Adsorption and reaction of bromine with Ag(110): A photoemission study

The adsorption of bromine on the (110) surface of silver has been studied by ultraviolet (hυ = 21.2 and 40.8 eV) photoelectron spectroscopy in the temperature range of 100–300 K. Four different adsorption and reaction states could be detected. For fractional monolayer coverages Br₂ adsorbs dissociatively on the Ag(110) surface. The chemisorption of bromide leads to new emission features at about 3 and 5.2 eV below E_F, which are assigned as occupied antibonding structures (3 eV) and as bonding Br4p_{x, y} orbitals (5.2 eV). At 100 K, further bromide adsorption leads to the formation of an AgBr layer with molecular adsorbed bromine on top of this corrosion layer. The He I spectrum is dominated by structures at 3.5, 5.8 and 7.5 eV which are due to emission from the π_g, π_u and σ_g molecular orbitals of Br₂. The buildup of the AgBr layer is clearly demonstrated by desorbing the molecular bromine at about 150 K. The resulting spectrum of the AgBr layer shows peaks at 2.5 and 3.4 eV with p- and mixed-in d-character and peaks at 4.1, 5.2 and 6.1 eV which are primarily d-like. Heating of the AgBr layer up to 300 K results in a transformation from a 2D layer into a 3D agglomeration of larger AgBr clusters on top of a Br/Ag(110) chemisorption layer.