Oxygen K-edge x-ray absorption near-edge structure in crystalline and amorphous molybdenum trioxides

X-ray absorption near-edge structure (XANES) signals at the oxygen K edge in polycrystalline α-MoO₃ and amorphous a-MoO₃ thin film were analysed within the full-multiple-scattering (FMS) formalism. Significantly different XANES signals were found for non-equivalent oxygen atoms in low-symmetry layered-type α-MoO₃ structure. The obtained results are in agreement with the experimental data and allow us to interpret all XANES peaks for α-MoO₃. Besides, the FMS XANES simulations, performed for several fragments of α-MoO₃ structure, allowed us to explain the O K-edge XANES in amorphous α-MoO₃ thin film. We found that although the crystallographic structures of α-MoO ₃ and α-MoO₃ are strongly different, a cluster consisting of six MoO₆ octahedra joined by vertices produces the main contribution to both XANES signals.