A. Martínez - Academia.edu (original) (raw)

Papers by A. Martínez

The Journal of Physical Chemistry C, 2018

The reaction of diatomic molecules on bimetallic surfaces, formed by one to few monolayers of a m... more The reaction of diatomic molecules on bimetallic surfaces, formed by one to few monolayers of a metal adsorbed on a different metal substrate, is relevant to understand the role of surface strain and substrate chemical binding in catalysis, which is interesting for industrial applications, challenges existing state-of-the-art theoretical methods, due to the additional complexity associated with having a molecule with triplet spin multiplicity. Here, we have studied the interaction of O 2 with Cu xML /Ru(0001) (x being the number of Cu monolayers), for which experimental data are available, by means of multidimensional classical dynamics simulations based on first-principles potential energy surfaces. Our results show, on the one hand, that the inclusion of the surface temperature on the simulations is essential to reproduce the experimental observations, and therefore, to analyze the physical mechanisms behind these observations, and, on the other hand, that electronic effects due to the binding between the two metallic species are only relevant for one Cu-monolayer, whereas strain is responsible for the observed reactivity in O 2 interacting with Cu (x≥2)ML /Ru(0001).

Se analiza la captura electronica simple por iones desnudos que impactan sobre blancos atomicos a... more Se analiza la captura electronica simple por iones desnudos que impactan sobre blancos atomicos a energias de colision intermedias y altas. Se desarrolla un modelo de onda distorsionada del continuo-estado final eikonal y se analiza su discrepancia con respecto a otro modelo de onda distorsionada del continuo-estado inicial eikonal. Se calculan secciones eficaces totales para los sistemas H+ + H(1s) -> H(nl) + H+ y He2 + H(2s) + H+. Se comparan los resultados con los obtenidos utilizando otros modelos de onda distorsionada y datos experimentales.

En el presente trabajo se analiza el proceso de doble captura electronica en el marco de una apro... more En el presente trabajo se analiza el proceso de doble captura electronica en el marco de una aproximacion de electron independiente. Se calculan secciones eficaces totales correspondientes a los procesos de captura al estado fundamental como asi tambien a estados simple y doblemente excitados del proyectil, por impacto de iones He2+, Li3+ y B5+ sobre blancos He(1s2). Las calculos teoricos son llevados a cabo utilizando los modelos de onda distorsionada Continuum Distorted Wave-Eikonal lnitial State y Continuum Distorted Wave-Eikonal Final State. Los resultados obtenidos se comparan con calculos previos correspondientes a la aproximacion Continuum Distorted Wave y con los resultados experimentales disponibles.

La perdida de energia de haces de protones en vapor de agua es estudiada usando una aproximacion ... more La perdida de energia de haces de protones en vapor de agua es estudiada usando una aproximacion de estado de carga por el metodo de onda distorsionada, dentro de un tratamiento totalmente mecanico cuantico. Este modelo tiene en cuenta el efecto debido a la distorsion del potencial Coulombiano. Se consideran energias de impacto entre 10kev/amu a 1 MeV/amu. Se calcula el poder de frenamiento electronico medio y las fracciones de carga en el equilibrio, comparandolo con resultados experimentales. El calculo utiliza diferentes aproximaciones para describir la molecula de agua. Encontramos que con una buena descripcion del canal de ionizacion por protones, es posible obtener una excelente descripcion del poder de frenamiento electronico en todo el rango de energia considerado, aun cuando se aplique aditividad de Bragg en los otros canales de reaccion.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1996

ABSTRACT

The Journal of Physical Chemistry C, 2016

We present a theoretical study of the dissociative adsorption of molecular hydrogen on PtRu bimet... more We 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), Pt 1ML /Ru(0001), for which we have obtained a minimum activation energy barrier for H 2 dissociation E b =0.32 eV, i.e. ∼ 0.3 eV and 0.26 eV higher than on Ru(0001), and Pt(111) respectively. Accordingly, the initial sticking probability for low energy impinging molecules (E i 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 Pt x Ru 1−x surface alloy provide active sites allowing non-activated H 2 dissociative adsorption. These two possible defects in a full pseudomorphic Pt monolayer deposited on Ru(0001) might be the responsible for the relatively high initial sticking probabilities obtained experimentally for ∼ 1.0-1.2 ML Pt evaporated over Ru(0001), only ∼ 30-65 % smaller than on Ru(0001).

