Integration procedure for the quantitative analysis of dispersive anomalous diffraction

Abstract

The development of the energy/angular dispersive diffraction setup, which can be used for anomalous diffraction, allows the collection of diffracted intensities around an absorption edge, either over a continuous energy range [for DAFS (diffraction anomalous fine structure) studies], or at discrete energies [for simultaneous MAD (multiwavelength anomalous diffraction) studies]. Used with a large two-dimensional detector and an oscillating single crystal, this setup allows simultaneous collection of many reflections for a given energy range. An integration procedure has been developed along with a program,DAD(dispersive anomalous diffraction), for the collection and analysis of the raw images, to yield finally data in the formI(h, k, l, λ) for all reflections. Wavelength calibration and intensity corrections are made during the integration process, and parameters that may be needed in later stages of the analysis are extracted and referenced within the integrated data. A general procedure to calculate the positions of diffracted reflections, for a monochromatic oscillation scan with a two-dimensional detector, when the incident beam is not perpendicular to the oscillation axis, is also described.