Generation of H-Atom Pulses and Associative Desorption of Hydrogen Isotopologues from Metal Surfaces

Part I of this work introduces a technique for the generation of H-atom pulses with unprecedented time resolution. In part II an extensive study of the associative desorption reaction of hydrogen isotopologues from metal surfaces is presented. Part I: Generation of H-Atom Pulses. Short intense pulses are of fundamental importance for scientific studies of dynamics. Equivalent-time experiments relying on the pump-probe technique are conducted routinely in physics, chemistry and biology. In contrast to the light pulses often utilized in such studies, chemical reactions are generally initiated by collisions. While methods for the generation of matter pulses exist, their performance is significantly inferior to modern laser pulses. Here, a new photolysis technique is introduced to produce pulses of neutral matter, which relies on well-known simple physical principles. This technique is implemented for the rst time and achieves an H-atom pulse duration of ~1.2 ns (time resolution of 0.03%), which corresponds to an improvement by one order of magnitude compared to established photolysis methods. From the full mathematical description of the concept presented here further improvements are predicted. These include the reduction of the pulse duration below the nanosecond timescale as well as a significant increase in the absolute pulse intensity. This new method extends the scientific toolbox and enables a new class of future experiments which involve time-resolved collisions of neutral matter. Part II: Hydrogen Permeation. The interaction of hydrogen with metal surfaces is one of the most fundamental reactions in surface chemistry. The H2/Cu(111) system serves as a benchmark for theoretical studies, which are nowadays able to describe the reactivity of certain systems with an accuracy of 1 kcal/mole, often referred to as "chemical accuracy". This study reports an extensive set of experimental data of the post-permeation associative desorption of H2, HD and D2 from single crystal surfaces of Cu(111), Cu(211) and Au(111). By invoking the principle of detailed balance initial state resolved reaction probability curves are obtained, which are compared to selected studies. For the H2/Cu(111) system small but significant deviations to the literature are found which are attributed to an improved calibration procedure in this work. The Cu(211) data revealed systematic differences to the Cu(111) sample on the order of the calibration uncertainty, which necessitated the direct comparison of both copper facets under the same experimental conditions. Furthermore, evidence for an additional desorption channel on both facets is presented and analyzed quantitatively. Several possible reaction mechanisms are speculated upon which include argumentations as to why this had not been reported in previous work. Finally, for the highly activated H2/Au(111) system the presented results provide a quantum-state-resolved experimental data set to which theoretical studies can be compared. In this data set an isotope-specific effect is observed, which questions the general validity of the adiabatic approximation generally assumed in description of the interaction of hydrogen with noble metal surfaces.