Mechanisms for ν/2 electron emission in ion-atom collisions

We have studied electron emission spectra in ionizing collisions in one dimension with interaction potentials of zero range. From low to intermediate collision energies the ionization mechanism is attributed to promotion of quasi-molecular orbitals formed between the collision partners into the continuum. At intermediate collision velocities we observe a hump in the ionization spectrum near νe ⋍ ν/2. The peak position follows approximately the motion of an improper saddle point as the charges of the projectile and of the target are varied. Double peak structures are observed at low collision energies in the forward emission spectra which can be traced to interferences between resonances in the projectile and target continuum.