A density functional theory investigation of the reactions of Fe and FeO2 with O2

The reactions of Fe and FeO2 with O-2 and the products of these reactions are investigated at the B3LYP/6-311+G(d) level. The reactions are considered in terms of the calculated potential energy surfaces, the interaction energies between reactant species, and the energies required to populate the higher electronic states such as the excited states of Fe(F-5, F-3) and O-2((1)Sigma(+)(g)). It is found that the reactions of Fe with O-2 are endothermic and that the direct formation of dioxide OFeO is due to an ionic interaction of Fe+ with O-2. Furthermore, the diabatic transitions from the covalent and ionic surfaces onto another ionic surface with energy barriers allow the Fe + O-2 reaction to proceed toward the formation of dioxide OFeO. There are other paths corresponding to the vertical excitation from peroxide Fe(O-2) to dioxide OFeO; these require excitation energies above 23, 34, and 48 kcal mol eta(1) in the low-lying triplet, quintet, and septet states, respectively. The OFeO + O-2 reactions are found to endothermically produce the eta(2)-(O-2) FeO2 and eta(1)-(O-2) FeO2 complexes, and the low-lying states of complexes are found to be closely located in the energy range of 5.6 kcal mol (1). The conversion of the eta(2)-complex to the eta(1)-complex and vice versa is caused by low energy. The NBO analyses show that the large atomic charges of peroxide Fe(O-2), superoxide FeOO, and the eta(2)- and eta(1)-complexes are caused by electron transfer between reactant species, whereas those of dioxide OFeO are dominated by the ionic character of the species. (C) 2016 Elsevier B.V. All rights reserved.