Showing papers by "Fritz Haber Institute of the Max Planck Society published in 1996"
TL;DR: IMAGIC's novel angular reconstitution approach allows for the rapid determination of three-dimensional structures of uncrystallized molecules to high resolution.
1,281 citations
TL;DR: In this article, a review discusses how CO 2 surface chemistry has developed since the early 1950s, focusing on studies of well-characterized surfaces of metals, oxides and some more complex systems involving in particular alkali modified surfaces and also of coadsorbed molecules.
745 citations
TL;DR: In this paper, the authors studied the dissociation of nitric oxide on a ruthenium(0001) surface by scanning tunneling microscopy and found that the distribution of nitrogen atoms after the decomposition allowed the identification of the active sites for this reaction.
Abstract: The dissociation of nitric oxide on a ruthenium(0001) surface was studied by scanning tunneling microscopy. The distribution of nitrogen atoms after the dissociation allowed the identification of the “active sites” for this reaction, which are formed by the low-coordinated, top metal atoms of atomic steps. It is proposed that their activity is caused by local changes in the electronic structure. The structure of the steps determines whether they remain active or become deactivated by oxygen atoms. The results demonstrate the complex manner in which the structure of a catalytic surface determines the reactivity ofthe catalyst and confirm the active sites concept.
552 citations
TL;DR: In this paper, the authors used variable temperature scanning tunneling microscopy at 150-106 K to study the dissociation of two oxygen atoms in pairs, with average distances of two lattice constants.
Abstract: The dissociation of ${\mathrm{O}}_{2}$ on a Pt(111) surface was studied by variable temperature scanning tunneling microscopy at 150--106 K. The two oxygen atoms created by the dissociation appear in pairs, with average distances of two lattice constants. Since thermal random walk sets in only at around 200 K, with a diffusion barrier of 0.43 eV and a preexponential factor of ${10}^{\ensuremath{-}6.3}{\mathrm{cm}}^{2}{\mathrm{s}}^{\ensuremath{-}1}$, the distribution of distances at around 160 K evidences nonthermal processes during the dissociation. It is concluded that transient ballistic motion exists, where the short range traveled is in agreement with recent molecular dynamics studies.
260 citations
TL;DR: In this article, the authors used X-ray photoelectron spectroscopy, ultraviolet photo-electron (UPS), and ion scattering spectroscopic (ISS) measurements to study the Ag(111) single-crystal surface after exposure to ion scattering at high temperature and at atmospheric pressure.
Abstract: X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and ion scattering spectroscopy (ISS) have been used to study the Ag(111) single-crystal surface after exposure to ${\mathrm{O}}_{2}$ at high temperature and at atmospheric pressure. The activated formation of a strongly bound surface layer has been observed, as identified by an asymmetry of the Ag 3${\mathit{d}}_{5/2}$ core-level peak at 367.3 eV and an O 1s peak at 529.0 eV (${\mathrm{O}}_{\ensuremath{\gamma}}$). In addition, oxygen was found to be dissolved in the bulk (${\mathrm{O}}_{\mathrm{\ensuremath{\beta}}}$), exhibiting an O 1s binding energy between 531 and 530 eV depending on its abundance. X-ray-excited oxygen KVV Auger electron spectroscopy revealed the presence of ${\mathrm{O}}_{\ensuremath{\gamma}}$ by additional peaks at 514.8 and 494.7 eV. UPS displayed oxygen-derived bands located above the emission from the Ag 4d band at 3.2 and 2.5 eV. Oxygen-related peaks below the Ag 4d band were identified as resulting from OH groups formed by reaction of surface oxygen (${\mathrm{O}}_{\mathrm{\ensuremath{\alpha}}}$) with residual hydrogen. The incorporated oxygen caused a pronounced charge separation as reflected by a 1 eV increase in the work function. ISS measurements revealed that ${\mathrm{O}}_{\ensuremath{\gamma}}$ is incorporated in the topmost surface layer, shielding underlying Ag atoms from the ${\mathrm{He}}^{+}$ beam. All spectroscopic data point to the presence of one monolayer of silver-embedded oxygen, which is in dynamic equilibrium with surface atomic oxygen segregated from the bulk at high temperature. The oxygen embedded in the topmost silver layer is strongly bound to the metal, with its interaction being different from adsorbed atomic oxygen and bulk ${\mathrm{Ag}}_{2}$O. It is stable up to 900 K, in contrast to the binary silver oxides, and relevant for high-temperature oxidation reactions catalyzed by Ag. A qualitative analysis is presented of the chemical bonding of the different surface species in comparison to the situation of a complex silver oxide reference. \textcopyright{} 1996 The American Physical Society.
