High Quality Content by WIKIPEDIA articles! X-ray absorption fine structure (XAFS) is a specific structure observed in X-ray absorption spectroscopy (XAS). By analyzing the XAFS, information can be acquired on the local structure and on the unoccupied electronic states. The X-ray absorption spectra show a steep rise at the core-level binding energy of X-ray-absorbing atoms and attenuates gradually with the X-ray energy. The XAS spectra are usually divided in three energy regions: 1) the edge region, 2) the X-ray Absorption Near Edge Structure (XANES); 3) the extended X-ray absorption fine structure (EXAFS). The absorption peaks at the absorption edges in a range of about 5 eV were first explained by Walther Kossel as due to electronic transitions to first unoccupied molecular levels above the chemical potential, and for many years was referred to as the Kossel structure now it is known as absorption edge region.