Low-velocity ionization in asymmetric systems:: a comparative study of the He+-Ne and Ne+-He cases

Single target ionization was investigated in the asymmetric collision systems He+-Ne and Ne+-He at projectile velocities of 0.25, 0.35 and 0.5 au employing electron and recoil momentum imaging techniques. At the two lower velocities the recoil transverse momentum distributions were found to be donut shaped. In addition, a concentric double-donut was observed in the He+-Ne system at 0.25 au. At 0.35 and 0.5 au the electron distributions are characterized by a pronounced asymmetry with respect to the beam axis, an asymmetry which is almost completely reversed by exchanging projectile and target. This latter finding is interpreted as confirmation of the molecular nature of the ionization process at these velocities.