Photoelectron and X-ray spectroscopy of minerals. Part 1.—Electronic structure of forsterite (magnesium orthosilicate)

Abstract

X-ray emission (Si Kβ_1,3, Si L_2,3M, Mg Kβ_1,3 and O Kα) and X-ray photoelectron spectra are presented for forsterite (Mg₂SiO₄) and aligned on a common energy scale using core ionisation energies. The energies and relative intensities of peaks in these spectra are discussed in terms of possible theoretical models for SiO^4–₄: ab initio, Xα etc. The magnesium Kβ X-ray emission peak profile and position relative to oxygen Kα shows that the O—Mg bond is more ionic than O—Si. The spatial position of magnesium ions relative to silicate anions would appear to facilitate σ—π mixing, i.e. the mixing of orbitals which to a first approximation could be regarded as either O—Si bonding or oxygen lone pairs.