Cold collisions of C$_{2}^{-}$ anions with Li and Rb atoms in hybrid traps

TL;DR

This study models low-temperature collisions between C$_{2}^{-}$ anions and alkali-metal atoms in hybrid traps, revealing slow associative detachment in ground states and faster reactions with excited states, impacting sympathetic cooling strategies.

Contribution

It provides the first detailed theoretical analysis of reactive and non-reactive collisions of C$_{2}^{-}$ with Li and Rb, including effects of excited states and micromotion in hybrid traps.

Findings

Associative detachment is slow in ground states but rapid with excited atoms.

Translational cooling of C$_{2}^{-}$ is faster than rotational cooling.

Excited atoms cause anion losses comparable to rotational cooling times.

Abstract

We present a theoretical investigation of reactive and non-reactive collisions of Li and Rb atoms with C$_{2}^{-}$ molecular anions at low temperatures in the context of sympathetic cooling in hybrid trap experiments. Based on recently reported accurate potential energy surfaces for the singlet and triplet states of the Li-C$_{2}^{-}$ and Rb-C$_{2}^{-}$ systems, we show that the associative electronic detachment reaction is slow if the colliding partners are in their ground state, but fast if they are excited. The results are expected to be representative of the alkali-metal series. We also investigate rotationally inelastic collisions in order to explore the cooling of the translational and rotational degrees of freedom of C$_2^-$ in hybrid ion-atom traps. The effect of micromotion is taken into account by considering Tsallis distributions of collision energies. We show that the translational cooling occurs much more rapidly than rotational cooling and that the presence of excited atoms leads to losses of anions on a timescale comparable to that of rotational cooling.