Dynamics of H₂Formation on a Graphite Surface

초록

We have studied the dynamics of energy-rich hydrogen molecules produced on a graphite surface using a classical trajectory procedure. The recombination reaction efficiently takes place on a subpicosecond time scale with most of the reaction exothermicity depositing in the product vibration, which leads to a strong vibrational population inversion. The total reaction cross section is 10.9Ų at gas temperature 100 K and surface temperature 10 K. Majority of the reaction events occur through the direct-mode Ely-Rideal mechanism. The direct-mode pathway is dominated by the adatom abstracted from the open region above by the incident gas atom. While the rotational alignment angle of H₂ produced in this region ranges widely from zero to 90˚, that of H₂ formed when the adatom is pulled from below by the incident atom is close to zero, which represents the rotational axis nearly parallel to the surface normal. Although its number is small, a group of trajectories in which the incident atom reaches below the adatom leads the recombination through a complex-mode mechanism, in which the incident atom is trapped on the surface for a long period of time before recombining. A significant fraction of trapped H(g) remains on the surface while the dissociating H(ad) recedes from the surface with a high translational energy.