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Figure 1
Anomalous dispersion curve for ytterbium and representative XFEL pulse spectra. Shown by the solid gray line is the measured ytterbium 3+ anomalous correction term [imaginary component; Shapiro et al. (1995BB146)]. This curve was used in the data synthesis to compute the anomalous protein structure factors. For each synthesized diffraction pattern, we used a unique XFEL pulse, with the mean energy spectrum given by the dashed orange line. The spectrum of each XFEL pulse was randomly selected from a set of 100 000 real SASE spectra that were measured at the Linac Coherence Light Source (LCLS) and shifted to a high-energy remote for ytterbium L-III absorption (9034 eV). A single SASE spectrum is also shown for reference, illustrating the energy variation and intensity variation observed on a per-shot basis at the XFEL. At this energy the anomalous scattering is essentially constant within the range of the SASE energy variation. If the experiment had been done with the XFEL tuned to the absorption edge (8944 eV), then each diffraction pattern would have a varying level of anomalous scattering as per the f′′ curve.

IUCrJ
Volume 7| Part 6| November 2020| Pages 1151-1167
ISSN: 2052-2525
https://doi.org/10.1107/S2052252520013007