A KINETIC AND MECHANISTIC STUDY OF THE REACTION OF NEOPENTYLPEROXY RADICALS WITH HO2

The kinetics and mechanism of the reaction between neopentylperoxy radicals and hydroperoxy radicals: neo-C5H11O2 + HO2 --> neo-C5H11OOH + O2 (1), have been studied between 248 and 365 K, using the flash photolysis/time-resolved UV absorption and the blacklamp photolysis/FTIR product analysis techniques. The rate constant for reaction 1, k1, is significantly larger than that for smaller primary alkylperoxy radicals, with k1/cm3 molecule-1 s-1 = (1.43 +/- 0.46) X 10(-13) exp((1380 +/- 100) K/T), giving k1/cm3 molecule-1 s-1 = (1.5 +/- 0.4) x 10(-11) at 298 K. Consideration of possible random and systematic errors results in absolute uncertainties of 25% in k1 over the experimental temperature range. Product analysis studies at 296 +/- 2 K show that the yield of hydroperoxide from reaction 1 is (92 +/- 2)%; possible systematic errors may add an additional 15% uncertainty. It is concluded that the rate constant for the generic reaction RO2 + HO2 Used in the modeling of non-methane hydrocarbon atmospheric chemistry should be increased. The rate constant for the reaction of chlorine atoms with neopentane, Cl + neo-C5H12 --> HCl + neo-C5H11 (3), was also measured relative to that for the reaction of chlorine atoms with methanol, Cl + CH3OH --> HCl + CH2OH (5). Within experimental error, k3 is independent of temperature over the range 248-366 K, with k3/cm3 molecule-1 s-1 = (1.16 +/- 0.05) x 10(-10), using k5/cm3 molecule-1 s-1 = 5.7 X 10(-11). The error in k3 does not include uncertainties in k5. Errors are 1-sigma.