State-selected ion-molecule reactions with Coulomb-crystallized molecular ions in traps

► First study of an ion-molecule reaction using state-selected, spatially localized molecular ions at milliKelvin temperatures. ► Rovibrational-state preparation/resolution for reactant/product ions. ► Characterization of translation-to-rotation energy transfer upon charge exchange between N2+ and N2. ► Experimental results interpreted with classical trajectory simulations on a full-dimensional PES.