Furthermore, there is reason to expect that the CO desorption per -C(O) complex should be significantly lower for -C(O) created by N2O adsorption, compared to O2 adsorption. That is because the presence of neighboring oxidized surface sites has been shown theoretically to lower the CO desorption energy from -C(O) sites by ~20% to ~80%, depending on the oxidized site structure (semiquinone, epoxy, carbonyl). Thus, the fact that O2 dissociative adsorption creates a pair of adjacent oxidized groups, while N2O adsorption at our low pressures creates only isolated oxidized groups, suggests that the energy for CO production from N2O-oxidized graphite is higher than from O2-oxidized graphite, further decreasing the branching between CO and O desorption in N2O etching, increasing the EEO2/EEN2O ratio. This competition with O desorption probably contributes to the relatively low values observed for both EEO2 and EEN2O.