247 citations
TL;DR: In this paper, modified perylene chromophores were adsorbed with virtually constant reaction distance on the surface of a spongelike TiO2 electrode and the dominant fast time constant was 190 fs.
Abstract: Modified perylene chromophores were adsorbed with virtually constant reaction distance on the surface of a spongelike TiO2 electrode. Interfacial electron transfer was probed with femtosecond resolution in ultrahigh vacuum via transient absorption and fluorescence up-conversion measurements. Identical time constants were measured for the decay of the reactant and rise of the product states. The dominant fast time constant was 190 fs. It remained constant between 300 and 22 K.
228 citations
TL;DR: Spectral analysis reveals the intermediate formation of electronically excited atoms and dimers as the source of the chemiluminescence in agglomeration of copper or silver atoms in a matrix of noble gas atoms to form small clusters.
Abstract: The agglomeration of copper or silver atoms in a matrix of noble gas atoms to form small clusters may be accompanied by the emission of visible light. Spectral analysis reveals the intermediate formation of electronically excited atoms and dimers as the source of the chemiluminescence. A mechanism is proposed, according to which the gain in binding energy upon cluster formation may even lead to the ejection of excited fragments as a result of unstable intermediate configurations. A similar concept was introduced in the field of nuclear reactions by Niels Bohr 60 years ago.
193 citations
TL;DR: The determination of the three-dimensional structure of the skeletal muscle Ca2+-release channel in an open state is presented using electron cryomicroscopy and angular reconstitution to establish a central opening in the transmembrane region of the channel tetramer.
Abstract: Here we present the determination of the three-dimensional structure of the skeletal muscle Ca2+-release channel in an open state using electron cryomicroscopy and angular reconstitution. In contrast to our reconstruction of the channel in its closed state, the density map of the channel driven towards its open state, by the presence of Ca2+ and ryanodine, features a central opening in the transmembrane region-the likely passageway for Ca2+ ions from the sarcoplasmic reticulum to the cytosol. The opening of the channel is associated with a 4 degree rotation of its transmembrane region with respect to its cytoplasmic region, and with significant mass translocations within the entire cytoplasmic region of the channel tetramer.
181 citations
TL;DR: A density-matrix calculation reveals the importance of dephasing in the excitation process and the slower relaxation rate induced by the Xe layer is attributed to a reduced overlap of the image-state wave function with bulk states.
Abstract: Lifetimes of electrons in the $n=1$ and $n=2$ image states on Cu(111) are studied with femtosecond time-resolved photoemission Adsorption of one monolayer of Xe results in a pronounced increase of the image-state lifetime, which for the $n=1$ state changes from 18\ifmmode\pm\else\textpm\fi{}5 fs at clean Cu(111) to 75\ifmmode\pm\else\textpm\fi{}15 fs at the Xe-covered surface The slower relaxation rate induced by the Xe layer is attributed to a reduced overlap of the image-state wave function with bulk states A density-matrix calculation reveals the importance of dephasing in the excitation process
152 citations
TL;DR: The calculated photon energies of the cross section minima based on the boundary conditions of the standing wave agree fairly well with experimental data.
Abstract: Recent photoelectron spectroscopy results from gas phase ${\mathrm{C}}_{60}$ exhibit the same partial cross section variation with photon energy as has been observed in its solid phase. We assume that the variations originate from a fullerene specific ability to form a spherical standing wave of the final state electron by intramolecular interference or virtual reflection at the center of the photoionized molecule. The calculated photon energies of the cross section minima based on the boundary conditions of the standing wave agree fairly well with experimental data.
143 citations
TL;DR: In this article, the dynamic behavior of N atoms adsorbed on a Ru(0001) surface was studied by scanning tunneling microscopy, and the diffusion constant was determined also at equilibrium, from statistical jumps of individual N atoms in a uniform overlayer, and was found to be identical to the Fickian value.
Abstract: The dynamic behavior of N atoms adsorbed on a Ru(0001) surface was studied by scanning tunneling microscopy. N atoms formed by dissociation of NO molecules show an initial sharp concentration profile at atomic steps. Its decay was followed as a function of time, providing a quasicontinuum diffusion constant; the activation energy is 0.94 eV and the prefactor is $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0ex}{0ex}}{\mathrm{cm}}^{2}{\mathrm{s}}^{\ensuremath{-}1}$. The diffusion constant was determined also at equilibrium, from statistical jumps of individual N atoms in a uniform overlayer, and is found to be identical to the Fickian value.
