Vibrational states of H monolayer on the Pt(111) surface

We present high-resolution electron energy-loss data and theoretical modeling for the vibrational properties of an atomic monolayer of H (D) on the Pt(111) surface. Experimentally we find three loss peaks, in contrast with two peaks visible in the low-coverage case. A three-dimensional adiabatic potential-energy surface at full coverage of hydrogen is obtained through first-principles calculations. When the zero-point energy effects are included, the minimum energy adsorption site is found to be the fcc site just as in the low-coverage case. Vibrational band states for motion in this potential-energy surface are computed and the excited states associated with the observed loss peaks identified.