The photolysis of aqueous peroxynitrite, ONOO-(aq), by 266 nm UV radiation is explored by femtosecond UV-UV and UV-IR transient absorption spectroscopies. The experiments show that 90 +/- 10% of the photolyzed ONOO- anions remain dissociated after 400 ps. We analyze the photolysis in terms of five potential reaction channels, using steady-state absorption spectra together with electron structure calculations on potential photoproducts in clusters of water molecules. In addition, calculations of all excited electronic states of ONOO-(g) below the excitation energy help to explore the reaction channels. The dominant reaction channel is hv + ONOO- -> O-2(center dot-) + NO center dot. (C) 2015 Elsevier B.V. All rights reserved.