Reaction CH ₃ + OH studied over the 294-714 K temperature and 1-100 bar pressure ranges

Reaction of methyl radicals with hydroxyl radicals, CH ₃ + OH → products (1) was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 294-714 K temperature and 1-100 bar pressure ranges (bath gas He). Methyl radicals were produced by photolysis of acetone at 193.3 nm. Hydroxyl radicals were generated in reaction of electronically excited oxygen atoms O( ¹D), produced in the photolysis of N ₂O at 193.3 nm, with H ₂O. Temporal profiles of CH ₃ were recorded via absorption at 216.4 nm using xenon arc lamp and a spectrograph; OH radicals were monitored via transient absorption of light from a dc discharge H ₂O/Ar low pressure resonance lamp at ca. 308 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 results of this study indicate that the rate constant of reaction 1 is pressure independent within the studied pressure and temperature ranges and has slight negative temperature dependence, k ₁ = (1.20 ± 0.20) × 10 ^-10(T/300) ^-0.49 cm ³ molecule ^-1 s ^-1.