Multiplet effects in resonant x-ray emission

Abstract

Abstract. After a short discussion of all conventional core level spectroscopies within the single particle model, the effects of the coupling of the core and valence wave function on the x-ray emission spectral shapes is discussed. It will be shown that these so-called multiplet effects strongly affect all x-ray emission spectra taken around the metal 2p resonances. In case of 1s resonances, valence band x-ray emission is not affected, but the spectral shapes of 1s2p and 1s3p x-ray emission can only be sensibly described with the inclusion of multiplets. A special example is the resonant excitation into the pre-edge region, which gives rise to a quadrupole resonance. CORE LEVEL SPECTROSCOPIESAll core level spectroscopies will be introduced using a simplified single particle model. This model is not expected to give a correct interpretation of the spectral shapes and intensities observed, but serves as a starting point on which more complete models build upon. The Single Particle ApproximationsIn order to get a first idea of how the x-ray and electron spectra will look like we use a simplified single particle model. A series of approximations have been made:1. Density-of-States approximation: The assumption that the single particle Density-of-States (DOS), as calculated for example by Local Spin Density (LSD) calculations or by real space Multiple Scattering codes, gives a good account of the electronic structure of the ground state. Spectroscopy approximation:The assumption that the ground state DOS can in fact be used to describe spectroscopic transitions. This implies, for example, that it is assumed that in photoemission the valence hole does not cause a redistribution of the electronic states.3. Core hole approximation: The assumption that the core hole created in x-ray absorption does not modify the DOS. Matrix Element approximation:The assumption that the transition matrix elements are constant over the energy range analyzed.