MICROSCOPIC MODEL OF ASSOCIATIVE DESORPTION FOR HYDROGEN ON Mo(110)

Adsorbed hydrogen layers on the Mo(110) surface have been investigated both experimentally by temperature programmed desorption (TPD) method and theoretically by means of DFT-based optimization of surface structures. We suggest a novel microscopic model of the associative hydrogen desorption, which explains essential features of the process. In this model, the process of hydrogen desorption can be described as association of hydrogen atoms on the surface, but molecular formation is actually accomplished while the molecule moves away from the surface. We also suggest a new algorithm for realistic Monte Carlo simulations of associative desorption, which implements the microscopic description of the association of hydrogen adatoms into a molecule with activation energy, found from the DFT calculations. Good agreement between simulated and experimental TPD spectra gives insight into different behavior of the spectra, obtained for low and high hydrogen coverages on the Mo(110) surface.Hydrogen, desorption, DFT calculations, Monte Carlo simulations, lateral interaction

ABSENCE OF CO DISSOCIATION ON Mo(110): TPD AND DFT STUDY

The problem of the CO dissociation on Mo(110) has been addressed by means of temperature-programmed desorption (TPD) and density-functional (DFT) calculations. The TPD spectra show a first-order CO desorption, which indicates the desorption from a "virgin" state, not a recombinative form of desorption. The height of the potential barrier for the dissociation (2.75 eV), estimated from DFT calculations, substantially exceeds the energy of CO chemisorption (2.1 eV), which makes the thermally induced CO dissociation on Mo improbable. Monte Carlo simulations of TPD spectra, performed using estimated chemisorption energies, are in good agreement with experiment and demonstrate that the two-peak shape of the spectra can be explained without involving the CO dissociation. Thus, the results of the present study finally refute the concept of a dissociative form of CO adsorption on Mo surfaces.Carbon oxide, dissociation, density functional calculations, Monte Carlo simulations

Monte Carlo simulations of hydrogen adsorption on the W(110) and Mo(110) surfaces

Kinetics of low-temperature hydrogen and deuterium adsorption on W(110) and Mo(110) surfaces have been studied by the “real-time” Monte Carlo simulations. Recently reported qualitative dependence of the adsorption characteristics on variation of the H 2 flux is described in terms of the dynamical equilibrium between incident and desorption fluxes and improved conditions for accommodation for the hydrogen molecules at high incident fluxes. The role of the intrinsic precursor state in hydrogen dissociative adsorption is analyzed. Copyright Springer-Verlag Berlin/Heidelberg 2004