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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

Time-dependent aspects of electron degradation: 4, Subexcitation electrons in nitrogen and carbon dioxide

Description: We discuss here the temporal behavior of subexcitation electrons and the yields of products due to these subexcitation electrons. Our examples concern cases in which resonance scattering of electrons occurs, such as vibrational and rotational excitation in N{sub 2} and negative-ion formation in CO{sub 2}. One focus of the present work is a test of the continuous-slowing-down-approximation (CSDA) which we compare to the full solution of the time-dependent Spencer-Fano theory, which has been developed recently. 11 refs., 6 figs., 1 tab.
Date: January 1, 1988
Creator: Kimura, Mineo; Inokuti, Mitio; Kowari, Ken-ichi; Dillon, M.A. & Pagnamenta, A.
Partner: UNT Libraries Government Documents Department