Direct measurement of the rate coefficient for the CH2=C(CH3)C(O)O-2+NO reaction using chemical ionization mass spectrometry

In the troposphere, the CH2=C(CH3)C(O)O-2, or peroxymethacryl, radical is formed as an intermediate in the photooxidation of isoprene, one of the most important biogenic hydrocarbons in the atmosphere. The reaction between CH2=C(CH3)C(O)O-2 and NO produces NO2 and subsequently ozone. The rate coefficient for the CH2=C(CH3)C(O)O-2 + NO reaction is measured directly over the temperature range 240-360 K and I pressures of 1.3-3.9 Torr using a flow tube reactor and chemical ionization mass spectrometry detection. The results are given by k(T) = 8.7 x 10(-12) exp(290/T) cm(3) molecule(-1) s(-1), accurate within +/-20% over the 240-360 K range, with a value at 298 K of(2.3 +/- 0.3) x 10(-11) cm(3) molecule(-1) s(-1). These results agree within the experimental uncertainties with the measured results for the analogous CH3(O)O-2 + NO reaction, suggesting that the rate coefficient for RC(O)O-2 + NO reactions may not be sensitive to the structure of the R group. Only NO2 could be positively identified as a reaction product.