Rotational Excitation of the OH⁺ Radical by Collision with H at Low Temperature

Abstract

A ro-vibrationally inelastic close coupling study of the rotational excitation of OH(+)(X(3)Σ(-)) by collisions with H((2)S) is presented. The two lowest potential energy surfaces of doublet and quadruplet spin multiplicity are involved. The former is the one we developed recently, and the latter is a modified version of the quadruplet surface of Martinez et al. to include the long-range charge-induced-dipole potential. The details of the modification of this surface are presented as well as the comparison of the rotational excitation resulting from collisions with hydrogen on these two surfaces. The effect of the coupling between vibration and rotation on the rotational excitation rate is also discussed, as the potential well depth of the doublet surface is quite large and allows the coupling between many vibrational channels of OH(+). As the hydrogen exchange reaction can occur for both potential energy surfaces, we discuss the reliability of the approximation made by the calculation of the cross sections with a quantum dynamics limited to the inelastic process. The relative importance of the collisions on the doublet or quadruplet surface within a given rotational transition is also discussed.

An Efficient Statistical Method to Compute Molecular Collisional Rate Coefficients

“…The method is expected to yield the best results for collisions in which an intermediate molecular complex can be formed. As an example, we consider rotationally inelastic OH + -H collisions, for which accurate close-coupling results are available in the literature (Stoecklin et al 2015;Bulut et al 2015). In this application, we only consider rigid-rotor collisions on the quartet potential energy surface thus neglecting the (low probability) exchange and reactive channels (Bulut et al 2015).…”

“…As a result, for collisions where the intermediate complex is a stable molecule or ion, close-coupling calculations have been restricted to the very simplest atom-diatom systems, see e.g. Stoecklin et al (2015); Bulut et al (2015) for OH + +H.…”

State-to-state chemistry and rotational excitation of CH+ in photon-dominated regions

“…We have also checked the reliability of the rigid-rotor approximation for the CH + excitation by H. It was shown recently that this approximation leads to good results in the case of the endothermic OH + +H reaction on the quartet PES whose minimum is similar to a van der Waals well (Bulut, Lique & Roncero 2015; Stoecklin et al 2015). Its accuracy was found, however, to degrade on the doublet PES where there is a much deeper potential well, like in CH + + H (Bulut, Lique & Roncero 2015).…”

State-to-state chemistry and rotational excitation of CH$^+$ in photon-dominated regions

“…We have also checked the reliability of the rigid-rotor approximation for the CH + excitation by H. It was shown recently that this approximation leads to good results in the case of the endothermic OH + +H reaction on the quar- tet PES whose minimum is similar to a van der Waals well (Bulut, Lique & Roncero 2015;Stoecklin et al 2015). Its accuracy was found, however, to degrade on the doublet PES where there is a much deeper potential well, like in CH + + H (Bulut, Lique & Roncero 2015).…”