Cristina Diaz | Universidad Autónoma de Madrid (original) (raw)
Papers by Cristina Diaz
The Journal of Chemical Physics, 2000
A collaborative experimental and theoretical study of rotationally inelastic collisions of fine-s... more A collaborative experimental and theoretical study of rotationally inelastic collisions of fine-structure Λ-doublet levels with argon is presented. Experimental state-to-state rate constants were determined with an opticaloptical double resonance technique. The CN radical was prepared by ...
![Research paper thumbnail of Experimental evidence of dynamic trapping in the scattering of H[sub 2] from Pd(110)](https://attachments.academia-assets.com/51738386/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2006
We have performed H 2 ͑D 2 ͒ diffraction experiments on a Pd͑110͒ surface using two different hig... more We have performed H 2 ͑D 2 ͒ diffraction experiments on a Pd͑110͒ surface using two different high-sensitivity set-ups. We have found that, although the total reflectivity of Pd͑110͒ is comparable to that observed in other reactive systems, the corresponding H 2 ͑D 2 ͒ diffraction patterns are quite different: no diffraction peak, including the specular one, is observed on Pd͑110͒. This unexpected result is the consequence of dynamic trapping. Such interpretation is supported by classical dynamics calculations based on accurate ab initio potential energy surfaces.
The Journal of Chemical Physics, 2005
We present a discretization method that allows one to interpret measurements on diffraction of di... more We present a discretization method that allows one to interpret measurements on diffraction of diatomic molecules from solid surfaces using six-dimensional (6D) classical trajectory calculations. It has been applied to the D2/NiAl(110) and H2/Pd(111) systems (which are models for activated and nonactivated dissociative chemisorption, respectively) using realistic potential energy surfaces obtained from first principles. Comparisons with experimental results and 6D
Chemical Physics Letters, 2004
We have measured the angular distribution of H 2 molecules with incident energies 100-150 meV ref... more We have measured the angular distribution of H 2 molecules with incident energies 100-150 meV reflected by the Pd(1 1 1) surface at 430 K. In spite of the low diffraction reflectivity ($0.5%), diffraction peaks have been resolved at nearly grazing incidence. Apart from specular reflection, out-of-plane diffraction has been found to be dominant, in agreement with classical simulations. We show that this behavior is a generic one for grazing incidence and discuss the relevance of this finding for the study of molecule/surface dynamics in systems for which dissociation is a non activated process.
Physical Review Letters, 2004
We have measured in-plane and out-of-plane diffraction of H2 and D2 molecular beams scattered by ... more We have measured in-plane and out-of-plane diffraction of H2 and D2 molecular beams scattered by reactive Pd(111) and nonreactive NiAl(110) surfaces at 140-150 meV. A comparison with six-dimensional quantum dynamics and classical trajectory calculations shows for the first time that accurate diffraction patterns can be obtained from state-of-the-art potential energy surfaces based on density functional theory. Our measurements show that, at general incidence conditions, out-of-plane diffraction is much more important than was assumed in previous experiments.
The interpretation of scanning tunneling spectroscopy (STS) and scanning tunneling microscopy mea... more The interpretation of scanning tunneling spectroscopy (STS) and scanning tunneling microscopy measurements of epitaxial graphene on lattice-mismatched substrates is a challenging problem, because of the spatial modulation in the electronic structure imposed by the formation of a moiré pattern. Here we describe the electronic structure of graphene adsorbed on Ru(0001) by means of density functional theory calculations that include van der Waals interactions and are performed on a large 11 × 11 unit cell to account for the observed moiré patterns. Our results show the existence of localized electronic states in the high and low areas of the moiré at energies close to and well above the Fermi level, respectively. Localization is due to the spatial modulation of the graphene-Ru(0001) interaction and is at the origin of the various peaks observed in STS spectra.
