title: Symmetry role on the preedge X-ray absorption fine structure at the metal K edge.
abstract: The preedge features in a system with "even" symmetry, apart from quadrupolar transition contribution, are mainly dipolar in character, associated with the existence of unoccupied states made up of mixed cation-4p with higher-neighboring cation-3d orbitals, and reflect the density of states due to the medium-range order of the system. In "odd" symmetry materials these preedge features are the result of a transition from the 1s to a final density of states of p symmetry due to an unsymmetrical mixing of the ligand wave functions with the central cation 3d orbitals, similar to atetrahedral configuration. These results are validated for Fe as a photoabsorber by comparing XAS spectra of Fe2SiO4 (fayalite) to ab initio full multiple scattering calculations at the Fe K edge, but pertain to all systems containing sixfold-coordinated cations.
authors.affiliation: Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, PR China.
authors.forename: Z
authors.initials: Z
authors.lastname: Wu
authors.forename: C R
authors.initials: CR
authors.lastname: Natoli
authors.forename: A
authors.initials: A
authors.lastname: Marcelli
authors.forename: E
authors.initials: E
authors.lastname: Paris
authors.forename: F
authors.initials: F
authors.lastname: Seifert
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.forename: T
authors.initials: T
authors.lastname: Liu