There are relatively few experimental studies concerning the structure and reactivity of NiO2 0/-. Neutral NiO2 was first studied in ideal gas matrices, where three isomers were identified in an Ar matrix: cyclic Ni(O2), bent NiOO, and linear ONiO (referred to as NiO2 hereafter). Subsequent work in Ne matrices found preferential formation of NiO2 with trace Ni(O2), allowing for the extraction of two and three vibrational frequencies for these species, respectively. In the gas phase, anion photoelectron spectroscopy (PES) has been used to probe the geometric and electronic structure of these species. The first PES study of NiO2¯ was performed by Wu and coworkers, The electronic and vibrational structure of NiO2 pose a considerable challenge to theory owing to its multireference nature. Treatments using density functional theory, coupled cluster methods, and multireference methods have found a Here, we utilize slow electron velocity-map imaging spectroscopy of cryogenically-cooled anions (cryo-SEVI), a high-resolution variant of anion photoelectron spectroscopy, to study the photodetachment of NiO2¯. In this method, cold ions are detached with a tunable laser and the resultant electron kinetic energy distribution is analyzed by a velocity-map imaging (VMI)