Recombination processes involving H and D atoms interacting with a graphite surface: collisional data relevant to fusion plasma devices

The recombination of atomic hydrogen on graphite surface via the Eley-Rideal mechanism has been studied in the framework of the semiclassical time-dependent method and a potential energy surface assumed in our previous work. The results show that at the surface temperature, T-S = 500 K, the probability for H-2 formation is large in a rather narrow range of collisional energies, from 0.01 up to 0.2 eV. At E-kin > 0.3 eV the recombination reaction is suppressed. Three other different mass combinations have been considered in the simulation: D + D-ad, D + H-ad and H + D-ad. A large isotope effect has been pointed out on the energy thresholds, the energy structure of the recombination probability as well as for the energy partitioning in the final states of the molecular species scattered in the gas phase.