Classical dynamics study of atomic oxygen sticking on the β-cristobalite (1 0 0) surface

The sticking of oxygen atoms with collision energies in the range 0.1-1 eV on a clean (1 0 0) β-cristobalite surface with surface temperatures between 300-1100 K has been investigated using classical trajectories for normal and off-normal incidence. A full dimensional adiabatic potential energy surface (PES) based on a dense grid of density functional theory (DFT) points was constructed by means of the corrugation reducing procedure. Sticking probabilities are very high (>0.9) for all conditions, increasing with collision energy and decreasing with surface temperature. This behavior can be interpreted by decomposing the sticking between adsorption and absorption, which show different trends. The large attractive character of the PES favors the absorption or penetration into the big unit cell of the β-cristobalite, with a predominant direct mechanism instead of a dynamic trapping, accordingly also with the quick dissipation of the oxygen energy into the slab. Calculated thermal initial sticking coefficients seem to depend on the type of silica structure. Moreover, these initial thermal coefficients are much higher than values derived using expressions obtained from standard transition state theory even when using as parameters values extracted from DFT calculations. Therefore, the use of these expressions in kinetic models for O or N recombination over silica should be reconsidered.