EXAFS cancellation

EXAFS cancellation is actually surprisingly common, and occurs when two EXAFS interactions are close to 180° out phase. Cancellation is most frequently only partial, but in some cases the presence of ligands can be entirely missed in an EXAFS analysis because of EXAFS cancellation. The EXAFS of Figure 4.8 shows a case of potential partial cancellation - the computed EXAFS for Mo-0 and Mo-S both at 2.2 A are essentially 180° out of phase, but the Mo-S EXAFS is approximately twice the amplitude of the Mo-0. If both of these were present in a refinement then the presenee of Mo-O would be obscured by partial cancellation of the EXAFS with that of the Mo-S. 

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