Time-of-flight spectroscopy (TOF) and REMPI-TOF (resonance enhanced multi-photon ionization-TOF) were applied to measure the angular and translational energy distribution, as well as the internal state resolved energy distribution of desorption and reaction products on some model systems. Desorption of hydrogen and deuterium from clean and modified Pd(111) surfaces was studied, where the palladium sample was part of a permeation source. Water formation by reaction of oxygen with hydrogen on palladium was investigated by using different types of hydrogen supply: molecular H-2 exposure and atomic H exposure from the gas phase, as well as H exposure by permeating hydrogen. Vanadium oxide nanostructures on Pd(111) were prepared and the influence on D-2 desorption and D2O production was investigated with the permeation technique. Additionally, deuterium desorption from sulfur and oxygen covered V(111) and V(100) surfaces was studied by TOF and REMPI-TOF spectroscopy. From the TOF spectra information concerning the reaction and desorption dynamics (activation barriers) could be gained.

The energy and angular distribution of deuterium molecules desorbing from a vanadium (111) surface modified either by oxygen or by sulfur has been studied, using time-of-flight spectroscopy. It has been shown that the desorption flux contains two contributions, a thermal and a hyperthermal contribution. The mean translational energy of the hyperthermal part can be described by 〈E〉=8.3⋅kTs and 5.8⋅kTs for the sulfur and oxygen covered V(111) surface, respectively. Interestingly, the mean translational energy of the hyperthermal contribution is independent of the desorption angle. The angular distribution of the hyperthermal desorption flux is forward focused and can be described by cos3.3 θ and cos4.3 θ functions for the sulfur and oxygen modified surface, respectively. From the angular flux distribution and the angle independent mean translational energy of the hyperthermal contribution one can conclude that normal energy scaling does not exist for this adsorption/desorption channel. This is mainly due to the strong geometric corrugation of the modified V(111) surfaces.

Using a time-of-flight spectrometer we have measured the translational energy distribution of deuterium molecules originating from a sulfur-covered vanadium(1 1 1) surface. We have studied the energy accommodation coefficient (EAC) of D2 after scattering of a room temperature D2 gas on the surface. An EAC of 0.37, independent of the surface temperature, is obtained. Furthermore, we have investigated the mean translational energy of D2 molecules desorbing isothermally from the surface at 950 K. A hyperthermal desorption flux has been observed, corresponding roughly to a Maxwellian of 3200 K. From these results we conclude that the potential energy surface for the D2–V(1 1 1) + S system is characterized by an activation barrier for dissociative adsorption of about 0.22 eV and a non-existing physisorption well in front of the barrier.

The interaction of atomic and to some extent molecular hydrogen (deuterium) with oxygen and carbon covered V(100) surfaces has been studied. The oxygen and carbon coverage has been well characterized with respect to composition and structure by low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). Thermal desorption spectroscopy (TDS) has been used to investigate the kinetics of adsorption, absorption and desorption quantitatively. In addition, the activation barriers for the individual reaction steps during adsorption and desorption have been determined. We have focused on the advantage of using atomic hydrogen to enhance the uptake of hydrogen into the bulk of a contaminated vanadium sample. Surface, subsurface and bulk sites are occupied upon exposure to the atomic H (D) even at a surface temperature of 90K. These adsorption states exhibit desorption peaks at 150K (α-state), between 200 and 500K (β-states), and at 1000K (γ-state). The corresponding desorption energies are 0.36eV, 0.4–1.1eV, and 0.9eV, respectively. The kinetics of adsorption and absorption for molecular hydrogen depend strongly on the chemical composition of the surface, whereas the interaction of atomic hydrogen (deuterium) with V(100) is much less influenced by surface contaminants.

An atomic hydrogen doser of the Bertel type was characterized in terms of the degree of dissociation and angular distribution of the effusing particles. In this doser hydrogen is dissociated in a tungsten tube which is heated by electron bombardment. Various experimental techniques were used to determine the degree of dissociation as function of temperature and gas flux. It is shown that simple equilibrium considerations cannot be applied to obtain the degree of dissociation accurately. Nevertheless, for sufficiently small gas flux and temperatures above 1850 K, the degree of dissociation approaches 100%. The angular distribution was determined by a gold foil on a goniometer as detector, which is sensitive to atomic hydrogen only. The experimental results were compared with Monte Carlo simulations. A strongly forward focused distribution is observed which allows efficient atomic hydrogen dosing. This doser was used to measure absolute initial sticking coefficients for atomic hydrogen on various single crystal metal surfaces: S0(H)=1.0 on Ni(111), 0.9 on Ni(110), 0.7 on Al(111), 0.6 on Al(100) and 0.5 on a polycrystalline gold foil, respectively.