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Double and single ionization of He and H{sub 2} by slow protons and antiprotons

Description: Double and single ionization of He and H{sub 2} by proton (p) and antiproton ({bar p})impact in the energy region below 50 keV was studied theoretically by using the semiclassical molecular picture. As the energy decreased, the ratio of the double- to the single-ionization cross section increased for impact and decreased for p impact for both He and H{sub 2}. These trends are consistent with recent measurements for He. Ionization mechanisms differ distinctly for p impact and {bar p} impact. For p impact, the dominant mechanism for double ionization at the lower energies is sequential ladder climbing by the two electrons through various excited channels and finally into the continuum. For {bar p} impact, in contrast, the approaching negative charge distorts both the He and H{sub 2} electron clouds toward the other side of the nucleus and decreases the electron binding energies. These effects enhance electron-electron interactions, increasing double ionization. For the H{sub 2}, an effect of molecular orientation is an additional complication in determining the dynamics.
Date: December 31, 1994
Creator: Kimura, Mineo; Shimamura, Isao & Inokuti, Mitio
Partner: UNT Libraries Government Documents Department