FULL MULTIPLE-SCATTERING CALCULATIONS OF THE X-RAY-ABSORPTION NEAR-EDGE STRUCTURE AT THE MAGNESIUM K-EDGE IN PYROXENE

We present a comparison between XANES experiments and full multiple-sc attering calculations at the magnesium K-edge for two pyroxenes, diops ide and enstatite, for which Mg atoms are only in the M1 site and in t wo distinct sites M1 and M2, respectively. The influence of the number of octahedral sites per unit cell and of the site distortion on ME K- edge XANES spectra is investigated. Good agreement between experiment and calculations is obtained. Full multiple-scattering calculations pe rmit identification of the contribution of each site. Comparison revea ls that the Mg K-edge spectra of enstatite and diopside M1 sites have the same XANES profile. Cluster size analysis shows that most Mg K-edg e XANES features are related to medium range order, i.e., 6 Angstrom a round the absorbing atom. We therefore clearly define the Mg K-edge si gnature of the geometrical arrangement of atoms around each site, M1 a nd M2.