X-ray Absorption Edges (theory vs reality)

Theory isn't good enough - measure it yourself

The Cromer/Liberman theoretical values for scattering factors are not accurate for energies very near an absorption edge. Here the interaction of the scattering atom with its chemical neighbors complicates the scattering behaviour considerably. Shown below is a comparison of the theoretical values of f' and f" with the values determined experimentally for the Cu site in single crystal of a blue copper protein [Guss et al, 1989]. In both cases the f' values were derived from the corresponding f" spectra via the Kramers-Kronig equation.

Note in particular:

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Ethan A Merritt ©1996-2001/ merritt@u.washington.edu / Biomolecular Structure Center at UW