Chemical Physics Letters vol:329 issue:5-6 pages:412-420
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(A(2)Delta --> X(2)Pi) chemiluminescence produced by their reaction with O-2. The rate coefficients k(HCC + CH4), over 295 less than or equal to T (K) < 800, exhibit strong non-Arrhenius behaviour, being k(T) = 1.39 x 10(-18)T(2.34+/-0.40) exp[(380 +/- 180) K/T] cm(3) molecule(-1) s(-1). Calculations at the CCSD(T)I 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). (C) 2000 Elsevier Science B.V. All rights reserved.