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Polarization analyzed DAFS

The electric dipole components usually dominate the DAFS transitions, and consequently the polarization selection rules are usually pure electric dipole rules. For linearly polarized incoming radiation and a pure electric dipole transition (i.e., no magnetic effects, chirality or dichroism), the outgoing radiation will have the same linear polarization as the incoming radiation. If there is a small additional component of electric quadrupole scattering, it can be measured easily and accurately by using a crossed polarizer to remove the electric dipole component.

A complete DANES polarization analysis versus photon energy will allow the symmetry and density of the empty antibonding and low continuum states to be determined. If the material is dichroic, chiral and/or magnetic, these additional effects can also be distinguished via a complete polarization analysis. DAFS polarization analysis represents an infusion of spectroscopic methods into crystallography, and vice versa; this will have important consequences for both fields. For example, the usual forbidden reflection rules of crystallography are based on electric dipole transitions, and it has been shown that these rules are modified in useful ways for resonantly excited transitions [14, 34, 41].