Reactions of CH3C(O)O2 radicals with CH3O2 and HO2 between 263 and 333 K. A product study

Abstract

Biacetyl (butane-2,3-dione) CH₃C(O)C(O)CH₃ has been photolysed (λ= 390–470 nm) at atmospheric pressure in Ar : O₂= 80 : 20 (mol/mol) mixtures between 263 and 333 K under steady-state conditions. Reaction products were analysed by matrix-isolation FTIR spectroscopy combined with a molecular-beam sampling technique. Observed reaction products were CO₂, CO, HCHO, HCOOH, CH₃C(O)OH, CH₃C(O)OOH, CH₃OH, H₂O₂ and O₃. Based on an assumed mechanism for the reaction, quantitative product data were used to determine the temperature dependence of the branching ratios β₁₀ and β₁₁ of the following two sets of CH₃C(O)O₂ radical reactions: CH₃C(O)O₂+ HO₂→ CH₃C(O)OOH + O₂(10a), CH₃C(O)O₂+ HO₂→ CH₃C(O)OH + O₃(10b), β₁₀=k_10a/k_10b= 330 × exp(–1430/T) and CH₃C(O)O₂+ CH₃O₂→ CH₃C(O)O + CH₃O + O₂(11a), CH₃C(O)O₂+ CH₃O₂→ CH₃C(O)OH + HCHO + O₂(11b), β₁₁=k_11a/k_11b= 2.2 × 10⁶ exp(– 3870/T)