EXAFS single-scattering

Fig. 5. Schematic view of the multiple scattering pathways in the EXAFS single scattering regime and in the XANES multiple scattering regime...

Figure 25. L3 absorption edge of metallic platinum. The upper figure shows experimental data (solid line) and calculated spectrum (dashed line). The figure at bottom shows the calculated partition of the EXAFS single scattering contribution (solid line), double scattering contribution (short dashed line), and the triple scattering contribution (long dashed line.) (From Ref. 88.)...

We will consider the theoretical description of EXAFS based on the single-scattering short-range order formalism. The EXAFS can... 

In a single scattering fcmialism (3), where the photoelectron interacts with a single scatterer before returning to the absorber, the theoretical expression for the EXAFS is (4)... 

Fig. 1. X-ray absorption spectrum (XAS) of Cu—Zn metallothionein at the Cu and Zn K-edges. The structure near the edge, referred to as XANES is dominated by multiple scattering events while the extended structure, referred to as EXAFS, at photoelectron energies greater than 30-50 eV is primarily due to single scattering events...

Equation (3.1) also assumes that the photoelectron is scattered off only one neighbouring atom i.e. EXAFS results from only a single scattering event. This is true for most cases particularly at relatively high energi es (200 eV above the edge). However,... 

The EXAFS formula in the approximation of single scattering is the following ... 

In the classical framework of single scattering (SS), the EXAFS signal, %(k), is related to the sum of sinusoidal oscillations for each shell of neighbours around the absorbing atom ... 

The region of single scattering at higher energies, called the "EXAFS region". EXAFS is used as a standard technique to measure interatomic distances and coordination numbers. 

N,Sq is a term that modifies the amplitude of the EXAFS signal. The subscript i denotes that this value can be different for each path of the photoelectron. For a single scattering path, N, represents the number of coordinating atoms within a particular shell (at the same radial distance from the absorber). For multiple scattering, N, represents the number of identical paths. The passive electron reduction factor, Sg, usually has a value between 0.7 and 1.0. It accounts for the slight relaxation of the remaining electrons in the presence of the core hole vacated by the photoelectron. 

Fig. 3. Comparison between the single-scattering (-----X the standard EXAFS (—) and the...

Fig. 15. Pictorial view of the scattering processes of the excited internal photoelectron determining the EXAFS oscillations (single-scattering regime) and the resonances in the XANES (multiple-scattering regime). From Bianconi (30).

Besides structural information (which is of minor interest in this case), EXAFS spectra reveal experimental scattering phases for the P-0 system and allow us to distinguish between resonances caused by single scattering processes and those caused by multiple scattering processes (so-called shape resonances). 

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