Furthermore, it is quite likely that these carbon-oxygen functional groups can form from intercalated oxygen atoms, as has been suggested by Paci and Paci . They found that the desorption of reaction products from below the surface would require the surmounting of multiple barriers, which would be consistent with a longer apparent residence time of oxygen on (or in) the surface. Chemisorption of intercalated N atoms has also been observed in a recent theoretical study by Guo and coworkers on the interaction of N atoms with a layered graphene surface here, showed that it could take more than three hours for the surface coverage to reach steady state on vitreous carbon at 1875 K . In the temperature survey study, the product fluxes were collected for approximately 25 minutes at each surface temperature. As a result, the surface coverage did not reach steady state during data collection at each surface temperature, and the surface coverage was thus constantly decreasing. The surface coverage was much lower after the sample temperature had been raised to 1875 K and then was decreasing, resulting in a lower flux of desorbed CO. A similar temperature-dependent hysteresis was first reported by Olander et al. , who observed it in the CO products of experiments with O2 scattering on pyrolytic graphite.