Model of anH2-Precursor State on Metal Surfaces

Dynamical effects of a surface-induced softening of the H—H bond during ${\mathrm{H}}_2$-surface collisions have been studied by numerical wave-packet simulations. The calculation shows that the zero-point vibrational energy released by the bond softening is fully transferred to the translational motion of the molecule (except for incident energies > 0.2 eV, where vibrational excitation also takes place), and that inelastic processes can trap the molecule in a mobile and long-lived state confined near the surface.