REACTION OF THE ETHYL RADICAL WITH OXYGEN AT MILLITORR PRESSURES AT 243-368-K AND A STUDY OF THE CL+HO2, ETHYL+HO2, AND HO2+HO2 REACTIONS

Ethyl radicals formed in the reaction of C2H6 + Cl are allowed to react with molecular oxygen in a very low pressure reactor (VLPR) experimental flow system over the temperature range of 243-368 K. Mass spectrometric analysis of reactants and products made possible the determination of rate constants (cm3/(molecules)) of all major reaction steps. Mass balances for C, H, and Cl are good to +/-4% on average. The elementary steps are the following: C2H5 + O2 --> HO2 + C2H4, k6 = (1.42 +/- 0.38) x 10(-17) exp[(5064 +/- 154)/RT], measured independently from recording C2H5 consumption or C2H4 formation rates; 2HO2 --> H2O2, k7 = (4.50 +/- 0.56) x 10(-13) exp[(1064 +/- 77)/RT]; C2H5 + HO2 --> H2O2 + C2H4, k8a = (2.98 +/- 0.11) x 10(-12); Cl + HO2 --> HCl + O2, k9 = (4.45 +/- 0.06) x 10(-11). Activation energies are given in cal/mol. Reactions 8a and 9 show no change in the temperature range of measurements, while reactions 6 and 7 both have negative temperature dependence. The radical oxidation reaction 6 is suggested to occur via excited ethylperoxy and 2-hydroperoxyethyl radical formations as consecutive reversible steps.