Sympathetic Cooling and Quantum State Dependent Reactions of Molecular Anions by a Localized Laser-Cooled Buffer Gas

The study of ion-neutral reactions moves rapidly towards cold chemistry which implies the need of well-controlled ion ensembles in a cold environment. An ideal tool to store and prepare ions are multipole radio frequency ion traps. Collisions with neutral atoms have proven to be a general approach to cool internal and translational degrees of freedom of trapped molecular ions. In our hybrid-ion-atom trap, hydroxyl anions are stored in a 8-pole radio frequency wire trap, combining the advantages of a flat potential in the radial center of a multipole trap and providing optical access required to laser cool the buffer gas atoms. A dense cloud of ultra-cold buffer gas, namely Rubidium, is confined in a dark spontaneous-force optical trap (Dark-SPOT), enabling the preparation of atoms in variable excited state fractions. Overlapping a dense cloud of ultracold Rubidium with hydroxyl anions, leads to elastic and inelastic collisions, cooling the internal and translational degrees of freedom of the anion. Furthermore reactive collisions occur, with a rate dependent on the electronic state of the Rubidium atoms. In this seminar, I will present first signs of sympathetic cooling and orbital dependent reaction rates.