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1997

We study the contribution to the double electron capture total cross sections coming from capture... more We study the contribution to the double electron capture total cross sections coming from capture into the ground state and into singly and doubly excited states of the projectile, within the framework of the Independent Electron Approximation (IEA). Theoretical total cross sections are analyzed by using different distorted wave approximations. Comparisons with experimental results are presented.

The Journal of chemical physics, Jan 14, 2014

Dynamics of the Eley-Rideal (ER) abstraction of H2 from W(110) is analyzed by means of quasi-clas... more 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. T...

Radiation Research, 1995

The energy loss of proton beams in water vapor is analyzed with a full quantum-mechanical treatme... more The energy loss of proton beams in water vapor is analyzed with a full quantum-mechanical treatment, the distorted-wave model. This model takes into account distortion effects due to the long-range Coulomb potential. Projectile energies from 10 keV up to 1 MeV are considered. Mean stopping power and equilibrium charge-state fractions are calculated and compared with experimental data. The validity of Bragg's additivity rule is investigated.

Physica Scripta, 1996

ABSTRACT

Physica Scripta, 1999

The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2005

The generalized continuum distorted wave-eikonal initial state (GCDW-EIS) approximation is employ... more The generalized continuum distorted wave-eikonal initial state (GCDW-EIS) approximation is employed to study single electron capture by impact of protons on Ne and Ar targets. We analyze the contributions to the total cross sections coming from the different target shells. Present results are compared with theoretical calculations obtained using the previous CDW-EIS formulation and to experimental data in order to

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1988

The Continuum Distorted Wave-Eikonal Initial State approximation is introduced to describe electr... more The Continuum Distorted Wave-Eikonal Initial State approximation is introduced to describe electron capture in ion-atom collisions. The model had been previously studied to represent electron ionization. Theoretical total cross sections for both processes are compared with expe~ental data for impact of light bare ions on heavier targets.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1989

Continuum Distorted Wave-Eikonal Initial State method previously introduced to describe electron ... more Continuum Distorted Wave-Eikonal Initial State method previously introduced to describe electron capture and ionization in asymmetric collisions is here applied to study the quasisymmetric reaction H+ + He+. Moreover, the H+ + Ne reaction is analysed with the purpose of estimating the ability of the theory to represent different physical mechanisms such as binding and polarization effects arising in the ionization case.

Langmuir, 2008

Density functional theory was used to investigate the reaction pathways for HSCH 3 adsorption on ... more Density functional theory was used to investigate the reaction pathways for HSCH 3 adsorption on Au(111) at low coverage. A molecular adsorbed state was found with the S atom bond on Top sites (E ∼-0.38 eV) and molecular adsorption is nonactivated. The H-SCH 3 dissociation process is energetically less favorable and becomes slightly exothermic only when surface relaxation is considered (∆E ∼-0.2 eV). All the reaction pathways present a sizable activation energy barrier, with the lowest being ∼0.52 eV (0.41 eV taking into account slab relaxation). In the corresponding saddle point of the potential energy surface, the S atom of the methylthiolate molecule is placed on Top sites and the H near a Bridge site. The high barrier obtained explains the complete absence of reactive methanethiol dissociation found in recent experiments.

Journal of Physics B: Atomic, Molecular and Optical Physics, 1995

For pt. I see Phys. Scr., vol. 51, p. 190 (1994). We study the single-electron capture process by... more For pt. I see Phys. Scr., vol. 51, p. 190 (1994). We study the single-electron capture process by impact of protons on hydrogen atoms, at intermediate and high collision energies. The emphasis is on differential cross sections for capture to specific nlm final states. The calculations use three distorted-wave models, a symmetric one (continuum distorted-wave approximation) and two asymmetric ones (continuum distorted-wave-eikonal initial state and eikonal final-state approximations). The various sets of differential cross sections are presented and compared to available experimental data. Distinguishing features appear most notably in the double scattering region revealing the different physical content of the approximations. An analysis of the post-prior discrepancy in the asymmetric models is sketched and the validity of a previously introduced criterion to select the appropriate distorted-wave model in a specific collision is also discussed.

