Several observations here and in the literature support the idea that O2 sticking must depend strongly on surface structure. For example, D'Evelyn et al. measured O2 sticking on Si(100) as a function of surface temperature and O2 kinetic energy, obtaining initial sticking coefficients (S0) for O2 on clean, oxygen-free Si(100) ranging from 1% at room temperature to 0.3% for 600 K and 2 kcal/mole O2 kinetic energy. Such small values for S0 imply that O2 sticking is quite inefficient for the Si(100) surface, even with no oxygen-blocked sites, and extrapolation of their results to the conditions of our experiments (thermal O2, TNP = 1200 K) suggests an even lower S0 ≈ 0.1%.