W (111): angle-resolved photoemission from the clean and H2 - covered surface

We report the results of new photoemission experiments from a clean and hydrogen-covered W(111) surface. Symmetry-related polarization effects are used to discriminate the symmetry of the initial states. Through a careful analysis of angle-resolved energy distribution curves and angle-resolved constant final-state spectra we are able to locate several surface bands in the clean surface emission and the hydrogen-induced states in the spectra from the covered surface. The experimental data are compared with the outcomes of semiempirical linear combination of atomic orbitals calculations both for the clean surface and for the adsorbed one, assuming a chemisorption geometry with H atoms bridging metal atoms of different layers. The model used shows a good agreement with the experiment and indicates the possible mechanisms of hydrogen bonding on this surface.