Branching ratios for the reaction of selected carbonyl-containing peroxy radicals with hydroperoxy radicals

Article abstract of DOI:10.1021/jp211799c

An important chemical sink for organic peroxy radicals (RO₂) in the troposphere is reaction with hydroperoxy radicals (HO₂). Although this reaction is typically assumed to form hydroperoxides as the major products (R1a), acetyl peroxy radicals and acetonyl peroxy radicals have been shown to undergo other reactions (R1b) and (R1c) with substantial branching ratios: RO₂ + HO₂ → ROOH + O₂ (R1a), RO ₂ + HO₂ → ROH + O₃ (R1b), RO₂ + HO₂ → RO + OH + O₂ (R1c). Theoretical work suggests that reactions (R1b) and (R1c) may be a general feature of acyl peroxy and α-carbonyl peroxy radicals. In this work, branching ratios for R1a-R1c were derived for six carbonyl-containing peroxy radicals: C₂H ₅C(O)O₂, C₃H₇C(O)O₂, CH₃C(O)CH₂O₂, CH₃C(O)CH(O ₂)CH₃, CH₂ClCH(O₂)C(O)CH ₃, and CH₂ClC(CH₃)(O₂)CHO. Branching ratios for reactions of Cl-atoms with butanal, butanone, methacrolein, and methyl vinyl ketone were also measured as a part of this work. Product yields were determined using a combination of long path Fourier transform infrared spectroscopy, high performance liquid chromatography with fluorescence detection, gas chromatography with flame ionization detection, and gas chromatography-mass spectrometry. The following branching ratios were determined: C₂H₅C(O)O₂, Y_R1a = 0.35 ± 0.1, Y_R1b = 0.25 ± 0.1, and Y_R1c = 0.4 ± 0.1; C₃H₇C(O)O₂, Y_R1a = 0.24 ± 0.15, Y_R1b = 0.29 ± 0.1, and Y_R1c = 0.47 ± 0.15; CH₃C(O)CH₂O₂, Y _R1a = 0.75 ± 0.13, Y_R1b = 0, and Y_R1c = 0.25 ± 0.13; CH₃C(O)CH(O₂)CH₃, Y _R1a = 0.42 ± 0.1, Y_R1b = 0, and Y_R1c = 0.58 ± 0.1; CH₂ClC(CH₃)(O₂)CHO, Y _R1a = 0.2 ± 0.2, Y_R1b = 0, and Y_R1c = 0.8 ± 0.2; and CH₂ClCH(O₂)C(O)CH₃, Y_R1a = 0.2 ± 0.1, Y_R1b = 0, and Y_R1c = 0.8 ± 0.2. The results give insights into possible mechanisms for cycling of OH radicals in the atmosphere.