Phys. Chem. Chem. …, Jan 1, 2012
The dissociation of H(2) on Ti-covered Al surfaces is relevant to the rehydrogenation and dehydro... more The dissociation of H(2) on Ti-covered Al surfaces is relevant to the rehydrogenation and dehydrogenation of the NaAlH(4) hydrogen storage material. The energetically most stable structure for a 1/2 monolayer of Ti deposited on the Al(100) surface has the Ti atoms in the second layer with a c(2 × 2) structure, as has been confirmed by both low-energy electron diffraction and low-energy ion scattering experiments and density functional theory studies. In this work, we investigate the dynamics of H(2) dissociation on a slab model of this Ti/Al(100) surface. Two six-dimensional potential energy surfaces (PESs) have been built for this H(2) + Ti/Al(100) system, based on the density functional theory PW91 and RPBE exchange-correlation functionals. In the PW91 (RPBE) PES, the lowest H(2) dissociation barrier is found to be 0.65 (0.84) eV, with the minimum energy path occurring for H(2) dissociating above the bridge to top sites. Using both PESs, H(2) dissociation probabilities are calculated using the classical trajectory (CT), the quasi-classical trajectory (QCT), and the time-dependent wave-packet methods. We find that the QCT H(2) dissociation probabilities are in good agreement with the quantum dynamics results in the collision energy range studied up to 1.0 eV. We have also performed molecular beam simulations and present predictions for molecular beam experiments. Our molecular beam simulations show that H(2) dissociation on the 1/2 ML Ti/Al(100) surface is an activated process, and the reaction probability is found to be 6.9% for the PW91 functional and 1.8% for the RPBE at a nozzle temperature of 1700 K. Finally, we have also calculated H(2) dissociation rate constants by applying transition state theory and the QCT method, which could be relevant to modeling Ti-catalyzed rehydrogenation and dehydrogenation of NaAlH(4).
… Theory, Computation, and Modeling …, Jan 1, 2011
We present a systematic density functional theory (DFT) study of the isolated manganese-phthalocy... more We present a systematic density functional theory (DFT) study of the isolated manganese-phthalocyanine, MnPc, by using both localized gaussian-type orbital (GTO) and plane-wave (PW) basis sets and the following exchange-correlation functionals: B3LYP, PBE, PBE0, HSE, and HSE06. We find a very good agreement between GTO and PW results, which is a necessary condition in order to extend the present methodology to MnPc molecules deposited on metal surfaces. We conclude that the HSE06 functional is the most suitable one for the study of MnPc/inorganic interfaces with a basis of plane waves. We compare our calculated electron energy spectra with two available experiments [Kraus et al. in Chem Phys Lett 469:121, 2009; Grobosch et al. in Organics Electron 11:1483, 2010; Papageorgiou et al. in Prog Surf Sci 77:139, 2004] in which the ultraviolet photoemission spectra (UPS) have been measured. Our results suggest that spectra obtained from MnPc molecules in the gas phase are closer to those obtained from thin films of MnPc deposited on inert surfaces than to those obtained from thick films. Finally, we report optical absorption spectra by using a time-dependent DFT approach. Our results are again compatible with measurements performed on thin MnPc films.
Physical review letters, Jan 1, 2011
Elaborate density functional theory (DFT) calculations that include the effect of van der Waals (... more Elaborate density functional theory (DFT) calculations that include the effect of van der Waals (vdW) interactions have been carried out for graphene epitaxially grown on Ru(0001). The calculations predict a reduction of structural corrugation in the observed moiré pattern of about 25% ($ 0:4 # A) with respect to DFT calculations without vdW corrections. The simulated STM topographies are close to the experimental ones in a wide range of bias voltage around the Fermi level.
