Polarization Analysis In Resonant X-Ray Bragg Diffraction By K(2)Cro(4) At The Crk-Edge

The creation of a circular polarization has been witnessed in resonant x-ray Bragg diffraction at the Cr K pre-edge (5.994 keV) of potassium chromate (K(2)CrO(4)). Interference between channels of diffraction and, specifically, the E1-E1, E2-E2, and E1-E2 channels provides an account of the observation. We report a theoretical analysis of polarization in the secondary beam for K(2)CrO(4), with a variation of the primary linear polarization that successfully accounts for all aspects of the observations. An angular anisotropy of the local environment at Cr sites in this material is revealed in time-even quadrupoles, octupoles, and hexadecapoles that appear in scattering amplitudes for parity-even (E1-E1 and E2-E2) and parity-odd polar (E1-E2) channels. Our estimates of the multipoles derived from a fitting to the data for the secondary polarization are exploited in simulations of the diffracted intensity as a function of the azimuthal angle. There is a satisfactory agreement between simulations and the total intensity measured at space-group-forbidden (140) and (340) reflections.