M. Foster

Fully Correlated Electronic Dynamics for Antiproton Impact Ionization of Helium

We present total cross sections for single and double ionization of helium by antiproton impact over a wide range of impact energies from 10 keV/amu to 1 MeV/amu. A nonperturbative time-dependent close-coupling method is applied to fully treat the correlated dynamics of the ionized electrons. Excellent agreement is obtained between our calculations and experimental measurements of total single and double ionization cross sections at high impact energies, whereas for lower impact energies, some discrepancies with experiment are found. At an impact energy of 1 MeV we also find that the double-to-single ionization ratio is twice as large for antiproton impact as for proton impact, confirming a long-standing unexpected experimental measurement.

Fully differential cross sections for C6+ single ionization of helium

We have examined the fully differential cross section (FDCS) for single ionization of helium by a 2 MeV amu−1 C6+ ion. The FDCS is presented for a variety of momentum transfers and ejected electron energies. The theoretical model we use, labelled 3DW-EIS (three-body distorted wave—eikonal initial state), treats the collision as a three-body problem (projectile, active electron, residual ion). In the final state, each two-particle pair is treated exactly and the initial state is an eikonal state which contains the proper asymptotic forms of the projectile–target ion and projectile–electron interactions. Most importantly, the final state of the ejected electron is treated as a distorted wave calculated numerically from the static Hartree–Fock potential for the ion. Our theoretical results are compared with both absolute experimental measurements and previous theoretical calculations. It is shown that the 3DW-EIS results are in good agreement with experiment for all cases except large momentum transfer and low ejected-electron energies.

Triply differential single ionization cross sections in fast ion-atom collisions: Large versus small perturbation

We compare experimental triply differential cross sections for single ionization of He for small (100 MeV/amu C6+ projectiles) and large perturbation (3.6 MeV/amu Au53+ projectiles). For electrons emitted into the scattering plane at the small perturbation, the data are well described by our calculations. For the large perturbation as well as outside the scattering plane for the small perturbation, in contrast, serious discrepancies especially with the continuum distorted wave-eikonal initial state (CDW-EIS) model are found.