A new reference for changes in X-ray scattering from water due to temperature changes at ambient conditions

The X-ray solution scattering from water S(Q)_H2O depends on temperature and density, a phenomenon that is utilized in, for example, temperature-resolved and ultrafast time-resolved X-ray solution scattering experiments. Whether this contribution to the acquired data arising from changes in scattering from water is merely a background signal to be subtracted or the primary subject of investigation, reference measurements of the differential changes ∂S(Q)/∂T|_ρ are essential. This work presents a newly measured reference dataset for the temperature differential scattering signal of water, acquired at the DanMAX beamline of the MAX IV synchrotron. We compare the new data set to previously archived reference signals and find that analysis based on the older reference may overestimate temperature changes in water by 30-40%. We further demonstrate how the difference scattering signal can be considered linear with temperature up to about a 10 K temperature increase. For larger temperature changes, a second-order contribution d²S(Q)/dT² should be taken into account. The new reference datasets and the analysis code are made publicly available for community use.