Understanding the interplay between inelastic and reactive processes in low temperature molecular collisions is a true theoretical challenge. This study addresses this challenge by employing the statistical adiabatic channel model (SACM) to quantify the rotational excitation processes in the ${\mathrm{OH}}^{+}+{\mathrm{H}}_2$ reactive system, such process being key in astrochemistry. The SACM approach demonstrates very good agreement with reduced dimensional close-coupling calculations in describing pure inelastic collisions in the low energy regime and satisfactory agreement with experimental measurement for treating reactive processes. Hence, the SACM approach can be considered as a good alternative to consider molecular collisions in reactive systems characterized by strongly bounded intermediate complexes, in absence of exact calculation in the low energy regime. Our findings reveal that reactive processes dominate the pure collisional excitation at all temperatures studied (5–300 K) by at least about one order of magnitude. This suggests a strong revision of the predicted abundance of ${\mathrm{OH}}^{+}$ in astrophysical environments since astrochemical models are presently significantly overestimating the impact of ${\mathrm{OH}}^{+}$ excitation induced by ${\mathrm{H}}_2$ collisions.

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• Atomic & molecular collisions
• Rotational states
• Scattering theory