The reaction of titanium monoxide molecules and 02 was studied by using matrix isolation infrared spectroscopy as well as theoretical calculations. The titanium monoxide molecule reacts with O-2 to form TiO3 spontaneously on annealing. The TiO3 molecule is characterized to be a side-on bonded peroxo titanium monoxide complex, (eta(2)-O-2)TiO, which has a nonplanar C-s symmetry with a (1)A' ground state. The (eta(2)-O-2)TiO complex can further coordinate another dioxygen to give TiO5, a disuperoxo titanium monoxide complex, (eta(2)-O-2)(2)TiO, which possesses a (3)A '' ground state and a nonplanar C-s geometry.