Experimental and theoretical study of the gas phase reaction of ethynyl radical with methane (HCC+CH4)

Absolute rate coefficients of the reaction of ethynyl radical with methane were measured for the first time at higher temperatures by a pulsed laser photolysis/chemiluminescence (PLP/CL) technique. Ethynyl radicals (HCC) radicals were generated pulsewise upon excimer laser photodissociation of acetylene at 193 nm and pseudo-first-order exponential decays of thermalized HCC were monitored in real-time by the CH(A2Δ → X2Π) chemiluminescence produced by their reaction with O2. The rate coefficients k(HCC+CH4), over 295⩽T (K)<800, exhibit strong non-Arrhenius behaviour, being k(T)=1.39×10−18T2.34±0.40exp[(380±180) K/T] cm3 molecule−1 s−1. Calculations at the CCSD(T)/aug-cc-pvTZ level reveal that the direct H-abstraction yielding HCCH+CH3 has the lowest energy barrier of about 10 kJ mol−1.