An ab initio/RRKM study of the reaction mechanism and product branching ratios of the reactions of ethynyl radical with 1,2-butadiene

► Ab initio/RRKM calculations reveal the mechanism of the C2H + 1,2-butadiene reaction. ► Reaction is predicted to be barrierless and to form C6H6 + H and C5H4 + CH3 products. ► 2-Ethynyl-1,3-butadiene + H are calculated as the dominant products (91-84%). ► Penta-1,4-diyne + CH3 (7-12%) and ethynylallene + CH3 (2-3%) are minor products.