Pressure-induced Chemistry of Fluid D₂-CO₂ Mixtures

Constraining the high-pressure chemical behavior of the H₂-CO₂ system extends the understanding of Fischer-Tropsch chemistry and elucidates the geochemical behavior of planets like the early Earth.  We investigated the high-pressure D₂-CO₂ system using the diamond anvil cell in conjunction with vibrational spectroscopy to characterize the phase and chemical changes that occur under static compression. We observe the 9:1 D₂:CO₂ mixture undergoes a multi-stage reduction to form a final equilibrium product of D₂O + CD₃OD, with spectroscopic data demonstrating this product assemblage's stability up to 10 GPa. Our experimental high-pressure chemistry results are compared with thermochemical calculations using first-principles simulations and literature values of candidate reaction pathways. These results provide experimental benchmarks for ongoing dynamic compression experiments, enabling the prediction of intermediate system assemblages, and constraining the final states relevant to planetary interior conditions.