Charge transfer in ion-molecule collisions at keV energy regime: Study of ${\mathrm{H}}^{+}$+${\mathrm{H}}_2$ collisions by the electron-translation-factor–modified molecular-orbital–expansion method

Charge transfer in ${\mathrm{H}}^{+}$+${\mathrm{H}}_2$(${\mathrm{X}}^1$ ${\mathrm{\Sigma }}_{\mathrm{g}}$; v=0) collisions has been studied theoretically at energies from 0.2 to 20 keV with use of a molecular-state–expansion method incorporating electron translation factors. Two-state semiclassical close-coupling calculations have been performed to investigate the ion-molecule collision dynamics. The molecular states, used as the expansion basis, have been obtained by using the diatoms-in-molecules (DIM) method as functions of the internuclear distance R and two molecular orientation angles θ and φ. The effect of orientation of the target molecule on the charge-transfer mechanism has been examined and the charge-transfer cross section is found to be very sensitive to the molecular orientation at energies below 0.5 keV or above 10 keV. Between these energies, however, the orientation effect was small (due to accidental near-degeneracy of the probability from different θ). Our results are in good agreement with experimental measurements in the energy range where they are available.