Abstract Absolute doubly-differential electron emission yields were measured as a function of angle and energy of ejection for projectile scattering angles of 0.3° to 3° in 30-, 100- and 300-keV proton-helium collisions. The secondary electron spectra correspond to impact parameters which are small compared to the He(1s 2) orbital radius. The experimental data clearly favor quantum mechanical and classical highest order theories for the description of the ionization process. Doubly-differential cross sections measured for 5 MeV/amu Ne 10+ + He collisions also show higher order effects which may be clearly distinguished from those at low impact energies. The coincidence data for H + + He exhibit a dominant line structure originating from the decay of the doubly excited 2s 21S state. The corresponding line intensity shows an angular anisotropy which is interpreted as a Fano interference between the amplitudes of autoionization and direct ionization.