Measuring the dispersion effect on the atomic scattering factor from X-ray diffraction data
What is it about?
The electronic states of atoms in a molecule are decisive for the coordination into specific crystalline structures. However, most of the commonly available analytical techniques cannot probe exactly both structural and spectroscopic properties simultaneously. As a result, a combination of analytical tools is required for the comprehensive characterization of compound of interest. Additionally, this limitation hinders the analysis of complex mixed-valence compounds, in which the weighted-average charge distribution may not reflect correctly the local chemical state of an atom associated with a specific atomic site of the structure. A solution is offered through the application of anomalous diffraction, from which the dispersion effect on the atomic scattering factor of the resonant atom can be measured. The dispersion effect correlates to the chemical state of the resonant atom, and hence, this technique allows to probe structural and spectroscopic properties using a single analytical technique.
Why is it important?
The measurement or refinement of the X-ray dispersion effect is quite challenging, with respect to data handling and interpretation. We have developed two new routines to handle anomalous diffraction datasets, and to refine the X-ray dispersion effect of the resonant atom in a straight-forward way. This approach may open new possibilities for the assessment of other, more complicated, materials such as mixed-valence compounds. Additionally, the methodology can offer a significant resource optimization because each data set contains both structural (diffraction) and chemical (spectroscopy) information, which can avoid the requirement to use multiple experimental stations at synchrotron sources.