Abstract
Supercritical fluids are characterized by unique thermodynamic properties. One of these properties is the existence of two-component dynamics that is associated with distinct low-frequency and high-frequency vibrational responses of the fluid. However, the origin of this behavior remains unknown. By combining inelastic X-ray scattering and molecular dynamics simulations, we show that this behavior can be connected to density heterogeneities arising from molecular clusters. Analyses of measurements and molecular trajectories suggest that the two-component dynamics emerges due to distinct momentum fluctuations of clustered and unbound molecules. This connection between clusters and two-component dynamics highlights the importance of molecular-structural heterogeneities in supercritical fluids, colloids, and condensed-matter systems.
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Data availability
The data supporting the findings of the study are included in the main text and supplementary information files. Source data have been deposited in the Supplementary Material and Stanford Digital Repository52: https://doi.org/10.25740/sj299gg3375. Additional data are available from the corresponding authors upon request.
Code availability
The MD simulations were performed with the open-source software LAMMPS (release date 8 April, 2021). Code for the analysis of the experimental data is available from the corresponding author upon request.
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Funding
Financial support from the U.S. Department of Energy, Office of Science under DOE (BES) Awards DE-SC0022222 and DE-SC0026165 (A.M. and M.I.) is gratefully acknowledged.
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A.M.: Data curation, Formal analysis, Investigation, Methodology, Software, Visualization, Writing original draft, Writing - review & editing; P.S.: Data curation, Formal analysis, Investigation, Methodology, Writing - review & editing; M.S.: Data curation, Formal analysis, Investigation, Methodology, Software, Writing - review & editing; L.P.: Investigation, Methodology, Resources, Writing - review & editing; A.B.: Investigation, Methodology, Resources, Writing - review & editing; A.Q.R.B.: Formal analysis, Investigation, Methodology, Software, Writing - review & editing; J.H.: Investigation, Methodology, Resources, Project administration, Supervision, Writing - review & editing; M.I.: Conceptualization, Investigation, Methodology, Resources, Funding acquisition, Project administration, Supervision, Writing - review & editing
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Majumdar, A., Sun, P., Singleton, M. et al. Two-component dynamics in supercritical \(\text {CO}_2\) from inelastic X-ray scattering. Sci Rep (2026). https://doi.org/10.1038/s41598-026-38697-z
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DOI: https://doi.org/10.1038/s41598-026-38697-z
