HD J ≠ 0 bound state resonances above the Cu (001) surface: The effects of physisorption anisotropy and the observation of anomalous Debye–Waller behavior at resonance conditions

Abstract

The laterally averaged HD–Cu (001) physisorption potential has been investigated in studies of rotationally mediated selective adsorption resonances. To first approximation the results are consistent with those from other isotope systems, i.e., H₂ and D₂ above Cu (001). The additional effects of the translational to rotational coupling, of HD, on the resonance levels have also been investigated theoretically. The measured resonance energies are in best agreement with calculations of the J = 1, 2 and m_J = 0 states. The zero temperature resonance energy widths are considerably broader than the experimental resolution function. In addition, surface temperature variations are shown to have two prominent effects: first on the strength of the resonant structure and, second, on resonance line widths. We attribute these effects to substrate phonon coupling with the resonantly bound HD species. Also, weak shifts of all resonance levels observed on hydrogen chemisorption are accompanied by further increases of resonance line widths.