Direct kinetics study of the temperature dependence of the CH 2 O branching channel for the CH 3 O 2 + HO 2 reaction

A direct kinetics study of the temperature dependence of the CH 2 O branching channel for the CH 3 O 2 + HO 2 reaction has been performed using the turbulent flow technique with high‐pressure chemical ionization mass spectrometry for the detection of reactants and products. The temperature dependence of the CH 2 O‐producing channel rate constant was investigated between 298 and 218 K at a pressure of 100 Torr, and the data were fitted to the following Arrhenius expression: 1.6   −0.7 +1.0× 10 −15 × exp[(1730 ± 130)/ T ] cm 3 molecule −1 s −1 . Using the Arrhenius expression for the overall rate of the CH 3 O 2 + HO 2 reaction and this result, the 298 K branching ratio for the CH 2 O producing channel is measured to be 0.11, and the branching ratio is calculated to increase to a value of 0.31 at 218 K, the lowest temperature accessed in this study. The results are compared to the analogous CH 3 O 2 + CH 3 O 2 reaction and the potential atmospheric ramifications of significant CH 2 O production from the CH 3 O 2 + HO 2 reaction are discussed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 363–376, 2001