Partitioning photochemically formed CO2 into clathrate hydrate under interstellar conditions

Abstract

Clathrate hydrates (CHs), host–guest compounds of water forming hydrogen-bonded cages around guest molecules, are now known to exist under interstellar conditions. Experimental evidence demonstrated that prolonged thermal treatment of a solid mixture of water and CO₂/CH₄ produces CHs at 10–30 K under simulated interstellar conditions. However, in the current study, we show that CO₂ produced photochemically by vacuum ultraviolet irradiation of H₂O–CO mixtures at 10 K and ∼10⁻¹⁰ mbar, gets partitioned into its CH phase and a matrix phase embedded in amorphous ice. The process occurring under simulated interstellar conditions was studied at different temperatures and H₂O–CO compositions. The formation of CO₂ CH and other photoproducts was confirmed using reflection absorption infrared spectroscopy. The UV-induced photodesorption event of CO₂ may provide the mobility required for the formation of CHs, while photoproducts like methanol can stabilize such CH structures. Our study suggests that new species originating during such energetic processing in ice matrices may form CH, potentially altering the chemical composition of astrophysical environments.