A measurement of the cross section for electron impact ionisation of Ne+, Ar+, Kr+and Xe+

Abstract

The crossed electron-ion beams technique has been used to measure the absolute cross sections for the single ionisation of Ne+, Ar+, Kr+ and Xe+ ions at electron energies ranging from the ionisation threshold to 2000 eV. The total error in the cross sections at a 90% confidence level is estimated to be +or-5% or less at energies more than a few eV above threshold. In contrast to some previous measurements, the metastable contents of the ion beams are negligible except in the case of Xe+. The cross section curves for Ar+, Kr+ and Xe+ show significant contributions from excitation-autoionisation and possibly direct ionisation of inner-shell electrons. The present results for Ne+ and Ar+ are in excellent agreement with those previously measured in the laboratory. Good agreement is also obtained with the more recent data from the Giessen group for Ne+, Ar+ and Xe+. Comparisons with theoretical calculations show that the scaled Born approximation of McGuire tends to underestimate the cross sections at all energies, but especially at low energies. The semi-empirical formula of Lotz also underestimates the cross sections at low energies. Comparisons are made with other available experimental and theoretical calculations.