Quantum dynamics study of the Langmuir–Hinshelwood H + H recombination mechanism and H2 formation on a graphene model surface

We examine in this paper the associative desorption of two hydrogen atoms on a slab model that mimics a C(0 0 0 1) surface. Initially the two separated H atoms are physisorbed onto the graphene surface, then diffuse and recombine and H₂ gets desorbed into the gas phase. We use density functional theory (DFT) on a supercell model and apply periodic boundaries to build a potential energy surface (PES). The reaction is barrier less and exhibits a small H₂ vdW well on the global potential energy surface. We employ a two-dimensional quantum dynamics method exploiting the hyperspherical coordinates and report reaction probabilities for this mechanism. The calculations are performed for collision energies ranging from 1 to 15 meV relevant to the interstellar medium (ISM). The entrance channel dominates the reaction and the vibrational excitation of the desorbed H₂ is important and peaked at v′ = 8.