Phys. Chem. Chem. Phys., Jan 1, 2011
We have studied the effect of lattice displacement on the interaction of H(2) with the Cu(111) su... more We have studied the effect of lattice displacement on the interaction of H(2) with the Cu(111) surface using the Specific Reaction Parameter (SRP) approach to Density Functional Theory (DFT). We have systematically investigated how the motion of the surface atoms affects some features of the Potential Energy Surface (PES), such as the dissociation barrier height and the barrier geometry corresponding to some representative reaction pathways, and the anisotropy of the potential at these geometries. This analysis has allowed us to identify the surface degrees of freedom that are likely to be most relevant for H(2) dissociation. In particular, we have found that the lattice coordinate displacements that have the largest effect on the H(2)/Cu(111) DFT-SRP barrier heights and locations concern the motion of the 1st layer and 2nd layer Cu atoms in the Z direction, and motion of the 1st layer atoms in the directions parallel to the surface. Whereas the first degree of freedom mostly affects the barrier geometry, the second and third motions can lower or raise the barrier height. The latter effect cannot be described with the usual surface oscillator dynamical models employed in the past to include surface motion, and its dynamical influence on the dissociative adsorption needs to be further investigated.
Surface Science, Jan 1, 2010
We have studied the scattering of vibrationally excited H2 molecules from metal surfaces under fa... more We have studied the scattering of vibrationally excited H2 molecules from metal surfaces under fast grazing incidence conditions, by means of quasi-classical calculations based on six-dimensional potential energy surfaces. We show that, in spite of the fast parallel motion, the reorientation of the molecule along the trajectory plays a fundamental role on the scattering, being responsible for the nonmonotonic behavior observed as a function of the normal incidence energy, similar to that observed under slow normal incidence conditions. The present study has allowed us to further prove that the interaction between a H2 molecule and an ordered metal surface under fast grazing incidence conditions is, in general, governed by the normal momentum of the molecule.
Physical Review B, Jan 1, 2010
... 12); the lack of diffraction peaks in H2/Pd(110) due to dynamic trapping;13 the ... stimulate... more ... 12); the lack of diffraction peaks in H2/Pd(110) due to dynamic trapping;13 the ... stimulated Raman pumping.19–22 However, only very recently, the advent of experimental setups based ... The latter experiments have provided direct evidence of the central role played by vibrational ...
Physical Review A, Jan 1, 2010
Phys. Chem. Chem. Phys., Jan 1, 2010
We have studied the interaction of H(2) on Cu(111) using quasi-classical and quantum dynamics, an... more We have studied the interaction of H(2) on Cu(111) using quasi-classical and quantum dynamics, and a chemically accurate six-dimensional potential energy surface (PES). The PES was computed using the specific reaction parameter (SRP) approach to density functional theory (DFT), in an implementation adapted to molecules interacting with metal surfaces. To perform this study we have applied the Born-Oppenheimer static surface (BOSS) approximation, i.e., we used both the Born-Oppenheimer (BO) and the static surface (SS) approximations. We show that our theoretical approach accurately describes experiments on dissociative adsorption, the effect of molecular vibrational and rotational motion on dissociative (associative) adsorption (desorption), and rotational excitation upon scattering. More specifically, dynamics calculations on reactive scattering of H(2) reproduce reaction probabilities measured in molecular beam experiments, effective barrier heights describing the dependence of reaction on the initial rovibrational state, and data on rotationally inelastic scattering with chemical accuracy (i.e., within 1 kcal mol(-1) approximately 4.2 kJ mol(-1)). These processes are not affected much by surface motion, either because they were measured using a low surface temperature, T(s), or because the computed observable is independent of T(s). However, we show that to account for the dependence of molecular orientation on a reaction the inclusion of surface motion is required. We have also found that vibrational excitation is poorly described within the BOSS approximation, suggesting a breakdown of this approximation.
Phys. Chem. Chem. …, Jan 1, 2010
We present a detailed experimental and theoretical study of elastic and rotationally inelastic di... more We present a detailed experimental and theoretical study of elastic and rotationally inelastic diffraction of D 2 from NiAl(110) in the energy range 85-150 meV. The experiments were performed using a high-resolution, fixed angle geometry apparatus. Quantum and classical dynamical calculations were performed by using a six-dimensional potential energy surface constructed upon interpolation of a set of DFT (density functional theory) data. We show that, although elastic diffraction peak intensities are accurately described by theory in the whole range of incidence energies and angles explored, significant discrepancies are obtained for RID peaks, especially for those involving rotational initial states with j i > 0. Possible reasons for this discrepancy are discussed.
