Reaction of Cr+, Mn+, Fe+, Co+, and Ni+ with O2 and N2O. Examination of the translational energy dependence of the cross sections of endothermic reactions

Abstract

Reactions of Cr+, Mn+, Fe+, Co+, and Ni+ with O2 and N2O to yield metal oxide ions are examined using an ion beam apparatus. Reaction cross sections σ as a function of ion translational energy E are reported. With one exception, Fe++N2O, the cross sections exhibit an energy threshold Eo. Several models are used to interpret the excitation functions for the O2 reactions and it is concluded that the classical line-of-centers form σ α (1–Eo/E) is most useful. Bond energies derived in this manner are D°(CrO+) = 3.45±0.1 eV, D°(MnO+) = 2.48±0.1 eV, D°(FeO+) = 3.01±0.1 eV, D°(CoO+) = 2.76±0.1 eV, and D°(NiO+) = 1.95±0.1 eV. Since these bond energies are all greater than D°(N2–O) = 1.7 eV, the observation of energy thresholds for the reactions with N2O are surprising. These results are explained in terms of a qualitative view of the electronic potential energy surfaces involved.