Direct detection of OH formation in the reactions of HO2 with CH3C(O)O-2 and other substituted peroxy radicals

This work details the first direct observation of OH as a product from (R1): HO2+ CH3C(O)O-2 -> (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 alpha(1) (298 K)=(0.5 +/- 0.2). This study of (R1) included the measurement of a rate coefficient k(1)(298 K) = ( 1.4 +/- 0.5) x 10(-11) cm(3) 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), alpha(2) approximate to 0.15. By contrast, OH was not observed (alpha < 0.06) as a major product from reactions where carbonyl functionality was absent, e. g. HO2+ HOCH2CH2O2 (R8), and HO2+ CH3CH(OH)CH2O2 (R9).