Phys. Chem. Chem. …, Jan 1, 2009
Phys. Chem. Chem. Phys., Jan 1, 2010
We have studied the interaction of H(2) on Cu(111) using quasi-classical and quantum dynamics, an... more We have studied the interaction of H(2) on Cu(111) using quasi-classical and quantum dynamics, and a chemically accurate six-dimensional potential energy surface (PES). The PES was computed using the specific reaction parameter (SRP) approach to density functional theory (DFT), in an implementation adapted to molecules interacting with metal surfaces. To perform this study we have applied the Born-Oppenheimer static surface (BOSS) approximation, i.e., we used both the Born-Oppenheimer (BO) and the static surface (SS) approximations. We show that our theoretical approach accurately describes experiments on dissociative adsorption, the effect of molecular vibrational and rotational motion on dissociative (associative) adsorption (desorption), and rotational excitation upon scattering. More specifically, dynamics calculations on reactive scattering of H(2) reproduce reaction probabilities measured in molecular beam experiments, effective barrier heights describing the dependence of reaction on the initial rovibrational state, and data on rotationally inelastic scattering with chemical accuracy (i.e., within 1 kcal mol(-1) approximately 4.2 kJ mol(-1)). These processes are not affected much by surface motion, either because they were measured using a low surface temperature, T(s), or because the computed observable is independent of T(s). However, we show that to account for the dependence of molecular orientation on a reaction the inclusion of surface motion is required. We have also found that vibrational excitation is poorly described within the BOSS approximation, suggesting a breakdown of this approximation.
The Journal of Chemical …, Jan 1, 2011
Based on a slab model of H 2 dissociation on a c(2 × 2) structure with Ti atoms in the first and ... more Based on a slab model of H 2 dissociation on a c(2 × 2) structure with Ti atoms in the first and third layers of Al(100), a six-dimensional (6D) potential energy surface (PES) has been built. In this PES, a molecular adsorption well with a depth of 0.45 eV is present in front of a barrier of height 0.13 eV. Using this PES, H 2 dissociation probabilities are calculated by the classical trajectory (CT), the quasiclassical trajectory (QCT), and the time-dependent wave-packet (TDWP) method. The QCT study shows that trajectories can be trapped by the molecular adsorption well. Higher incident energy can lead to direct H 2 dissociation. Vibrational pre-excitation is the most efficient way to promote direct dissociation without trapping. We find that both rotational and vibrational excitation have efficacies close to 1.0 in the entire range of incident energies investigated, which supports the randomization in the initial conditions making the reaction rate solely dependent on the total (internal and translational) energy. The H 2 dissociation probabilities from quantum dynamics are in reasonable agreement with the QCT results in the energy range 50-200 meV, except for some fluctuations. However, the TDWP results considerably exceed the QCT results in the energy range 200-850 meV. The CT reaction probabilities are too low compared with the quantum dynamical results.
The Journal of Physical …, Jan 1, 2010
We have constructed first principle based six-dimensional (6D) potential energy surfaces (PESs) d... more We have constructed first principle based six-dimensional (6D) potential energy surfaces (PESs) describing the interaction of H 2 with Cu(111) obtained by interpolation of a set of density functional theory (DFT) total energy data. The DFT calculations have been performed within the generalized gradient approximation (GGA) framework. In applying the GGA we have tested the two exchange-correlation (XC) functionals most popular in surface science, i.e., the PW91 and RPBE functionals. The interpolation of the PW91 PES has been performed using two different methods, the corrugation reducing procedure (CRP), which has been proven to be one of the most successful interpolation methods to build 6D PESs, and the modified Shepard (MS) interpolation method, a very promising method to build high dimensional (nD) PESs, which is computationally cheaper than the CRP. We show that, in spite of the difference between the CRP-PES and the MS-PES and the inaccuracies found in the latter, quantum and classical reaction and scattering probabilities obtained for both PESs are very similar. We also show that PW91 predicts higher reactivity than RPBE, due to the presence of lower energy dissociation barriers in the PW91-PES. The differences between the PW91-PES and the RPBE-PES are also reflected in the vibrational excitation and rotational excitation probabilities, and the diffraction patterns.
