Flash photolysis study of the UV spectrum and kinetics of reactions of the acetonylperoxy radical

Abstract

The flash-photolysis–UV-absorption method was used to study the UV spectrum and the kinetics of the CH₃C(O)CH₂O₂ radical formed in the presence of oxygen via the reaction between Cl atoms and acetone. Results were analysed in the light of the results of the preceding article describing work using end-product analysis. The peroxy radical CH₃C(O)CH₂O₂ absorbs in the UV with two maxima at around 230 and 290 nm. This peroxy radical reacts according to: 2CH₃C(O)CH₂O₂→ 2CH₃C(O)CH₂O + O₂(7a) and → CH₃C(O)CH₂OH + CH₃C(O)CHO + O₂(7b) with k₇=(8.0 ± 2.0)× 10^–12 cm³ molecule^–1 s^–1 and k_7a/k₇=(0.75 ± 0.1). The kinetics of the reactions between CH₃C(O)CH₂O₂ and the CH₃C(O)O₂, CH₃O₂ and HO₂ radicals were determined by adding acetaldehyde, methane or methanol to the photolysis mixtures: CH₃C(O)CH₂O₂+ CH₃C(O)O₂→ O₂+ CH₃C(O)CH₂O + CH₃+ CO₂(11a); → O₂+ CH₃C(O)OH + CH₃C(O)CHO (11b); k₁₁=(5.0 ± 2.0)× 10^–12 cm³ molecule^–1 s^–1; CH₃C(O)CH₂O₂+ CH₃O₂→ O₂+ CH₃C(O)CH₂O + CH₃O (14a); → O₂+ CH₃C(O)CHO + CH₃OH (14b); → O₂+ CH₃C(O)CH₂OH + HCHO (14c); k₁₄=(3.8 ± 0.4)× 10^–12 cm³ molecule^–1 s^–1 and k_14a/k₁₄= 0.3 ± 0.1 while k_14b and k_14c could not be distinguished; CH₃C(O)CH₂O₂+ HO₂→ CH₃C(O)CH₂O₂H + O₂(16), k₁₆=(9.0 ± 1.0)× 10^–12 cm³ molecule^–1 s^–1. All experiments were performed at 298 K and 760 Torr.