Direct kinetics study of the temperature dependence of the CH2O branching channel for the CH3O2+HO2 reaction

A direct kinetics study of the temperature dependence of the CH2O branching channel for the CH3O2 + HO2 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 CH2O-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) X 10(15) X exp[(1730 +/- 130)/T] cm(3) molecule(-1) s(-1). Using the Arrhenius expression for the overall rate of the CH3O2 + HO2 reaction and this result, the 298 K branching ratio for the CH2O 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 CH3O2 + CH3O2 reaction and the potential atmospheric ramifications of significant CH2O production from the CH3O2 + HO2 reaction are discussed. (C) 2001 John Wiley & Sons. Inc.