Photodetachment spectroscopy of cold trapped near threshold.

We have studied photodetachment of the amidogen anion as a function of photon energy near the detachment threshold. The detachment spectrum is obtained over the energy range of 6190-6355 cm from the loss rate of the anions from a cryogenic radiofrequency multipole ion trap. By modeling all accessible rotational state-to-state photodetachment transitions, we can assign rotational state-specific thresholds to the measured spectrum. In this way, we have determined the electron affinity of NH to be 6224 ± 1 cm.