New methods in time-resolved Laue pump–probe crystallography at synchrotron sources

Abstract

Newly developed methods for time-resolved studies using the polychromatic and in particular the pink-Laue technique, suitable for medium and small-size unit cells typical in chemical crystallography, are reviewed. The order of the sections follows that of a typical study, starting with a description of the pinkLaue technique, followed by the strategy of data collection for analysis with the RATIO method. Novel procedures are described for spot integration, orientation matrix determination for relatively sparse diffraction patterns, scaling of multi-crystal data sets, use of Fourier maps for initial assessment and analysis of results, and least-squares refinement of photo-induced structural and thermal changes. In the calculation of Fourier maps a ground-state structure model, typically based on monochromatic results, is employed as reference, and the laser-ON structure factors for the Fourier summations are obtained by multiplying the reference ground-state structure factors by the square root of the experimental ON/OFF ratios. A schematic of the procedure followed is included in the conclusion section.

Seed-skewness algorithm for X-ray diffraction signal detection in time-resolved synchrotron Laue photocrystallography

“…We used the already published data (now available in the Repository for Open Data, RepOD; Interdisciplinary Centre for Mathematical and Computational Modelling, University of Warsaw, Warsaw, Poland; doi: 10.18150/repod.6395772) measured with the Mar165 CCD-type round-shape detector (diameter: 165 cm; frame size: 2048 pixels in the vertical and horizontal directions; pixel size: 80 mm in both directions; Table 3). The four originally examined datasets were integrated applying both KW and SS methods implemented in our software and further processed using the overall procedure of the Laue data treatment (orientation matrix determination, frame-to-frame orientation refinement, indexing, ratio computation) (Coppens & Fournier, 2015). It is worth mentioning that our implementation of the KW-test method is not entirely identical to that in the LAUEUTIL software used previously.…”

The dramatic development of X-ray photocrystallography over the past six decades

“…The narrow band Laue technique makes much more efficient use of the available synchrotron photons and thus shortens the data collection time and increases accuracy if appropriate procedures are followed (Coppens and Fournier, 2015). The spectral assignment of the individual reflections can be bypassed in the time-resolved Laue work by use of the Ratio Method (Coppens et al , 2009).…”

Analysis of multicrystal pump–probe data sets. II. Scaling of ratio data sets

“…Time-resolved single-crystal Laue X-ray data were collected at the 14-ID BioCARS beamline of the Advanced Photon Source (Chicago). For the current study, each raw frame data set has been reprocessed using the latest version of the toolkit LaueUtil Coppens & Fournier, 2015). The laser-ON structure model defined in the original paper, which assumes a random distribution (RD) of the excited molecules (Vorontsov & Coppens, 2005), is used.…”

“…Their independence is expected when the number of observations N obs is significantly larger than the number of variables N X (N obs > 10N X ). Recent studies by Henn & Meindl (2014a,b, 2015 emphasize the relevance of statistical analysis of weighted residual terms to identify systematic errors in data sets or model refinement bias.…”

“…Each exposed particle provides a separate diffraction pattern, such that thousands of patterns on the same substance need to be analyzed. All techniques discussed in this publication were developed specifically for pump-probe Laue data using the RATIO method (Coppens et al, 2009;Coppens & Fournier, 2015). This method consists in using the ratios of the intensities with and without light exposure I ON =I OFF instead of the absolute intensities I ON , and thus avoids the necessity to identify the wavelength for each of the reflection spots in the Laue pattern as well as differential absorption effects.…”