Halogen–metal interaction: bromine on Pt(110)

The adsorption of Br 2 on the missing-row reconstructed Pt(110)-(1×2) surface is studied. At room temperature, bromine atoms adsorb in pairs. For Θ=0.5 ML the BrBr pairs form a (2×2) structure. Upon annealing the bromine dimers dissociate into substitutionally adsorbed bromine atoms forming PtBrPt chains. The activation energy for substitution seems to depend on coverage. The PtBrPt arrange either in a p(2×1) or in a c(2×2) structure, whose relative amounts depend on the annealing temperature. After annealing to 780 K a c(2×2) overlayer forms for Θ=0.5 ML. For the dimer as well as for the substitutional structures, a small work function change (∼130 meV) and hence a small dipole moment of the bromine species is found. The mesoscopic corrugated-iron structure of the clean Pt(110)-(1×2) surface is altered into a simple staircase structure. Based on these 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.