Molecular dynamics study of hydrogen atom recombination over silica, based on a new analytical DFT potential energy surface

Abstract

A new analytical potential energy surface (PES) based on new density functional theory data is constructed for the interaction of atomic hydrogen with both a clean and an H-preadsorbed -cristobalite (001) surface. For the atomic interaction, six adsorption sites have been considered, the Si site (T1') being the most stable one. The PES was developed as a sum of pairwise atom-atom interactions between the gas-phase hydrogen atoms and the Si and O atoms of the -cristobalite surface. A preliminary molecular dynamics semiclassical study of the different heterogeneous processes (e.g., H2 formation via Eley-Rideal reaction, H adsorption) that occur when H collides with an H-preadsorbed beta-cristobalite (001) surface was carried out. The calculations were performed for collisional energy in the range (0.06 ≤ Ekin ≤ 3.0 eV), normal incidence and a surface temperature Tsurf = 1000 K. The recombination probability reaches its maximum value of approximately 0.1 for collisional energies in the range 0.3 ≤ Ekin ≤ 0.8 eV. The H2 molecules are formed in medium-lying vibrational levels, while the energy exchanged with the surface in the recombination process is very low.