The Journal of Chemical Physics, 2000
A collaborative experimental and theoretical study of rotationally inelastic collisions of fine-s... more A collaborative experimental and theoretical study of rotationally inelastic collisions of fine-structure Λ-doublet levels with argon is presented. Experimental state-to-state rate constants were determined with an opticaloptical double resonance technique. The CN radical was prepared by ...
The Journal of Chemical Physics, 2006
We have performed H 2 ͑D 2 ͒ diffraction experiments on a Pd͑110͒ surface using two different hig... more We have performed H 2 ͑D 2 ͒ diffraction experiments on a Pd͑110͒ surface using two different high-sensitivity set-ups. We have found that, although the total reflectivity of Pd͑110͒ is comparable to that observed in other reactive systems, the corresponding H 2 ͑D 2 ͒ diffraction patterns are quite different: no diffraction peak, including the specular one, is observed on Pd͑110͒. This unexpected result is the consequence of dynamic trapping. Such interpretation is supported by classical dynamics calculations based on accurate ab initio potential energy surfaces.
The Journal of Chemical Physics, 2005
We present a discretization method that allows one to interpret measurements on diffraction of di... more We present a discretization method that allows one to interpret measurements on diffraction of diatomic molecules from solid surfaces using six-dimensional (6D) classical trajectory calculations. It has been applied to the D2/NiAl(110) and H2/Pd(111) systems (which are models for activated and nonactivated dissociative chemisorption, respectively) using realistic potential energy surfaces obtained from first principles. Comparisons with experimental results and 6D
Chemical Physics Letters, 2004
We have measured the angular distribution of H 2 molecules with incident energies 100-150 meV ref... more We have measured the angular distribution of H 2 molecules with incident energies 100-150 meV reflected by the Pd(1 1 1) surface at 430 K. In spite of the low diffraction reflectivity ($0.5%), diffraction peaks have been resolved at nearly grazing incidence. Apart from specular reflection, out-of-plane diffraction has been found to be dominant, in agreement with classical simulations. We show that this behavior is a generic one for grazing incidence and discuss the relevance of this finding for the study of molecule/surface dynamics in systems for which dissociation is a non activated process.
Physical Review Letters, 2004
We have measured in-plane and out-of-plane diffraction of H2 and D2 molecular beams scattered by ... more We have measured in-plane and out-of-plane diffraction of H2 and D2 molecular beams scattered by reactive Pd(111) and nonreactive NiAl(110) surfaces at 140-150 meV. A comparison with six-dimensional quantum dynamics and classical trajectory calculations shows for the first time that accurate diffraction patterns can be obtained from state-of-the-art potential energy surfaces based on density functional theory. Our measurements show that, at general incidence conditions, out-of-plane diffraction is much more important than was assumed in previous experiments.
The interpretation of scanning tunneling spectroscopy (STS) and scanning tunneling microscopy mea... more The interpretation of scanning tunneling spectroscopy (STS) and scanning tunneling microscopy measurements of epitaxial graphene on lattice-mismatched substrates is a challenging problem, because of the spatial modulation in the electronic structure imposed by the formation of a moiré pattern. Here we describe the electronic structure of graphene adsorbed on Ru(0001) by means of density functional theory calculations that include van der Waals interactions and are performed on a large 11 × 11 unit cell to account for the observed moiré patterns. Our results show the existence of localized electronic states in the high and low areas of the moiré at energies close to and well above the Fermi level, respectively. Localization is due to the spatial modulation of the graphene-Ru(0001) interaction and is at the origin of the various peaks observed in STS spectra.
