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Tensor X-ray optical properties of the bromate ion

Tensor X-ray optical properties of the bromate ion Linearly 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 sodium bromate. The principal values of f" are as high as 12 and 17 electrons atom-1 and of f' as low as -13 and -15 for polarization respectively parallel and perpendicular to the threefold axis. The anisotropy is as much as 6.6 for f" and 4.6 for f', or a few percent more after correction for thermal motion and for incomplete polarization of the beam. A consequence of this large anisotropy is that reflections forbidden by the screw-axis rules are observed. Applications and possible adverse consequences of these effects in structure research are discussed. An energy calibration gives 13 482.1 (10) eV or 0.91960 (7) A for the peak of the first K-edge absorption line in sodium bromate. These results suggest that X-ray optical activity in sodium bromate can be observed most readily near 0.9205 A, where the magnitude is estimated to be of the order of 0.1Degrees cm-1. Crystal structures were redetermined for KBrO3, R3m, a = 6.011 (1), c = 8.152 (2) A, Z = 3, 295K, R = 0.010 for 308 unique reflections, and for NaBrO3, P213, a = 6.705 (2) A, Z = 4, 296 K, R = 0.013 for 433 unique reflections. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Crystallographica Section A: Foundations of Crystallography International Union of Crystallography

Tensor X-ray optical properties of the bromate ion

Tensor X-ray optical properties of the bromate ion


Abstract

Linearly 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 sodium bromate. The principal values of f" are as high as 12 and 17 electrons atom-1 and of f' as low as -13 and -15 for polarization respectively parallel and perpendicular to the threefold axis. The anisotropy is as much as 6.6 for f" and 4.6 for f', or a few percent more after correction for thermal motion and for incomplete polarization of the beam. A consequence of this large anisotropy is that reflections forbidden by the screw-axis rules are observed. Applications and possible adverse consequences of these effects in structure research are discussed. An energy calibration gives 13 482.1 (10) eV or 0.91960 (7) A for the peak of the first K-edge absorption line in sodium bromate. These results suggest that X-ray optical activity in sodium bromate can be observed most readily near 0.9205 A, where the magnitude is estimated to be of the order of 0.1Degrees cm-1. Crystal structures were redetermined for KBrO3, R3m, a = 6.011 (1), c = 8.152 (2) A, Z = 3, 295K, R = 0.010 for 308 unique reflections, and for NaBrO3, P213, a = 6.705 (2) A, Z = 4, 296 K, R = 0.013 for 433 unique reflections.

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Publisher
International Union of Crystallography
Copyright
Copyright (c) 1985 International Union of Crystallography
ISSN
0108-7673
DOI
10.1107/S0108767385000277
Publisher site
See Article on Publisher Site

Abstract

Linearly 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 sodium bromate. The principal values of f" are as high as 12 and 17 electrons atom-1 and of f' as low as -13 and -15 for polarization respectively parallel and perpendicular to the threefold axis. The anisotropy is as much as 6.6 for f" and 4.6 for f', or a few percent more after correction for thermal motion and for incomplete polarization of the beam. A consequence of this large anisotropy is that reflections forbidden by the screw-axis rules are observed. Applications and possible adverse consequences of these effects in structure research are discussed. An energy calibration gives 13 482.1 (10) eV or 0.91960 (7) A for the peak of the first K-edge absorption line in sodium bromate. These results suggest that X-ray optical activity in sodium bromate can be observed most readily near 0.9205 A, where the magnitude is estimated to be of the order of 0.1Degrees cm-1. Crystal structures were redetermined for KBrO3, R3m, a = 6.011 (1), c = 8.152 (2) A, Z = 3, 295K, R = 0.010 for 308 unique reflections, and for NaBrO3, P213, a = 6.705 (2) A, Z = 4, 296 K, R = 0.013 for 433 unique reflections.

Journal

Acta Crystallographica Section A: Foundations of CrystallographyInternational Union of Crystallography

Published: Mar 1, 1985

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