Examining the Structure of Supercritical CO2 using X-ray Raman Spectroscopy and Atomistic Scale Modeling

Abstract:

Supercritical carbon dioxide is important in many different areas of applications, ranging from carbon capture and sequestration (CCS) to planetary environments. In this work, X-ray Raman Spectroscopy (XRS) is used to examine the structural changes of supercritical CO₂ during phase-transition. We combine XRS measurements, molecular dynamics simulations, and first principles density functional theory (DFT) calculations to characterize the local electronic structure of CO₂ in regions surrounding the critical point and crossing the Widom line. We observe clear differences in spectral fingerprint the oxygen K-edge spectra of liquid CO₂, which is supported by DFT-based calculations. These experimental measurements are complemented by molecular-dynamics simulations to explain the observations and examine the molecular structure during the phase-transition.