Rate Coefficients of the Reaction of OH with Allene and Propyne at High Temperatures

Allene (H₂C=C=CH₂; a-C₃H₄) and propyne (CH₃C≡CH; p-C₃H₄) are important species in various chemical environments. In combustion processes, the reactions of hydroxyl radicals with a-C₃H₄ and p-C₃H₄ are critical in the overall fuel oxidation system. In this work, rate coefficients of OH radicals with allene (OH + H₂C=C=CH₂ → products) and propyne (OH + CH₃C≡CH → products) were measured behind reflected shock waves over the temperature range of 843-1352 K and pressures near 1.5 atm. Hydroxyl radicals were generated by rapid thermal decomposition of tert-butyl hydroperoxide ((CH₃)₃-CO-OH), and monitored by narrow line width laser absorption of the well-characterized R₁(5) electronic transition of the OH A-X (0,0) electronic system near 306.7 nm. Results show that allene reacts faster with OH radicals than propyne over the temperature range of this study. Measured rate coefficients can be expressed in Arrhenius form as follows: k_allene+OH(T) = 8.51(±0.03) × 10^-22T^3.05 exp(2215(±3)/T), T = 843-1352 K; k_propyne+OH(T) = 1.30(±0.07) × 10^-21T^3.01 exp(1140(±6)/T), T = 846-1335 K.