Titanium Superoxide as a Carrier of a "Long-Lived" Superoxide Anion: An Investigation.

The photoinduced generation of a superoxide anion on the surface of a semiconductor photocatalyst is usually attributed to the reduction of O with conduction-band electrons. In the current work, the reaction of TiO with O giving rise to TiO in superoxide and peroxide states has been investigated with (CAS, CCSD) and DFT (B3LYP) calculations. The ground triplet state and two substates (open-shell singlet (OSS) and closed-shell singlet (CSS)) of a doubly degenerate excited singlet state (Δ) are considered as reactive states of oxygen, participating in spontaneous or photoinduced processes, respectively. The triplet and OSS singlet states of TiO contain as structural units and can be defined as titanium superoxides. Both states have energy less than the level of the initial pair TiO+O by about 30 kcal/mol. The CSS state of TiO has a diperoxide structure () and also lies in energy below the initial pair TiO+O. Titanium superoxide is considered to be the carrier of an "exceptionally stable" and "long-lived" superoxide anion, which was earlier synthesized or detected on the surface of TiO. The low-energy location of the conical intersections on the way from reagents to TiO allows us to explain the literature data on the spontaneous generation of the "long-lived" superoxide anion on the TiO surface.