Simultaneous capture and ionisation for fast ion impact on helium

The ratio R* between the cross sections for transfer ionisation and single capture is determined experimentally for 1 MeV H+ and 0.35-1.5 MeV amu-1 He2+ ions colliding with He atoms. The experimental data are compared with recent theoretical results based on direct and rearrangement mechanisms. It is pointed out that for even higher projectile velocities, some capture processes lead directly to transfer ionisation, and that this fact should be taken into account when the asymptotic value of R* is estimated. (author)