Electron Recombination in Hydrocarbon—Oxygen Reactions behind Shock Waves

Abstract

The rate of recombination of electrons with ions behind shock waves in argon containing dilute lean mixtures of hydrocarbons and oxygen has been measured with a microwave system. The recombination reaction was found to be two body, as evidenced by insensitivity of the recombination coefficient α to changes in pressure and concentration; and the recombination coefficient for acetylene—oxygen and methane—oxygen mixtures was found to depend upon temperature as T−1.98 between 2500° and 5000°K. Extrapolating to room temperature gives a value of α=1.3×10−5 cm3/sec, consistent with the electron removal process being a dissociative recombination involving a complex ion. In the case of acetylene, the reaction is probably a previously proposed scheme: H3O++e−→neutral products. Measurements made at a temperature of about 3800°K, using ethane, ethylene, propane, and benzene, gave recombination coefficients similar in magnitude to those obtained for the acetylene and methane, consistent with the recombining ion being the same for all these hydrocarbon—oxygen reactions.