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

Article abstract of DOI:10.1021/ja00072a038

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/(molecule·-s)) 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) × 10^-17 exp[(5064 ± 154)/RT], measured independently from recording C₂H₅ consumption or C₂H₄ formation rates; 2HO₂ → H₂O₂, k₇ = (4.50 ± 0.56) × 10^-13 exp[(1064 ± 77)/RT]; C₂H₅ + HO₂ → H₂O₂ + C₂H₄, k_8a = (2.98 ± 0.11) × 10^-12; Cl + HO₂ → HCl + O₂, k₉ = (4.45 ± 0.06) × 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.