Data repository for XPCS of supercritical normal water and heavy water

Collective dynamics, arising from coherent molecular motion under the influence of interatomic interactions, play a central role in governing thermodynamic and transport processes in materials, including heat transfer and sound propagation. In supercritical fluids, these dynamics are strongly influenced by the heterogeneous microstructure that emerges due to formation of molecular clusters. Understanding how such structural heterogeneity affects collective dynamics is essential for explaining transport phenomena in supercritical fluids. However, capturing such dynamics in supercritical fluids is challenging due to their ultrafast evolution time and strong diffusion processes which overshadows collective dynamics. To address these issues and capture collective dynamics in supercritical fluids, we performed split-pulse X-ray Photon Correlation Spectroscopy measurements of supercritical water and heavy water. The damped oscillation in the measured correlation function is a clear evidence of collective dynamics. The distinct response between regular water and heavy water is a result for difference in hydrogen bond strength. We developed a cluster vibration model to demonstrate that the measured collective dynamics is the vibration modes of clusters at different length scales.