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

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 + O-3 (R8b); RO2 + HO2 --> RO + OH + O-2 (R8c); and RO2 + HO2 --> R'CHO + H2O + O-2 (R8d). Branching ratios for reaction R8 were measured for three organic peroxy radicals: ethyl peroxy (C2H5O2), acetyl peroxy (CH3C(O)O-2), 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.