Free radicals by mass spectrometry. XLIL Ionization potentials and ionic heats of formation for C1—C4 alkyl radicals

Abstract

Ionization potentials for C1—C4 alkyl free radicals have been re-measured by electron impact, using an energy-resolved electron beam from a double-hemispherical electrostatic monochromator. From these values and kinetic data for heats of formation of the radicals, ionic heats of formation for C1—C4 alkyl ions have been calculated. New values for the four isomeric butyl ions are given. The ionization efficiency curves for the simpler radicals show linear sections corresponding to excitation of vibrational levels; for larger radicals these segments are not resolved and only a smooth upward curvature is seen. In disagreement with earlier results, no evidence for formation of low-lying excited states of the ions could be found, either for parent or fragment ions.