B3LYP and CCSD(T) calculations with various basis sets have been performed to investigate the potential energy surface for the ScO+H 2 ->Sc+H 2 O reaction, which is shown to proceed by formation of the HScOH molecule. HScOH can isomerize to the molecular Sc-OH 2 complex and dissociate to Sc atoms and water with endothermicity of 51-59 kcal/mol. The HScOH molecule is thermodynamically stable and the barrier required to release H 2 , ~28 kcal/mol, is much lower than the energy needed for the Sc+H 2 O dissociation. The Sc-OH 2 molecular complex has a binding energy of 7-11 kcal/mol and is stabilized kinetically with respect to isomerization to HScOH by a significant barrier.