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 syste ms He+-Ne and Ne+-He at projectile velocities of 0.25, 0.35 and 0.5 au empl oying electron and recoil momentum imaging techniques. At the two lower vel ocities 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 charac terized by a pronounced asymmetry with respect to the beam axis, an asymmet ry 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.