Journal of Physics B: Atomic, Molecular and Optical Physics, 1996

Single electron capture by impact of bare heavy ions on He targets is studied for intermediate an... more Single electron capture by impact of bare heavy ions on He targets is studied for intermediate and high collision energies. We focus our analysis on the use of distorted wave models within the impact parameter approximation. For proton impact, total cross sections for capture to selective final states are presented. Results corresponding to capture to any final state are also shown for several projectiles with charge 1 Z P 9. Theoretical total cross sections calculated in the present work using the continuum distorted wave-eikonal initial state and the continumm distorted wave-eikonal final state approximations are compared with continuum distorted wave results and available experimental data. A criterion to determine which, among the distorted wave approximations analysed in the present work, is the most appropriate to describe a given collision system is discussed.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2004

A generalization of the continuum distorted wave eikonal initial state (CDW-EIS) approximation, f... more A generalization of the continuum distorted wave eikonal initial state (CDW-EIS) approximation, for the description of single-electron capture in ion–atom collisions involving multielectronic targets is presented. This approximation is developed within the framework of the independent electron model taking particular care of the representation of the bound and continuum target states. Total cross sections for single-electron capture from the K-shell of He, Ne and Ar noble gases by impact of bare ions are calculated. Present results are compared to previous CDW-EIS ones and to experimental data.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2002

We employ the independent-event model to study the transfer-ionization (TI) process in H+, He2+ +... more We employ the independent-event model to study the transfer-ionization (TI) process in H+, He2+ + He collisions. We consider both the ionization-capture and capture-ionization paths. The single-particle probabilities for all channels are calculated with the continuum distorted wave eikonal initial state model. With the probabilities for TI we calculate doubly differential and total cross sections which are compared with the

Applied Surface Science, 2007

ABSTRACT The interactions of H and H2 with W(100)-c(2×2)Cu and W(100) have been investigated thro... more ABSTRACT The interactions of H and H2 with W(100)-c(2×2)Cu and W(100) have been investigated through density functional theory (DFT) calculations to elucidate the effect of Cu atoms on the reactivity of the alloy. Cu atoms do not alter the attraction towards top-W sites felt by H2 molecules approaching the W(100) surface but make dissociation more difficult due to the rise of late activation barriers. This is mainly due to the strong decrease in the stability of the atomic adsorbed state on bridge sites, the most favourable ones for H adsorption on W(100). Still, our results show unambiguously that H2 dissociative adsorption on perfect terraces of the W(100)-c(2×2)Cu surface is a non-activated process which is consistent with the high sticking probability found in molecular beam experiments at low energies.

The Journal of Physical Chemistry C, 2018

The reaction of diatomic molecules on bimetallic surfaces, formed by one to few monolayers of a m... more The reaction of diatomic molecules on bimetallic surfaces, formed by one to few monolayers of a metal adsorbed on a different metal substrate, is relevant to understand the role of surface strain and substrate chemical binding in catalysis, which is interesting for industrial applications, challenges existing state-of-the-art theoretical methods, due to the additional complexity associated with having a molecule with triplet spin multiplicity. Here, we have studied the interaction of O 2 with Cu xML /Ru(0001) (x being the number of Cu monolayers), for which experimental data are available, by means of multidimensional classical dynamics simulations based on first-principles potential energy surfaces. Our results show, on the one hand, that the inclusion of the surface temperature on the simulations is essential to reproduce the experimental observations, and therefore, to analyze the physical mechanisms behind these observations, and, on the other hand, that electronic effects due to the binding between the two metallic species are only relevant for one Cu-monolayer, whereas strain is responsible for the observed reactivity in O 2 interacting with Cu (x≥2)ML /Ru(0001).

Se analiza la captura electronica simple por iones desnudos que impactan sobre blancos atomicos a... more Se analiza la captura electronica simple por iones desnudos que impactan sobre blancos atomicos a energias de colision intermedias y altas. Se desarrolla un modelo de onda distorsionada del continuo-estado final eikonal y se analiza su discrepancia con respecto a otro modelo de onda distorsionada del continuo-estado inicial eikonal. Se calculan secciones eficaces totales para los sistemas H+ + H(1s) -> H(nl) + H+ y He2 + H(2s) + H+. Se comparan los resultados con los obtenidos utilizando otros modelos de onda distorsionada y datos experimentales.

En el presente trabajo se analiza el proceso de doble captura electronica en el marco de una apro... more En el presente trabajo se analiza el proceso de doble captura electronica en el marco de una aproximacion de electron independiente. Se calculan secciones eficaces totales correspondientes a los procesos de captura al estado fundamental como asi tambien a estados simple y doblemente excitados del proyectil, por impacto de iones He2+, Li3+ y B5+ sobre blancos He(1s2). Las calculos teoricos son llevados a cabo utilizando los modelos de onda distorsionada Continuum Distorted Wave-Eikonal lnitial State y Continuum Distorted Wave-Eikonal Final State. Los resultados obtenidos se comparan con calculos previos correspondientes a la aproximacion Continuum Distorted Wave y con los resultados experimentales disponibles.

