Kinetic studies of the reactions of atomic hydrogen with iodoalkanes

Rate constants for the reaction of H atoms with the alkyl iodides iodomethane (1), deuterated iodomethane (1d), iodoethane (2), 2-iodopropane (3), and 2-iodo-2-methyl propane (4) have been measured using the flash-photolysis resonance fluorescence technique. The results are k(1) (6.3 +/- 0.6) x 10(-11) exp[((-5.0 +/- 0.3) kJ mol(-1))/RT] (T = 297-757 K), k(1d) = (8.0 +/- 1.7) x 10(-11) exp[((-5.3 +/- 0.7) kJ mol(-1))/RT] (T = 296-728 K), k(2) = (1.1 +/- 0.2) x 10(-10) exp[((-5.9 +/- 0.8) kJ mol(-1))/RT] (T = 295-624 K), k(3) = 1.4 x 10(-11) (T = 295 K) and k(4) = 2.0 x 10(-11) (T = 294 K) cm(3) molecule(-1) s(-1). The transition state for the substitution reaction H + CH3I --> I + CH4 was characterized at the Gaussian-2 level of ab initio theory, and the process was shown to be slow. Evidence is presented showing that H-atom abstraction is also slow, and that the dominant pathway for the reactions of H atoms with iodoalkanes is I-atom abstraction.