Vibrational spectrum of H and D on the (0001) graphite surface from scattering experiments

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Abstract
We have investigated the vibrational spectrum of hydrogen and deuterium atoms adsorbed on the (0001) surface of a graphite single crystal by means of atomic beam scattering in UHV conditions. Bound state resonances, which appear as minima in the specularly reflected beam have been detected over a wide range of incidence and azimuthal angles. Energy levels at 31.6±0.2 and 15.3±0.3 meV for 1H and at 35.4 ±2; 21.35±0.1; 12.0±0.1, and 5.9±0.3 meV for 2H have been determined. By fitting the experimental energy levels to those calculated with the potential the following values of the parameters are obtained: D=43.3±0.5 meV; λ=1.36±0.03 Å−1; p=4.4±0.6. The hypothesis that the interaction potential is the sum over all crystal layers of an atom–single layer potential V*(z) is used. V*(z) has a well depth D*=39.2±0.5 meV and a long range behavior given by C*4/z4 with C*4=5.2±0.3 eV Å4.