Dissociative adsorption ofO2molecules on O-precovered Fe(110) and Fe(100): Density-functional calculations

Abstract

The dissociative adsorption of ${\mathrm{O}}_{2}$ molecules on clean and oxygen-precovered Fe(110) and Fe(100) surfaces has been studied from first principles. For the relatively open Fe(100) surface, we find that along the most favorable reaction channel, ${\mathrm{O}}_{2}$ dissociation remains a nonactivated process up to almost full monolayer coverage. The differential heat of adsorption decreases only slowly with increasing oxygen precoverage. The potential energy profile for dissociation shows a dip, which is indicative of the formation of a very short-lived nonmagnetic peroxo precursor. On the close packed Fe(110) surface, the differential heat of adsorption begins to decrease already at a modest precoverage. For dissociation on a surface precovered with about 0.44 monolayer of oxygen, a low barrier begins to appear in the entrance channel. In the transition state, the incoming molecule is in a superoxo state with a magnetic moment of $1{\ensuremath{\mu}}_{B}$. Our results are discussed in relation to the electronic and magnetic properties of the partially precovered surfaces and to the available experimental results.