Sequential Oxygen Atom Chemisorption on Surfaces of Small Iron Clusters

We report photoelectron spectra of iron oxide clusters, FeₓOy^0ex0ex- (x0ex0ex=0ex0ex1--4,y0ex0ex=0ex0ex1--6). For a given x, we find that the electron affinity increases with the number of O atoms, consistent with an increasing degree of oxidation. The results are interpreted based on charge transfer interactions between the Feₓ clusters and the O atoms, and provide key information about the oxide cluster structures, in which each O atom is suggested to locate on the surface of the clusters for the x0ex0ex=0ex0ex3 and 4 series. These clusters provide novel model systems to understand the electronic structure of bulk iron oxides.