Chapter 4 - Collecting Diffraction Data

Abstract

This chapter discusses the geometric principles of diffraction, revealing, in both the real space of the crystal's interior and in reciprocal space, the conditions that produce reflections. It also discusses how these conditions allow the crystallographer to determine the dimensions of the unit cell and the symmetry of its contents, and how these factors determine the strategy of data collection. Also, it highlights the devices used to produce and detect X-rays, and to measure precisely the intensities and positions of reflections. The other topics covered in the chapter are geometric principles of diffraction—the generalized unit cell, indices of the atomic planes in a crystal, conditions that produce diffraction, the reciprocal lattice, Bragg's law in reciprocal space, number of measurable reflections, unit–cell dimensions, unit–cell symmetry; collection X-ray diffraction data—X-ray sources, detectors, cameras, scaling, and postrefinement of intensity data, determining unit–cell dimensions and symmetry, and the strategy of collecting data.