Phys. Chem. Chem. …, Jan 1, 2012
The dissociation of H(2) on Ti-covered Al surfaces is relevant to the rehydrogenation and dehydro... more The dissociation of H(2) on Ti-covered Al surfaces is relevant to the rehydrogenation and dehydrogenation of the NaAlH(4) hydrogen storage material. The energetically most stable structure for a 1/2 monolayer of Ti deposited on the Al(100) surface has the Ti atoms in the second layer with a c(2 × 2) structure, as has been confirmed by both low-energy electron diffraction and low-energy ion scattering experiments and density functional theory studies. In this work, we investigate the dynamics of H(2) dissociation on a slab model of this Ti/Al(100) surface. Two six-dimensional potential energy surfaces (PESs) have been built for this H(2) + Ti/Al(100) system, based on the density functional theory PW91 and RPBE exchange-correlation functionals. In the PW91 (RPBE) PES, the lowest H(2) dissociation barrier is found to be 0.65 (0.84) eV, with the minimum energy path occurring for H(2) dissociating above the bridge to top sites. Using both PESs, H(2) dissociation probabilities are calculated using the classical trajectory (CT), the quasi-classical trajectory (QCT), and the time-dependent wave-packet methods. We find that the QCT H(2) dissociation probabilities are in good agreement with the quantum dynamics results in the collision energy range studied up to 1.0 eV. We have also performed molecular beam simulations and present predictions for molecular beam experiments. Our molecular beam simulations show that H(2) dissociation on the 1/2 ML Ti/Al(100) surface is an activated process, and the reaction probability is found to be 6.9% for the PW91 functional and 1.8% for the RPBE at a nozzle temperature of 1700 K. Finally, we have also calculated H(2) dissociation rate constants by applying transition state theory and the QCT method, which could be relevant to modeling Ti-catalyzed rehydrogenation and dehydrogenation of NaAlH(4).
… Theory, Computation, and Modeling …, Jan 1, 2011
We present a systematic density functional theory (DFT) study of the isolated manganese-phthalocy... more We present a systematic density functional theory (DFT) study of the isolated manganese-phthalocyanine, MnPc, by using both localized gaussian-type orbital (GTO) and plane-wave (PW) basis sets and the following exchange-correlation functionals: B3LYP, PBE, PBE0, HSE, and HSE06. We find a very good agreement between GTO and PW results, which is a necessary condition in order to extend the present methodology to MnPc molecules deposited on metal surfaces. We conclude that the HSE06 functional is the most suitable one for the study of MnPc/inorganic interfaces with a basis of plane waves. We compare our calculated electron energy spectra with two available experiments [Kraus et al. in Chem Phys Lett 469:121, 2009; Grobosch et al. in Organics Electron 11:1483, 2010; Papageorgiou et al. in Prog Surf Sci 77:139, 2004] in which the ultraviolet photoemission spectra (UPS) have been measured. Our results suggest that spectra obtained from MnPc molecules in the gas phase are closer to those obtained from thin films of MnPc deposited on inert surfaces than to those obtained from thick films. Finally, we report optical absorption spectra by using a time-dependent DFT approach. Our results are again compatible with measurements performed on thin MnPc films.
Physical review letters, Jan 1, 2011
Elaborate density functional theory (DFT) calculations that include the effect of van der Waals (... more Elaborate density functional theory (DFT) calculations that include the effect of van der Waals (vdW) interactions have been carried out for graphene epitaxially grown on Ru(0001). The calculations predict a reduction of structural corrugation in the observed moiré pattern of about 25% ($ 0:4 # A) with respect to DFT calculations without vdW corrections. The simulated STM topographies are close to the experimental ones in a wide range of bias voltage around the Fermi level.
Phys. Chem. Chem. Phys., Jan 1, 2011
We have studied the effect of lattice displacement on the interaction of H(2) with the Cu(111) su... more We have studied the effect of lattice displacement on the interaction of H(2) with the Cu(111) surface using the Specific Reaction Parameter (SRP) approach to Density Functional Theory (DFT). We have systematically investigated how the motion of the surface atoms affects some features of the Potential Energy Surface (PES), such as the dissociation barrier height and the barrier geometry corresponding to some representative reaction pathways, and the anisotropy of the potential at these geometries. This analysis has allowed us to identify the surface degrees of freedom that are likely to be most relevant for H(2) dissociation. In particular, we have found that the lattice coordinate displacements that have the largest effect on the H(2)/Cu(111) DFT-SRP barrier heights and locations concern the motion of the 1st layer and 2nd layer Cu atoms in the Z direction, and motion of the 1st layer atoms in the directions parallel to the surface. Whereas the first degree of freedom mostly affects the barrier geometry, the second and third motions can lower or raise the barrier height. The latter effect cannot be described with the usual surface oscillator dynamical models employed in the past to include surface motion, and its dynamical influence on the dissociative adsorption needs to be further investigated.
