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

Abstract

The interaction of methyl iodine with the surface ofamorphous, cubic, and hexagonal ices has been investigated. TheCH3I desorption process has also been evaluated. We havehighlighted the difference in CH3I behavior depending on thetrapping on the ice surface. The broadband UV photochemistry ofCH3I trapped at the surface of ices has been studied. Those resultshave been compared with UV broadband photochemistry of CH3Ibare monomer complexed with water and trapped in argoncryogenic matrices. It appears that if CH3I interacts with watermolecules or water ice by hydrogen bonding, then CH3I does notfragment under UV irradiation. Thus, energy transfer to thenetwork of hydrogen bonds in the ice or matrix is effective. On theother hand, to a first approximation, if CH3I interacts by picnogen-type bonding (I···O), then CH3I fragments, because theelectronic relaxation seems to take place mainly at the intramolecular levels of CH3I. Finally, we demonstrated that water ice doesnot catalyze the photofragmentation of CH3I. Rather, it modifies the electronic relaxation paths, some of which lead to thefragmentation of iodomethane. This fundamental work provides an understanding of the molecular processes involved in water/ice−CH3I interaction and the role of these molecular interactions on CH3I photochemistry in the atmosphere.