Unveiling Oxygen formation from the High-Pressure Reactivity of CO2–H2O solid-solid ice mixtures in laser-heated Diamond Anvil Cell

The fate of carbon dioxide (CO2) at very high pressures (up to Mbar) and temperatures (>5000 K) in the presence of water (H2O) has yet to be fully understand. Despite their wide diffusion in astrochemically relevant contexts, no extended characterisation of their behaviour of these mixtures has been reported so far. While bulk CO2 is well known to form amorphous non-molecular phases that can be converted to crystalline polymeric CO2 phase V at high temperature, it remains unclear how it will behave in solid-solid ice mixtures with water ice. Recent studies perform at the ESRF have provided hints of an intriguing chemical reactivity taking place at 40-50 GPa and resulting in the production of at least solid molecular oxygen. A deep and comprehensive study is therefore needed to better understand this reaction pathway, unveil all its products and investigate its extension to even more drastic pressure and temperature conditions, relevant to deep interiors of icy planets and satellites.