Ab initio calculations have been carried out to investigate interaction of titanium dioxide TiO2 with oxygen O-2 in ground triplet and excited singlet states. On a singlet potential energy surface (PES) formation of a stable compound of titanium peroxide TiO4 is revealed which should appear in reaction of TiO2 with singlet oxygen without activation barrier. This peroxide is lower in energy than the ground state of two individual molecules TiO2 + 3O(2) by 34.6 kcal/mol. Location of conical intersection between triplet and singlet PESs of TiO(2)AO(2) is also investigated. (C) 2016 Elsevier B.V. All rights reserved.