Induced Migration of CO 2 from Hydrate Cages to Amorphous Solid Water under Ultrahigh Vacuum and Cryogenic Conditions.

Restricted migration of reactive species limits chemical transformations within interstellar and cometary ices. We report the migration of CO ₂ from clathrate hydrate (CH) cages to amorphous solid water (ASW) in the presence of tetrahydrofuran (THF) under ultrahigh vacuum (UHV) and cryogenic conditions. Thermal annealing of sequentially deposited CO ₂ and H ₂ O ice, CO ₂ @H ₂ O, to 90 K resulted in the partitioning of CO ₂ in 5 ¹² and 5 ¹² 6 ² CH cages (CO ₂ @5 ¹² , CO ₂ @5 ¹² 6 ² ). However, upon preparing a composite ice film composed of CO ₂ @5 ¹² , CO ₂ @5 ¹² 6 ² and THF distributed in the water matrix at 90 K, and annealing the mixture for 6 h at 130 K produced mixed CO ₂ -THF CH, where THF occupied the 5 ¹² 6 ⁴ cages (THF@5 ¹² 6 ⁴ ) exclusively while CO ₂ in 5 ¹² 6 ² cages (CO ₂ @5 ¹² 6 ² ) got transferred to the ASW matrix and CO ₂ in the 5 ¹² cages (CO ₂ @5 ¹² ) remained as is. This cage-matrix exchange may create a more conducive environment for chemical transformations in interstellar environments.