Coupling between adsorbate vibrations and an electronic surface state

We report direct angle-resolved photoemission measurements of the coupling between the symmetric stretch vibrational mode of adsorbed hydrogen and a s urface band on W(110). This coupling is manifested by the surface band bein g split into two branches at a binding energy comparable to the vibrational mode energy, as confirmed by observation of a dramatic hydrogen/deuterium isotope effect. The electron-phonon coupling parameter lambda is found to b e significantly larger than that for bulk W, and to be closely related to t he degree of surface localization of the surface state wave function.