Orientation-dependent atomic model for electron transfer in ion-molecule collisions: Applications to ${\mathrm{H}}^{+}$+${\mathrm{H}}_2$ and ${\mathrm{He}}^{2+}$+${\mathrm{H}}_2$

Single-electron-capture cross sections in collisions of protons and α particles with ground-state ${\mathrm{H}}_2$ molecules have been studied for projectile energies in the range of 1–500 keV/amu. By treating the ground-state ${\mathrm{H}}_2$ wave function as a linear combination of atomic orbitals from the two atoms, the electron-capture amplitude in ion-molecule collisions is expressed as the coherent superposition of two single-electron-capture amplitudes in ion-atom collisions with the relative phase between the two amplitudes dependent on the collision velocity and the orientation of the molecule. The dependence of the capture cross sections with respect to the molecular orientation was examined. Total electron-capture cross sections averaged over the molecular orientations were obtained and found to be in good agreement with experiments.