Helium-3 surface spin echo spectroscopy (HeSE) has been used to measure the diffusive dynamics of adsorbates on close-packed metal surfaces, namely hydrogen on Cu(111), Pd(111) and Ru(0001), carbon and oxygen on Ru(0001), and oxygen on Cu(111). Chapter 2 reviews the HeSE technique and describes the relevant dynamical models and statistical methods used to interpret data in later chapters. The performance of the ionizing detector is analysed, with a focus on the signal-to-noise ratio. In Chapter 3 expressions for the classical intermediate scattering function (ISF) are introduced for open and closed systems. The effects of corrugation and surface-perpendicular motion on the amplitude of different components in the ISF are modelled analytically and compared with simulation. The exact ISF for a particle on a flat surface, obeying the Generalized Langevin Equation with exponential memory friction, is calculated analytically. In Chapter 4 the analytical ISF is calculated for quantum Brownian motion and for coherent tunneling dynamics in a tight binding system. The bounce method for calculating quantum mechanical hopping rates in dissipative systems is applied to model diffusion of hydrogen on Ru(0001). Chapter 5 presents the first HeSE measurements of carbon and oxygen diffusion. C/Ru(0001) diffusion is assigned to a small carbon cluster. The jump rate has an activation energy $E_{A}=292\pm7\,$meV in the temperature range $550\,\textrm{K}\leq T \leq 1300\,$K. Oxygen diffusion is significantly slower. By comparison of literature data with the new HeSE results, the activation energy for oxygen diffusion at low coverage is estimated as $650\pm10$meV. Oxygen measurements at high coverage $\theta\approx0.22\,$ML are consistent with strong mutual O-O interactions. Surface diffusion is also observed after exposing Cu(111) to oxygen. Chapter 6 presents low-coverage measurements of protium (H) and deuterium (D) diffusion on Ru(0001), Pd(111) and Cu(111). In the quantum activated regime there is evidence for multiple jumps in all three systems, suggesting a low dynamical friction. The measurements on Ru(0001) indicate that the deep tunneling rate is much slower for D than for H.

The work carried out during this thesis focuses on the quantum dynamics of the diffusion of hydrogen atoms on a surface of palladium (111). The study of the 3D system allowed us to detail the infrared spectrum of H/Pd (111), showing the existence of different adsorption sites on which localized states exist that are strongly coupled (Fermi resonance). This phenomenon governs the diffusion of hydrogen atoms in an ultra-fast time scale (fs).The study of the (6D) H2/Pd(111) system has shown that the transitions observed are in fact transition bands between several quasi-degenerate adsorption states. The agreement between the calculated and measured values is significantly less good than that between the data calculated for the 3D system and the measured data. Does adsorbed hydrogen on palladium exist in the form of a weakly bound H2 molecule? This thesis has provided some answers to this question, which remains open, hovewer, to some extent.

Les travaux réalisés au cours de cette thèse portent sur la dynamique quantique de diffusion d'atomes d'hydrogène sur une surface de palladium (111). L'étude du système 3D a permis de détailler le spectre infrarouge de H/Pd(111) en mettant en évidence l'existence sur différents sites d'adsorption d'états localisés fortement couplés (résonance de Fermi). Ce phénomène gouverne la diffusion des atomes d'hydrogène sur une échelle de temps ultra-rapide (fs).L'étude du système 6D (H2/Pd(111)) a montré que les transitions observées sont, en fait, des bandes de transition entre plusieurs états d'adsorption quasi-dégénérés. L'accord entre les valeurs calculées et mesurées est, par contre, significativement moins bon qu'entre celles calculées pour le système 3D et les données mesurées. Est-ce que l'hydrogène adsorbé sur le palladium existe sous la forme d'une molécule diatomique faiblement lié? Cette thèse a fourni certains éléments de réponse à cette question, qui reste cependant encore ouverte. / The work carried out during this thesis focuses on the quantum dynamics of the diffusion of hydrogen atoms on a surface of palladium (111). The study of the 3D system allowed us to detail the infrared spectrum of H/Pd (111), showing the existence of different adsorption sites on which localized states exist that are strongly coupled (Fermi resonance). This phenomenon governs the diffusion of hydrogen atoms in an ultra-fast time scale (fs).The study of the (6D) H2/Pd(111) system has shown that the transitions observed are in fact transition bands between several quasi-degenerate adsorption states. The agreement between the calculated and measured values is significantly less good than that between the data calculated for the 3D system and the measured data. Does adsorbed hydrogen on palladium exist in the form of a weakly bound H2 molecule? This thesis has provided some answers to this question, which remains open, hovewer, to some extent.