Molecular Dynamics Simulations of Surface Processes: Oxygen Recombination on Silica Surfaces at High Temperature

摘要

The interaction between a molecule and a solid surface can lead to a great variety of elementary processes such as elastic, inelastic and reactive. Of particular importance is the dissociative chemisorption of a diatomic molecule where a molecule chemisorbed at the surface in a specific roto- vibrational state (v,j) dissociates with the two atoms adsorbed or scattered into the gas-phase. Of great importance is also the atom recombination on surfaces. Here two atoms recombine thus forming a diatomic molecule that can be either chemisorbed or reflected in the gas-phase in a given internal energy state. Reactions (1)-(2) are very often the rate determining step of complex heterogeneous systems of interest in different branches of industrial and technological applications, as for example in the ammonia synthesis, hydrocarbon production, chemical vapour deposition, etching and thin solid film deposition via plasma, nuclear rector technologies. Both processes are of central importance in aerothermodynamics and the chemistry of interstellar media. Thus, the recombination of atomic O and N on silica and UHTC materials plays a central role for the thermal protection system of the space shuttles entering into the terrestrial atmosphere, whereas the recombination of hydrogen atoms on ice grains covered by carbon is, very likely, the main source of molecular hydrogen observed in the interstellar media. The interaction of chemical species with surfaces can lead to other non-reactive chemico-physical processes such as the inelastic processes and adsorption. The adsorption processes occur when the particle is trapped in a chemisorption site and its available energy is not enough to escape from the chemisorption potential well. The inelastic processes can be of two types: direct and indirect.