Mechanisms of the Ethynyl Radical Reaction with Molecular Oxygen

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The Journal of Physical Chemistry


The ethynyl radical, •C2H, is a key intermediate in the combustion of various alkynes. Once produced, the ethynyl radical will rapidly react with molecular oxygen to produce a variety of products. This research presents the first comprehensive high level theoretical study of the reaction of the •C2H (2Σ+) radical with molecular oxygen (3Σg–). Correlation methods as complete as CCSDT(Q) were used; basis sets as large as cc-pV6Z were adopted. Focal point analysis was employed to approach relative energies within the bounds of chemical accuracy (≤1 kcal mol–1). Two dominate reaction pathways from the ethynyl peroxy radical include oxygen–oxygen cleavage from the ethynyl peroxy radical that is initially formed to produce HCCO (2A″) and O (3P) and an isomerization of the ethynyl peroxy radical to eventually yield HCO (2A′) and CO (1Σ+). The branching ratio between these two competitive reaction pathways was determined to be 1:1 at 298 K. Minor reaction pathways leading to the production of CO2 (1Σg+) and CH (2Π, 4Σ–, 2Δ) were also characterized. The absence of CCO (3Σ–) and OH (2Π) was explained in terms competition with more accessible reaction pathways.

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