An improved crossed-beams technique for the measurement of absolute cross sections for electron impact ionisations of ions and its application to Ar⁺ions

Abstract

Based on the animated-beam method of Brouillard and co-workers (1983) an improved experimental technique has been developed to measure cross sections for electron impact ionisation of ions. In a crossed-beams arrangement the overlap of the electron and the ion beam is periodically varied by a mechanical displacement of the complete electron gun system. Simultaneously with the ionisation signal, the parent ion beam current and the velocity of the gun movement are registered. As a test of the new method cross sections for single ionisation of Ar+ ions are measured from threshold up to 850 eV electron energy. The results are in excellent agreement with the crossed-beams data of Woodruff et al.