Theoretical study of the 4f photoemission spectrum in Au₅₅ aggregates

Abstract

In the photoemission process of a core level electron a satellite structure may appear due to the simultaneous excitations of valence electrons (many-electron effects). We study this phenomenon in Au₅₅ aggregates. In this calculation we assume that the excitations can be limited to the 6s electrons which are described by means of tight-binding Hamiltonians in the initial (no core hole) and the final (hole present on a core level) states. An extension of a Anderson's formula strictly valid for the bulk is discussed and the possible use of the phase shift concept is analyzed. Our calculated satellite structure depends only on two parameters: Δ, the core hole attractive diagonal term and β, the normal transfer integral. We fix Δ/β=3 by comparison of our results to experiment performed on Au₅₅ (P Ph₃)₁₂Cl₆ compounds. The various experimental features are roughly reproduced by the calculation (number of peaks as well as their intensities and positions). Another interpretation of the experimental structure was proposed in the original experimental work. A more extensive investigation on other polyhedral metallic aggregates is necessary for allowing a choice between the two models.