MERGED-BEAMS ENERGY-LOSS TECHNIQUE FOR ELECTRON-ION EXCITATION - ABSOLUTE TOTAL CROSS-SECTIONS FOR O5-]2P)((2S)

A merged-beams electron-energy-loss technique is described, by which a bsolute cross sections can be measured for near-threshold electron-imp act excitation of multipy charged ions. Results are reported here for absolute total electron-impact excitation cross sections for the O5+(2 s --> 2p) transition from below threshold to 1.6 eV above threshold. T he experimental data are in good agremeent with a seven-state close-co upling calculation throughout the energy range of the experiment. Resu lts agree with calculations showing that more than 90% of the electron s causing excitation are ejected in the backward direction in the cent er-of-mass frame. This backscattering is shown in both quantum-mechani cal and semiclassical calculations. Evidence is observed for high-lyin g metastable autoionizing states with a lifetime of approximately 0.9 mus which are made to ionize by electron impact.