Pressure dependent OH yields in the reactions of CH3CO and HOCH2CO with O2

Abstract

OH-formation in the reactions of CH₃CO (R1) and HOCH₂CO (R4) with O₂ was studied in He, N₂ and air (27 to 400 mbar) using OH-detection by laser induced fluorescence (LIF). 248 nm laser photolysis of COCl₂ in the presence of CH₃CHO or HOCH₂CHO was used as source of the acyl radicals CH₃CO and HOCH₂CO. The LIF-system was calibrated in back-to-back experiments by the 248 nm laser photolysis of H₂O₂ as OH radical precursor. A straight-forward analytical expression was used to derive OH yields (α) for both reactions. A Stern–Volmer-analysis results in α_1b⁻¹(N₂) = 1 + (9.4 ± 1.7) × 10⁻¹⁸ cm³ molecule⁻¹ × [M], α_1b⁻¹(He) = 1 + (3.6 ± 0.6) × 10⁻¹⁸ cm³ molecule⁻¹ × [M] and α_4b⁻¹(N₂) = 1 + (1.85 ± 0.38) × 10⁻¹⁸ cm³ molecule⁻¹ × [M]. Our results for CH₃CO are compared to the previous (divergent) literature values whilst that for HOCH₂CO, for which no previous data were available, provide some insight into the factors controlling the yield of OH in these reactions.