Effect of atomic vibrations on the x-ray absorption spectra at the K edge of Al in α-Al2O3 and of Ti in TiO2 rutile

The influence of atomic vibrations on x-ray absorption near-edge structure 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 alpha-Al2O3 and of Ti in TiO2 rutile and compared with experiment. At the Al K edge, sizeable transitions toward 3s final states are obtained, leading to a clear improvement of the agreement with experimental spectra. At the Ti K edge, electric-dipole transitions toward 3d final states explain the temperature dependence of the pre-edge features.