Charge-transfer processes in collisions of ground ($2s^{2}2p{}^{2}P$) and metastable ($2s2p^2{}^{4}P$) states of ${\text{C}}^{+}$ ions with ${\text{H}}_2$ are investigated using the quantum-mechanical molecular-orbital close-coupling method in the energy range of 10–1000 eV/u. Molecular potential energy curves and nonadiabatic couplings are calculated using the ab initio multireference single- and double-excitation configuration-interaction method. For the ground-state system, the Franck-Condon approximation is adopted due to the large electronic energy defect relative to the ${\text{H}}_2$ vibrational spacing, and total cross sections rise significantly above 100 eV/u, where capture into the $\mathrm{C}2p^2{}^{1}S, 2p^2{}^{3}P$, and $2p^2{}^{1}D$ states dominates, with interference among these channels. For the metastable system, vibrational effects need to be treated with the electronic-vibrational close-coupling method, since the electronic energy defect is comparable to the vibrational spacing. In contrast to the ground-state system, the vibrationally near-resonant exothermic mechanism enhances total cross sections by an order of magnitude, populating high ${\text{H}}_2{}^{+}$ vibrational levels ($v=5,6$) at energies below 100 eV/u, while above 100 eV/u the cross sections remain constant, with Stueckelberg oscillations arising from short-range potential-well interference. Total cross sections for both initial state-resolved ions agree well with the respective experimental data, and mixed-beam cross sections obtained using the known fraction are in good agreement with the available experimental data.

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• Chemical charge transfer
• Scattering of atoms, molecules, clusters & ions
• Vibronic effects
• Configuration interaction
• Nonperturbative methods