Kinetics of the gas phase reaction CH3 + HO2.

Reaction of methyl radicals with hydroperoxy radicals, CH3 + HO2 → products (1) was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy at 295 K and 1 bar (He). Photolysis of N2O/H2O2/CH4/H2O/He mixtures at 193.3 nm (ArF excimer laser) was used to simultaneously produce methyl radicals and hydroperoxy radicals in reactions of electronically excited oxygen atoms O((1)D) with CH4 and OH radicals with H2O2, respectively. Temporal profiles of CH3 and HO2 were recorded via absorption at 216.4 and 224 nm. The absolute intensity of the photolysis light inside the reactor was determined by an accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The measured rate constant of reaction 1 is k1 = (3.7 ± 1.8 × 10(-11) cm(3) molecule(-1) s(-1) (295 K, 1 bar, He).