As mentioned above, negative ion photodetachment is uniquely suited to carry out transition state spectroscopy experiments on bimolecular reactions. Much of this work has been carried out on triatomic systems. However, a cryo-SEVI experiment on CH3OHFˉ successfully mapped out a series of exit channel Feshbach resonances corresponding to metastable vibrational states of the CH3OHF complex that predissociate to CH3O + HF, yielding considerably higher resolution than a previous study of this system via conventional photoelectron spectroscopy. We recently measured cryo-SEVI spectra of the related system FNH3ˉ to investigate the bimolecular F + NH3 reaction. This reaction has been studied previously by infrared chemiluminescence and with crossed molecular beams scattering. Potential energy surfaces for this reaction have been reported and dynamics on these surfaces were explored using quasi-classical trajectory calculations. The relevant energetics and geometries for this system are shown in Figure . The reaction is exothermic by 1.3 eV and has a submerged barrier between reactant FNH3 and product FHNH2 complexes. The anion is strongly hydrogen-bonded with a calculated dissociation energy of 0.70 eV and has good geometric overlap with the neutral transition state. The goal of the experiment, then, was to observe vibrational structure associated with not only the product complex, as was seen in CH3OHFˉ, but also the transition state and reactive complex, and, possibly, dynamical resonances lying above the F + NH3 reactant asymptote.