Abstract
An absorption spectrum can be considered in two parts: the EXAFS, beyond about 50 eV above the absorption edge, and the x‐ray absorption near edge structure (XANES), within about 50 eV of threshold. Although there is no exact division, and the figure of 50 eV is somewhat arbitrary, there are real physical differences between the two parts of the spectrum. In the EXAFS region, scattering is weak, electron mean‐free‐paths are short, and phase‐shifts are readily calculable or transferable from model compounds. The single scattering approximation holds good, and bond lengths can be derived from Fourier transform analysis of the data, but the spectrum contains information only on pairwise atomic correlations. By contrast, in the XANES régimé, scattering is strong and mean‐free‐paths are long, making multiple scattering important and data analysis difficult, but the spectrum in consequence is rich in information on three‐body and other correlations.
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