Rate Constant and Branching Ratio for the Reactions of the Ethyl Peroxy Radical with Itself and with the Ethoxy Radical

Abstract

The self-reaction of the ethyl peroxy radical (C 2 H 5 O 2 ) (R1) has been studied using laser photolysis coupled to a selective time resolved detection of two different radicals by continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared range: C 2 H 5 O 2 was detected in the Ã-electronic transition at 7596 cm -1 , and HO 2 was detected in the 2 1 vibrational overtone transition at 6638.21 cm -1 . Radicals were generated from pulsed 351 nm photolysis of C 2 H 6 / Cl 2 mixture in presence of O 2 . The reaction can proceed via a radical maintain channel leading to two C 2 H 5 O radicals (R1a) or to stable products (R1b/1c). Because C 2 H 5 O radicals react subsequently with O 2 leading to HO 2 , which in term reacts rapidly with C 2 H 5 O 2 , knowledge of the branching ratio is indispensable for retrieving the rate constant. A strong disagreement exists about the rate constant and the branching ratio between the IUPAC recommendation (Atkinson et al., ACP, 3525, 2006) and a recent, more direct measurement (Noell et al., JPC A, 6983, 2010). The rate constant for the self-reaction has been found at k 1 = (1.0±0.2) ×10 -13 cm 3 s -1 with the branching fraction of the C 2 H 5 O radical channel being  = (0.31±0.06), being in contradiction with the IUPAC recommendation, but confirms the most recent measurement and indicates that the current recommendation for this reaction should be revised. The reaction of C 2 H 5 O 2 with the ethoxy radical (C 2 H 5 O) can also been involved in the reaction mechanism, and its rate constant is also extracted from modelling. It is found to be k 9 = (7±1.5) ×10 -12 cm 3 s -1 , two times slower than the only available measurement from Noell et al. JPC A, 6983, 2010.

Dimeric Product of Peroxy Radical Self-Reaction Probed with VUV Photoionization Mass Spectrometry and Theoretical Calculations: The Case of C2H5OOC2H5

“…The current IUPAC database therefore recommends, for the C 2 H 5 O 2 self-reaction, based on the analysis of stable end products, a yield of 0.63 for the alkoxy path (1), 0.37 for the molecular path (2) and 0 for the dimer path (3) [ 24 ]. More recent studies directly measuring the radical yield (1) from the self-reaction of C 2 H 5 O 2 found only a minor yield of 0.28 [ 25 ] and 0.31 [ 26 ] for the alkoxy path (1), in strong disagreement with the IUPAC recommendation. A possible explanation for this strong disagreement could be a higher yield of the dimer path (3), which could, due to its instability, appear in the stable end-product studies as a radical path.…”

Bimolecular Peroxy Radical (RO2) Reactions and Their Relevance in Radical Initiated Oxidation of Hydrocarbons

“…Despite several efforts to measure the branching ratio between reactions and , − there is still substantial uncertainty in these branching ratios even at room temperature, spanning from 27:72 to 74:26. Recent studies by Shamas et al and Noell et al indicates lower branching to reaction (∼30%) at room temperature.…”

“…Despite several efforts to measure the branching ratio between reactions and , − there is still substantial uncertainty in these branching ratios even at room temperature, spanning from 27:72 to 74:26. Recent studies by Shamas et al and Noell et al indicates lower branching to reaction (∼30%) at room temperature. Considering the uncertainty in the branching ratios at high temperatures, we first assumed equal branching to reactions and (50:50).…”

Rate Constants and Branching Ratios for the Self-Reaction of Acetyl Peroxy (CH3C(O)O2•) and Its Reaction with CH3O2

“…The setup has been described in detail before [32][33][34][35][36][37] and is only briefly discussed here. The setup consisted of a 0.79 m long flow reactor made of stainless steel.…”