Collective motion and structural order in adsorbate vibrational dynamics

A simple, broadly applicable theory is developed to describe resonant vibra tional coupling between adsorbates and a substrate lattice. This is one of the principal mechanisms governing the relaxation of adsorbate vibrations. This theory can be applied to widely varying surface coverages and arbitrar y overlayer structures, and it correctly incorporates collective adsorbate motion, which has been shown to have a critical impact on the relaxation dy namics. Vibrational lifetimes predicted by this theory are in excellent qua ntitative agreement with experiments on adsorbate systems ranging from a di ffuse, disordered overlayer to a dense, periodic overlayer.