Basic Principles of X-ray Absorption Spectroscopy XAS

Physically, the core electron (the s electron for a K-edge) is ejected by the X-ray photon. This core electron then has a kinetic energy, k which is equal to Ek = hv — Ek where b = the binding energy. 

The intensity of the EXAFS osdllation is dependent on a number of factors. First, the number and nature of backscattering atoms is a major contributor to the intensity of the oscillations. Different absorbers have different backscattering powers so the amplitude is dependent on the element which is the next nearest neighbor to the absorber atom. Depending on the absorber and the system, not all ejected electrons take part in the scattering process-up to 30% of the photoelectrons go into shake-up/down processes and are not available for EXAFS or XANES spectroscopy (see below). 

A simplified form of the EXAFS equation can be written as follows  

The main parameters in this equation are X(k) = EXAFS interference function 

N = coordination number of neighboring atom R = distance to neighboring atom 

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