TL;DR: In this paper, the authors extended the linearized augmented plane wave code WIEN by the evaluation of forces, and demonstrated the high accuracy of the force calculation, and use them for an efficient geometry optimization of poly-atomic systems.
TL;DR: In this article, the angle-resolved N 1s photoelectron spectrum was measured with high resolution in the threshold region and the vibrational energy of the core ionized molecule was analyzed.
Abstract: The angle-resolved N 1s photoelectron spectrum of has been measured with high resolution in the threshold region An analysis of the vibrational fine structure yields a vibrational energy of and a lifetime broadening of for the core-ionized molecule As in the case of C 1s ionization of CO, the vibrational fine structure changes considerably with photon energy in the region of both the shape resonance and the double excitations Both the vibrationally resolved partial photoionization cross sections and asymmetry parameters have been determined in this photon energy range The calculated cross sections in the literature are in reasonable agreement with experiment In addition, we have measured the cross sections and asymmetry parameters of the most intense direct and conjugate shake-up satellites The behaviour of the satellites is found to differ significantly from that of the corresponding C 1s satellites of CO
TL;DR: In this article, the potential energy surface of dissociative adsorption was investigated using density-functional theory and the full-potential linear augmented plane-wave method, and the topology of the PES is related to the dependence of the covalent H(s)-Pd(d) interactions on the orientation of the molecule.
Abstract: The potential-energy surface (PES) of dissociative adsorption of ${\mathrm{H}}_{2}$ on Pd(100) is investigated using density-functional theory and the full-potential linear augmented plane-wave method. Several dissociation pathways are identified which have a vanishing energy barrier. A pronounced dependence of the potential energy on ``cartwheel'' rotations of the molecular axis is found. The calculated PES shows no indication of the presence of a precursor state in front of the surface. Both results indicate that steering effects determine the observed decrease of the sticking coefficient at low energies of the ${\mathrm{H}}_{2}$ molecules. We show that the topology of the PES is related to the dependence of the covalent H(s)-Pd(d) interactions on the orientation of the ${\mathrm{H}}_{2}$ molecule. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this article, a mesoscopic description of surface chemical reactions, aimed to provide a link between microscopic lattice models and reaction−diffusion equations, is formulated, which is needed when large populations of nanoscale structures are considered or patterns characterized by a combination of macroscopic and microscopic lengths are investigated.
Abstract: A mesoscopic description of surface chemical reactions, aimed to provide a link between microscopic lattice models and reaction−diffusion equations, is formulated. Such a description is needed when large populations of nanoscale structures are considered or patterns characterized by a combination of macroscopic and microscopic lengths are investigated. By using the example of an adsorbate with attractive lateral interactions between molecules, the mesoscopic evolution equation for fluctuating coverages is derived from the microscopic master equation of the respective kinetic lattice model. This stochastic equation is applied to study phenomena of pattern formation related to adsorbate phase transitions.
TL;DR: In this paper, the effect of coke formed by conversion of ethylbenzene as well as ethene on the sorption capacity and diffusivity of benzene and ethyl benzene in H-ZSM-5 was investigated using the in-situ Fourier transform infrared (FTIR) technique.
Abstract: The effect of coke formed by conversion of ethylbenzene as well as ethene on the sorption capacity and diffusivity of benzene and ethylbenzene in H-ZSM-5 was investigated using the in-situ Fourier-transform infrared (FTIR) technique. Conversion of ethene at T = 475 K and T = 575 K, respectively, results in the formation of different coke species as evidenced by clearly distinguishable IR spectra as well as different H C ratios as determined ex-situ by analysis of the oxidation products of the coked zeolite. Both coke modifications, however, result in a similar and almost linear decrease of diffusivity and sorption capacity as a function of the amount of coke deposited. Only for higher loadings with low-temperature coke the decrease of the diffusivity of benzene becomes slightly more pronounced. In the case of coke formation via ethylbenzene conversion the diffusivity of ethylbenzene starts to decrease only after deposition of higher amounts of coke, while the sorption capacity is reduced almost linearily with the coke coverage.
TL;DR: In this article, diffusion-induced turbulence in distributed dynamical systems near a supercritical Hopf bifurcation can be controlled by means of global delayed feedback, which is shown to suppress phase and amplitude turbulence inside a window of delay times under increasing the intensity of the control signal.
