Ionization of aligned Rydberg atoms by ion impact

The classical trajectory Monte Carlo method has been used to calculate capture and ionization cross sections and final-state electron momentum distributions in H+ + H(n = 25) collisions to show how the collision mechanisms evolve over the range of intermediate projectile speeds upsilon* = upsilon(p)/upsilon(e) = 1.0-5.0. A circular Rydberg target was aligned in two orientations defined by the orbital angular momentum vector of the electron being either antiparallel or perpendicular to the incident momentum vector of the projectile. Aligning the target atom in this manner helps us to single out specific collision processes otherwise obscured in. randomly oriented atom. A plot of the capture and ionization cross sections shows a crossover in the capture and ionization curves as soft collisions get replaced by harder, more head-on collisions, which leads to more ionization events than captures. The ratio of ionization cross sections, ion(0 degrees)/ion(90 degrees), indicates a further change in collision dynamics around upsilon* approximate to 2.5. It is believed that the collision dynamics for upsilon* greater than or equal to 2.5 become dominated by the geometric size of the target. Plots of the ionized electron final momentum spectra for both alignments, projected onto the projectile-projectile collision plane, show specific types of two- and three-body interactions and show their evolution as a function of upsilon*. The presence of these interactions can be identified and monitored by observing electrons captured to the continuum, backward scattered and saddle-point electrons, and binary collision rings and how each interaction evolves as a function of upsilon*.