Daniela Veronika Fries

• The present thesis reports on studies of atomically precise, size-selected tantalum cluster ions \(Ta_n^±\) under cryogenic conditions in a FT-ICR mass spectrometer with respect to surface adsorbate interactions at the fundamental level, focusing on \(N_2\) and \(H_2\) adsorption and activation. The wealth of results presented here is the result of systematic studies that have revealed valuable kinetic, spectroscopic, and quantum chemical information, which together paint a comprehensive picture of the elementary adsorption steps and mechanisms in detail. The \(N_2\) and \(H_2\) adsorption processes to \(Ta_n^+\) clusters exhibit dependencies on cluster size n and on adsorbate load. In terms of \(N_2\) adsorption, there is evidence for spontaneous \(N_2\) activation and cleavage by \(Ta_2^+\) - \(Ta_4^+\), while it appears to be suppressedby \(Ta_5^+\) - \(Ta_8^+\). The activation and cleavage of \(N_2\) molecules proceeds across surmountable barriers and along much-involved multidimensional reaction paths. Underlying reaction processes and involved intermediates are elucidated. Two different processes are characteristic of \(H_2\) adsorption: There are fast adsoprtion processes without competing desorption reactions at low \(H_2\) loadings, indicating dissociative adsorption processes, followed by slow adsorption reactions accompanied by multiple desorption reactions at high \(H_2\) loadings, indicating molecular \(H_2\) adsorption. The threshold is the completion of the first adsorbate shell. The \(N_2\) adsorption study of \(Ta_n^-\) clusters revealed that the \(N_2\) adsorption ability of anionic tantalum clusters depends strongly on cluster size n. The cluster size n = 9 is the minimum size for \(N_2\) adsorption onto \(Ta_n^-\) clusters to yield stable and detectable cluster adsorbate species \([Ta_n(N_2)_m]^-\).