Reactivity of (H+)(e−) color centers at the MgO surface: formation of O2− and N2− radical anions

We have considered the interaction of O2 and N2 molecules with electrons trapped at the surface of MgO by performing embedded cluster DFT calculations. Trapped electrons at the surface of MgO react instantaneously with O2 and N2 leading to the formation of the corresponding O2− and N2− molecular anions stabilized at specific surface sites. So far, the atomistic model for this process was based on the idea that the electrons are trapped at oxygen vacancies, the FS+ centers. Recently, it has been shown that morphological sites at the MgO surface like a reverse corner, a step or a corner, can adsorb hydrogen and stabilize (H+)(e−) pairs giving rise to a new class of paramagnetic color centers. Here we show that these centers exhibit reactivity towards O2 and N2, which is fully consistent with the experimental observations, providing further support to the new model of electron traps at the MgO surface.