Antiproton collisions with molecular hydrogen

Theoretical antiproton and proton cross sections for ionization and excitation of hydrogen molecules as well as energy spectra of the ionized electrons were calculated in the impact-energy range from 8 to 4000 keV. The cross sections were computed with the close-coupling formulation of the semi-classical impact-parameter method. The target was described using a one-active electron model centered on the target and assuming a fixed internuclear distance during the collision process. The dependence of the ionization cross sections on the internuclear distance is examined. The present cross sections are compared with experimental and theoretical data from the literature. For impact energies E > 90 keV the obtained results for ionization by antiproton impact are comparable to the experimental data while they disagree for energies E < 80 keV.