Adsorption of benzene on Mo(100) and MgO(100)/Mo(100) studied by ultraviolet photoelectron and metastable impact electron spectroscopies

By employing metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS) together with work-function measurements, three adsorption states of benzene have been identified on the clean Mo(100) surface at 100 K: a chemisorbed layer, a second physisorbed layer with the aromatic rings plane parallel to the surface, and at higher coverages, an adsorbed layer with the molecular planes essentially perpendicular to the surface. The rapid appearance of the upright (edge-on) phase for benzene adsorbed on the MgO-covered Mo(100) surface suggests that the adsorption dynamics on MgO are similar to those for the Mo(100) surface, but no chemisorbed layer forms for the MgO surface. In addition, it was found that benzene adsorption on the MgO-covered Mo(100) surface does not lead to perfectly formed, closely packed layers. (C) 1998 Elsevier Science B.V. All rights reserved.