Dynamics Of Dissociative Adsorption Research Articles

Dissociative adsorption dynamics of nitrogen on a Fe(111) surface.

We study the dissociative adsorption dynamics of N2 on clean bcc Fe(111) surfaces. We base our theoretical analysis on a multidimensional potential energy surface built from density functional theory. The dissociative sticking probability is computed by means of quasi-classical trajectory calculations. For normal incidence and impact energies of the order of a few eV, our theoretical results agree well with existing experimental values. For these energies, the dynamics of the dissociated molecules shows that dissociation is a direct process that follows narrow paths in the multidimensional space. For lower energies of the beam, this direct process is not enough to explain the measured values. A better agreement with the experiment is obtained if we increase the surface temperature to promote the transfer to dissociation of molecules previously trapped. Most of the molecules dissociate very close to the Fe(111) third layer atoms and with an orientation parallel to the surface. A comparison between the dissociation of N2 on Fe(111) and Fe(110) highlights the role of the different energy barriers in both surfaces.

Dynamics simulation of N2 scattering onto W(100,110) surfaces: A stringent test for the recently developed flexible periodic London–Eyring–Polanyi–Sato potential energy surface

An efficient method to construct the six dimensional global potential energy surface (PES) for two atoms interacting with a periodic rigid surface, the flexible periodic London-Eyring-Polanyi-Sato model, has been proposed recently. The main advantages of this model, compared to state-of-the-art interpolated ab initio PESs developed in the past, reside in its global nature along with the small number of electronic structure calculations required for its construction. In this work, we investigate to which extent this global representation is able to reproduce the fine details of the scattering dynamics of N(2) onto W(100,110) surfaces reported in previous dynamics simulations based on locally interpolated PESs. The N(2)/W(100) and N(2)/W(110) systems are chosen as benchmarks as they exhibit very unusual and distinct dissociative adsorption dynamics although chemically similar. The reaction pathways as well as the role of dynamic trapping are scrutinized. Besides, elastic/inelastic scattering dynamics including internal state and angular distributions of reflected molecules are also investigated. The results are shown to be in fair agreement with previous theoretical predictions.

Dynamics of dissociative adsorption of hydrogen on a CO-precovered Ru(0001) surface: a comparison of theoretical and experimental results

We have studied hydrogen dissociation on a CO-precovered Ru(0001) surface, by means of six-dimensional (6D) quasi-classical and quantum dynamics. The 6D potential energy surface has been built by applying a modified Shepard interpolation method to a set of density functional theory (DFT) data, for a coverage of 1/3 monolayer CO. We compared our theoretical results to the experimental ones obtained by Ueta et al. [ChemPhysChem, 2008, 9, 2372]. In order to do so, we have simulated the supersonic molecular beam used in the experiments by taking into account the energy distribution and rovibrational states population in the molecular beam. We find that both the energy and rovibrational states distributions of the molecular beam influence the reactivity, with the largest effect being caused by the energy distribution. However, a significant discrepancy between theory and experiment persists. We argue that this discrepancy could be due to the RPBE functional used in the DFT calculations and/or the neglect of CO-motion in the calculations.

Detailed description of the flexible periodic London–Eyring–Polanyi–Sato potential energy function

An extension of the periodic London–Eyring–Polanyi–Sato (PLEPS) function has been recently proposed in order to accurately describe the six-dimensional potential energy surface for two atoms interacting with a periodic rigid surface. However, only the main features were presented so that the present paper aims at precisely describing the necessary details to achieve the fitting procedure of the so-called flexible periodic LEPS function (FPLEPS) to a set of ab initio electronic structure calculations. The topology of the resulting global potential energy surface is compared to that of previously developed models, including a state-of-the-art ab initio potential, for N 2 interacting with W(1 0 0). The dynamics of dissociative adsorption using these different models is analyzed.

The dynamics of dissociative adsorption on metal surfaces: “First principles” theory – Experiment confrontations

This review tries to asses our current state of understanding of the dynamics of dissociative adsorption on single crystal metal surfaces by quantitatively comparing “first principles” theory, i.e. that based on density function theory, with detailed dynamical experimental results. Examples are chosen for H 2 and N 2 dissociation on transition metal surfaces.

