Structure and reactivity at the halogen/metal interface: Chemisorption, corrosion and reaction pathways in the Pd(111)Cl 2 system

Abstract

Chlorine chemisorbs dissociatively on Pd(111) with an initial sticking probability of ∼1.0 to form an atomic overlayer. Continued uptake leads to the formation of PdCl 2, the initial growth mode apparently being characterised by a field-assisted mechanism. Three-dimensional microcrystallites of the dihalide are eventually formed such that PdCl 2(110)||Pd(111). Evaporation of the surface phase occurs principally as a mixture of atomic chlorine and PdCl 2, the relative proportions of these species depending on the initial coverage. Modulated molecular beam measurements reveal that in the high temperature regime, atomic chlorine desorbs by a first-order process with Arrhenius parameters 176±4 kJ/mol and ≈10 9 s −1. These values are shown to be in quantitative accord with the thermal desorption data and provide the basis for rationalising some unusual features in the desorption kinetics. Defect sites apper to be involved in mediating overlayer desorption and also give rise to a distinct binding site for chemisorbed halogen.