DISSOCIATIVE ADSORPTION OF H-2 ON CU(100) - A 4-DIMENSIONAL STUDY OF THE EFFECT OF ROTATIONAL MOTION ON THE REACTION DYNAMICS

The reaction of H-2 on Cu(100) is investigated using a four-dimensiona l (4D) quantum dynamical fixed-site model to assess the influence of m olecular rotation on dissociation over the most reactive (the bridge) site. The potential energy surface (PES) is a fit to the results of de nsity functional calculations performed using a generalized gradient a pproximation treating a Cu slab with a periodic overlayer of H-2. Diss ociation probabilities for molecules with ''helicoptering'' (m(j)=j) a nd ''cartwheeling'' (m(j)=0) rotational motions are here found to be c omparable because of the strong corrugation in the azimuthal coordinat e. The calculations indicate that reaction is accompanied by significa nt rotationally inelastic scattering, Surprisingly, vibrational excita tion is also found to be an efficient process in collisions with the r eactive bridge site. Ln these collisions, the molecular axis is tilted away from the orientation parallel from the surface. Considering the approximate nature of the 4D model used, the calculated reaction proba bilities are in good agreement with experiment, indicating that the PE S that was used is accurate. (C) 1997 American Institute of Physics.