Resonant transfer and excitation (rte) and nonresonant electron transfer and excitation (nte) in Si 11+ on He collisions

Abstract

Recently, crossed electron-ion beam experiments, involving 2s-2p or 3s-3p excitations designed to measure the scale for dielectronic recombination (DR) cross sections have been reported. At TUNL, the scale for DR cross sections in 1s-2p excitations is obtained in a manner similar to that of Tanis et al. [1]. Si 11+ ion beams with energies varying from 15–100 MeV are incident on He and Si K X-rays in coincidence with Si 10+ ions are recorded so that cross sections can be extracted. At 85 MeV, RTE is the dominant process. We conclude that Hahn's [2] DR cross section calculations are somewhat too high. At 20 MeV NTE dominates. Impact parameter dependent models of capture and excitation describe the shape the the NTE feature quite well. The energy dependence of Si K X-ray excitation cross sections is reasonably well described by a semiclassical calculation with a straight line trajectory and screened hydrogenic wavefunctions. The capture cross sections are compared with an impact parameter dependent Bohr-Lindhard model, scaled OBK, and empirical scaling rules.