Data Analysis
In most of the time-resolved X-ray diffraction experiments, the direct output from the measurements are 2-dimensional images containing little or no direct information regarding the phenomena investigated. These 2-dimensional images need significant further processing before the information about the system dynamics can be extracted and the development of software for this has been of significant importance for a number of projects.
In the case of the thin-film investigations, notably the perylene experiments, the analysis&simulation package developed by the former group member Dag Breiby and colleagues (D. Breiby, 2008) has been extensively utilized and new programs designed to allow data analysis of time-resolved experiments almost as soon as the data are downloaded from the detector. The position and intensity of individual peaks can be monitored to allow rough online structure refinement and simulation, which is an invaluable help during the course of experiments.
The measurements on structures of transient chemical species in solution face another set of challenges as e.g. the inherent signal amplification from long-range order in crystals is absent. Additionally, as there is rotational freedom for the molecules at the time scales investigated, the molecular form factors are rotationally averaged and the scattering from all the chemical species present are superimposed. This effectively means that the change in scattering due to structural changes is very small, typically less than a thousandth of the signal itself, so careful scaling and averaging of many exposures is a first step in the analysis. Subsequently, a large contribution from the thermodynamic response of the solvent needs to be accounted for, before the structure-related change in scattering intensity is isolated and can be analysed.
