Electron-electron interaction and two-center effects in projectile ionization at backward emission angles

We analyze the electron emission spectrum into backward angles for projectile ionization in 0.5-MeV/u H⁰ and He⁺ on He collisions. The energy and angular distributions of the ejected electron are calculated taking into account both scattering correlations and two-center effects. Two-center effects are treated using the continuum-distorted-wave approximation and the classical-trajectory Monte Carlo method. Correlation effects are described in terms of a Born series including contributions up to second order. Both contributions are found to enhance significantly the electron-loss cross section in near-symmetric projectile-target collision systems. We find improved agreement with experiment for He⁺ on He collisions. Extensions to heavier targets are also discussed.