Density functional calculations of potential energy surfaces in the CO2/H-2/ScO((2)Sigma(+)) system have been performed to investigate the reaction mechanism Of CO2 hydrogenation to formic acid in the presence of ScO. The results show that ScO can easily form a variety of complexes with CO2 and H-2, complexes Of CO2 with HScOH, and a highly exothermic cyc-OC(H)OScOH molecule. Although transformation of the latter to ScO + HCOOH is impeded by the high barrier for hydrogen transfer from ScOH to HCO2, it is expected to be fast in the gas phase because the transition state is only 2.3 kcal/mol higher in energy than the reactants CO2 + H-2 + SCO. (C) 2004 Elsevier B.V. All rights reserved.