Direct detection of OH formation in the reactions of HO₂ with CH₃C(O)O₂ and other substituted peroxy radicals

Abstract. This work details the first direct observation of OH as a product from (R1): HO₂+CH₃C(O)O₂→(products), which has generally been considered an atmospheric radical termination process. The technique of pulsed laser photolysis radical generation, coupled to calibrated laser induced fluorescence detection was used to measure an OH product yield for (R1) of α₁(298 K)=(0.5±0.2). This study of (R1) included the measurement of a rate coefficient k₁(298 K)=(1.4±0.5)×10⁻¹¹cm³ molecule⁻¹ s⁻¹, substantially reducing the uncertainties in modelling this important atmospheric reaction. OH was also detected as a product from the reactions of HO₂ with three other carbonyl-containing peroxy radicals, albeit at smaller yield, e.g. (R2): HO₂+CH₃C(O)CH₂O₂→(products), α₂≈0.15. By contrast, OH was not observed (α<0.06) as a major product from reactions where carbonyl functionality was absent, e.g. HO₂+HOCH₂CH₂O₂ (R8), and HO₂+CH₃CH(OH)CH₂O₂ (R9).