10.1021/jp055168r.s001 M. Colberg M. Colberg G. Friedrichs G. Friedrichs Room Temperature and Shock Tube Study of the Reaction HCO + O<sub>2</sub> Using the Photolysis of Glyoxal as an Efficient HCO Source American Chemical Society 2006 HCO radicals RT rate constants Efficient HCO Source H atoms HO cm 3 mol FM 193 nm excimer laser photolysis temperature range 739 K O 2 193 nm photolysis room temperature Shock Tube Study CHO 2006-01-12 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Room_Temperature_and_Shock_Tube_Study_of_the_Reaction_HCO_O_sub_2_sub_Using_the_Photolysis_of_Glyoxal_as_an_Efficient_HCO_Source/3244195 The rate of the reaction 1, HCO + O<sub>2</sub> → HO<sub>2</sub> + CO, has been determined (<i>i</i>) at room temperature using a slow flow reactor setup (20 mbar < <i>p < </i>500 mbar) and (<i>ii</i>) in the temperature range 739 K < <i>T < </i>1108 K behind reflected shock waves (0.82 bar < <i>p < </i>1.84 bar) employing a perturbation approach. Following the 193 nm excimer laser photolysis of mixtures of glyoxal in Ar, concentration−time profiles were measured using frequency modulation (FM) detection of HCO at a wavelength of λ = 614.752 nm. Observed differences between HCO concentration−time profiles measured with and without O<sub>2</sub> added to the reaction mixtures could be almost exclusively attributed to reaction 1. The determined rate constants, <i>k</i><sub>1</sub>(295 K) = (3.55 ± 0.05) × 10<sup>12</sup> cm<sup>3</sup> mol<sup>-1</sup> s<sup>-1</sup>, <i>k</i><sub>1</sub>(739−1108 K) = 3.7 × 10<sup>13</sup> exp(−13 kJ mol<sup>- 1</sup>/<i>RT)</i> cm<sup>3</sup> mol<sup>-1</sup> s<sup>-1</sup> (Δ log <i>k</i><sub>1</sub> = ± 0.16), reveal a slightly positive temperature dependence of reaction 1 at high temperatures. Furthermore, the 193 nm photolysis of glyoxal, (CHO)<sub>2</sub>, has been proven to be an efficient HCO source. Besides HCO, photolysis of the precursor also produces H atoms. The ratio of initially generated H atoms and HCO radicals, <i>f</i> = [H]<sub>0</sub>/[HCO]<sub>0</sub><sup>total</sup>, was found to depend on the total density ρ. At room temperature, it varies from <i>f</i> = 1.6 at ρ = 8 × 10<sup>-7</sup> mol cm<sup>-3</sup> to <i>f</i> = 3.0 at ρ = 2 × 10<sup>-5</sup> mol cm<sup>-3</sup>. H atoms are transformed via reaction 4, H + (CHO)<sub>2</sub> → H<sub>2</sub> + HCO + CO, into additional HCO radicals. The rate constants of reaction 4 were determined from unperturbed photolysis experiments to be <i>k</i><sub>4</sub>(295 K) = (3.6 ± 0.3) × 10<sup>10</sup> cm<sup>3</sup> mol<sup>-1</sup> s<sup>-1</sup> and <i>k</i><sub>4</sub>(769−1107 K) = 5.4 × 10<sup>13</sup>exp(−18 kJ mol<sup>- 1</sup>/<i>RT)</i> cm<sup>3</sup> mol<sup>-1</sup> s<sup>-1</sup>(Δ log <i>k</i><sub>4</sub> = ±0.12).