lectron – phonon coupling in W ( 110 ) - ( 1 3 1 ) H

Recently, we reported high resolution angle-resolved photoemission measurements that indicated unusually strong coupling between adsorbate vibrations and a surface-localized electron state in the system W(110)-(131)H. We have now extended these measurements to probe the electron–phonon coupling strength as a function of position on the relevant Fermi contour. We find that the strength of the coupling is strongly dependent on Fermi wave vector, with the electron–phonon coupling constant l varying between zero and |0.8. Qualitatively, the strength of the coupling is related to the position of the surface band in the projected bulk band gap, and therefore to the degree of surface localization of the surface state wave function. Such effects should play an important role in all adsorbate vibronic interactions, since the vibrational modes are generally highly localized to the outermost surface layer. We discuss these results in relation to the surface phonon anomalies observed on this surface.  2002 Elsevier Science B.V. All rights reserved.