A crossed-beam technique previously developed and used in this laboratory for studies of ionisation and electron capture in H+-He and He2+-He collisions down to 64 keV amu-' and 50 keV amu-l has been adapted to extend measurements down to 9 keV amu-' and 6 keV amu-' respectively. The method, which incorporates time-of-flight spectroscopy together with electron-ion and ion-ion coincidence counting of the collision products, provides high precision cross sections for individual collision channels. Some serious discrepancies are obtained with previous cross sections for single ionisation measured by Afrosimov er a2 and the important role of transfer ionisation at low energies is confirmed. The need for better theoretical descriptions of low-energy ionisation is demonstrated.

A pulsed crossed-beam technique incorporating time-of-flight spectroscopy which was recently developed in this laboratory has been applied to measurements of the cross sections for single and double ionisation of helium. Measurements over the unusually wide energy range from near threshold to 10 000 eV provide valuable checks on previous measurements based on different experimental approaches and an assessment of the range of validity of a number of theoretical predictions.

A pulsed crossed beam technique incorporating time-of-flight spectroscopy of the collision products, which was developed previously in this laboratory, has been successfully adapted to allow studies of multiple ionization of metallic atoms. Cross sections sigma n for the formation of n=1-4 times ionized magnesium have been determined over the wide energy range 8-5300 eV by normalization to cross sections for single ionization of Mg recently measured by Freund et al using a fast crossed beam technique. Cross sections sigma 2 are found to closely approach the authors' values of sigma 1 at our highest impact energies. Comparison is made with previous experiments based on different methods and, in the case of single ionization, results are compared with theoretical predictions.

A pulsed crossed beam technique incorporating time-of-flight spectroscopy previously developed in this laboratory has now been applied to studies of the multiple ionization of argon by electron impact. Cross sections sigma n for the production of n=1-5 times ionized argon have been determined for impact energies in the range from near threshold to 5300 eV. The measurements cover a wider energy range and extend to higher charge states n than most previous experiments. The results also provide valuable checks on the results of previous measurements which exhibit unexplained discrepancies. In the case of single ionization, the authors' values of sigma 1 are compared with available threshold predictions.

A crossed-beam technique previously used in the authors' laboratory for studies of ionisation of H2 by H+ and He2+ impact in the ranges 38-1500 and 31-550 keV amu-1, respectively, has been adapted to permit measurements to be extended down to 10 keV amu-1. Both ionisation and electron capture have been studied using time-of-flight mass spectroscopy together with electron-slow-ion and slow-ion-fast-ion coincidence counting of the collision products. Separate cross sections for non-dissociative and dissociative electron capture and ionisation channels have been determined. Some significant discrepancies between the authors' results and previous measurements due to Afrosimov et al. (1969) are noted. At their lowest impact energies electron capture substantially exceeds ionisation. In addition, for He2+ impact, unlike protons, dissociative ionisation and transfer ionisation cross sections substantially exceed those for non-dissociative ionisation.