Pulse Radiolysis of Methane.

The pulse radiolysis of methane has been studied in the absence and presence of electron scavengers such as SF and CDI and positive ion scavengers such as -CD in order to define the role of the intermediates H, C, CH, CH, CH, , and in product formation. The dose rate was varied from 0.68 to 15.2 × 10 eV/g-s, the dose (number of pulses) was varied, and the duration of the pulse was changed from 3 ns to 100 ns. The variation of the yields of the ethylene and ethane products with dose is explained by the reaction of H-atoms with accumulated ethylene product. The fast reacting C, CH, and CH species insert into methane to form acetylene, ethylene, and ethane products, but all of the reactions of these species cannot be completely specified since they may originate in upper electronic states, whose reactions with methane are unknown. Product formation by the slow reacting CH and CH radicals is also examined; for instance, evidence is presented for the occurrence of the reaction: CH + CH → CH + H. Results indicate that the ions and undergo neutralization mainly through the processes When -CD is added, a fraction of the and react with the additive rather than undergo neutralization. A calculation demonstrates that the fraction of ions undergoing reaction with a given concentration of -CD can be correctly predicted by assuming that the rate constant for neutralization of and is the same as that determined recently for the -butyl ion.