Cold collisions and reactions of trapped negative ions

In this presentation I will discuss results on cold collisions and reactions of trapped negative ions with neutral atoms or molecules. The experiments are carried out using a 16-pole radiofrequency wire ion trap. Using optical pumping via an electronic excited state below the detachment threshold we have prepared carbon dimer anions in excited vibrational levels. A photodetachment signal is used to measure the vibrational population. We have then measured the vibrationally inelastic scattering rate coefficient. This serves as a stringent test of multidimensional quantum scattering calculations. Using these collisions we could also close the optical cycle and observe the fluorescence of the trapped anions. Work is in progress to measure the rotational population using photodetachment spectroscopy and to add repumping lasers instead of the quenching step. Furthermore, we have added a source for cold atomic hydrogen to the ion trap. Using this we have studied the associative detachment reaction of several negative ions, in particular several interstellar negative ions, with atomic hydrogen as a function of the collision temperature.