First electronic transition (A←X) of interfacial water on an α-alumina substrate was studied using attenuated total reflection far-ultraviolet (ATR-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 (&gt;10 nm) on the alumina surface. For the liquid water-alumina interface, a variation in the penetration depth of the evanescent wave of the probe light (25–19 nm) provided individual FUV spectra associated with bulk water (distance from the alumina surface &gt; 2 nm) and interfacial water (&lt;2 nm). The A←X band of the interfacial water was markedly blue-shifted and red-tailed relative to bulk water, indicating that the hydrogen bond (H-bond) network of the interfacial water involves an ice-like structure with broken H-bond acceptors. This reveals that the first layer might be hydrophobic to the subsequent layers, because the strong H-bond structure in the first layer makes fewer dangling OH bonds to the second layer. For the thin water layer on the alumina surface, the A←X band was red-shifted relative to bulk water, indicating that the H-bond network of the adsorbed water is very disordered. These electronic state differences of the interfacial water from bulk water mainly arise from the H-bond structure and hydration energy affected by the alumina surface.

First electronic transition of interfacial water on alpha-alumina studied by far-ultraviolet spectroscopy

252nd National Meeting (2016)

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