Electron capture inAr++H2collisions in the keV energy regime

Electron capture in ${\mathrm{Ar}}^{+}$ ${(\mathrm{}}^2$P)${+\mathrm{H}}_2$(X ${\mathrm{}}^1$ ${\mathrm{\Sigma }}_{\mathrm{g}}$) collisions in the keV energy regime has been studied theoretically. The molecular-orbital expansion method was used within a semiclassical formalism and an electron translation factor correction was incorporated to the first order in the magnitude of the relative velocity V. The molecular wave function and eigenenergy were obtained using the diatoms-in-molecules (DIM) method. We have examined the effect of the orientation of the target ${\mathrm{H}}_2$ molecule on the electron-capture mechanism within the sudden adiabatic approximation. Since π symmetry arising from the p orbital of the ${\mathrm{Ar}}^{+}$ ion is involved in this system, a strong influence on the probability of the molecular orientation was found in all energies studied. As the collision energy increases, the Π-symmetry state in the initial channel becomes more important through the rotational coupling to the electron-capture mechanism, while at lower energies the Σ-symmetry state in the initial channel is the dominant source for the electron capture through strong radial coupling. Agreement of the present theory with measurements is good, but marked disagreement is seen with the atomic-orbital calculation.