Single and double ionisation of helium by H⁺, He²⁺and Li³⁺ions

A crossed-beam technique incorporating time-of-flight spectroscopy together with electron-ion and ion-ion coincidence counting of the collision products has been used to study the ionisation of He by H+, He2+ and Li3+ ions. Cross sections for single and double ionisation have been determined with high precision at energies within the range 50-2380 keV amu-1. Cross sections for single ionisation have been compared with the predictions of the first Born approximation, while cross sections for double ionisation have been considered in terms of the 'two-step' and 'shake-off' mechanisms. The authors have also measured the corresponding cross sections for one- and two-electron capture and for the transfer-double-ionisation process; the latter is shown to be the main He2+ production mechanism at the lower impact energies.

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