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-H,O-CO and of CO-H,O 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),(H,O), complexes. For the production of mixed species, higher deposition temperatures are more effective than temperature cycling. Formation is due more to H,O than to CO surface migration. Conclusions were applied to a previous study of porous ices produced by temperature cycling of noble gas-H,O solid mixtures onto which CO was deposited as a probe. They confirm that porous ices from Ar-H,O 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-H,O 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.

FTIR Studies of Annealing Processes in Low Temperature Pure and Mixed Amorphous Ice Samples

“…The pure ice sample deposited on a bare CsI window ( Figure 1A) did not reveal these bands above noise level at all. 27 The 3623 cm -1 band detected in the 1:10 CO in H 2 O sample ( Figure 1F) has previously been discussed in terms of CO‚H 2 O species 27,34 and, again, is not evidence for the existence of dangling or free OH bonds in these samples.…”

“…Increasing H 2 O ratio four times, reveals a very weak band at 3520 cm -1 , close to the frequency attributed 34,55 to (H 2 O) 3 cyclic trimer ( Figure 11B). At higher deposition temperatures (10 and 15 K), this band gains intensity and gets broader (∆ν 1/2 ) 20 cm -1 ), and in a 20 K deposition it broadens further (50 cm -1 ) and three additional broad bands appear: a strong doublet at 3380, 3320 cm -1 ((∆ν 1/2 about 100 cm -1 ), and a very weak line at 3230 cm -1 ( Figure 11C), with no monomer bands being observed.…”

“…In a 400:1 argon/H 2 O depostion at 5 K ( Figure 11A), monomeric and dimeric bands were recorded, the lowest frequency in the OH stretch region being at 3574 cm -1 , a dimeric 34,53,54 feature. Increasing H 2 O ratio four times, reveals a very weak band at 3520 cm -1 , close to the frequency attributed 34,55 to (H 2 O) 3 cyclic trimer ( Figure 11B).…”

“…The lowest bandwidth (318 cm -1 ) is that of the ice formed from a 1:10 CO/H 2 O mixture ice. In this sample with only a few percent of CO in the ice lattice, H 2 O condenses around small CO clusters (27,34) which fulfill the role of nucleation grains.…”

An FTIR study on the catalytic effect of water molecules on the reaction of CO successive hydrogenation at 3K

“…Some previous theoretical and experimental works focused on the study of the H 2 O-CO complex, [18][19][20][21][22][23][24][25][26][27] and on the interaction of CO with water ice [28]. The formation of H 2 -H 2 O clusters [29][30][31][32] has also been studied, as well as radical-molecule interactions between H and H 2 O [33].…”