Photodissociation of trapped Rb${}_2^{+}$ : Implications for simultaneous trapping of atoms and molecular ions

The direct photodissociation of trapped ${}^{85}$Rb${}_2^{+}$ (rubidium) molecular ions by the cooling light for the ${}^{85}$Rb magneto-optical trap (MOT) is studied, both experimentally and theoretically. Vibrationally excited Rb${}_2^{+}$ ions are created by photoionization of Rb${}_2$ molecules formed photoassociatively in the Rb MOT and are trapped in a modified spherical Paul trap. The decay rate of the trapped Rb${}_2^{+}$ ion signal in the presence of the MOT cooling light is measured and agreement with our calculated rates for molecular ion photodissociation is observed. The photodissociation mechanism due to the MOT light is expected to be active and therefore universal for all homonuclear diatomic alkali metal molecular ions.