The overall rate constant and an upper limit for the CH 3 ONO 2 product channel for the CH 3 O 2 + 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 cm 3 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: (9.2 -3.9+6.0 × 10 -13 ) exp[(600 ( 140)/T] cm 3 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 CH 3 -ONO 2 product was detected from the CH 3 O 2 + NO reaction (using direct CH 3 ONO 2 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.

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