Dissociation of Water During Formation of Anodic Aluminum Oxide

According to model computations at the B3LYP/6-311+G** level, an external electric field can facilitate the heterolytic dissociation of properly oriented water molecules significantly. Depending on the models used, the maximum predicted change of the dissociation energy in the field is ca. -3 to -4 kcal nm mol(-1) V-1, and decreases with the cosine of the angle between the external field and the breaking OH bond. These microscopic results can be related semiquantitatively to macroscopic observables from mechanistic studies on the pore formation of anodic aluminum oxide, thus lending support to the equifield strength model and field-enhanced water dissociation at the growing oxide surface that has been put forward in these studies.