Rotational Transitions of CO+Induced by Atomic Hydrogen

The CO + molecular ion has been observed in photon-dominated regions. Recent modeling has not been able to explain the abundances of CO + in these regions. The most abundant collision partners are believed to be hydrogen atoms, hydrogen molecules, and electrons. The reactions of these species with CO + have been studied previously and found to be fast. The only inelastic processes studied before were collisions of CO + with electrons. Here we investigate the inelastic collisions of CO + with hydrogen atoms. We argue that this can be done on the lowest triplet electronic state. This implies that CO + ions, in a hydrogen atom dominated surrounding, experiences a few inelastic collisions before reacting. Rotationally inelastic state-to-state cross sections ( j ⩽ 8) are presented together with state-resolved thermal rate coefficients. The results suggest that the rotationally inelastic collision cross sections can be of comparable magnitude to the reactive ones. Implications for the rotational temperature of CO + in PDRs are discussed. To perform the calculations, a potential energy surface is fitted using the reproducing-kernel Hilbert space method based on multireference configuration-interaction calculations employing the aug-cc-pVQZ basis set.