Marcel Meta

• In the field of catalyst development, model systems play a crucial role. For instance, when investigating the activation of methane and carbon dioxide, transition metal ions emerge as particularly suitable candidates. Utilizing isolated model systems in the gas phase enables the investigation of reaction dynamics, which provides insights into the reaction mechanism at the atomic level. Molecular reaction dynamics reveal the classification of indirect and direct reac tion dynamics. This classification elucidates the duration of a reactive intermediate’s existence, which may be accompanied by a redistribution of energy into internal energy, if the intermediate exists several rotaional periods. However, the reaction dynamics at the atomic level between methane/carbon dioxide and transition metal ions are so far unexplored. In this thesis, the re action dynamics between tantalum, niobium, and zirconium cations and carbon dioxide were investigated, as well as between methane and tantalum and zirconium cations. Under con- trolled single collision conditions, these reactions were investigated using a crossed-beam 3D velocity map imaging spectrometer. For nearly all reactions, energy and angle differential cross sections revealed dominant indirect dynamics. In a collaborative effort, the experimental results were complemented by additional experiments (selected-ion flow-tube mass spectrometry) and quantum chemical considerations containing stationary points on a reaction pathway, as well as potential hypersurfaces combined with simulated trajectories. From this, it was possible to derive specific proposals for the reaction mechanism at the atomic level, identifying how the energy could be redistributed during the reaction. In the context of this work, it can be validated that the oxygen-atom transfer reaction is trapped in the pre-reaction well. Mainly a non-statistical distribution of the internal energy is observed. In contrast, the activation of methane is trapped after the ISC where the first hydrogen atom has been abstracted. Whereas a statistical distribution is observed.