INFLUENCE OF SPHERICAL WAVE CORRECTIONS ON THE TEMPERATURE-DEPENDENCE OF XAFS MULTIPLE-SCATTERING PROCESSES

Curved-wave corrections to the Debye-Waller factor have to be included in the calculation to describe the temperature dependence of XAFS. This evaluation is extended to multiple scattering loops. The result is that, in each scattering process a --> b --> c, the t-matrix element t(l) has to be replaced by t(l)(TD) = t(l) + 0.5k(2)(sigma(ab)(2) + sigma(bc)(2) - sigma(ac)(2))F-l. F-l contains the scattering angle; sigma(ij)(2) is the relative mean square displacement between the atoms i and j. Numerical results are given for loops containing shadowed atoms. It is shown that these spherical wave corrections are important if the magnitude of the anharmonic movement is to be estimated by the analysis of measured spectra.