Chlorine adsorption on the (110) faces of Ni, Pd and Pt

The chemisorption of chlorine on the (110) faces of the platinum group metals Ni, Pd and Pt has been studied at 300 K by LEED, AES, thermal desorption and work function measurements. On all three surfaces chlorine adsorbs dissociatively. From the initial linear part of the chlorine uptake curves sticking probabilities close to untiy have been estimated. At a chlorine coverage of θ = 0.5, c(2 × 2) and p(2 × 1) LEED patterns are formed on the (110) faces of Ni and Pt, respectively. At coverages above θ = 0.5, on Ni(110) and Pd(110) more complex structures are formed. In the case of Pd this structure undergoes two transitions during heating to 770 K. For all observed LEED patterns appropriate surface models could be found which are in good agreement with the experimentally derived coverages. Besides Ni(110), from which chlorine is assumed to desorb in the form of a chloride, both Pd and Pt show a single desorption peak of atomic chlorine. From these data activation energies for desorption of 65 and 59.5 kcal for Pd and Pt are derived, respectively. A work function increase during chlorine exposure is observed for all three faces as expected for the adsorption of electron-negative particles.