Branching Ratios for the Reaction of Selected Carbonyl-Containing Peroxy Radicals with Hydroperoxy Radicals

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 116; no. 24; pp. 6264 - 6281
• Main Authors: Hasson, Alam S, Tyndall, Geoffrey S, Orlando, John J, Singh, Sukhdeep, Hernandez, Samuel Q, Campbell, Sean, Ibarra, Yesenia
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 21.06.2012
• Subjects: Carbonyls; Cycles; Flame ionization; Fourier transforms; Free Radicals - chemical synthesis; Free Radicals - chemistry; Gas chromatography; Infrared spectroscopy; Peroxides - chemical synthesis; Peroxides - chemistry; Peroxy radicals; Radicals
• ISSN: 1089-5639; 1520-5215
• 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), RO2 + 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: C2H5C­(O)­O2, C3H7C­(O)­O2, CH3C­(O)­CH2O2, CH3C­(O)­CH­(O2)­CH3, CH2ClCH­(O2)­C­(O)­CH3, 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.