A Product Yield Study of the Reaction of HO₂ Radicals with Ethyl Peroxy (C₂H₅O₂), Acetyl Peroxy (CH₃C(O)O₂), and Acetonyl Peroxy (CH₃C(O)CH₂O₂) Radicals

Abstract

The reaction between HO2 and RO2 radicals represents an important chemical sink for HOx radicals in the atmosphere. On the basis of a few product yield studies, these reactions are believed to form hydroperoxides almost exclusively (R8a), although several different reaction channels may be thermodynamically accessible (R8a−d): RO2 + HO2 → ROOH + O2 (R8a); RO2 + HO2 → ROH + O3 (R8b); RO2 + HO2 → RO + OH + O2 (R8c); and RO2 + HO2 → R‘CHO + H2O + O2 (R8d). Branching ratios for reaction R8 were measured for three organic peroxy radicals: ethyl peroxy (C2H5O2), acetyl peroxy (CH3C(O)O2), and acetonyl peroxy (CH3C(O)CH2O2) radicals. Product yields were measured using a combination of long-path Fourier transform infrared spectroscopy and high-performance liquid chromatography with fluorescence detection. Measured branching ratios for the reaction of the three organic peroxy radicals with HO2 are as follows: ethyl peroxy, Y8a-ETH > 0.93 ± 0.10, Y8b-ETH = Y8c-ETH = Y8d-ETH = 0; acetyl peroxy, Y8a-ACT = 0.40 ± 0.16, Y8b-ACT = 0.20 ± 0.08, Y8c-ACT = 0.40 ± 0.16, and Y8d-ACT = 0; acetonyl peroxy, Y8a-ACN = 0.33 ± 0.10, Y8b-ACN = Y8d-ACN = 0, and Y8c-ACN = 0.67 ± 0.20. The atmospheric implications of these branching ratios are discussed.