Theoretical characterization of charge-transfer reactions between N 2 and O 2 molecules and paramagnetic oxygen vacancies on the MgO surface

Abstract

In this work we have studied computationally, at the Hartree–Fock and density functional levels, the interaction of O 2 and N 2 molecules with paramagnetic oxygen vacancy ( F S + centers) located at the (1 0 0) MgO surface. We have employed the molecular cluster approach, which describes the adsorption site by means of a limited number of ions embedded in a large array of point charges, as well as the more sophisticated perturbed cluster method, where the selected cluster is self-consistently embedded in the quantum-chemical description of the regular host crystal. We found that, at short distances from the surface, an electron transfer from the surface to the admolecules occurs, with formation of charge-transfer complexes F S 2+/N 2 − or F S 2+/O 2 − that are stabilized by the electrostatic interaction between the charged fragments. However, F S 2+/O 2 − is stable with respect to the dissociation into F S ++O 2 fragments, while F S 2+/N 2 − results to be a metastable product.