Interaction of H-2 with photoexcited TiO2 surface is modeled using density functional theory. Amorphous Ti8O16 molecular cluster in triplet electronic state represents defect surface of the dioxide under illumination. The calculations reveal repulsion, physisorption, and dissociative photoadsorption interaction scenarios. The computed standard enthalpies of physisorption range from -0.02 to -0.11 eV. Dissociative photoadsorption proceeds on holes via an energy barrier (<0.04 eV). The reaction is exothermic (Delta H-0 = -0.85 eV). Neither its energetics nor the mechanism depends on the hole's stability. The calculated Ti3+ g-tensors of Ti8O16H species match the experimentally observed surface Ti3+ EPR signal. (C) 2015 Elsevier B.V. All rights reserved.