Vibrationally-assisted dissociative adsorption of oxygen on Ru(0 0 0 1)-p(2 × 1)-O

Supersonic molecular beam technique combined with high resolution X-ray photoelectron spectroscopy using synchrotron radiation was applied to the study of the dynamics of dissociative adsorption of oxygen on Ru(0 0 0 1) surface in high coverage region. The Ru(0 0 0 1) surface pre-covered with oxygen atoms of 0.5 monolayer, which corresponds to the p(2 × 1)-O structure, was dosed to oxygen molecules with translational energy of 0.5 eV. Oxygen uptake was compared between the cases with and without the beam source heated in order to verify the effects of internal energy of oxygen. We found drastic enhancement in initial sticking probability of oxygen when the beam source was heated to 1400 K. We concluded that the enhancement of sticking probability is mainly caused by molecular vibrational excitation, indicating that dissociation barrier is located in the exit channel on potential energy surface.

Ethane dissociation on Pt{1 1 0}-(1 × 2): New low-energy pathways

Ethane dissociative adsorption dynamics provide a key model for catalysis involving molecules with carbon–carbon bonds, however earlier studies have been limited to translational energies above 50 kJ/mol. Here we use a novel application of supersonic molecular beam scattering to enable accurate data to be obtained over the more relevant energy range 3–80 kJ/mol. Three new low-energy pathways have been identified for ethane adsorption on Pt{1 1 0}-(1 × 2). One involves ethane molecules in the ground state, one is enhanced by excitation of the C–H stretch modes and the third is enhanced by excitation of the incident ethane methyl deformation modes.

Quantum dynamics study on the interaction of H 2 on a Pt(111) surface

By performing quantum dynamics calculations on ab initio potential energy surfaces (PESs), we investigate and discuss the effects of the initial kinetic and vibrational energies and the orientation of the incident hydrogen molecule (H 2) on the dissociative adsorption dynamics of H 2 on a Pt(111) surface. Using the coupled channel method, we calculate the sticking probabilities for H 2 in the kinetic energy range E t = 0.01–1.2 eV and initially in the vibrational ground state and in the first two excited states. Our results indicate that the sticking probability plots for H 2 show very weak or no vibrationally assisted sticking (VAS) effect in the various configurations we considered. This is attributed to the early barrier position along the path of minimum potential with respect to the onset of hydrogen dissociation. Compared to other surfaces we studied, this behavior is similar to the cases of the dissociative adsorption of H 2 on the surfaces of Ti(0001) and La(0001), and to the armchair and zigzag edges of graphite.

Scattering and dissociative adsorption of H2 on the armchair and zigzag edges of graphite

We performed quantum dynamics calculations on the scattering and dissociative adsorption of hydrogen molecules incident on the armchair and zigzag edges of graphite layers, using relevant potential-energy surfaces (PESs) recently obtained by Diño et al. [e-J. Surf. Sci. Nanotech. 2, 77 (2003), and references therein]. By employing the coupled channel method to determine the reflection and sticking probabilities, we compared the hydrogen scattering and dissociative adsorption dynamics on the two graphite surfaces. Our findings show the different scattering behaviors of H2 for the armchair edge and for the zigzag edge, which enable the identification of an unknown graphite edge from its interaction with H2. The scattering on the zigzag edge is due to the highly curved region of the PES reaction path for H2 interacting with the zigzag edge, whereas the scattering for the armchair edge is caused by a potential barrier. The reflection probability initially decreases with increasing the kinetic energy in both cases but gradually increases for the zigzag edge. Our findings also indicate that the zigzag edge can adsorb hydrogen better than the armchair edge, mainly due to the absence (presence) of an activation barrier in the zigzag (armchair) edge. There is a very weak dependence of the sticking probability on the initial vibrational state of H2 for both graphite edges. The difference in the vibrational effect is due to the relative position of the curved region with respect to the potential barrier (well).

Time-Dependent Quantum Dynamics of Dissociation for CH4on an Ni(100) Surface

The semirigid vibrating rotor target (SVRT) modelproposed by Zhang [J. Chem. Phys. 111 (1999) 3929] isapplied to study the dynamics of dissociative adsorption for CH4on a flat and static Ni(100) surface. The molecule CH4 is treatedas a semirigid vibrating rotor CH3-H, and theLondon–Eyring–Polanyi–Sato potential energy surface is utilized. Thenumerical calculation for the reaction system is carried out by usingthe time-dependent wave packet approach, and the propagation of wavepackets is obtained by the split-operator method. The resultsdemonstrate many important properties of the CH4 moleculedissociation process on the metal Ni. The dissociation probability is astrongly increasing function of the incident kinetic energy, and isenhanced significantly when the molecule CH4 is excited, whichdenotes the clear vibration-excitation effect, as observed in themolecular beam studies of Holmblad et al. [J. Chem. Phys.102 (1995) 8255] The isotopic effect is also studied formolecules CH4 and CD4 at the ground rovibrational states.

