spectrometer that is optimized for the detection of slow electrons, yielding photoelectron spectra with sub-meV resolution. Revisiting the photoelectron spectra of NiO2¯ with cryo-SEVI provides substantial improvements in resolution over previous work. Beyond well-resolved vibrational structure in the ground and excited states, we observe a number of FC-forbidden transitions in the ground state that display behavior distinct from that of the FC-allowed transitions near the photodetachment threshold. These features are ascribed to vibronic coupling to an excited electronic state. Our findings are supported by scalar-relativistic coupled-cluster calculations, with computed term energies and vibrational frequencies in good agreement with our observed spectra.