The excited states of N2O2 have been characterized by studies of the dissociative photodetachment of N2O2- at 266 nm. Photoelectron-photofragment coincidence spectroscopy reveals the correlation between features observed in the photoelectron spectrum and different neutral dissociation pathways. Evidence for at least two isomers of N2O2- is presented and upper limits for their stabilities are determined. One isomer, ONNO-, is stable relative to NO + NO + e(-) by < 1.70 +/- 0.05 eV, while the second isomer, trigonal N2O2-, is stable relative to O- + N2O by < 0.57 +/- 0.05 eV. The observed dissociation channels are assigned to ONNO --> NO + NO, N2O2 --> O (P-3) + N2O, and either O(D-1) + N2O or N(S-4) + NO2. No evidence for stable N2O2 was found, and the dissociation dynamics of the excited states of N2O2 are discussed.