Chapter

Background theory for data collection

Jacqueline Cole

in Crystal Structure Analysis

Second edition

Published in print June 2009 | ISBN: 9780199219469
Published online September 2009 | e-ISBN: 9780191722516 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780199219469.003.0005

Series: International Union of Crystallography Texts on Crystallography

Background theory for data collection

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This chapter describes the theory behind X-ray diffraction data collection, and reduction. A diffraction pattern is the Fourier transform of the crystal structure, and can be described in terms of reciprocal space; Fourier transformation of the diffraction pattern should recover an image of the electron density of the crystal structure, but can not be directly achieved because the relative phases of the diffracted beams are lost and only the directions and amplitudes (as intensities) are available. The geometry of diffraction is described by Bragg's law and the Ewald sphere construction. Methods are explained for assigning indices to X-ray reflections and finding the orientation of the crystal. Aspects of data collection strategies include the selection of data to be measured and the impact of the crystal mosaic spread. Integration is the process of extracting reflection intensities. Corrections are necessary for various effects such as the diffraction geometry, absorption, and incident X-ray variations.

Keywords: data collection; data reduction; integration; Fourier transform; Bragg's law; Ewald sphere; mosaicity; absorption correction

Chapter.  7319 words.  Illustrated.

Subjects: Crystallography

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