Polarized X-ray Absorption. Quantitative Determination by Fluorescence Measurements

For non-cubic crystals, polarized X-ray absorption due to anisotropic anomalous scattering (AAS) occurring in the vicinity of absorption edges can be determined, both qualitatively and quantitatively, from polarized fluorescence measurements. For crystals exhibiting `large' faces, a method is presented that allows the simultaneous determination of all absorption-tensor elements from a single-crystal rotation experiment. Energy variation included, the method may be used for single-crystal polarized absorption and fluorescence spectroscopy. Depending on the crystal system and the face investigated, the experimental set-up can require a tilt of the polarization direction(s) against the plane of measurement as well as a precession of the crystal face normal about the rotation axis Ψ. For all systems except triclinic, the experimental conditions are discussed and fluorescence intensity functions I_F(Ψ) are developed and illustrated by model calculations.