62 research outputs found
Differential cross sections for electron capture from H 2+ within the continuum-distorted-wave approximation
No full textIn the present work, the molecular continuum-distorted-wave approximation is formulated for the single-electron capture reaction from [Formula Presented] targets. The initial bound wave function is distorted by a projectile-electron continuum factor. In the exit channel, the final electronic wave function is distorted by a product of the continuum factors corresponding to the interaction between the electron and each one of the nuclei of the target. The doubly differential cross sections as a function of the projectile scattering angle are evaluated for different molecular alignments for the case of proton impact. © 1997 The American Physical Society
Single electron capture from molecular hydrogen targets by impact of protons and alpha particles
No full textThe present work deals with single electron capture processes from [Formula Presented] targets by impact of heavy bare ions at intermediate and high collision energies. Within the distorted wave formalism, the one active electron model developed to describe collisions with multielectronic atomic targets is used for the case of [Formula Presented] targets. Three different distorted wave models are employed: the continuum distorted wave, the continuum distorted wave–eikonal initial state, and the continuum distorted wave–eikonal final state. Using these distorted wave approximations, total cross sections for [Formula Presented] and [Formula Presented] impact are calculated employing two different representations of the initial bound molecular wave function. The variation of the total cross sections due to this change in the description of the initial wave function and due to changes of the distortion factors in the entrance and exit channels is studied. The theoretical results are compared with available experimental data. © 1998 The American Physical Society
7D Quantum Dynamicsof H2 scattering form Cu(111): the accuracy of the phonon sudden approximation
No full textThe correct prediction of elementary processes occurring when H 2 scatters from a metal surface is one of the main challenges of surface science. In the field, the scattering of H 2 from Cu(111) has been considered a prototype system for activated dissociative chemisorption. Experimental and theoretical work suggested that a proper description of some scattering experiments on this system might require going beyond the static surface approximation, to consider how the motion of the Cu atoms affects the scattering event. Previous work suggested that important effects of phonons on the dynamics can be incorporated in the Potential Energy Surface (PES) by including four degrees of freedom, that have approximately additive couplings with the hydrogen molecule: the 3 dimensional motion of the nearest 1st layer copper atom and the displacement of the nearest 2nd layer copper atom along the direction perpendicular to the surface [3]. In the present work, we extend the 6D dynamical model by including the perpendicular motion of the 2nd layer surface atom and we study this novel dynamical model with two techniques: an approximate method based on the Phonon Sudden Approximation (PSA) and an exact description using 7D wavepacket quantum dynamics. We consider how the inclusion and the excitation of the lattice degree of freedom affect some relevant processes: dissociative chemisorption, vibrational excitation of H2 and state-to-state scattering probabilities fully resolved with respect to the vibrational states of the surface. We show that the PSA works in an excellent way for the system, thereby suggesting that this might be a viable way to study higher dimensional quantum models, incorporating four surface degrees of freedom that appear to be most relevant for H2 scattering.Fil: Bonfanti, Matteo. Leiden University; Países BajosFil: Somers, Mark F.. Leiden University; Países BajosFil: Díaz, Cristina. Universidad Autónoma de Madrid; EspañaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Kroes, Geert Jan. Leiden University; Países Bajo
Normal and off-normal incidence dissociative dynamics of O 2 ( v , J ) on ultrathin Cu films grown on Ru(0001)
No full textThe dissociative adsorption of molecular oxygen on metal surfaces has long been controversial, mostly due to the spin-triplet nature of its ground state, to possible non-adiabatic effects, such as an abrupt charge transfer from the metal to the molecule, or even to the role played by the surface electronic state. Here, we have studied the dissociative adsorption of O2on CuML/Ru(0001) at normal and off-normal incidence, from thermal to super-thermal energies, using quasi-classical dynamics, in the framework of the generalized Langevin oscillator model, and density functional theory based on a multidimensional potential energy surface. Our simulations reveal a rather intriguing behavior of dissociative adsorption probabilities, which exhibit normal energy scaling at incidence energies below the reaction barriers and total energy scaling above, irrespective of the reaction channel, either direct dissociation, trapping dissociation, or molecular adsorption. We directly compare our results with existing scanning tunneling spectroscopy and microscopy measurements. From this comparison, we infer that the observed experimental behavior at thermal energies may be due to ligand and strain effects, as already found for super-thermal incidence energies.Fil: Fallaque, J. G.. Universidad Autónoma de Madrid; España. Instituto Madrileño de Estudios Avanzados en Nanociencia; EspañaFil: Ramos Acevedo, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Martín, F.. Universidad Autónoma de Madrid; España. Instituto Madrileño de Estudios Avanzados en Nanociencia; EspañaFil: Díaz, C.. Universidad Complutense de Madrid; Españ
Site-Specific Product Selectivity of Stepped Pt Surfaces for Methane Dehydrogenation
No full textThrough density functional theory (DFT) calculations, we show that, in contrast to terrace sites of Pt(211) and Pt(111), on steplike sites of Pt(211) and Pt(110)-(2 × 1), methylene is more stable than methyl. The resulting site-dependent product selectivity for methane dissociation allows us to conciliate between theory and recent reflection absorption infrared spectroscopy (RAIRS) experiments, which might open a door to new applications of vicinal surfaces of Pt in heterogeneous catalysis and as templates for nanoscale patterning of self-assembled monolayers.Fil: Torio, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin
