Lieselotte K. Templeton

L3-Edge Anomalous Scattering by Gadolinium and Samarium Measured at High Resolution with Synchrotron Radiation

The anomalous scattering terms f′ and f′′ for Gd and Sm near their L3 absorption edges, measured in diffraction experiments with synchrotron radiation more nearly monochromatic than the natural level widths, show even larger effects than earlier measurements with a larger X-ray bandwidth. A test of angular dependence shows f′ for Sm to decrease in magnitude with increasing diffraction angle, while f′′ is essentially constant.

LIII-Edge Anomalous X-ray Scattering by Cesium Measured with Synchrotron Radiation

Diffraction of monochromatized synchrotron radiation by crystals of cesium hydrogen tartrate has been used to measure the magnitude and phase of x-ray scattering for cesium near the LIII absorption edge. In this wavelength region the scattering amplitude of cesium is reduced by as much as 25 electrons per atom, compared to scattering of copper Kα x-rays. This change, which varies as a function of wavelength, affects the diffraction intensities in a manner similar to isomorphous substitution, and it is large enough to have promise for phase determination in the study of macromolecular structures. This experiment also demonstrates that accurate diffractometer measurements are possible with synchrotron radiation produced by an electron storage ring.

Crystal and molecular structure of xenon bis(oxopentafluoroselenate(VI)), Xe(OSeF5)2

Nach Einkristallrontgenstrukturanalyse sind die Kristalle von Xe(OSeF5)2 rhomboedrisch mit der Raumgruppe Ram, Z=3.

Polarized Dispersion of X-rays in Pyrite

Diffraction of synchrotron radiation in a crystal of FeS2 reveals dipolar anisotropy of anomalous scattering by Fe near its K-absorption edge, in spite of the almost-regular octahedral geometry of the nearest S neighbors. At 7121 eV, the magnitude of f changes with polarization direction by as much as 0.7 electron units. No effects of quadrupolar anisotropy were detected.

Anomalous Scattering of Polarized X-Rays

Some elements in some chemical states exhibit strong dichroism and birefringence near x-ray absorption edges. The atomic scattering factor is a complex tensor. This polarization anisotropy has profound effects on the transmission and scattering of x-rays even when the incident radiation is unpolarized. The linear polarization of synchrotron radiation makes it easier to study the effects and to use them for new methods of structure determination. Several of these anomalous scattering tensors have been measured by absorption spectroscopy and in diffraction experiments. New polarization terms enter the calculation of diffraction intensities, with interesting consequences. Reflections forbidden by a screw-axis rule are observed in sodium bromate near the Br K edge and permit direct observation of the structure factor phases of their second order reflections. This technique is a method of selective diffraction in which atoms of single element in a single chemical state contribute to the signal, and it can reveal their positions with precision. These effects can be a handicap for some applications of near-edge anomalous scattering in the study structures of crystals and amorphous materials.