No abstract

Diffraction of synchrotron radiation in crystals of potassium chromate and germanium reveals a tetrahedral anisotropy of anomalous {resonant) scattering with respect to polarization and wave vectors that introduces a third-rank tensor into the intensity equations. This tensor arises from a mixed dipolequadrupole term that vanishes for forward scattering and for centrosymmetric atoms. At resonances 13 eV below the Cr K edge and 7 eV above the Ge E edge large changes of intensities with rotation of azimuth are observed for weak and forbidden Bragg reAections in agreement with the optical model.

J. HAUCK 237 smaller interaction. For alloys with small M content such as A 5 M the interaction seems to be too small for a formation of ordered alloys with cubic close packing because of the entropy at elevated temperatures, where A and M are mobile. (1969a). Z. Naturforsch. Teil B, 24, 251. (1969b). Z. Naturforsch. Teil B, 24, 455--456. (1969c). Z. Naturforsch. Teil B, 24, 1064Teil B, 24, -1066Teil B, 24, . ( 1970a. Z. Naturforsch. Teil B, 25, 226. (1970b). Z. Naturforsch. Teil B, 25, 109-110. (1970c). Z. Naturforsch. Teil B, 25, 749-752. (1970d). Z. Naturforsch. TeiI B, 25, 468-471. (1973). Z. Naturforsch. Teil B, 28, 215-216. (1974). J. Inorg. Nucl. Chem. 36, 2291-2298. HAUCK, J. (1976a. Z. Naturforsch. TeilB, 31, 1179-1182. HAUCK, J. (1976b structure is polarized as a result of the symmetries of molecular orbitals in this strongly anisotropic molecule. The extended X-ray absorption fine structure is polarized because of the difference in distance to the axial and equatorial oxygen neighbors. In this wavelength region, the anomalous-scattering terms and © 1980 International Union of Crystallography 238 DOUBLE REFRACTION IN VANADYL BISACETYLACETONATE the index of refraction vary with the direction of polarization. Some of the consequences and possible applications of these properties are discussed.

.~ : ' AbstractLinearly polarized synchrotron radiation has been used to observe X-ray dichroism of the bromate ion near the bromine K edge by transmission absorption spectroscopy using a crystal of potassium bromate, and to measure the anomalous scattering of bromine and its anisotropy in diffraction experiments with

Both real and imaginary components of the anomalous X-ray scattering were measured by single-crystal diffraction experiments with synchrotron radiation at wavelengths through the region of the three L absorption edges of cesium, the first such experiment for any element at the L edges. Near the L 3 edge f' varies between -26.7 and -13.9 and f" between 4.0 and 16.1 electrons in a wavelength interval of 0.008 A. Similar but smaller changes occur near the L 2 edge, and still smaller ones at Lt. Fine structure in the f" curve corresponds to that observed in an absorption curve and also, by a dispersion relation, to fine structure in the f' curve. These effects offer promise as a substitute for isomorphous replacement for solving the phase problem for macromolecular crystal structure. Similar experiments with cobalt near the K edge give f' values in agreement with measurements by other workers for nickel and copper by different methods at corresponding wavelengths; the lowest value observed is f' = -7.5 electrons.