Photodetachment of cold OH- in a multipole ion trap
  The absolute photodetachment cross section of OH- anions at a rotational and translational temperature of 170K is determined by measuring the detachment-induced decay rate of the anions in a multipole radio-frequency ion trap. In comparison with previous results, the obtained cross section shows the importance of the initial rotational state distribution. Using a tomography scan of the photodetachment laser through the trapped ion cloud, the derived cross section is model-independent and thus features a small systematic uncertainty. The tomography also yields the column density of the OH- anions in the 22-pole ion trap in good agreement with the expected trapping potential of a large field free region bound by steep potential walls. 
S. Trippel, J. Mikosch, R. Berhane, R. Otto, M. Weidem\"uller, and R.   Wester