Investigation of Relativistic Effectsin Electronic Decay Processesin Small and Large Noble Gas Clustersby Ab Initio and New Simulation Approaches

Abstract

The Interatomic/ Intermolecular Coulombic Decay (ICD) as well as the Electron Transfer Mediated Decay (ETMD) are electronic decay processes, which occur in a multidude of systems ranging from noble gas dimers to biological systems. If heavy atoms are involved in these processes, relativistic effects cannot be neglected. However, their influence has so far not been investigated thoroughly. In this thesis, the influence of the spin-orbit coupling as well as scalar-relativistic effects on openings and closings of decay channels as well as on the corresponding decay widths are studied. For this purpose, asymptotic expressions for the decay widths of both ICD and ETMD are derived. They allow for analytic studies of basic properties and estimations of the decay widths based on properties of the constituting atoms or molecules of the total system. A more precise description of the decay widths required the transfer of the non-relativistically known FanoADC-Stieltjes method to the relativistic regime and its implementation into the relativistic quantum chemical program package Dirac. Using this method, small noble gas systems are investigated. Experimentally, these decay processes are usually studied in noble gas clusters consisting of 100 – 2000 atoms. These clusters are too large to be treated with ab initio methods. In order to allow for a comparison of theoretical and experimental results, the influence of the cluster environment on the secondary electron spectra are investigated. These findings are used for the development of a method for the decay width estimation of clusters based on the asymptotic expressions or calculated decay widths for a multitude of geometries. This method was implemented as the program HARDRoC and is used for the investigation of the two competing processes ICD and ETMD in ArXe clusters. Additionally, it is the foundation of a new structure determination method of heteronuclear noble gas clusters, which is exemplarily explained for NeAr clusters.