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 pink-Laue 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.

Keywords: multicrystal data sets; orientation matrix determination; photocrystallography; pink-Laue; spot integration.

Figure 1

Intensity versus wavelength and energy ranges for two different settings at the BIOCARS 14-ID beamline at the Advanced Photon Source.

Figure 2

Collection of the profile along a single pixel-line. Reproduced from Kalinowski et al. (2012 ▶).

Figure 3

Intensities for one pixel on successive frames (ground state). A single frame was measured at each setting, 1° step scan. Red spots assigned as part of a peak, blue spots background. CuI(phenanthroline)(PPh₃)₂][BF₄]. Data from Makal et al. (2012 ▶). Modified from Kalinowski et al. (2012 ▶).

Figure 4

Two examples of pixel count plots for repeated measurements in each of 11 blocks of 20 frames (10 × ON/OFF) at each angular setting, 1° step scan. The blue dotted blocks are assigned as background by the Kruskal–Wallis statistical method. CuI(phenanthroline)(PPh₃)₂][BF₄]. Data from Makal et al. (2012 ▶). Modified from Kalinowski et al. (2012 ▶).

Figure 5

Morphological treatment of the spot masks on a frame after analysis of the counts along the pixel lines. (a) Pixel intensity in color with the boundaries of the originally selected pixel clusters in black. (b) Boundaries of the originally selected pixel clusters in grey, pixels remaining in the mask after erosion in blue and pixels added by two successive dilations in orange. The resulting mask of reflections after morphological operations is the union of orange and blue pixels. From Kalinowski et al. (2012 ▶).

Figure 6

Visualization of projections of points in reciprocal space on a unit sphere. Left: monochromatic data; eight equivalent asymmetric units in reciprocal space are represented with different colors. Right: points from a Laue data set. [Reproduced from Kalinowski et al. (2011 ▶).]

Figure 7

(a) Photodifference map of a complex with an Ag₂Cu₂ core. Isosurfaces at 0.55 and 0.35. (b) Photodeformation map (defined in §7.3) based on the refined model parameters. Blue positive, red negative. (Isosurfaces, ±0.30 e Å⁻³; blue, positive; red, negative; k _B = 1.06.) [Jarzembska et al. (2014 ▶). Reprinted with permission from Inorg. Chem. (2014), 53, 10594–10601, Copyright 2014 American Chemical Society.]

Figure 8

Three-dimensional photodeformation maps of Rh₂(μ-PNP)₂(PNP)₂ (BPh₄)2 {PNP = CH₃N[P(OCH₃)₂)₂, Ph = phenyl} with isosurfaces of 0.25 e Å⁻³. (a) Observed hkls only; (b) all hkls with maximal experimental resolution of 0.5317 Å⁻¹, showing also shifts of the lighter P atoms. [Reproduced from Makal et al. (2011 ▶); Fournier & Coppens (2014a ▶).]

Figure 9

Schematic of options in data collection, relative scaling and refinement.