Quenching of molecular ions by He buffer loading at ultralow energies: rotational cooling of OH+(3Σ-) from quantum calculations

An ab initio computed potential energy surface is employed to evaluate the interaction of the OH+(3Σ -) molecule with 4He(1S) atom and an analytic fitting of the raw points is directly employed in quantum scattering calculations at ultralow collision energies. The Hund's case (b) chosen to handle the spin-rotation coupling allows to extract from the numerous inelastic cross sections the relative importance of pure “spin flip" vis-a- vis rotational cooling cross sections. The final rates of all the above processes as a function of the initial |N〉 state are analysed in detail and possible propensity rules are discussed.