Sequential oxygen atom chemisorption on surfaces of small iron clusters

We report photoelectron spectra of iron oxide clusters, FecOy- (x = 1-4, y = 1-6). 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 Fe-x clusters and the O atoms, and provide key information about the oxide cluster structures, in which each O atom is suggested to locate pn the surface of the clusters for the x = 3 and 4 series. These clusters provide novel model systems to understand the electronic structure of bulk iron oxides.