The H + H recombination in molecular hydrogen on graphite occurring according to the Langmuir-Hinshelwood mechanism was studied in the framework of density functional theory. Graphite was modelled by a single layer cluster and the activation energies were computed for H diffusion and for Langmuir-Hinshelwood recombination. The influence of the neglected under- and over-lying layers was discussed below for the in-bulk recombination. The occurrence of this mechanism under thermal desorption spectroscopy experimental condition was discussed and compared with the well-known Eley-Rideal recombination mechanism. It was concluded that the Langmuir-Hinshelwood pathway had to play an important role in thermal desorption spectroscopy experiments.

Density Functional Theory Investigation of the Diffusion and Recombination of H on a Graphite Surface. Ferro, Y., Marinelli, F., Allouche, A.: Chemical Physics Letters, 2003, 368[5-6], 609-15