Ionization and Excitation Processes in Argon, Krypton, and the C2 Hydrocarbons Produced by Various Means

Abstract

Multiple ionization produced in argon and krypton by 3.5-keV electrons is reported. The ionization mechanism is tentatively proposed to be similar to that known for nuclear transitions, namely, a combination of electron shakeoff with primary ionization in one of the inner-orbital-electron shells (n=1 or 2) followed by Auger transitions. The relative proportions of fragment ions produced in the C2 hydrocarbons by 3.5-keV electrons are also reported. These data bear a marked similarity to those obtained by the dissociative ionization of the C2 hydrocarbons with 75-eV electrons. However, ions produced by 3.5-keV electrons retain excitation energy longer as is shown by their respective rates of intramolecular decomposition (metastable transitions). Despite the longer retention of excitation energy, the reaction rate for 3.5-keV electron-induced ions in ion—molecule reactions is the same as that for 75-eV electron-induced ions. Reaction rates between neutral molecules and C2H4+ ions from different parent molecules appear to be independent of the parent, thus suggesting that the ions, initially probably different in configuration, all rearrange to the same configuration before reacting. The fragment ion pattern produced in ethane by 50–75-eV electrons is strikingly similar to that produced by either 3.5-keV electrons or by 5-MeV α particles. In ethylene, likewise, the fragment ion patterns produced by 5-MeV α particles, β particles from Ni63, 3.5-keV electrons and 50–75-eV electrons are quite similar. This lends some support to the common practice of using 50–75-eV mass spectra to predict primary ion products in radiation chemistry.