Measurements of the electron impact ionisation cross sections of He, C, O and N atoms

Abstract

Absolute measurements are reported of the electron impact ionisation cross sections of ground-state atoms of helium, carbon, nitrogen and oxygen for electron energies ranging from 7 to 1000 eV. The method used was that of crossed beams in which fast beams of atoms are produced by charge capture of 2 to 4 keV ions in a gas target. The data for helium atoms above 100 eV are in excellent agreement (+or-5%) with the absolute data of Rapp and Englander-Golden (1965) who used a static gas target technique. However, the present data are smaller in magnitude at lower energies. Data for oxygen and nitrogen atoms are in adequate agreement with data from earlier crossed-beams experiments that employed thermal-energy atom beams.