X-ray absorption spectra are generally produced in the range 200 - 35 000 eV. In this energy range the main process for X-ray absorption is that whereby the photon is completely absorbed and kicks out a core photoelectron from the absorbing atom leaving behind a core hole. This photoelectron will be ejected with an energy equal to energy of the incoming photon less its binding energy, when in the core. This photoelectron will interact with the surrounding atoms.
To extract information about the inter-atomic distances and the number of the surrounding atoms (i.e the radii rn of the near-neighbor coordination shells and the number of atoms at rn) a Fourier transformation of the EXAFS equation is applied. EXAFS oscillations consist of different frequencies corresponding to the different radii of each coordination shell (which leads to the application of the Fourier analysis).