Analysis of multicrystal pump–probe data sets. I. Expressions for the RATIO model

Abstract

The RATIO method in time-resolved crystallography [Coppens et al. (2009). J. Synchrotron Rad. 16, 226-230] was developed for use with Laue pump-probe diffraction data to avoid complex corrections due to wavelength dependence of the intensities. The application of the RATIO method in processing/analysis prior to structure refinement requires an appropriate ratio model for modeling the light response. The assessment of the accuracy of pump-probe time-resolved structure refinements based on the observed ratios was discussed in a previous paper. In the current paper, a detailed ratio model is discussed, taking into account both geometric and thermal light-induced changes.

Shedding Light on the Photochemistry of Coinage-Metal Phosphorescent Materials: A Time-Resolved Laue Diffraction Study of an AgI–CuI Tetranuclear Complex

“…56 Recent advances in application of the pink-Laue time-resolved (TR) synchrotron technique, 57–60 using modified data collection 61 and data processing procedures, 62–64 have speeded the application of the method, which is, by its nature, limited by the ≈100 ps temporal resolution of synchrotron sources. However, this resolution suffices for the study of phosphorescence and many fluorescence processes.…”

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

“…Similar expressions have been derived for the thermal model based on the temperature scale factor k B (Fournier & Coppens, 2014b). Summarizing, the observations in this weighted leastsquares refinement are the ratios collected from each block, with as variables the model ðHÞ for each unique reflection H, the relative excited state population parameters Q i and the temperature increase variables ÁB i Q or k i B for each of the data sets.…”

“…L model H ð Þ is the structural change for 100% conversion, expressions for which have been reported earlier (Fournier & Coppens, 2014b). They depend on the distribution of the excited-state species, for which two models have been defined, corresponding to a random distribution (RD model) or formation of clusters of excited-state molecules (CF model) .…”

“…Summarizing, the observations in this weighted leastsquares refinement are the ratios collected from each block, with as variables the model ðHÞ for each unique reflection H, the relative excited state population parameters Q i and the temperature increase variables ÁB i Q or k i B for each of the data sets. In the case where the laser-ON and laser-OFF frames have not been collected in sequence but in separate runs, in addition the ratio of the scale factors of the laser-ON and laser-OFF sets have to be included as variables (Fournier & Coppens, 2014b).…”

On the scaling of multicrystal data sets collected at high-intensity X-ray and electron sources

“…The weighted least-squares method as applied to the η values (Fournier and Coppens, 2014a), defined in expression (1), follows a procedure described by Hamilton in 1965 (Hamilton et al , 1965) for the layer scaling of Weissenberg photographs and further developed by Fox and Holmes (Fox and Holmes, 1966). …”