FREQUENCY-SHIFT AND RELAXATION OF LOCALIZED VIBRATIONS AT SURFACES MEDIATED BY SUBSTRATE ANHARMONICITY

A vibrational mode localized at an adsorbed atom or molecule experienc es a temperature-dependent frequency shift and line broadening, due ii i part to its interaction with substrate phonons. When the bilinear co upling between the adatom and surface is treated nonperturbatively, th e anharmonic interactions between neighbouring substrate atoms couples to the local mode. The effects of the anharmonicity of the substrate on the vibration spectra are demonstrated in a simple model calculatio n applied to the adsorption systems CO/Pt(111) and CO/Ni(100).