Electron-ion dissociative recombination rate constants: Effects for benzene analogs with varying degrees of methylation

An in-depth study of the effects of varying degrees of methyl substitution on protonated benzene's electron-ion dissociative recombination (e-IDR) rate constants has been conducted. The e-IDR rate constants for protonated benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, pentamethylbenzene, hexamethylbenzene, and all of their corresponding isomers have been measured using a Flowing Afterglow equipped with an electrostatic Langmuir probe (FALP) at 300 K. The addition of the first methyl substitution decreases the measured e-IDR rate constant by ∼50%. The addition of successive methyl substituents has little effect on the e-IDR rate constant. Isomeric forms also have no effect on the measured e-IDR rate constant. Implications of the observed trends to the chemistry of the Titan ionosphere are discussed.