Phase-shift calculations for extended X-ray absorption fine structure (EXAFS) and the fine structure of As2O3

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Abstract
Theoretical calculations are presented of three factors involved in Extended X-ray Absorption Fine Structure (EXAFS). It is found that multiple scattering within the atom gives rise to characteristic structure of the back-scattering amplitude. The back-scattering is not sensitive to charge and alters little with small changes in atomic number (Z), but exhibits a wide variety of shapes with large changes of 2. The back-scattering phase-shifts also show a trend similar to that of the amplitude. A comparison of the ionized atom and neutral atom Z=1 phase-shift shows a constant shift of the phase and little change in its k- dependence. Experimental measurements of the fine-structure of cubic and glassy As, O, are reported and are discussed in terms of the preceding calculations. It is found that As, O, molecules do not exist as a major constituent of the glass.