Trends in electron-ion dissociative recombination of benzene analogs with functional group substitutions: Positive Hammett σ_para constants

An in-depth study of the effects of functional group substitution on benzene's electron-ion dissociative recombination (e-IDR) rate constants has been conducted. The e-IDR rate constants for nitrobenzene, benzonitrile, acetophenone, benzyl methyl ether, and phenyl isothiocyanate have been measured using a flowing afterglow equipped with an electrostatic Langmuir probe (FALP). A trend has been indicated between the associated positive Hammett σ_para constant for each functional group substitution and the e-IDR rate constants for the protonated form of the benzene analog. Such a plot has indicated that protonated benzene analogs which have functional groups substitutions with a positive Hammett σ_para constant value have approximately the same e-IDR rate constant of 4.6 × 10^-7 cm³ s^-1. Implications of the observed trends to the predictions of e-IDR rate constants for unmeasured benzene analogs are discussed.