Dynamics of H2 Eley-Rideal abstraction from W(110): Sensitivity to the representation of the molecule-surface potential

Dynamics 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

Eley-Rideal reaction dynamics between O atoms on β-cristobalite (100) surface: a new interpolated potential energy surface and classical trajectory study

We present a theoretical study of the collisions of atomic oxygen with O-precovered b-cristobalite (100) surface. We have constructed a multidimensional potential energy surface for the O2/b-cristobalite (100) system based mainly on a dense grid of density functional theory points by using the interpolation corrugation reducing procedure. Classical trajectories have been computed for quasithermal (100-1500 K) and state-specific (e.g., collision energies between 0.01-4 eV) conditions of reactants for different O incident angles. Atomic sticking and O2(adsorbed) formation are the main processes, although atomic reflection and Eley-Rideal (ER) reaction (i.e., O2 gas) are also significant, depending their reaction probabilities on the O incident angle. ER reaction is enhanced by temperature increase, with an activation energy derived from the atomic recombination coefficient (gamma_O(0,T)) equal to 0.24±0.02 eV within the 500-1500 K range, in close agreement with experimental data. Calculated gamma_O(0,T) values compare quite well with available experimental gamma_O(T) although a more accurate calculation is proposed. Chemical energy accommodation coefficient beta_O(T) is also discussed as a function of ER and other competitive contributions

Site Selective Detection of Methane Dissociation on Stepped Pt Surfaces

We report a combined experimental and theoretical study comparing methane dissociation on three di erent platinum surfaces Pt(111), Pt(211), and Pt(110)-(1 × 2). Re ection absorption infrared spectroscopy (RAIRS) was used to detect chemisorbed methyl species formed by dissociative chemisorption of CH4 on speci c surface sites and to measure surface- site-speci c sticking coe cients of CH4 on the terrace, step, and ridge sites as function of incident translational energy. Methane dissociation is observed to be direct on all sites and di usion of the chemisorbed methyl species is absent for surface temperature below 150 K. The experimental data are compared with the results of density functional (DFT) calculations that give minimum energy barriers for CH4 chemisorption that properly account for the experimental relative site-speci c reactivities. Also in agreement with experiments, DFT results predict a negligible e ect of co-adsorbed H and CH3 species on the vibrational frequency of a methyl group chemisorbed on terrace and step sites of Pt(211). However, the origin of the red-shift of the RAIRS peak of CH3 chemisorbed on terrace sites compared with that on step sites of Pt(211) remains elusive and still demands further investigation

Reactive scattering of H2 from Cu(100): comparison of dynamics calculations based on the specific reaction parameter approach to density functional theory with experiment

We present new experimental and theoretical results for reactive scattering of dihydrogen from Cu(100). In the new experiments, the associative desorption of H2 is studied in a velocity resolved and final rovibrational state selected manner, using time-of-flight techniques in combination with resonance-enhanced multi-photon ionization laser detection. Average desorption energies and rota- tional quadrupole alignment parameters were obtained in this way for a number of (v = 0, 1) ro- tational states, v being the vibrational quantum number. Results of quantum dynamics calculations based on a potential energy surface computed with a specific reaction parameter (SRP) density func- tional, which was derived earlier for dihydrogen interacting with Cu(111), are compared with the results of the new experiments and with the results of previous molecular beam experiments on sticking of H2 and on rovibrationally elastic and inelastic scattering of H2 and D2 from Cu(100). The calculations use the Born-Oppenheimer and static surface approximations. With the functional derived semi-empirically for dihydrogen + Cu(111), a chemically accurate description is obtained of the molecular beam experiments on sticking of H2 on Cu(100), and a highly accurate descrip- tion is obtained of rovibrationally elastic and inelastic scattering of D2 from Cu(100) and of the orientational dependence of the reaction of (v = 1, j = 2 − 4) H2 on Cu(100). This suggests that a SRP density functional derived for H2 interacting with a specific low index face of a metal will yield accurate results for H2 reactively scattering from another low index face of the same metal, and that it may also yield accurate results for H2 interacting with a defected (e.g., stepped) surface of that same metal, in a system of catalytic interest. However, the description that was obtained of the average desorption energies, of rovibrationally elastic and inelastic scattering of H2 from Cu(100), and of the orientational dependence of reaction of (v = 0, j = 3 − 5, 8) H2 on Cu(100) compares less well with the available experiments. More research is needed to establish whether more accurate SRP-density functional theory dynamics results can be obtained for these observables if surface atom motion is added to the dynamical model. The experimentally and theoretically found dependence of the rotational quadrupole alignment parameter on the rotational quantum number provides evidence for rotational enhancement of reaction at low translational energies.Fil: Sementa, L.. Leiden University; Países Bajos. Istituto per i Processi Chimico-Fisici of the Consiglio Nazionale delle Ricerche; ItaliaFil: Wijzenbroek, M.. Leiden University; Países BajosFil: Van Kolck, B. J.. Leiden University; Países BajosFil: Somers, M. F.. Leiden University; Países BajosFil: Al-Halabi, A.. Leiden University; Países BajosFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Olsen, R. A.. Leiden University; Países Bajos. SINTEF Materials and Chemistry; NoruegaFil: Kroes, G. J.. Leiden University; Países BajosFil: Rutkowski, M.. Westfalische Wilhelms Universitat; AlemaniaFil: Thewes, C.. Westfalische Wilhelms Universitat; AlemaniaFil: Kleimeier, N. F.. Westfalische Wilhelms Universitat; AlemaniaFil: Zacharias, H.. Westfalische Wilhelms Universitat; Alemani

Charge exchange and ionisation in N7+^{7+}, N6+^{6+}, C6+^{6+} - H(n=1,2n=1, 2) collisions studied systematically by theoretical approaches

The introduction of gases like nitrogen or neon for cooling the edge region of magnetically confined fusion plasmas has triggered a renewed interest in state selective cross sections necessary for plasma diagnostics by means of charge exchange recombination spectroscopy. To improve the quality of spectroscopic data analysis, charge exchange and ionisation cross sections for N$^{7+}$ + H($n=1,2$) have been calculated using two different theoretical approaches, namely the atomic-orbital close-coupling method and the classical trajectory Monte Carlo method. Total and state resolved charge exchange cross sections are analysed in detail. In the second part, we compare two collision systems involving equally charged ions, C$^{6+}$ and N$^{6+}$ on atomic hydrogen. The analysis of the data lead to the conclusion that deviations between these two impurity ions are practically negligible. This finding is very helpful when calculating cross sections for collision systems with heavier not completely stripped impurity ions.Comment: 21 pages, 10 figures, 6 data table

Differential cross sections for electron capture from [Formula Presented] within the continuum-distorted-wave approximation

In 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. \ua9 1997 The American Physical Society

Single electron capture from molecular hydrogen targets by impact of protons and \u3b1 particles

The 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\u2013eikonal initial state, and the continuum distorted wave\u2013eikonal 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. \ua9 1998 The American Physical Society

Site-Specific Product Selectivity of Stepped Pt Surfaces for Methane Dehydrogenation

Through 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