TL;DR: In this article, a consistent microkinetic model for ammonia synthesis based on a LHHW mechanism was proposed, which describes the results of steady-state and transient experiments performed with a Cs-promoted ruthenium catalyst supported on MgO in agreement with kinetic data obtained under ultrahigh vacuum conditions.
TL;DR: In this paper, a femtosecond time-resolved two-photon photoemission (2PPE) was used to investigate the hot electron dynamics of Cu(111, Ag(110), and Ta(poly) in 2PPE.
TL;DR: In this paper, a mathematical model of this process is developed using parameters derived from previous independent independent experiments and numerical simulations fitting new data to experimental findings, and the model is applied to the case of photo emission electron microscopy.
TL;DR: D density functional theory calculations of the interaction potentials of He and Ne with Rh(110) are presented, finding that, and explaining why, the nature of the interactions of the two probe particles is qualitatively different, which implies that the topographies of their scattering potentials are indeed anticorrugated.
Abstract: Recent measurements of the scattering of He and Ne atoms at Rh(110) suggest that these two rare-gas atoms measure a qualitatively different surface corrugation: While Ne atom scattering seemingly reflects the electron-density undulation of the substrate surface, the scattering potential of He atoms appears to be anticorrugated. An understanding of this perplexing result is lacking. We present density functional theory calculations of the interaction potentials of He and Ne with Rh(110). We find and explain why the nature of the interaction of the two probe particles is qualitatively different, which implies that the topographies of their scattering potentials are indeed anticorrugated.
TL;DR: These findings rationalize the absence of island formation and of a well-ordered 2\ifmmode\times\else\texttimes\fi{}2 phase for the N/Ru(0001) system: at temperatures 300 K the attractive interaction on the third-neighbor site is too weak, while at lower temperatures the diffusion barrier represents a kinetic obstacle.
Abstract: Atomic nitrogen on Ru(0001) was prepared by dissociative chemisorption of ${\mathrm{N}}_{2}$ and studied by scanning tunneling microscopy (STM) at 300 K. Nitrogen occupies the hcp threefold hollow site and is imaged as a depression with a diameter of about 5 \AA{}. Interactions between the adsorbed nitrogen atoms were obtained by statistical analysis of STM images, by extraction of the two-dimensional pair distribution function from the arrangement of the N atoms. Since the nearest-neighbor separations could be identified with atomic precision, the pair distribution function $g$ and hence the potential of mean force ${V}_{\mathrm{eff}}$ were obtained as a function of the discrete neighbor sites $j$ up to the tenth nearest neighbor. A comparison with Monte Carlo calculations for balls with a hard-sphere potential provides information about the pair potential ${V}_{\mathrm{pair}}(j)$: The nearest-neighbor site is strongly repulsive, the second-neighbor site is weakly repulsive, and the third-neighbor site is weakly attractive. These findings rationalize the absence of island formation and of a well-ordered 2\ifmmode\times\else\texttimes\fi{}2 phase for the N/Ru(0001) system: At temperatures \ensuremath{\ge}300 K the attractive interaction on the third-neighbor site is too weak, while at lower temperatures the diffusion barrier of 0.9 eV represents a kinetic obstacle. The fact that the range of the interaction is identical to the diameter of the N-atom features in the STM topographs is taken as evidence that the interaction is caused by substrate-mediated electronic forces.
TL;DR: It is shown that the poisoning effect of S originates from the formation of energy barriers hindering the dissociation of H2.
Abstract: The modification of the potential-energy surface (PES) of ${\mathrm{H}}_{2}$ dissociation over Pd(100) as induced by the presence of a (2 \ifmmode\times\else\texttimes\fi{} 2) S adlayer is investigated by density-functional theory and the linear augmented plane wave method It is shown that the poisoning effect of S originates from the formation of energy barriers hindering the dissociation of ${\mathrm{H}}_{2}$ The barriers are in the entrance channel of the PES and their magnitude strongly depends on the lateral distance of the ${\mathrm{H}}_{2}$ molecule from the S adatoms
TL;DR: In this article, sufficient and necessary conditions for the occurrence of Hopf bifurcation in chemical reaction mechanisms are presented using the formalism of stoichiometric networks, which are applied to determine the mechanistic basis of chemical oscillations in isothermal surface reactions.
