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 α1b(-1)(N2) = 1 + (9.4 ± 1.7) × 10(-18) cm(3) molecule(-1) × [M], α1b(-1)(He) = 1 + (3.6 ± 0.6) × 10(-18) cm(3) molecule(-1) × [M] and α4b(-1)(N2) = 1 + (1.85 ± 0.38) × 10(-18) cm(3) 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.

Direct measurements of OH and other product yields from the HO<sub>2</sub> + CH<sub>3</sub>C(O)O<sub>2</sub> reaction

“…Our reported value k (R5) = (2.4 ± 0.4) × 10 −11 cm 3 molecule s −1 , is slightly larger than the reported value by Groß et al (2014a), though within experimental error, and also inside the upper bound quoted in the IUPAC recommendation (k (R5) = (1.4 +1.4 −0.7 ) × 10 −11 cm 3 molecule s −1 ). Here, k (R5) was determined by measuring all products from Reaction (R5) directly and using the chemical simulation outlined in Table 2 to fit to the measured data, summing the individual rate coefficients of branching pathways.…”

“…The determination of k (R5) by Dillon and Crowley (2008) relied on the more sensitive and specific LIF detection of OH; however, the calibration of the LIF setup, calculation of HO 2 and RO 2 concentrations and chemical modelling of the system all relied on the determination of [Cl] 0 through a Joule meter reading of laser fluence, resulting in the ±30 % uncertainty in k (R5) quoted by the authors. This study has been superseded by the determination of k (R5) = 2.1 × 10 −11 cm 3 molecule s −1 -underpinned by direct HO 2 and RO 2 observations, so avoiding this reliance on a Joule meter (Groß et al, 2014a).…”

“…The simultaneous and direct detection of (R5) precursors, reactants and products, using FTIR (Fourier transform infrared spectroscopy), gas chromatography and an O 3 analyser offered unprecedented, detailed coverage of the key species. This study therefore combined the advantages of the previous chamber studies by Hasson et al (2004) and Jenkin et al (2007) and the direct OH detection experiments of Dillon and Crowley (2008) and Groß et al (2014a); (Groß et al, 2014b). The implications of the study have been assessed using a global chemical transport model's (GEOS-Chem) predictions of OH, O 3 , NO and PAN concentrations with the revised values of rate coefficient and yields compared to those of the IUPAC (International Union of Pure and Applied Chemistry) recommendation.…”

CH3CO + O2 + M (M = He, N2) Reaction Rate Coefficient Measurements and Implications for the OH Radical Product Yield

“…Absolute Method: Groß et al 35 used 248 nm pulsed laser photolysis to produce CH 3 CO radicals via the Cl + CH 3 CHO reaction (Cl atoms were produced by photolysis of analysis to lower pressure would also lead to erroneously higher OH yields than obtained in the present work.…”

“…This method has been applied in the Groß et al 35 study. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 First, a Stern-Volmer (SV) analysis has been used in several of the literature studies and warrants further consideration.…”