X-ray dichroism and polarized anomalous scattering of the uranyl ion

Dichroism is observed near the L₁ and L₃ edges of uranium in X-ray absorption spectra of single-crystal rubidium uranyl nitrate, Rb.UO₂.3NO₃, recorded with linearly polarized synchrotron radiation. The anomalous X-ray scattering terms f' and f'' calculated from these spectra are anisotropic functions of polarization direction at these wavelengths, adding new complexity to diffraction optics. These terms are measured independently in diffraction experiments with sodium uranyl acetate at five wavelengths near L₃. The cubic symmetry permits the diffraction effects to be observed without the complications of macroscopic dichroism and birefringence. Both f' and f'' change with polarization direction by as much as 2 electrons atom^-l. These values agree with those derived from the absorption experiments.