Abstract: Sufficient and necessary conditions for the occurrence of a Hopf bifurcation in chemical reaction mechanisms are presented using the formalism of stoichiometric networks. The conditions are applied to determine the mechanistic basis of chemical oscillations in isothermal surface reactions. Realistic examples are given for the different oscillatory mechanisms.
TL;DR: In this article, photoelectron diffraction in the scanned energy mode has been used to determine the structure of benzene adsorbed on to an Ni{111} surface, and the results are compared with photoemission measurements and quantum chemical calculations.
TL;DR: The present study demonstrates the successful application of the LAPW pseudopotential approach to the calculation of ground-state properties of magnetic 3 d transition metals.
Abstract: The ground-state properties of Fe, Co, and Ni are studied with the linear-augmented-plane-wave (LAPW) method and norm-conserving pseudopotentials. The calculated lattice constant, bulk modulus, and magnetic moment with both the local-spin-density approximation (LSDA) and the generalized gradient approximation (GGA) are in good agreement with those of all-electron calculations, respectively. The GGA results show a substantial improvement over the LSDA results, i.e., better agreement with experiment. The accurate treatment of the nonlinear core-valence exchange and correlation interaction is found to be essential for the determination of the magnetic properties of 3d transition metals. The present study demonstrates the successful application of the LAPW pseudopotential approach to the calculation of ground-state properties of magnetic 3d transition metals. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this article, the adsorption and temperature-dependent decomposition of SO+O+S on Cu(100) and Cu(111) were studied by fast and high-resolution core-level photoemission.
Abstract: The adsorption and temperature-dependent decomposition of ${\mathrm{SO}}_{2}$ on Cu(100) and Cu(111) have been studied by fast and high-resolution core-level photoemission. The analysis of the S 2p and O 1s data shows that molecular ${\mathrm{SO}}_{2}$ adsorption dominates at 170 K. On heating the ${\mathrm{SO}}_{2}$-covered surfaces to about room temperature, ${\mathrm{SO}}_{2}$ decomposes into SO+O+S. On further heating SO+O recombine to form ${\mathrm{SO}}_{2}$, which is the only species detected in corresponding temperature-programmed desorption (TPD) experiments. From the temperature- (time-) dependent S and O coverages a ``TPD curve'' can be constructed. \textcopyright{} 1996 The American Physical Society.
TL;DR: Circular dichroism in the double photoionization of He by circularly polarized light has been observed in an angle resolved coincidence experiment at 93.5 eV photon energy.
Abstract: Circular dichroism in the double photoionization of He by circularly polarized light has been observed in an angle resolved coincidence experiment at 93.5 eV photon energy. The use of a transmission multilayer, which acts as a quarter-wave plate for the linearly polarized incident light, together with time-of-flight spectrometers, which enable simultaneous detection of all electron pairs, has made the measurements possible. The results show strong dependence of the dichroism on the relative emission angles and the energy sharing between the ejected electrons in good agreement with our numerical calculations.
TL;DR: When the temperature of a substance in thermal equilibrium is lowered, it often becomes more ordered as mentioned in this paper, and when externally excited, such systems can exhibit new structures that are not in equilibrium.
Abstract: When the temperature of a substance in thermal equilibrium is lowered, it often becomes more ordered. When externally excited, such systems can exhibit new structures that are not in equilibrium. Mikhailov and Ertl describe in their Perspective such structures that have recently been observed in films of ordered molecules (called Langmuir-Blodgett films) by a group at the Electrotechnical Laboratory in Tsukuba, Japan. The results show important connections with similar behavior in reacting chemical systems.
TL;DR: Investigation about the bioavailability of Pt from these particles a model substance with approx.
Abstract: Automobile catalytic converters emit nanocrystalline platinum attached to alumina particles. For investigations about the bioavailability of Pt from these particles a model substance with approx. 5% Pt on alumina has been prepared and characterized by physical methods (ESCA, XRD, TEM, DTA, TG). Measuring the platinum solubility of these samples in different solvents revealed high amounts that can be explained assuming a corrosion process. The portion of soluble platinum is dependent on the particle size distribution. For a comparative study platinum black has been used. In general the platinum determination has been carried out by electrothermal atomic absorption spectrometry (ET-AAS). The comparison of ET-AAS results with determinations by adsorptive voltammetry (formazone method) allowed to distinguish between elemental and ionic platinum; in solution samples only ionic platinum has been present. UV spectra of extracts have been used for the semi-quantitative platinum speciation in solutions.