ADSORPTION OF HYDROGEN ON ZINC CALCULATION OF POTENTIAL-ENERGY SURFACE AND DYNAMICS

Notwithstanding the important technological applications of hydrogen adsorption on zinc, experimentally it is only known that hydrogen is adsorbed in its atomic state, after pre-dissociation. We calculated the potential energy surface of H{single bond}Zn(0001) with an ab initio Cl embedding technique, using a monolayer cluster of 12 Zn atoms. The three-fold site is more stable than bridge and on-top sites, with binding energies -1.99, -1.07 and -0.92 eV. The H-Zn potential has been used to build a LEPS potential for the H2{single bond}Zn(0001) system, where the adsorption is endothermic by 0.76 eV with an activation barrier of 1.31 eV. With this LEPS potential, quasi-classical trajectories calculations have been computed to study the dynamical aspects of adsorption. We observed chemisorption only when the H2 total energy overcomes a threshold value of 2.4 eV. Vibrational component of energy is somewhat more efficient than the translational one in dissociative adsorption of H2. The sticking probability is a maximum for normal approaches to the surface, decreases with increasing incidence angle, and is scarcely influenced by the azimuthal angle of approach. © 1990 Pergamon Press plc.