Coexistence of Atomic and Molecular Chemisorption States:H2/Pd(210)

A novel H{sub 2} molecular adsorption state on metal surfaces has been detected by temperature-programmed desorption and electron energy loss spectroscopy experiments of the H{sub 2}/Pd (210) system. The molecular nature of this state has been verified by isotope exchange experiments. This molecular state leads to a decrease of the surface work function while atomic hydrogen on Pd(210) causes an increase. Ab initio total-energy calculations have confirmed all experimental findings. Through these calculations the microscopic nature of this novel molecular adsorption state could be identified; it turns out that this state is stabilized by the presence of atomic hydrogen on the Pd(210) surface.