Classical dynamics of dissociative adsorption for a nonactivated system: The role of zero point energy

We present dissociative adsorption probabilities of H2 on Pd(111) computed with the classical trajectory method. We perform both classical (C) and quasiclassical (QC) calculations, the latter including, by contrast with the former, the initial zero point energy (ZPE) of H2. We analyze in detail the role played by the ZPE and demonstrate the strong and weak points of both C and QC calculations. We show that ZPE is crucial in accelerating the molecules toward the surface through vibrational softening. However, at low energies, dynamic trapping is quenched in QC calculations by processes of vibration to rotation energy transfer that would be associated with closed channels in a quantum approach. In this study we use a new representation of the H2/Pd(111) potential energy surface (obtained by interpolation of ab initio data) with a significantly better accuracy in the entrance channel region which plays a decisive role in the dissociation dynamics.

Six-dimensional quantum and classical dynamics study of H2(ν=0,J=0) scattering from Pd(1 1 1)

We present results of a six-dimensional quantum dynamics study of H2(ν=0,J=0) scattering from Pd(111) using a potential energy surface obtained from density functional theory calculations. Quantum dissociative adsorption probabilities agree with experimental data and provide new evidence on the importance of dynamic trapping (induced by translation to rotation energy exchange) at low energies. We analyse the role of the vibrational zero point energy in classical calculations and the suitability of the so-called classical and quasi-classical approaches to describe dissociative adsorption dynamics for a non-activated system.

Implication of palladium geometric and electronic structures to hydrogen activation on bulk surfaces and clusters

A great body of theoretical results obtained preferentially with density-functional methods in the last decade is analyzed with emphasis on the relationship between the orientation of the surface for semiinfinite mono-metallic bulk palladium and the cluster-size for finite palladium particles. It is demonstrated that the crystallographic orientation of a surface influences the local electronic structure and the geometric configuration of catalytic centers and this way changes their catalytic properties. Weakly bound molecularly adsorbed states and atomic adsorbates in the most reactive low-coordinated positions are especially sensitive to such changes. The unique feature of small palladium clusters, their ground state magnetism affects mainly the dynamics of dissociative adsorption and leads to the stabilization of pre-dissociated forms of adsorbate.

Effects of surface corrugation on the molecular rotational dependence of H 2 dissociative adsorption dynamics on Cu(100)

We investigate and discuss how surface corrugation affects the molecular rotational dependence of H 2 dissociative adsorption dynamics on Cu(100) by performing six-dimensional (6D) quantum dynamics calculations. We calculate the dissociative adsorption probability as a function of the initial rotational state J and the normal energy E norm of incident molecules, and compare with the dissociative adsorption results obtained by four-dimensional (4D) quantum dynamics calculations where the surface is treated as flat. In our calculation, for the case of normal incidence, the increase in dissociative adsorption probability with increasing E norm and the non-monotonic behavior of dissociative adsorption probability with respect to J are suppressed on a corrugated surface as compared to that on a flat surface.

Dissociative adsorption dynamics of H 2 at the atop-Pt, atop-Cu, and CuPt bridge sites of an ordered Cu 3Pt(1 1 1) — orientational effects

We present a comparative theoretical study on how orientation influences H 2 dissociative adsorption dynamics at different sites along the Cu 3Pt(1 1 1) surface lateral direction where Cu and Pt alternate. Our total energy calculation results show non-activated H 2 dissociation at the atop-Pt site, and activated H 2 dissociation at the atop-Cu and CuPt bridge sites. The activation barrier for H 2 dissociation across the CuPt bridge site has a strong dependence on the H 2 orientation with respect to the surface. Strong sensitivity of the dissociation dynamics to the orientation dependence of the reaction suggests that further information on the orientational dependence of the effective activation barrier could be obtained by comparing the orientation of the H 2 before impinging on and after scattering from a surface.

