Induced Migration of CO2 from Hydrate Cages to Amorphous Solid Water under Ultrahigh Vacuum and Cryogenic Conditions.

Abstract

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.