Scattering of Atomic Hydrogen Off a H-Covered W(110) Surface: Hot-Atom versus Eley-Rideal Abstraction Dynamics
No full textNormal incidence scattering of hydrogen atoms off a H-covered tungsten W(110) surface is simulated via quasiclassical trajectories. A density functional theory (DFT) based multiadsorbate potential is developed to model a wide range of surface coverages, θ = 0.25–1 monolayer (ML), reproducing the surface arrangements observed at low temperature. The competition between hot-atom (HA) and Eley–Rideal (ER) abstraction mechanisms is studied for collision energies of the projectile atom in the range Ep = 0.1–5.0 eV (Ep = 0.1–2.0 eV) for θ = 0.25 ML (θ = 0.5, 0.75, and 1 ML) coverage. Cross sections, final energies of the recombination products, and reaction times are analyzed. At low coverage and low collision energy, HA dominates the abstraction, whereas HA and ER cross-sections become similar when collision energy increases. The vibrational distribution of recombined H2 molecules at finite coverage is found to be in better agreement with experiments than the one computed within the single adsorbate limit. At high surface coverage, ER dominates abstraction but the dynamical observables highlight the similarity between both reaction mechanisms, thus suggesting that abstraction may be considered as a unique process.Fil: Pétuya, R.. Institut des Sciences Moléculaires; FranciaFil: Larrégaray, P.. Institut des Sciences Moléculaires; FranciaFil: Crespos, C.. Institut des Sciences Moléculaires; FranciaFil: Aurel, P.. Institut des Sciences Moléculaires; FranciaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Martinez, Alejandra Elisa. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentin
Dissociative and non-dissociative adsorption of O2 on Cu(111) and CuML/Ru(0001) surfaces: Adiabaticity takes over
No full textThe role of spin non-adiabatic effects in the reactivity of O2 on metal surfaces has been a matter of debate for several years. By means of density functional theory with a semi-local exchange-correlation functional, and classical dynamics calculations, we show that the recently observed activated character of O2 adsorption on Cu(111) and CuML/Ru(0001), as well as the delicate interplay between dissociative and non-dissociative O2 sticking on Cu(111) at different surface temperatures, can be explained by assuming an adiabatic evolution of the molecular spin. This suggests that spin adiabaticity during O2 adsorption on metal surfaces could be a more general scenario than anticipated.Fil: Ramos, M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Díaz, C.. Universidad Autónoma de Madrid; EspañaFil: Martinez, Alejandra Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Martín, F.. Universidad Autónoma de Madrid; Españ
Dynamics of H2 Eley-Rideal abstraction from W(110): Sensitivity to the representation of the molecule-surface potential
No full textDynamics of the Eley-Rideal (ER) abstraction of H2 from W(110) is analyzed by means of quasi-classical trajectory calculations. Simulations are based on two different molecule-surface potential energy surfaces (PES) constructed from Density Functional Theory results. One PES is obtained by fitting, using a Flexible Periodic London-Eyring-Polanyi-Sato (FPLEPS) functional form, and the other by interpolation through the corrugation reducing procedure (CRP). Then, the present study allows us to elucidate the ER dynamics sensitivity on the PES representation. Despite some sizable discrepancies between both H+H/W(110) PESs, the obtained projectile-energy dependence of the total ER cross sections are qualitatively very similar ensuring that the main physical ingredients are captured in both PES models. The obtained distributions of the final energy among the different molecular degrees of freedom barely depend on the PES model, being most likely determined by the reaction exothermicity. Therefore, a reasonably good agreement with the measured final vibrational state distribution is observed in spite of the pressure and material gaps between theoretical and experimental conditions.Fil: Petuya, R.. Universite de Bordeaux; Francia. Centre National de la Recherche Scientifique. Institut des Sciences Moléculaires; FranciaFil: Larregaray, P.. Universite de Bordeaux; Francia. Centre National de la Recherche Scientifique. Institut des Sciences Moléculaires; FranciaFil: Crespos, C.. Universite de Bordeaux; Francia. Centre National de la Recherche Scientifique. Institut des Sciences Moléculaires; FranciaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Martinez, Alejandra Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentin
Dissociative Adsorption of H2 on PtRu Bimetallic Surfaces
No full textWe present a theoretical study of the dissociative adsorption of molecular hydrogen on PtRu bimetallic surfaces based on density functional theory (DFT) calculations. We focus on the reactivity of a pseudomorphic Pt monolayer deposited on Ru(0001), Pt1ML/Ru(0001), for which we have obtained a minimum activation energy barrier for H2 dissociation, Eb = 0.32 eV, i.e., ∼0.3 and 0.26 eV higher than on Ru(0001) and Pt(111), respectively. Accordingly, the initial sticking probability for low energy impinging molecules (Ei ≲ 0.1 eV) derived from classical trajectory calculations is various orders of magnitude smaller than on Ru(0001) in apparent contradiction with available experimental data. However, undercoordinated Pt atoms in the borders of Pt pseudomorphic islands and isolated Ru atoms or small Ru aggregates in a Pt-rich two-dimensional PtxRu1-x surface alloy provide active sites allowing nonactivated H2 dissociative adsorption. These two possible defects in a full pseudomorphic Pt monolayer deposited on Ru(0001) might be responsible for the relatively high initial sticking probabilities obtained experimentally for ∼1.0-1.2 ML of Pt evaporated over Ru(0001), only ∼30-65% smaller than on Ru(0001).Fil: Ramos Acevedo, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Martinez, Alejandra Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin
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