Light-assisted cold chemical reactions of barium ions with rubidium atoms

Light-assisted reactive collisions between laser-cooled Ba+ ions and Rb atoms were studied in an ion–atom hybrid trap. The reaction rate was found to strongly depend on the electronic state of the reaction partners with the largest rate constant [7(2) × 10−11 cm3 s−1] obtained for the excited Ba+(6s)+Rb(5p) reaction channel. Similar to the previously studied Ca++Rb system, charge transfer and radiative association were found to be the dominant reactive processes. The generation of molecular ions by radiative association could directly be observed by their sympathetic cooling into a Coulomb crystal. Potential energy curves up to the Ba+(6s)+Rb(5p) asymptote and reactive-scattering cross sections for the radiative processes were calculated. The theoretical rate constant obtained for the lowest reaction channel Ba+(6s)+Rb(5s) is compatible with the experimental estimates obtained thus far.