Surface Science, Jan 1, 2010
We have studied the scattering of vibrationally excited H2 molecules from metal surfaces under fa... more We have studied the scattering of vibrationally excited H2 molecules from metal surfaces under fast grazing incidence conditions, by means of quasi-classical calculations based on six-dimensional potential energy surfaces. We show that, in spite of the fast parallel motion, the reorientation of the molecule along the trajectory plays a fundamental role on the scattering, being responsible for the nonmonotonic behavior observed as a function of the normal incidence energy, similar to that observed under slow normal incidence conditions. The present study has allowed us to further prove that the interaction between a H2 molecule and an ordered metal surface under fast grazing incidence conditions is, in general, governed by the normal momentum of the molecule.
Physical Review B, Jan 1, 2010
... 12); the lack of diffraction peaks in H2/Pd(110) due to dynamic trapping;13 the ... stimulate... more ... 12); the lack of diffraction peaks in H2/Pd(110) due to dynamic trapping;13 the ... stimulated Raman pumping.19–22 However, only very recently, the advent of experimental setups based ... The latter experiments have provided direct evidence of the central role played by vibrational ...
Physical Review A, Jan 1, 2010
Phys. Chem. Chem. Phys., Jan 1, 2010
We have studied the interaction of H(2) on Cu(111) using quasi-classical and quantum dynamics, an... more We have studied the interaction of H(2) on Cu(111) using quasi-classical and quantum dynamics, and a chemically accurate six-dimensional potential energy surface (PES). The PES was computed using the specific reaction parameter (SRP) approach to density functional theory (DFT), in an implementation adapted to molecules interacting with metal surfaces. To perform this study we have applied the Born-Oppenheimer static surface (BOSS) approximation, i.e., we used both the Born-Oppenheimer (BO) and the static surface (SS) approximations. We show that our theoretical approach accurately describes experiments on dissociative adsorption, the effect of molecular vibrational and rotational motion on dissociative (associative) adsorption (desorption), and rotational excitation upon scattering. More specifically, dynamics calculations on reactive scattering of H(2) reproduce reaction probabilities measured in molecular beam experiments, effective barrier heights describing the dependence of reaction on the initial rovibrational state, and data on rotationally inelastic scattering with chemical accuracy (i.e., within 1 kcal mol(-1) approximately 4.2 kJ mol(-1)). These processes are not affected much by surface motion, either because they were measured using a low surface temperature, T(s), or because the computed observable is independent of T(s). However, we show that to account for the dependence of molecular orientation on a reaction the inclusion of surface motion is required. We have also found that vibrational excitation is poorly described within the BOSS approximation, suggesting a breakdown of this approximation.
Phys. Chem. Chem. …, Jan 1, 2010
We present a detailed experimental and theoretical study of elastic and rotationally inelastic di... more We present a detailed experimental and theoretical study of elastic and rotationally inelastic diffraction of D 2 from NiAl(110) in the energy range 85-150 meV. The experiments were performed using a high-resolution, fixed angle geometry apparatus. Quantum and classical dynamical calculations were performed by using a six-dimensional potential energy surface constructed upon interpolation of a set of DFT (density functional theory) data. We show that, although elastic diffraction peak intensities are accurately described by theory in the whole range of incidence energies and angles explored, significant discrepancies are obtained for RID peaks, especially for those involving rotational initial states with j i > 0. Possible reasons for this discrepancy are discussed.
