Rate constant and branching ratio of the reaction of ethyl peroxy radicals with methyl peroxy radicals

Abstract

The cross-reaction of ethyl peroxy radicals (C₂H₅O₂) with methyl peroxy radicals (CH₃O₂) (R1) has been studied using laser photolysis coupled to time resolved detection of the two different peroxy radicals by continuous wave cavity ring down spectroscopy (cw-CRDS) in their AÖ electronic transition in the near-infrared region, C₂H₅O₂ at 7602.25 cm⁻¹, and CH₃O₂ at 7488.13 cm⁻¹. This detection scheme is not completely selective for both radicals, but it is demonstrated that it has great advantages compared to the widely used, but unselective UV absorption spectroscopy. Peroxy radicals were generated from the reaction of Cl-atoms with the appropriate hydrocarbon (CH₄ and C₂H₆) in the presence of O₂, whereby Cl-atoms were generated by 351 nm photolysis of Cl₂. For different reasons detailed in the manuscript, all experiments were carried out under excess of C₂H₅O₂ over CH₃O₂. The experimental results were best reproduced by an appropriate chemical model with a rate constant for the cross-reaction of k = (3.8 ± 1.0) × 10⁻¹³ cm³ s⁻¹ and a yield for the radical channel, leading to CH₃O and C₂H₅O, of (ϕ_1a = 0.40 ± 0.20).