To study cold negative ions we trap the ions at variable temperatures from 3 to 300 K in a high-order multipole ion trap. For many years we have been using a 22-pole radiofrequency ion trap featuring a large field-free trapping volume with steep walls. Recently, we have developed a 16-pole wire-based ion trap, which provides an excellent optical access to the cold ions from all directions. Using photodetachment spectroscopy near threshold, we study the influence of rotational and vibrational quantum states in inelastic collisions. Furthermore, we search for tunneling effects and study the role of long-range interactions on anion-molecule reactions. The main emphasis of our work is on interstellar negative ions, such as the first identified interstellar anion C6H-. Both ion-molecule reactions and photodetachment of these systems are of great interest to understand the role and the abundance of negative ions in the interstellar medium.
