Unexplained features of capture and ionization for ion-aligned-Rydberg-atom collisions - art. no. 042709

Observed but unexplained features, namely, oscillations in the capture cros s sections and an unexpected increase in the ionization cross sections at l ower velocities, are discussed using classical trajectory Monte Carlo simul ated results for ion-aligned-Rydberg-atom collisions. The initial alignment (m = 0, 1, and 2) dependence of the cross sections shows evidence of "capt ure through quasimolecular ion formation," identified as the most likely ca use for the oscillations. Spatial overlap, in addition to the velocity matc hing mechanism, is shown to play an important role in the collision process . The unexpected rise in the ionization cross section toward lower reduced velocities is explained qualitatively in terms of the multiple encounter mo del [Perumal and Tripathi, Nucl. Instrum. Methods B 143, 429 (1998)].