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

OH-formation in the reactions of CH3CO (R1) and HOCH2CO (R4) with O-2 was studied in He, N-2 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 (alpha) for both reactions. A Stern-Volmer-analysis results in alpha(-1)(1b)(N-2) = 1 + (9.4 +/- 1.7) x 10(-18) cm(3) molecule(-1) x [M], alpha(-1)(1b)(He) = 1 + (3.6 +/- 0.6) x 10(-18) cm(3) molecule(-1) x [M] and alpha(-1)(4b)(N-2) = 1 + (1.85 +/- 0.38) x 10(-18) cm(3) molecule(-1) x [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.