Cold reactive and non-reactive collisions of Li and Rb with C$_2^-$: implications for hybrid trap experiments

TL;DR

This study provides a detailed theoretical analysis of cold collisions between Li/Rb atoms and C$_{2}^{-}$ ions, exploring reaction mechanisms, cross sections, and implications for hybrid trap experiments and cooling techniques.

Contribution

It introduces new potential energy surfaces for Li--C$_{2}^{-}$ and Rb--C$_{2}^{-}$ systems using advanced quantum chemistry methods, and investigates collision dynamics relevant for cold ion-atom experiments.

Findings

Potential energy surfaces characterized for singlet and triplet states.

Calculated rotationally inelastic cross sections for the systems.

Discussed the feasibility of Doppler thermometry and sympathetic cooling.

Abstract

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 by means of the close-coupling method. The effect of the core correlation on the potential energy surfaces is discussed and we estimate the error on the collisional cross sections induced by freezing the $1s$ orbitals of the carbon atoms. The results are compared to those obtained for the Rb-OH$^{-}$ system and the applications for hybrid trap experiments are explored. Furthermore, we discuss the possibility to perform Doppler thermometry on the C$_{2}^{-}$ anion and investigate the collision process involving excited states. The implications for sympathetic cooling experiments are also discussed.