The reactions of bismuth atoms and O-2 have been investigated using matrix isolation infrared spectroscopy and density functional theory calculations. The ground state bismuth atoms react with dioxygen to form the BiOO and Bi(O-2)(2) complexes spontaneously on annealing. The BiOO molecule is characterized to be an end-on bonded superoxide complex, while the Bi(O-2)(2) molecule is characterized to be a superoxo bismuth peroxide complex, [Bi3+(O-2(-))(O-2(2-))]. Under UV-visible light irradiation, the Bi(O-2)(2) complex rearranges to the more stable OBiOOO isomer, an end-on bonded bismuth monoxide-ozonide complex. The end-on-bonded OBiOOO complex further rearranges to a more stable side-on bonded OBiO3 isomer upon sample annealing. In addition, the bent bismuth dioxide anion is also formed and assigned.