FTIR studies of CO–water complexes in argon matrices and in porous ices

Abstract

Solid layers produced by the deposition at cryogenic temperatures of Ar–H₂O–CO and of CO–H₂O mixtures have been investigated by FTIR spectroscopy. Effects of variations in concentration ratios, in deposition temperature and of temperature cycling were studied. It is possible to assign all observed bands to single-component and to mixed (CO)_m(H₂O)_n complexes. For the production of mixed species, higher deposition temperatures are more effective than temperature cycling. Formation is due more to H₂O than to CO surface migration. Conclusions were applied to a previous study of porous ices produced by temperature cycling of noble gas–H₂O solid mixtures onto which CO was deposited as a probe. They confirm that porous ices from Ar–H₂O mixtures consist of small clusters with ‘surface porosity’ and a large proportion of dangling OH bonds. The CO gets attached to more than a single OH bond. Ice so formed from Ne–H₂O mixtures has ‘bulk porosity’ with scattered free OH bonds. Deposited CO penetrates it and forms small solid-like clusters or bonds to single OH bonds.