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

We have considered the interaction of O-2 and N-2 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 O-2 and N-2 leading to the formation of the corresponding O-2 and N-2 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 F-s(+) 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 O-2 and N-2 which is fully consistent with the experimental observations, providing further support to the new model of electron traps at the MgO surface. (C) 2003 Elsevier B.V. All rights reserved.