FORMATION OF O(3P) ATOMS AND EPOXIDES FROM THE GAS-PHASE REACTION OF O3 WITH ISOPRENE

The formation yields of 1,2-epoxy-2-methyl-3-butene and 1,2-epoxy-3-methyl-3-butene have been measured from the reaction of O3 with isoprene at room temperature and one atmosphere total pressure of N2 and air diluents, with and without cyclohexane to scavenge the OH radicals formed in this reaction system. In addition, a relative rate method was used to determine a rate constant for the gas-phase reaction of O3 with 1,2-epoxy-2-methyl-3-butene of (2.5 +/- 0.7) x 10(-18) cm3 molecules-1 s-1 at 296 +/- 2 K. Our data show that the epoxide yields in N2 and air diluents are the same, with formation yields of 1,2-epoxy-2-methyl-3-butene of 0.028 +/- 0.007 and of 1,2-epoxy-3-methyl-3-butene of 0.011 +/- 0.004. These data further show that the epoxides arise from the primary O3 reaction with isoprene, and not via the formation of O(3P) atoms from the O3 - isoprene reaction followed by reaction of these O(3P) atoms with isoprene.