Recombination pathways for atomic hydrogen on the graphite (0001) and single-wall carbon nanotubes

Using density functional theory we investigated the lowest energy configurations of two H atoms on a graphite surface, and found two states with an approximately identical binding energy. These states are the dimer A state with two hydrogen atoms adsorbed on two neighbour carbon atoms and the dimer B state with two hydrogen atoms adsorbed on carbon atoms at opposite sides of a carbon hexagon. Hydrogen atoms in the dimer A state will recombine via diffusion into state B and then directly recombine from B. We also studied the corresponding pathways for molecular hydrogen formation from H atoms adsorbed at the single-wall carbon nanotubes and compared results to those obrained for the graphite surface.