Calculation of multipole transitions at the Fe K pre-edge through p - d hybridization in the Ligand Field Multiplet model

For the first time, commonly unaccessible local electronic structure parameters of Fe 2+ and Fe 3+ in minerals are derived from the calculation of the pre-edge features of X-ray absorption spectra at the Fe K edge. The Ligand Field Multiplet approach is used to calculate the eigenstates of the ions and the absolute intensities of the electric-quadrupole and dipole transitions involved in the pre-edge. For ions in tetrahedral symmetry, a new model for p - d hybridization is developed. The degree of admixture between 3 d and 4 p levels is derived and local structure parameters (crystal field, bond covalency) are obtained.