Exact electron spectra in collisions of two zero-range potentials with nonzero impact parameters

The Sturmian theory of ion-atom collisions is constructed for arbitrary (nonzero) impact parameters. The approach is essentially nonperturbative, and has a wide range of applicability: from low velocities, provided that quantum motion of heavy particles can be neglected, to high velocities, as long as the relativistic effects are not important. The theory is applied to calculation of electron spectra at low and high collision velocities. For slow collisions we describe Fermi oscillations in the spectra of ejected electrons. At higher velocities our theory confirms the possibility of cusp formation even when the heavy particles are neutral in the final state.