title: 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.
authors.affiliation: Department of Physical and Theoretical Chemistry, Faculty of Natural Sciences, Comenius University , Mlynská dolina CH1, 84215 Bratislava, Slovakia.
authors.forename: Mária
authors.initials: M
authors.lastname: Sudolská
authors.forename: Florent
authors.initials: F
authors.lastname: Louis
authors.forename: Ivan
authors.initials: I
authors.lastname: Cernušák