Ionization of hydrogen and hydrogenic ions by antiprotons

Light antiproton one-electron quasi-molecular ions within the relativistic A-DKB method

In the present work, two quasi-molecular compounds each involving one antiproton and one electron (p̄), He+-p̄ and H-p̄, are investigated. Using completely relativistic calculations within the finite-basis method adapted to systems with axial symmetry, the adiabatic potential curves are constructed by numerically solving the two-center Dirac equation. The binding energies of electron are obtained as a function of the inter-nuclear distance and compared with the corresponding nonrelativistic values and relativistic leading-order corrections calculated in the framework of other approaches. A semantic analysis of antiproton quasi-molecular ions with compounds containing a proton (p) instead of an antiproton is given. The advantages of the A-DKB method are demonstrated.

Target structure-induced suppression of the ionization cross section for low-energy antiproton-molecular hydrogen collisions: theoretical confirmation

Theoretical confirmation of the experimentally observed phenomenon [Knudsen et al., Phys. Rev. Lett. 105, 213201 (2010)] of target structure-induced suppression of the ionization cross section for low-energy antiproton-molecular hydrogen collisions is given. To this end a novel time-dependent convergent close-coupling approach to the scattering problem that accounts for all possible orientations of the molecular target, has been developed. The approach is applied to study single ionization of molecular hydrogen on the wide energy range from 1 keV to 2 MeV with a particular emphasis on low energies. Results for the orientation-averaged total single ionization cross section are compared with available experimental data and good agreement is found at low (<20 keV) and high (>90 keV) energies. A minor discrepancy is found within a small energy gap near the maximum of the cross section.

Monocentric close-coupling expansion to provide ejected electron distributions for ionization In atomic collisions

A new monocentric close-coupling expansion, in terms of spherical Bessel functions confined in a finite box, is presented and implemented for &pmacr;+H(1s) collisions. Besides total ionization cross sections, this method also provides reliable ejected electron distributions, which are beyond the scope of usual close-coupling expansions and basically confirm the recent classical description of Illescas and Riera [Phys. Rev. Lett. 80, 3029 (1998)].