The self-reaction of acetylperoxy radicals (CH
3C(O)O
2•) (R1) as well as their reaction with methyl peroxy radicals (CH
3O
2•) (R2) have been studied using laser photolysis coupled to a selective time resolved detection of three
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The self-reaction of acetylperoxy radicals (CH
3C(O)O
2•) (R1) as well as their reaction with methyl peroxy radicals (CH
3O
2•) (R2) have been studied using laser photolysis coupled to a selective time resolved detection of three different radicals by cw-CRDS in the near-infrared range: CH
3C(O)O
2• was detected in the Ã-
electronic transition at 6497.94 cm
−1, HO
2• was detected in the 2ν
1 vibrational overtone at 6638.2 cm
−1, and CH
3O
2• radicals were detected in the Ã-
electronic transition at 7489.16 cm
−1. Pulsed photolysis of different precursors at different wavelengths, always in the presence of O
2, was used to generate CH
3C(O)O
2• and CH
3O
2• radicals: acetaldehyde (CH
3CHO/Cl
2 mixture or biacetyle (CH
3C(O)C(O)CH
3) at 351 nm, and acetone (CH
3C(O)CH
3) or CH
3C(O)C(O)CH
3 at 248 nm. From photolysis experiments using CH
3C(O)C(O)CH
3 or CH
3C(O)CH
3 as precursor, the rate constant for the self-reaction was found with
k1 = (1.3 ± 0.3) × 10
−11 cm
3s
−1, in good agreement with current recommendations, while the rate constant for the cross reaction with CH
3O
2• was found to be
k2 = (2.0 ± 0.4) × 10
−11 cm
3s
−1, which is nearly two times faster than current recommendations. The branching ratio of (R2) towards the radical products was found at 0.67, compared with 0.9 for the currently recommended value. Using the reaction of Cl
•-atoms with CH
3CHO as precursor resulted in radical profiles that were not reproducible by the model: secondary chemistry possibly involving Cl
• or Cl
2 might occur, but could not be identified.
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