Phys. Chem. Chem. …, Jan 1, 2009
Phys. Chem. Chem. Phys., Jan 1, 2010
We have studied the interaction of H(2) on Cu(111) using quasi-classical and quantum dynamics, an... more We have studied the interaction of H(2) on Cu(111) using quasi-classical and quantum dynamics, and a chemically accurate six-dimensional potential energy surface (PES). The PES was computed using the specific reaction parameter (SRP) approach to density functional theory (DFT), in an implementation adapted to molecules interacting with metal surfaces. To perform this study we have applied the Born-Oppenheimer static surface (BOSS) approximation, i.e., we used both the Born-Oppenheimer (BO) and the static surface (SS) approximations. We show that our theoretical approach accurately describes experiments on dissociative adsorption, the effect of molecular vibrational and rotational motion on dissociative (associative) adsorption (desorption), and rotational excitation upon scattering. More specifically, dynamics calculations on reactive scattering of H(2) reproduce reaction probabilities measured in molecular beam experiments, effective barrier heights describing the dependence of reaction on the initial rovibrational state, and data on rotationally inelastic scattering with chemical accuracy (i.e., within 1 kcal mol(-1) approximately 4.2 kJ mol(-1)). These processes are not affected much by surface motion, either because they were measured using a low surface temperature, T(s), or because the computed observable is independent of T(s). However, we show that to account for the dependence of molecular orientation on a reaction the inclusion of surface motion is required. We have also found that vibrational excitation is poorly described within the BOSS approximation, suggesting a breakdown of this approximation.
The Journal of Chemical …, Jan 1, 2011
Based on a slab model of H 2 dissociation on a c(2 × 2) structure with Ti atoms in the first and ... more Based on a slab model of H 2 dissociation on a c(2 × 2) structure with Ti atoms in the first and third layers of Al(100), a six-dimensional (6D) potential energy surface (PES) has been built. In this PES, a molecular adsorption well with a depth of 0.45 eV is present in front of a barrier of height 0.13 eV. Using this PES, H 2 dissociation probabilities are calculated by the classical trajectory (CT), the quasiclassical trajectory (QCT), and the time-dependent wave-packet (TDWP) method. The QCT study shows that trajectories can be trapped by the molecular adsorption well. Higher incident energy can lead to direct H 2 dissociation. Vibrational pre-excitation is the most efficient way to promote direct dissociation without trapping. We find that both rotational and vibrational excitation have efficacies close to 1.0 in the entire range of incident energies investigated, which supports the randomization in the initial conditions making the reaction rate solely dependent on the total (internal and translational) energy. The H 2 dissociation probabilities from quantum dynamics are in reasonable agreement with the QCT results in the energy range 50-200 meV, except for some fluctuations. However, the TDWP results considerably exceed the QCT results in the energy range 200-850 meV. The CT reaction probabilities are too low compared with the quantum dynamical results.
The Journal of Physical …, Jan 1, 2010
We have constructed first principle based six-dimensional (6D) potential energy surfaces (PESs) d... more We have constructed first principle based six-dimensional (6D) potential energy surfaces (PESs) describing the interaction of H 2 with Cu(111) obtained by interpolation of a set of density functional theory (DFT) total energy data. The DFT calculations have been performed within the generalized gradient approximation (GGA) framework. In applying the GGA we have tested the two exchange-correlation (XC) functionals most popular in surface science, i.e., the PW91 and RPBE functionals. The interpolation of the PW91 PES has been performed using two different methods, the corrugation reducing procedure (CRP), which has been proven to be one of the most successful interpolation methods to build 6D PESs, and the modified Shepard (MS) interpolation method, a very promising method to build high dimensional (nD) PESs, which is computationally cheaper than the CRP. We show that, in spite of the difference between the CRP-PES and the MS-PES and the inaccuracies found in the latter, quantum and classical reaction and scattering probabilities obtained for both PESs are very similar. We also show that PW91 predicts higher reactivity than RPBE, due to the presence of lower energy dissociation barriers in the PW91-PES. The differences between the PW91-PES and the RPBE-PES are also reflected in the vibrational excitation and rotational excitation probabilities, and the diffraction patterns.