Ionization Potentials of Alkyl Free Radicals and of Benzene, Toluene, and Triethylamine by the RPD Technique

Abstract

A time-of-flight mass spectrometer with a source of effectively monoenergetic electrons has been utilized to determine the ionization potentials and ionization-efficiency curves of the stable compounds benzene, toluene, triethylamine and of the free radicals, methyl, ethyl, n-propyl, and isopropyl. The appearance potentials in electron volts observed for the stable compounds were C6H6: 9.20, 9.40, 9.65; C6H5CH3: 8.80, 9.20, 9.50; (C2H5)3N: 7.68, 8.18, 8.55, 8.95, 9.40. Published values for the appearance potentials by electron impact of these compounds tend to converge upon one of the higher values observed in this work. The radicals were produced by thermal—catalytic decomposition of appropriate alkyl nitrites, isopropyl ether, and isobutane. Appearance potentials (electron volts) determined for the free radicals were as follows: methyl—9.80, 10.3, 10.7, 11.4; ethyl—8.25, 8.7, 9.3; n-propyl—8.15, 8.6, 8.8, 9.2, 9.6; isopropyl—7.52, 8.1, 8.6. The measured ionization potentials of methyl, ethyl, and propyl free radicals were considerably lower than published values by electron impact.