Reactivity of CHI₃ with OH Radicals: X-Abstraction Reaction Pathways (X = H, I), Atmospheric Chemistry, and Nuclear Safety

Abstract

The X-abstraction (X = H, I) pathways in the reaction of CHI3 with OH radical, a possible iodoform removal process relevant to the Earth's atmosphere and conditions prevailing in the case of a nuclear accident, have been studied applying highly correlated ab initio quantum chemistry methods and canonical transition-state theory to obtain reaction energy profiles and rate constants. Geometry optimizations of reactants, products, molecular complexes, and transition states determined at the MP2/cc-pVTZ level of theory have been followed by DK-CCSD(T)/ANO-RCC single-point energy calculations. Further improvement of electronic energies has been achieved by applying spin-orbit coupling, corrections toward full configuration interaction, vibration contributions, and tunneling corrections. Calculated reaction enthalpies at 0 K are -108.2 and -5.1 kJ mol(-1) for the H- and I-abstraction pathways, respectively; the strongly exothermic H-abstraction pathway is energetically favored over the modestly exothermic I-abstraction one. The overall rate constant at 298 K based on our ab initio calculations is 4.90 × 10(-11) cm(3) molecule(-1) s(-1), with the I-abstraction pathway being the major channel over the temperature range of 250-2000 K. The CHI3 atmospheric lifetime with respect to the removal reaction with OH radical is predicted to be about 6 h, very short compared to that of other halomethanes.

Atmospheric chemistry of alkyl iodides: theoretical studies on the mechanisms and kinetics of CH3I/C2H5I + NO3reactions

“…Similar theoretical results can be also found in the reaction of C 2 H 5 I with a Cl atom 45 and for other alkyl iodides reactions with O( 3 P) and OH radicals. 19,47,48 Fig. 4a and b show the temperature dependence of the branching ratios for the reactions of CH 3 I and C 2 H 5 I with a NO 3 radical, respectively.…”

Limonene: A scented and versatile tropospheric free radical deactivator

“…• OBr has been detected at marine surfaces worldwide [61]. In addition, the chemistry of halogen-containing species is regarded as highly influential in the atmosphere [62][63][64][65][66][67].…”