We have performed a systematic ab initio study on alkali and alkaline earth hydroxide neutral (MOH) and anionic (MOH − ) species where M = Li, Na, K, Rb, Cs or Be, Mg, Ca, Sr, Ba. The CCSD(T) method using extended basis sets and MDF electron core potentials as been used to study their equilibrium geometries, interaction energies, adiabatic electron affinities and potential energy surfaces. All neutral and anionic species exhibit a linear shape with the exception of BeOH, BeOH − and MgOH − , for which the equilibrium structure is bent. In the context of sympathetic cooling of OH − by collision with ultracold alkali and alkaline earth atoms, we investigate the M-OH − potential energy surfaces and the associative detachment reaction M+OH − → MOH+e − , which is the only energetically allowed reactive channel in the cold regime. We discuss the implication for the sympathetic cooling of OH − and conclude than Li and K are the best candidates for ultracold buffer gas.

A theoretical rate constant for the associative detachment reaction Rb((2)S) + OH(-)((1)Σ(+)) → RbOH((1)Σ(+)) + e(-) of 4 × 10(-10) cm(3) s(-1) at 300 K has been calculated. This result agrees with the experimental rate constant of 2-1 (+2)×10(-10)cm(3)s(-1) obtained by Deiglmayr et al. [Phys. Rev. A 86, 043438 (2012)] for a temperature between 200 K and 600 K. A Langevin-based dynamics which depends on the crossing point between the anion (RbOH(-)) and neutral (RbOH) potential energy surfaces has been used. The calculations were performed using the ECP28MDF effective core potential to describe the rubidium atom at the CCSD(T) level of theory and extended basis sets. The effect of ECPs and basis set on the height of the crossing point, and hence the rate constant, has been investigated. The temperature dependence of the latter is also discussed. Preliminary work on the potential energy surface for the excited reaction channel Rb((2)P) + OH(-)((1)Σ(+)) calculated at the CASSCF-icMRCI level of theory is presented. We qualitatively discuss the charge transfer and associative detachment reactions arising from this excited entrance channel.

We present a theoretical investigation of cold reactive and non-reactive collisions of Li and Rb atoms with C − 2 . The potential energy surfaces for the singlet and triplet states of the Li-C − 2 and Rb-C − 2 systems have been obtained using the CASSCF/ic-MRCI+Q approach with extended basis sets. The potential energy surfaces are then used to investigate the associative detachment reaction and to calculate rotationally inelastic cross sections at low collision energies by means of the close-coupling method. The results are compared to those obtained for other anionic systems such as Rb-OH − , and the implications for hybrid trap experiments and sympathetic cooling experiments are explored. Furthermore, we discuss the possibility to perform Doppler thermometry on the C − 2 anion and investigate the collision process involving excited electronic states.

Associative electronic detachment (AED) between anions and neutral atoms leads to the detachment of the anion’s electron resulting in the formation of a neutral molecule. It plays a key role in chemical reaction networks, like the interstellar medium, the Earth’s ionosphere and biochemical processes. Here, a class of AED involving a closed-shell anion (OH−) and alkali atoms (rubidium) is investigated by precisely controlling the fraction of electronically excited rubidium. Reaction with the ground state atom gives rise to a stable intermediate complex with an electron solely bound via dipolar forces. The stability of the complex is governed by the subtle interplay of diabatic and adiabatic couplings into the autodetachment manifold. The measured rate coefficients are in good agreement with ab initio calculations, revealing pronounced steric effects. For excited state rubidium, however, a lower reaction rate is observed, indicating dynamical stabilization processes suppressing the coupling into the autodetachment region. Our work provides a stringent test of ab initio calculations on anion-neutral collisions and constitutes a generic, conceptual framework for understanding electronic state dependent dynamics in AEDs.