The reaction mechanisms of Br and I atoms with HO have been investigated using DFT and high-level ab initio calculations. The H-abstraction and OH-abstraction channels were highlighted. The geometries of the stationary points were optimized at the B3LYP/aug-cc-pVTZ level of theory, and the energetics were recalculated with the coupled cluster theory. Spin-orbit coupling for each halogenated species was also explicitly computed by employing the MRCI level of theory. Thermochemistry for HOBr and HOI has been revised and updated standard enthalpies of formation at 298 K for HOBr and HOI are the following: ΔH°(HOBr) = (-66.2 ± 4.6) kJ mol and ΔH°(HOI) = (-66.8 ± 4.7) kJ mol. The rate constants have been estimated using transition state theory (TST), canonical variational transition state theory (CVT), and CVT with small curvature tunneling (CVT/SCT) over a wide temperature range (250-2500 K). For the direct abstraction mechanism, the overall rate constant at 300 K was predicted to be 2.58 × 10 and 7.42 × 10 cm molecules for the Br + HO and I + HO reactions, respectively. The modified Arrhenius parameters have been estimated for the overall reactions: k(T) = 4.80 × 10 T exp(-5.51 (kJ mol)/RT) and k(T) = 3.41 × 10 T exp(-56.32 (kJ mol)/RT).

This work reports for the first time the structures and the thermodynamics of the microhydrates of iodine nitrogen oxides (INO x ). Monohydrates and dihydrates were investigated for five different INO x species (INO, INO 2 , cis-IONO, trans-IONO, and IONO 2 ). The structures of the water complexes were characterized at the ωB97XD/aug-cc-pVTZ level of theory. Coupled-cluster calculations were performed with the ANO-RCC-VQZP basis sets. Standard reaction enthalpy and standard Gibbs free reaction energy (Δ r G 298 K ) were computed for all aggregates. The variation of Δ r G[T] as a function of temperature reveals that only IONO 2 will be hydrated at tropospheric temperatures (T < 270 K). Its dihydration reaction remains a favored process in the same conditions. All INO x species will not be hydrated in gas phase in the containment building of a pressurized water reactor for which temperatures are greater than 400 K.