Electron loss at backward observation angles

A theoretical study of electron emissions resulting from ionzation of light hydrogenlike projectiles in ion (atom)-atom collisions with heavy targets is presented with emphasis on backward observation angles. Angular and energy distributions of the ejected electrons have been calculated with various approximation methods, which agree with or can be traced to the impulse approximation with the exact off-energy-shell transition amplitudes. Comparisons with experimental data have been made for collisions of H⁰ and He⁺ with Ar. We find good agreement for both the electron angular distributions and the angular variation of the peak position. Our results show that electron loss at backward angles is dominated by elastic scattering of the projectile electron in the strong field of the heavy target. A reliable representation of the potential and a high-order theory for scattering at this potential are required to describe the experiment accurately.