Exploring the electronic states of the hydroxyl dication OH2+: thermodynamic (meta)stability, bound-free emission spectra, and charge transfer processes

Abstract

Accurate potential energy curves were constructed for a manifold of electronic states of the hydroxyl dication using a highly correlated electronic structure approach (SA-CASSCF/MRCI+Q/aug-cc-pV5Z). The existence of a bound (meta)stable ground state and bound low-lying states for OH²⁺ are ruled out, but do not exclude the possibility of its transient formation and dissociation along the repulsive ground state potential energy curve. Our results do not support the conclusion reported for the observation of OH²⁺ by electron ionization from ground state OH⁺. Despite the repulsive character of the low-lying states, thermodynamic stability was indeed verified for the states 2 ⁴Π and 3 ⁴Σ⁻ along with a series of metastable high-lying doublet states. For the (quasi)bound states, we obtained vibrational levels, spectroscopic parameters, and dipole moment functions. Using accurate transition dipole moment functions, we also evaluated bound-free emission transition probabilities and radiative lifetimes. For transitions from v′= 0, our estimates of 92.8 ns (⁴Π) and 9.3 ns (⁴Σ⁻) indicate that the ones obtained by a multichannel theory of predissociating states are too short (2–60 ps). Landau–Zener cross sections averaged over the Maxwellian distribution of relative velocities, and rate coefficients for the reaction O²⁺ + H → O⁺ + H⁺ were obtained using the potential energy curves of the states ⁴Π and ⁴Σ⁻ associated with the channel O²⁺ + H and the repulsive ones dissociating into O⁺ + H⁺ leading to good results for the rate constant thus supporting its importance to explain the distribution of O⁺ in astrophysical plasmas.