Dynamics of gas-surface interactions: Reaction of atomic oxygen with chemisorbed hydrogen on tungsten

The reaction of gas-phase atomic oxygen with hydrogen atoms chemisorbed on a tungsten surface is studied by means of classical trajectory procedures. Flow of energy between the reaction zone and the bull solid phase is treated in the generalized Langevin equation approach. Most reactive events occur in small-impact-parameter collisions, in which the incident gas atom undergoes only one impact with the adatom, producing vibrationally excited OH radicals on a subpicosecond scale via the Eley-Rideal mechanism. Short-time calculations show that, in these collisions, the formation of the OH bond and subsequent dissociation of the H-surface bond occur in -100 fs. A small fraction of reactive events occurs in a multiple-impact collision, forming a long-lived complex on the surface. As the impact parameter increases, both reaction probability and vibrational excitation decrease, thus producing a population inversion. The dissipation of reaction energy to the heat bath can be adequately described using a 10-atom chain with the chain end bound to the rest of the solid. The probability of OH(g) formation is not sensitive to the variation of surface temperatures between 0 and 300 K, whereas it rapidly rises with the gas temperature up to 1000 K, above which it remains nearly constant. A modified LEPS potential energy surface is used for the reaction zone interaction, whereas the framework of harmonic representation is used in modelling chain atoms.