La perdida de energia de haces de protones en vapor de agua es estudiada usando una aproximacion ... more La perdida de energia de haces de protones en vapor de agua es estudiada usando una aproximacion de estado de carga por el metodo de onda distorsionada, dentro de un tratamiento totalmente mecanico cuantico. Este modelo tiene en cuenta el efecto debido a la distorsion del potencial Coulombiano. Se consideran energias de impacto entre 10kev/amu a 1 MeV/amu. Se calcula el poder de frenamiento electronico medio y las fracciones de carga en el equilibrio, comparandolo con resultados experimentales. El calculo utiliza diferentes aproximaciones para describir la molecula de agua. Encontramos que con una buena descripcion del canal de ionizacion por protones, es posible obtener una excelente descripcion del poder de frenamiento electronico en todo el rango de energia considerado, aun cuando se aplique aditividad de Bragg en los otros canales de reaccion.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1996

ABSTRACT

The Journal of Physical Chemistry C, 2016

We present a theoretical study of the dissociative adsorption of molecular hydrogen on PtRu bimet... more We 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), Pt 1ML /Ru(0001), for which we have obtained a minimum activation energy barrier for H 2 dissociation E b =0.32 eV, i.e. ∼ 0.3 eV and 0.26 eV higher than on Ru(0001), and Pt(111) respectively. Accordingly, the initial sticking probability for low energy impinging molecules (E i 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 Pt x Ru 1−x surface alloy provide active sites allowing non-activated H 2 dissociative adsorption. These two possible defects in a full pseudomorphic Pt monolayer deposited on Ru(0001) might be the responsible for the relatively high initial sticking probabilities obtained experimentally for ∼ 1.0-1.2 ML Pt evaporated over Ru(0001), only ∼ 30-65 % smaller than on Ru(0001).

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1997

We study the contribution to the double electron capture total cross sections coming from capture... more We study the contribution to the double electron capture total cross sections coming from capture into the ground state and into singly and doubly excited states of the projectile, within the framework of the Independent Electron Approximation (IEA). Theoretical total cross sections are analyzed by using different distorted wave approximations. Comparisons with experimental results are presented.

The Journal of chemical physics, Jan 14, 2014

Dynamics of the Eley-Rideal (ER) abstraction of H2 from W(110) is analyzed by means of quasi-clas... more 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. T...

Radiation Research, 1995

The energy loss of proton beams in water vapor is analyzed with a full quantum-mechanical treatme... more The energy loss of proton beams in water vapor is analyzed with a full quantum-mechanical treatment, the distorted-wave model. This model takes into account distortion effects due to the long-range Coulomb potential. Projectile energies from 10 keV up to 1 MeV are considered. Mean stopping power and equilibrium charge-state fractions are calculated and compared with experimental data. The validity of Bragg's additivity rule is investigated.

Physica Scripta, 1996

ABSTRACT

Physica Scripta, 1999

The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2005

The generalized continuum distorted wave-eikonal initial state (GCDW-EIS) approximation is employ... more The generalized continuum distorted wave-eikonal initial state (GCDW-EIS) approximation is employed to study single electron capture by impact of protons on Ne and Ar targets. We analyze the contributions to the total cross sections coming from the different target shells. Present results are compared with theoretical calculations obtained using the previous CDW-EIS formulation and to experimental data in order to

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1988

The Continuum Distorted Wave-Eikonal Initial State approximation is introduced to describe electr... more The Continuum Distorted Wave-Eikonal Initial State approximation is introduced to describe electron capture in ion-atom collisions. The model had been previously studied to represent electron ionization. Theoretical total cross sections for both processes are compared with expe~ental data for impact of light bare ions on heavier targets.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1989

Continuum Distorted Wave-Eikonal Initial State method previously introduced to describe electron ... more Continuum Distorted Wave-Eikonal Initial State method previously introduced to describe electron capture and ionization in asymmetric collisions is here applied to study the quasisymmetric reaction H+ + He+. Moreover, the H+ + Ne reaction is analysed with the purpose of estimating the ability of the theory to represent different physical mechanisms such as binding and polarization effects arising in the ionization case.

