Theoretical Analysis of X-Ray-Absorption near-Edge Structure at the Mg K Edge in Forsterite, Mg2SiO4-Pbnm, Under Extreme Conditions

We calculated the Mg K edge X-ray absorption spectra of forsterite both for the M1 and M2 sites and for the overall edge by using the one-electron multiple-scattering theory. The validity of the theoretical model is well illustrated by comparison of calculations with experimental data at the Mg K edge of MgO (periclase). Based on these results, XAS experiments at the Mg K edge of forsterite are suggested, in as much as calculations performed up to 1020 Celsius and 149 kbar indicate variation of fine structures in the multiple scattering region. We show for the first time that the information, which can be obtained by using this spectroscopy have implications on the structure of the Earth's upper mantle.