Adsorption and decomposition of ammonia on a W(110) surface: Photoemission fingerprinting and interpretation of the core level binding energies using the equivalent core approximation

Abstract

We report the first XPS data for ammonia adsorption, condensation and decomposition on a W(110) surface. Monolayer, “second layer” and multilayer NH 3 as well as NH 2, NH and N species can be characterized by a specific N(1s) electron binding energy. We discuss the observed binding energies within a thermodynamic framework, using the “equivalent core approximation”. This model has been previously successfully applied to core level binding energies of gaseous molecules and solids. The agreement between calculated and experimental N(1s) binding energies for some species is excellent, and we conclude that for the considered adsorbates the variation of the N(1s) binding energies is primarily determined by the ground state properties rather than by different relaxation energies in the final state. We also briefly discuss the activity of the W(110) face towards NH 3 decomposition and also present some data for NH 3 dissociation on an oxygen predosed surface.