Quantum dynamics of dissociative adsorption of H2 and D2: The time-dependent wave packet method

A time-dependent quantum wave packet method was used to study the dynamics of dissociative adsorption of H2 and D2 on a flat and static surface. The molecule-surface interaction is described using a modified London-Eyring-Polanyi-Sato (LEPS) type potential for the H2/Ni(100) system. The three-dimensional (3-D) dissociation probabilities were calculated for different initial rovibrational states as a function of initial incident energies. Our results show that the dissociation of the diatomic rotational states whose quantum numbers satisfyj+m = odd is forbidden at low energies for the homonuclear Hz and D2 due to the selection rule. The effect of the rotational orientation of diatoms on adsorption predicts that the in-plane rotation (m = j) is more favorable for dissociation than the out-of-plane rotation (m = 0). Enhanced dissociation for vibrationally excited molecules and the significant enhancement of the dissociation probability of H2 when compared to D2 were explained reasonably in terms of quantum mechanical zero-point energies, the tunneling effect and the reflection from an activation barrier.

Rotational Effects in the Dissociative Adsorption Dynamics of Hydrogen on a Pd Surface

We show that the recently observed nonmonotonous dependence of the adsorption probability of H 2 /Pd(111) on the initial rotational state j of the impinging H 2 can be accounted for by considering the two factors- Steering ( Dynamical Reorientation ) and Rotational-Translational Energy Transfer ( Bond-Length Extension ), and the importance of the incidence energy (velocity) of the impinging hydrogen molecule. Furthermore, we show that considerable isotope effects can be observed for the j -dependence of the adsorption probability of hydrogen on Pd.

Reaction dynamics of molecular hydrogen on silicon surfaces

Experimental and theoretical results on the dynamics of dissociative adsorption and recombinative desorption of hydrogen on silicon are presented. Using optical second-harmonic generation, extremely small sticking probabilities in the range ${10}^{\mathrm{\ensuremath{-}}9}$-${10}^{\mathrm{\ensuremath{-}}5}$ could be measured for ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ on Si(111)7\ifmmode\times\else\texttimes\fi{}7 and Si(100)2\ifmmode\times\else\texttimes\fi{}1. Strong phonon-assisted sticking was observed for gases at 300 K and surface temperatures between 550 K and 1050 K. The absolute values as well as the temperature variation of the adsorption and desorption rates show surprisingly little isotope effect, and they differ only little between the two surfaces. These results indicate that tunneling, molecular vibrations, and the structural details of the surface play only a minor role for the adsorption dynamics. Instead, they appear to be governed by the localized H--Si bonding and Si--Si lattice vibrations. Theoretically, an effective five-dimensional model is presented taking lattice distortion, corrugation, and molecular vibrations into account within the framework of coupled-channel calculations. While the temperature dependence of the sticking is dominated by lattice distortion, the main effect of corrugation is a reduction of the preexponential factor by about one order of magnitude per lateral degree of freedom. Molecular vibrations have practically no effect on the adsorption/desorption dynamics itself, but lead to vibrational heating in desorption with a strong isotope effect. Ab initio calculations for the ${\mathrm{H}}_{2}$ interaction with the dimers of Si(100)2\ifmmode\times\else\texttimes\fi{}1 show properties of the potential surface in qualitative agreement with the model, but its dynamics differs quantitatively from the experimental results. \textcopyright{} 1996 The American Physical Society.

Combined effect of molecular rotational and surface vibrational excitations on the dissociative adsorption dynamics of [formula omitted

To study the surface temperature dependence of the dynamics of dissociative adsorption processes (e.g. D 2 Cu(111) ), we invoked the Born-Oppenheimer approximation and did quantum mechanical calculations using the coupled-channel method. Based on physical arguments and our numerical results, we show that in order to explain experimental observations, it is necessary to consider the coupling between the rotational degree of freedom of the impinging molecule and the vibrational degree of freedom of the surface.

Dissociative adsorption dynamics of formaldehyde on a platinum electrode surface; one-dimensional domino?

When a potentiostatically controlled polycrystalline platinum electrode is dipped into a sulfuric acid aqueous solution containing formaldehyde, the surface is covered by CO, which is formed as a result of the dissociative adsorption of formaldehyde. The kinetics of this dissociative adsorption process is investigated by the combination of the electrochemical and the laser desorption methods. The surface CO coverage is linearly increased as a function of time. This zeroth order kinetics is explained by the domino mechanism.