Kinetics of the CH₃O₂ + NO Reaction:  Temperature Dependence of the Overall Rate Constant and an Improved Upper Limit for the CH₃ONO₂ Branching Channel

The overall rate constant and an upper limit for the CH3ONO2 product channel for the CH3O2 + NO reaction have been measured using the turbulent flow technique with high-pressure chemical ionization mass spectrometry for the detection of reactants and products. At room temperature and 100 Torr pressure, the rate constant (and the two standard deviation error limit) was determined to be (7.8 ± 2.2) × 10-12 cm3 molecule-1 s-1. The temperature dependence of the rate constant was investigated between 295 and 203 K at pressures of either 100 or 200 Torr, and the data was fit to the following Arrhenius expression: ( × 10-13) exp[(600 ± 140)/T] cm3 molecule-1 s-1. Although the room-temperature rate constant value agrees well with the current recommendation for atmospheric modeling, our values for the rate constant at the lowest temperatures accessed in this study (203 K) are about 50% higher than the same recommendation. No CH3ONO2 product was detected from the CH3O2 + NO reaction (using direct CH3ONO2 detection methods for the first time), but an improved upper limit of 0.03 (at 295 K and 100 torr) for this branching channel was determined.