| Abstract
| - Spectroscopic characterization of adsorbed water has been carried out on (111) surfaces of Pt, Pd, Rh, Au, and Cu in sulfuric acid solution using infrared reflection−absorption spectroscopy (IRAS). The absorption band of the HOH bending mode (δHOH) is measured below the onset potential of (bi)sulfate adsorption. The band frequency of δHOH of adsorbed water is lower than that of bulk water. The δHOH band shifts to higher frequencies with the increase of the positive potentials on Pt, Pd, and Rh, whereas the band intensity is unchanged between the potentials of hydrogen evolution and (bi)sulfate adsorption. This suggests that water is adsorbed through an oxygen lone pair, with its molecular plane slightly tilted from the surface. On Au(111), the δHOH band intensity decreases with the increase of the electrode potential. This result indicates that the orientation of water depends on the applied potential. No absorption band of water is found on Cu(111), which indicates different behavior of adsorbed water compared with the other metal electrode surfaces.
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