Electronic structure of a catalyst poison: Br/Pt(110)

The system Br/Pt(110) is studied by scanning tunneling microscopy, low ener gy electron diffraction, angle resolved photoemission and self-consistent a b initio calculations. Bromine is molecularly adsorbed at 300 K, but dissoc iates at T>400 K. The Br atoms adsorb substitutionally and form quasi-one-d imensional (1D) Pt-Br-Pt chains. The 1D character of the chains gives rise to a charge density wave ground state, which can be triggered by surface do ping. A Fermi surface yielding an appropriate nesting vector is identified by photoemission. Furthermore, a Br-induced lowering of Pt d-bands is obser ved, which accounts in part for the halogen-induced poisoning. The Pt-Br bo nd is shown to be essentially covalent, ruling out electrostatic poisoning mechanisms. (C) 2000 Elsevier Science B.V. All rights reserved.