H Atom Branching Ratios from the Reactions of CH with C2H2, C2H4, C2H6, and neo-C5H12 at Room Temperature and 25 Torr

Branching ratios for H atom production from the reaction of CH(X 2 Π) with C 2 H 2, C 2 H 4, C 2 H 6, and neo -C 5 H 12 have been measured relative to that from the CH + CH 4 reaction using laser-induced fluorescence at 121.56 nm (Lyman α). Assuming that the reaction with methane proceeds solely to the formation of H + C 2 H 4, then the observed branching ratios are as follows: C 2 H 2 1.05 ± 0.09, C 2 H 4 1.09 ± 0.14, C 2 H 6 0.14 ± 0.06, and neo -C 5 H 12 −0.10 ± 0.12 (errors refer to ±1σ). The results for the reaction of CH with acetylene and ethene are in good agreement with previous experimental and theoretical calculations. The yield of H atoms from the reaction of CH with ethane is consistent with a competition between C−H and C−C cleavage in an initially formed 1-propyl radical. The absence of H production for the reaction of CH with 2,2-dimethylpropane can be rationalized by the opening of isomerization pathways that lead to intermediates that dissociate only via C−C cleavage.