Molecular-state treatment of ${\mathrm{He}}^{+}$(2p) excitation through electron capture in ${\mathrm{He}}^{2+}$-${\mathrm{H}}_2$ collisions at low energies

We report the calculation of low-energy state-selective electron-capture cross sections in an α-particle collision with molecular hydrogen. The semiclassical molecular-orbital expansion method is used and electron translation effects are taken into account. The calculated ${\mathrm{He}}^{+}$(2p) formation cross sections are in good overall agreement with the recent measurements of Hoekstra et al. [J. Phys. B 22, L603 (1989)]. However, the experimental cross sections show a pronounced plateau between E=0.7 and 2.0 keV/amu. In the same energy region the calculated results exhibit an oscillatory structure that arises from a combination of Landau-Zener and Rosen-Demkov oscillations.