Atmospheric reactivity of CH3I and CH2I2 with OH radicals: A comparative study of the H- versus I-abstraction

Reactants, weak molecular complexes, transition states, and products for the H- and I-abstraction channels in the reactions OH + CH3I and OH + CH2I2 as well as the energy profiles at 0 and 298 K have been determined using high-level all-electron ab initio methods. The results showed that all-electron DK-CCSD(T)/ANO-RCC approach performed very well in predicting the reactivity of iodine. The energy profiles for the I-abstraction, in contrast to the H-abstractions, had the position of the transition states below the products. The H-abstractions were strongly exothermic (−80 to −90 kJ mol−1), while the I-abstractions were modestly endothermic (20-40 kJ mol−1). Based on our calculations with the ANO-RCC-L(I) basis set, we recommend the following values for the heats of formation at 298 K (in kJ mol−1): 218.6 (CH2I), 106.0 (CH2I2), and 298.3 (CHI2).