Characterization of iron oxides by x-ray absorption at the oxygen K edgeusing a full multiple-scattering approach

\ensuremath{\alpha}-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$,${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$, and FeO compounds are characterized by means of x-ray-absorption near-edge-structure spectroscopy at the oxygen K edge. Using increasing cluster sizes around the excited atom in the full multiple-scattering simulations, we are able to link the features present in the spectra of each iron oxide to its specific atomic arrangement and electronic structure. The prepeak structure is successfully reproduced and interpreted as transitions from the oxygen 1s core state to antibonding oxygen 2p states hybridized with Fe 3d orbitals. Their intensity and shape depends on the Fe site symmetry, the occupation number of the d levels, and the O-Fe bond length of each different iron oxide. Higher lying spectral features are shown to be related to scattering of the photoelectron by a particular oxygen shell and an extended x-ray absorption fine structure--like relation is established between their energy position and the distance of the corresponding shell from the photoabsorber.