The adsorption and reaction of water on the preoxidized Fe(100) surface is studied using LEED, AES, thermal desorption and high resolution EELS. Oxidation of the Fe(100) surface by water adsorption results in a disordered c(2 × 2) surface, with a saturation oxygen coverage of 0.39 ML. This surface cannot be further oxidized by exposure to water, but can be further oxidized by molecular oxygen. When water is adsorbed on the submonolayer oxygen pre-exposed surface, hydrogen transfer from water to adsorbed atomic oxygen occurs, forming a hydroxyl group. This group migrates from the fourfold hollow site, where it is formed, to the bridge site on this surface. Adsorbed oxygen facilitates water decomposition via this hydrogen transfer process. On the oxygen precovered surface with an oxygen coverage of 1 ML (p(1 × 1)O surface), water adsorbs molecularly and desorbs at 175 K without decomposition.
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