Initial stages of oxidation of (100) and (110) surfaces of iron caused by water - art. no. 115426

The initial stages of the oxidation of the (100) and (110) surfaces of iron caused by the adsorption of water have been investiagted using ab initio l ocal-spin-density functional calculations including generalized gradient co rrections. It is shown that at low coverages water dissociates spontaneousl y into hydrogen atoms and hydroxyl groups. Further adsorption of water mole cules in the presence of preadsorbed H and OH does not lead to spontaneous dissociation. On both surfaces dissociation is a weakly activated process. This explains the presence of molecular water as observed experimentally. E specially on the (110) surface H2O dissociation in the presence of preadsor bed H and OH is found to be a complex process involving the formation of an intermediate molecular species.