Cold ion-neutral chemistry: Measurement of charge-exchange reaction rates in the $\textrm{Na} + \textrm{Ca}^+$ system using a hybrid atom- ion trap

We present new state-selective measurements of charge-exchange reaction rates between Na[$^2\textrm{S}$, $^2\textrm{P}$] and $\textrm{Ca}^+$[$^2\textrm{S}$, $^2\textrm{D}$] using a hybrid trap consisting of a linear Paul trap and a concentric magneto-optical trap (MOT). We measure reaction rates by monitoring the decay of the trapped ion population when overlapped with a MOT, which depend strongly on the ion-cloud temperature and laser-controlled quantum states of the Na and $\textrm{Ca}^+$ reactants. The optically dark $\textrm{Ca}^+$[$^2\textrm{S}$, $^2\textrm{D}$] ion temperature is controlled by either excess micromotion heating or sympathetic cooling from the Na MOT. We find evidence of both endothermic and exothermic reactions, the strongest of which is the Na[$^2\textrm{P}$] on $\textrm{Ca}^+$[$^2\textrm{D}$] with a reaction rate ~$10^{-8}\;\textrm{cm}^3/\textrm{s}$, which exceeds the classical Langevin limit. This work was supported by NSF PHY-1307874.