The rate constant k(R) for the highly exothermic, spin-allowed reaction FeO+(6SIGMA+) + H-2 --> Fe+(6D) + H2O is 2 orders of magnitude smaller than the collision rate constant k(L) (k(R) = 1.6 X 10(-11) cm3 molecule-1 s-1; k(L) = 1.5 X 10(-9) cm3 molecule-1 s-1). Labeling experiments using HD and D2 reveal that no strong intermolecular kinetic isotope effects are operative on the rate constant of this reaction. Extremely low reactivities are also observed for the reactions of CoO+ and NiO+ with H-2 (k(R) = 1.2 and 2.1 X 10(-12) cm3 molecule-1 s-1), and there are no kinetic isotope effects within experimental error in the reactions of these metal oxides with D2 as well. The experimental data and theoretical considerations point to a reaction mechanism involving a multicentered transition structure in the rate-determining step.