Kinetics of the reactions H+C₂H₄->C₂H₅, H+C₂H₅->2CH₃ and CH₃+C₂H₅->products studies by pulse radiolysis combined with infrared diode laser spectroscopy

Formation of methyl radicals via the consecutive reactions H+C2H4+M-->C2H5+M (1) and H+C2H5-->CH3+CH3 (2a) was initiated by pulse radiolysis of 10-100 mbar H-2 in the presence of ethylene. The kinetics of CH3 Were studied by monitoring the transient infrared absorption at the Q(3, 3) line of the v2=0-->1 vibrational transition at 606.12 cm-1. Reaction (2a) proceeds in competition with the reaction H+C2H5+M-->C2H6+M (2b). The methyl radicals are consumed by CH3+CH3+M-->C2H6+M (3), CH3+C2H5-->products (4), and H+CH3+M-->CH4+ M (5). By computer simulations based on determined absolute radical yields, the observed formation and decay kinetics could be reproduced using the rate constants k2a = (7.5 +/- 0.7) x 10(10) M-1 s-1, k2b = (1.0+/-0.1) X 10(11) M-1 s-1, and k4 = (4.0+/-0.2) X 10(10) M-1 s-1 at 298 K and a total pressure of p(H-2) = 100 mbar.