Theoretical treatment of IO-X (X = N₂, CO, CO₂, H₂O) complexes

Iodine monoxide (IO) is an important component of the biogeochemical cycle of iodine. For instance, it is present in the troposphere, where it plays a crucial role in the physical chemical processes involving iodine containing compounds. Here, we present a theoretical study on a series of atmospherically relevant complexes of IO with N₂, CO, CO₂ and H₂O, where their structural and spectroscopic properties and their interaction energies are computed. Calculations are carried out by means of ab initio post Hartree-Fock (RCCSD(T) and RMP2) methods and density functional theory DFT (PBE0 and M05-2X) based approaches with and without the inclusion of dispersion correction. After comparison to RCCSD(T), we highlight the good performance of M05-2X(+D3) DFT in describing the bonding between IO and X (X = N₂, CO, CO₂, H₂O). Moreover, we found that the IO-X (X = N₂, CO, CO₂, H₂O) complexes are formed by non-covalent interactions between the two monomers. In sum, we characterized two types of complexes: I-bonded and O-bonded, where the former is more stable. The atmospheric implications of the present findings are also discussed such as in the formation of the iodine oxide particles (IOPs).