Dynamics of hydrogen adsorption on clean and alkali-metal covered Cu(110)

Abstract

The activated dissociative adsorption of H₂ and D₂ on a clean Cu(110) and a Cu(110)-K(1 × 2) reconstructed surface has been studied using supersonic molecular beams. Enhanced sticking of H₂ over D₂ at any particular normal energy in the pure beam experiment on Cu(110) is interpreted as an indication of the importance of the vibrational coordinate in the dissociation dynamics. The relative contributions of vibrational and translational energy in accessing the barrier is separated in vibrationally hot, translationally cold seeded beams. Results for hydrogen are presented which indicate a translational onset for the first vibrationally excited state H₂(v= 1) at 130 meV. This result is consistent with a theoretically predicted barrier to dissociation of ca. 700 meV which lies somewhat in the exit channel of a two-dimensional potential-energy surface (2D-PES). The effect of alkali-metal adsorption on the (1 × 2) reconstructed surface is shown to enhance hydrogen adsorption, increase the activation energy to desorption and reduce the activation energy to adsorption. This result is consistent with a reduction in the height of a late barrier caused by a deeper atomic potential in the ‘product’ region of the 2D-PES.