Effect of N atoms on O-Atom Reactivity with Carbon

Molecular beam-surface scattering experiments have been used to study the effect of N atoms on the reactivity of O atoms with a high-temperature carbon surface to produce CO. The CO flux produced from bombardment of a vitreous carbon surface by a beam containing N and O atoms was compared with the CO flux produced from bombardment by beams containing either N or O atoms. The presence of small mole fractions of N atoms of 0.02-0.08 enhanced the reactivity of O atoms by a factor of 1.4-1.6 in the range of surface temperatures from 1100 to 1700 K. A detailed explanation of the observed results requires more study, but it appears that N atoms can act as a catalyst to increase the reactivity of O with carbon and that a relatively low flux of N atoms may be sufficient to saturate the catalytic effect. This catalytic effect seems to be fairly insensitive to the surface temperature, at least over the temperature range used in this study. This observation is important in the development of finite-rate models of air-carbon ablation during hypersonic flight.