XAS involves the measurement of the absorption of X-rays as a function of their energy. When X-rays are directed at a sample, they can be absorbed by the atoms, causing core electrons to be excited to unoccupied states. The absorption pattern, known as the XAS spectrum, contains two main regions: the X-ray Absorption Near Edge Structure (XANES) and the Extended X-ray Absorption Fine Structure (EXAFS). XANES provides information about the electronic state and oxidation state of the absorbing atom, while EXAFS gives details about the distances, coordination numbers, and types of neighboring atoms.
