Kinetics of the Reaction of CH₃O₂ Radicals with OH Studied over the 292–526 K Temperature Range

Reaction of methyl peroxy radicals with hydroxyl radicals, CH₃O₂ + OH → CH₃O + HO₂ (1a) and CH₃O₂ + OH → CH₂OO + H₂O (1b) was studied using pulsed laser photolysis coupled to transient UV–vis absorption spectroscopy over the 292–526 K temperature range and pressure 1 bar (bath gas He). Hydroxyl radicals were generated in the reaction of electronically excited oxygen atoms O­(¹D), produced in the photolysis of N₂O at 193.3 nm, with H₂O. Methyl peroxy radicals were generated in the reaction of methyl radicals, CH₃, produced in the photolysis of acetone at 193.3 nm, and subsequent reaction of CH₃ with O₂. Temporal profiles of OH were monitored via transient absorption of light from a DC discharge H₂O/Ar low-pressure resonance lamp at ca. 308 nm. The absolute intensity of the photolysis light was determined by accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The overall rate constant of the reaction is <i>k</i>_1a+1b = (8.4 ± 1.7) × 10^–11(<i>T</i>/298 K)^−0.81 cm³ molecule^–1 s^–1 (292–526 K). The branching ratio of channel 1b at 298 K is less than 5%