The effect of methanol on the self reaction of HO₂ radicals

The rate constant for the HO 2 self reaction has been determined as a function of methanol vapor concentration at 278 K and 299 K. A molecular modulation technique was used in which HO 2 radicals were photochemically produced in flowing gas mixtures comprised of Cl 2 , CH 3 OH, N 2 and O 2 with HO 2 monitored in the UV at 220 nm. A positive linear dependence of the second order rate constant on methanol concentration was found and this effect increased with decreasing temperature. The rate constant for the HO 2 self reaction can be described by in nitrogen at atmospheric pressure and in the methanol concentration range 1 · 10 16 to 3 · 10 17 molecules cm −3 .