Electron loss to the continuum for H2+and He+ions colliding with H2, He, Ne and Ar. I. Electron cusp widths and shapes

Differential spectra for electron production in the forward direction have been obtained by collision of H 2 + and He + ions with H 2 , He, Ne and Ar gases. The measurements where made with ions of energy 0.8-2.8 MeV. The target consisted of a jet of gas from a multicapillary array, thereby providing a well localised and directed gas beam. A 30 degrees parallel-plate electrostatic analyser having a FWHM resolution (dE/E)=10 -3 was used to study the energy of the ejected electrons. A cusp-shaped peak centred on v e =v i was observed for all the electron spectra, suggesting that these electrons were ejected with only a small energy relative to the parent ions. This process has been called electron loss to the continuum (ELC) since in some ways it mimics the now well established phenomenon of charge exchange to the continuum (CEC). In contrast to data for ELC from heavy ions the cusps observed here were generally asymmetric. They did, however, show a width approximately independent of projectile velocity, a feature which seems to distinguish ELC from CEC. Both the cusp shapes and widths are compared with theoretical predictions and other experimental measurements.