  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.
