Induced Migration of CO₂ 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 CO₂ 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 CO₂ and H₂O ice, CO₂@H₂O, to 90 K resulted in the partitioning of CO₂ in 5¹² and 5¹²6² CH cages (CO₂@5¹², CO₂@5¹²6²). However, upon preparing a composite ice film composed of CO₂@5¹², CO₂@5¹²6² and THF distributed in the water matrix at 90 K, and annealing the mixture for 6 h at 130 K produced mixed CO₂-THF CH, where THF occupied the 5¹²6⁴ cages (THF@5¹²6⁴) exclusively while CO₂ in 5¹²6² cages (CO₂@5¹²6²) got transferred to the ASW matrix and CO₂ in the 5¹² cages (CO₂@5¹²) remained as is. This cage-matrix exchange may create a more conducive environment for chemical transformations in interstellar environments.