The first electronic transition (A←X) of liquid water is observed around the wavelength of ~150 nm in the far-UV (FUV) region and is very sensitive to hydrogen bonding (H-bonding) and hydration states because of the excitation of the non-bonding electrons on the oxygen atom. In this study, the A←X transition of interfacial water on an α-alumina surface was studied with using attenuated total reflection FUV spectroscopy (wavelength: 140–180 nm or 8.86–6.89 eV). The interfacial water was examined for a liquid water-alumina interface and an ultra-thin water layer of nano-meter thickness (&lt;10 nm) between two alumina surfaces. For the liquid water-alumina interface, a variation in the penetration depth of the evanescent wave of the probe light (25–19 nm) determined the individual FUV spectra associated with bulk water and interfacial water. The A←X band of the interfacial water was markedly blue-shifted and red-tailed relative to that of bulk water, indicating that the H-bond network of the interfacial water involves an ice-like structure with broken H-bond acceptors. The ultra-thin water layers of nano-meter thickness were prepared between a highly polished alumina plate and alumina prism. The A←X band of the thin water layer was blue-shifted or red-shifted, which depends on the H-bonding states of the formed thin layer. In either case, the hydrogen bond structure of bulk water is completely lost below 4 nm thickness, caused by steric hydration forces between the two alumina surfaces.

First electronic transition and hydrogen bonding state of interfacial water on alpha-alumina surface studied by far-ultraviolet spectroscopy

254th National Meeting (2017)

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