Langmuir, 2008

Density functional theory was used to investigate the reaction pathways for HSCH 3 adsorption on ... more Density functional theory was used to investigate the reaction pathways for HSCH 3 adsorption on Au(111) at low coverage. A molecular adsorbed state was found with the S atom bond on Top sites (E ∼-0.38 eV) and molecular adsorption is nonactivated. The H-SCH 3 dissociation process is energetically less favorable and becomes slightly exothermic only when surface relaxation is considered (∆E ∼-0.2 eV). All the reaction pathways present a sizable activation energy barrier, with the lowest being ∼0.52 eV (0.41 eV taking into account slab relaxation). In the corresponding saddle point of the potential energy surface, the S atom of the methylthiolate molecule is placed on Top sites and the H near a Bridge site. The high barrier obtained explains the complete absence of reactive methanethiol dissociation found in recent experiments.

Journal of Physics B: Atomic, Molecular and Optical Physics, 1995

For pt. I see Phys. Scr., vol. 51, p. 190 (1994). We study the single-electron capture process by... more For pt. I see Phys. Scr., vol. 51, p. 190 (1994). We study the single-electron capture process by impact of protons on hydrogen atoms, at intermediate and high collision energies. The emphasis is on differential cross sections for capture to specific nlm final states. The calculations use three distorted-wave models, a symmetric one (continuum distorted-wave approximation) and two asymmetric ones (continuum distorted-wave-eikonal initial state and eikonal final-state approximations). The various sets of differential cross sections are presented and compared to available experimental data. Distinguishing features appear most notably in the double scattering region revealing the different physical content of the approximations. An analysis of the post-prior discrepancy in the asymmetric models is sketched and the validity of a previously introduced criterion to select the appropriate distorted-wave model in a specific collision is also discussed.

Journal of Physics B: Atomic, Molecular and Optical Physics, 1996

Single electron capture by impact of bare heavy ions on He targets is studied for intermediate an... more Single electron capture by impact of bare heavy ions on He targets is studied for intermediate and high collision energies. We focus our analysis on the use of distorted wave models within the impact parameter approximation. For proton impact, total cross sections for capture to selective final states are presented. Results corresponding to capture to any final state are also shown for several projectiles with charge 1 Z P 9. Theoretical total cross sections calculated in the present work using the continuum distorted wave-eikonal initial state and the continumm distorted wave-eikonal final state approximations are compared with continuum distorted wave results and available experimental data. A criterion to determine which, among the distorted wave approximations analysed in the present work, is the most appropriate to describe a given collision system is discussed.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2004

A generalization of the continuum distorted wave eikonal initial state (CDW-EIS) approximation, f... more A generalization of the continuum distorted wave eikonal initial state (CDW-EIS) approximation, for the description of single-electron capture in ion–atom collisions involving multielectronic targets is presented. This approximation is developed within the framework of the independent electron model taking particular care of the representation of the bound and continuum target states. Total cross sections for single-electron capture from the K-shell of He, Ne and Ar noble gases by impact of bare ions are calculated. Present results are compared to previous CDW-EIS ones and to experimental data.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2002

We employ the independent-event model to study the transfer-ionization (TI) process in H+, He2+ +... more We employ the independent-event model to study the transfer-ionization (TI) process in H+, He2+ + He collisions. We consider both the ionization-capture and capture-ionization paths. The single-particle probabilities for all channels are calculated with the continuum distorted wave eikonal initial state model. With the probabilities for TI we calculate doubly differential and total cross sections which are compared with the

Applied Surface Science, 2007

ABSTRACT The interactions of H and H2 with W(100)-c(2×2)Cu and W(100) have been investigated thro... more ABSTRACT The interactions of H and H2 with W(100)-c(2×2)Cu and W(100) have been investigated through density functional theory (DFT) calculations to elucidate the effect of Cu atoms on the reactivity of the alloy. Cu atoms do not alter the attraction towards top-W sites felt by H2 molecules approaching the W(100) surface but make dissociation more difficult due to the rise of late activation barriers. This is mainly due to the strong decrease in the stability of the atomic adsorbed state on bridge sites, the most favourable ones for H adsorption on W(100). Still, our results show unambiguously that H2 dissociative adsorption on perfect terraces of the W(100)-c(2×2)Cu surface is a non-activated process which is consistent with the high sticking probability found in molecular beam experiments at low energies.