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

The system Br/Pt(110) is studied by scanning tunneling microscopy, low energy electron diffraction, angle resolved photoemission and self-consistent ab initio calculations. Bromine is molecularly adsorbed at 300 K, but dissociates at T>400 K. The Br atoms adsorb substitutionally and form quasi-one-dimensional (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 doping. A Fermi surface yielding an appropriate nesting vector is identified by photoemission. Furthermore, a Br-induced lowering of Pt d-bands is observed, which accounts in part for the halogen-induced poisoning. The PtBr bond is shown to be essentially covalent, ruling out electrostatic poisoning mechanisms.