Mechanisms of Reactions between HOI and HY (Y = Cl, Br, I) on a Water Nanodroplet Surface

Iodine chemistry has a broad range of implications for atmospheric processes including new particle formation. Hypoiodous acid (HOI) is a major iodine reservoir species. Its heterogeneous recycling in marine aerosols influences the lifetime of ozone in the troposphere. One important step of such recycling is the reaction between HOI and HY (Y = Cl, Br, I). In this article, we employ ab initio molecular dynamics (AIMD) and quantum chemistry to investigate these reactions at the surface of atmospheric aerosols. Di-halogen (XY) can be formed in a picosecond time scale, with the formation of a loop structure connected by hydrogen and halogen bonds. The photolysis of XY at the surface of an aerosol is faster than in the gas phase. In addition to the formation of di-halogen, a new pathway to forming a [H₂O···I···OH₂]⁺ complex by the direct or indirect proton transition is identified. Results presented in this study deepen our understanding of the faster iodine-heterogeneous recycling at the surface of aerosols.