Measurement of the cross sections for electron impact ionization of multi-electron ions; I. O⁺to O²⁺and O²⁺to O³⁺

Abstract

The technique of crossed electron-ion beams has been used to make absolute measurements of the electron impact ionization cross section for the reaction O++e to O2++2e. Incident electron energies ranged from below threshold up to 1000 eV. A similar measurement is made for O2++e to O3++2e up to an incident energy of 500 eV. Evidence for the presence of metastable oxygen ions in the parent ion beams is presented and their influence on the measured cross sections discussed. The experimental results are compared with a Coulomb-Born calculation by Moores, a classical binary encounter calculation by Thomas and Garcia, and a semiempirical estimate by Lotz.