial water from the bulk water mainly arose from the hydrogen-bond structure and energy affected by the alumina surface.