Adsorbate Vibrational Energies: Relation between Experiments and Rigid-Lattice Calculations

Experimental vibration spectra for ordered overlayers of O and S on Ni(100) are analyzed in terms of surface-lattice dynamics in relation to rigid-lattice calculations. It is shown how spectral differences for the consecutive p(2×2) and c(2×2) structures are primarily due to differences in the coupling to the substrate phonon modes.