Synchrotron radiation and fluorescence: Quantitative investigations on electronic processes in atoms, molecules, and clusters

Photoelectron and photoion spectrometries are the most frequently used methods to investigate electron excitation and emission processes from atoms, molecules and clusters. In this talk I will elaborate on the use of a complementary method for such kind of investigations, namely on fluorescence spectrometry in combination with excitation of atoms, molecules and clusters by synchrotron radiation. The advantages of this specific technique will be exemplified by the investigation of electronic processes, where electron correlations and interference processes can be quantitatively measured. Electron correlations in atoms and molecules, although energetically not at all negligible, pose the most severe difficulty in describing accurately atomic or molecular shells. When trying to describe them the classical Coulomb repulsion as well as quantum mechanical effects like Pauli repulsion play significant roles. The interplay between quantitative experiments and model calculations will be highlighted, demonstrating that only due to joint experimental and theoretical efforts such difficult problems may be approximately solved. Recent results of first steps towards investigations of electron dynamics in chiral systems and of the Interatomic Coulomb Decay will be discussed.