Infrared matrix-isolation and theoretical studies of interactions between CH3I and water

Photochemistry of CH3I···(H2O)n Complexes: From CH3I···H2O to CH3I in Interaction with Water Ices and Atmospheric Implications

“…We can then easily transpose this reasoning to iodomethane in its interaction with ice. We remind here that excepted CH 3 I···OH 2 , (i.e., 1wb heterodimer presented in Figure ), all the other species identified in argon matrix are H-bonded. Contrary to what we observed for namely pyridine-water dimers trapped in cryogenic matrices, in which water is a “spectator” partner, here, water is the key of CH 3 I electronic relaxation.…”

“…Indeed, intensity of an absorption band cannot be easily linked to the quantity of molecules trapped, while it is directly linked to the derivative of molecular dipole moment with respect to normal coordinates, thus, to geometry. In the present case, it is accompanied by low intensities (as calculated in the case of the bare iodomethane molecule) for the molecules trapped on dH site and, on the other hand, by an increase in these signals for those on dO and s4 sites (see Figure ). In other words, molecules trapped on the dH site obviously show ν CH /δ CH signatures, but with intensities so low that no trace of desorption can be detected by heating to 70 K.…”

“…) n complexes and aggregates trapped in argon cryogenic matrices, we observed some mixed aggregates and complexes, but the main phenomenon was the homoaggregation of CH 3 I making the association with water less favorable. 34,35 Earth's atmosphere also contains water ice, which is able to trap at its surface (ASW, I c and I h ) but also in pores (ASW), 28 a significant quantity of iodomethane. Indeed, in the case of adsorption of small molecules on amorphous ice, including methane, Roubin and co-workers 29 gave a specific area of ≈100 m 2 g −1 while Loerting and co-workers, 36 gave a specific area comprised between <0.1 to 280 m 2 g −1 .…”

“…Can these observations be linked to the geometry of the “local complexes” created by trapping at the dH, dO, and s4 sites? And, can we, as a first rough approximation, compare them with the geometries of the CH 3 I⋯H 2 O complexes calculated in our previous work? If we look at the two forms 1wa and 1wb presented in Figure , the former seems to be more suitable for trapping at dH sites, while the latter seems to be more suitable for trapping at dO and s4 sites. We can then assume that the transfer of photon energy is more efficient through hydrogen bonds than through picnogen bonds (i.e., I⋯O).…”

“…Figure 7. Two most stable heterodimers CH 3 I•••H 2 O calculated at the ωB97X-D/aug-cc-pVTZ(O,C) and aug-cc-pVTZ-PP(I) level of theory together with illustration of the four dangling modes of ASW 35. …”