Halogen-metal interaction: bromine on Pt(110)

The adsorption of Br-2 on the missing-row reconstructed Pt(110)-(1 x 2) sur face is studied. At room temperature, bromine atoms adsorb in pairs. For Th eta =0.5 ML the Br-Br pairs form a (2 x 2) structure. Upon annealing the br omine dimers dissociate into substitutionally adsorbed bromine atoms formin g Pt-Br-Pt chains. The activation energy for substitution seems to depend o n coverage. The Pt-Br-Pt arrange either in a p(2 x 1) or in a c(2 x 2) stru cture, whose relative amounts depend on the annealing temperature. After an nealing to 780 K a c(2 x 2) overlayer forms for Theta =0.5 ML. For the dime r as well as for the substitutional structures, a small work function chang e (similar to 130 meV) and hence a small dipole moment of the bromine speci es is found. The mesoscopic corrugated-iron structure of the clean Pt(110)- (1 x 2) surface is altered into a simple staircase structure. Based on thes e results, we discuss (1) substitutional adsorption as a general phenomenon with respect to halogen adsorption on (110) surfaces of face-centred cubic metals, (2) the dissipation of the adsorption energy, and (3) implications for catalytic poisoning mechanisms. (C) 2000 Elsevier Science B.V. All rig hts reserved.