Isomers of IO 2 , I 2 O, and I 2 O 2 have been characterized by ab initio methods. Vibrational frequencies and geometries were obtained at the MP2/6-31G(d) and MP2/6-311+G(3df) levels of theory, respectively. The thermochemistry was derived using approximate QCISD(T)/6-311+G(3df) (Gaussian-2) energies coupled with isodesmic reactions. Computed values of ∆ f H 298 for these molecules are the following (in kJ mol

The kinetics of the reaction of hydroxyl radicals with trifluoroiodomethane were investigated by the flash photolysis-resonance fluorescence technique. A rate constant of k ) 5.8 × 10 -12 exp((-11.3 kJ mol -1 )/RT) cm 3 molecule -1 s -1 was measured over the temperature range 280-450 K with accuracy limits of 20% (450 K) to 30% (280 K). Different product channels were investigated by ab initio methods, and the dominant products are CF 3 + HOI. The enthalpy of formation of hypoiodous acid was analyzed with Gaussian-2 theory, in conjunction with G2 energies for INO, ICN, ClCN, and other species. The transition state and reaction coordinate for OH + CF 3 I was characterized at the G2(MP2) level, and the results suggest a negligible barrier to the reverse reaction of CF 3 + HOI, so that the measured forward activation energy can be used to derive ∆ f H 298 (HOI) ) -69.6 ( 5.4 kJ mol -1 . The implications of the kinetics and thermochemistry for iodine chemistry in flames and the atmosphere are discussed, and for the range 280-2000 K a proposed rate expression is k ) 2.9 × 10 -16 (T/K) 1.5 exp(-(960 K)/T) cm 3 molecule -1 s -1 .

No abstract