The structure and energy of the bicyclic nitrogen tetroxide cation, D-2d NO4+, and its C-2v transition state for dissociation into NO2+ and O-2 have been studied theoretically by the coupled-cluster (CC) and similarity-transformed equation-of-motion coupled-cluster methods (STEOM-CC). The computed 137 kcal/mol energy of decomposition and 370 kcal/mol gas-phase heat of formation identify NO4+ as a highly energetic species. Nevertheless, its low dissociation barrier (12-17 kcal/mol) and high vertical electron affinity (8.4 eV) indicate that NO4+ will have a low stability, which will complicate its experimental observation.