Effect of vibrations on the pre-edge features of x-ray absorption spectra

TL;DR

This paper investigates how atomic vibrations influence pre-edge features in X-ray absorption spectra, showing that vibrations enable additional transitions and improve agreement with experimental data.

Contribution

The study introduces a theoretical approach to account for vibrational effects on XANES pre-edge features, explaining temperature dependence and transition enhancements.

Findings

Vibrations enable electric dipole transitions to 3s and 3d states.

Improved match between theory and experiment for Al K-edge spectra.

Temperature dependence of pre-edge features explained by vibrational effects.

Abstract

The influence of atomic vibrations on x-ray absorption near edge structure (XANES) is calculated by assuming that vibrational energies are small with respect to the instrumental resolution. The resulting expression shows that, at the K-edge, vibrations enable electric dipole transitions to 3s and 3d final states. The theory is applied to the K-edge of Al in Al2O3 corundum and of Ti in TiO2 rutile and compared with experiment. At the Al K-edge, sizeable transitions towards 3s final states are obtained, leading to a clear improvement of the agreement with experimental spectra. At the Ti K-edge, electric dipole transitions towards 3d final states explain the temperature dependence of the pre-edge features.