The experimental spectra are shown as blue (overview) and black (high resolution composite) traces in Figure ; the lower two traces are simulated spectra from reduced dimensionality quantum dynamics calculations. The energies of the transition state and reactant asymptote are shown as grey and black arrows, respectively. There is substantial vibrational structure in the spectrum whose appearance evolves notably with increasing electron binding energy. Peaks a-j are spaced by about 300 cm -1 . They lie below the transition state energy and are attributed to resonances associated with the product complex that can undergo vibrational predissociation to NH2 + HF. Quantum dynamics calculations of the resonance wavefunctions show that the peaks correspond to progressions in the NH2HF hindered translational mode at 251 cm -1 and a more complex vibration at 829 cm -1 in which pseudo-rotation of the HF is coupled to NH2 out-of-plane wagging. The out-of-plane motion is activated by the flattening of the NH3 pyrimidal structure in the anion upon photodetachment to the NH2HF product complex.