Formation of molecular ions by radiative association of cold trapped atoms and ions

TL;DR

This paper theoretically investigates radiative association of cold trapped atoms and ions, predicting formation of molecular ions with significant cross sections and vibrational distributions, and compares results with experiments.

Contribution

It provides detailed quantum chemistry calculations predicting molecular ion formation via radiative association in cold atom-ion collisions, including cross sections and vibrational states.

Findings

Radiative association cross sections are 2-10 times larger than charge transfer.

Narrow shape resonances are predicted and potentially detectable.

Molecular ions are formed in excited vibrational states.

Abstract

Radiative emission during cold collisions between trapped laser-cooled Rb atoms and alkaline-earth ions (Ca$^+$, Sr$^+$, Ba$^+$) and Yb$^+$, and between Li and Yb$^+$, are studied theoretically, using accurate effective-core-potential based quantum chemistry calculations of potential energy curves and transition dipole moments of the related molecular ions. Radiative association of molecular ions is predicted to occur for all systems with a cross section two to ten times larger than the radiative charge transfer one. Partial and total rate constants are also calculated and compared to available experiments. Narrow shape resonances are expected, which could be detectable at low temperature with an experimental resolution at the limit of the present standards. Vibrational distributions are also calculated, showing that the final molecular ions are not created in their ground state level.