Ionic interactions and quenching dynamics in cold traps: rotationally cooling collisions of OH-('Σ+) with Rb(2S)

A newly computed potential energy surface, which describes the forces at play between the OH−(X1Σ+) anionic molecule (treated as a rigid rotor at its equilibrium geometry) and the Rb(2S) atomic gas was obtained from fully ab initio methods, yielding highly correlated electronic wavefunctions for the interacting partners. It is in turn employed to calculate their rotationally quenching collision cross sections at ultralow energies and for different initial rotational states of the molecular anion. The results suggest that these strongly interacting partners are among the most efficient systems in providing very large internal de-excitation rates whenever the collision regime of an ultracold trap can occur for the partners. The collision encounters at such vanishing values of translational energies are seen to be strongly controlled by the behaviour of the real part of the scattering length as a function of the initial rotational state: the latter indicates, in fact, the presence of several virtual states close to the dissociation threshold of the complex.