Appearance Potentials of Atomic and Molecular Hydrogen Ions from Small Hydrocarbons

Abstract

Ionization efficiency curves of atomic and molecular hydrogen ions from acetylene, ethylene and ethane have been measured over the energy ranges near their appearance thresholds by using a monoenergetic electron beam. The appearance potentials for the ions were determined with the Initial Onset method, and some of them were confirmed with the Straightening-through-Smoothings method. The determined values are not always in agreement with those by the Vanishing Current method. Barrier energies for formation of these ions were estimated and the energies are much higher than those of larger fragment ions.