Reaction Mechanisms of IO Radical Formation from the Reaction of CH3I with Cl Atom in the Presence of O2

The yields of IO radical from the reaction of CH3I with Cl atom in the presence of O-2 were determined as functions of total pressure from 5 to 250 Torr of N-2 diluent and temperature over the range of 278 to 328 K using cavity ring-down spectroscopy. The yields are pressure and temperature dependent. The rate constants and product branching ratios of the reaction of CH2I radical with O-2 were investigated. We determined a rate constant of (1.28 +/- 0.22) x 10(-12) cm(3) molecule(-1) s(-1) at 298 K (2 sigma uncertainty) for this reaction. Theoretical calculations were performed to determine energetics of the reactions of CH2I + O-2, and CH2Br + O-2. The present results suggest that non-negliggible IO radicals will be formed from the reactions of CH3I/CH2I2 + OH/Cl/NO3 at atmospheric conditions.