Showing papers by "Fritz Haber Institute of the Max Planck Society published in 2001"
TL;DR: In this article, the Gibbs free energy was calculated to determine the lowest energy structure of a transition metal oxide surface in thermodynamic equilibrium with an oxygen-rich environment, and it was shown that the commonly assumed stoichiometric termination is only favorable at low oxygen chemical potentials, i.e., low pressures and/or high temperatures.
Abstract: Using density-functional theory we calculate the Gibbs free energy to determine the lowest-energy structure of a ${\mathrm{RuO}}_{2}(110)$ surface in thermodynamic equilibrium with an oxygen-rich environment. The traditionally assumed stoichiometric termination is only found to be favorable at low oxygen chemical potentials, i.e., low pressures and/or high temperatures. At a realistic O pressure, the surface is predicted to contain additional terminal O atoms. Although this O excess defines a so-called polar surface, we show that the prevalent ionic model, that dismisses such terminations on electrostatic grounds, is of little validity for ${\mathrm{RuO}}_{2}(110).$ Together with analogous results obtained previously at the (0001) surface of corundum-structured oxides, these findings on (110) rutile indicate that the stability of nonstoichiometric terminations is a more general phenomenon of transition metal oxide surfaces.
1,612 citations
TL;DR: The authors showed that CO preference for low-coordination binding sites on Pt(111) and vicinals to it is not consistent with a host of low-temperature experimental studies.
Abstract: Notwithstanding half a dozen theoretical publications, well-converged density- functional calculations, whether based on a local-density or generalized-gradient exchange-correlation potential, whether all-electron or employing pseudopotentials, underestimate CO's preference for low-coordination binding sites on Pt(111) and vicinals to it. For example, they imply that CO should prefer hollow- to atop-site adsorption on Pt(111), in apparent contradiction to a host of low-temperature experimental studies.
627 citations
TL;DR: Control of spatiotemporal chaos is one of the central problems of nonlinear dynamics and suppression of chemical turbulence by global delayed feedback using catalytic carbon monoxide oxidation on a platinum single-crystal surface andcarbon monoxide partial pressure as the controlled feedback variable is reported on.
Abstract: Control of spatiotemporal chaos is one of the central problems of nonlinear dynamics. We report on suppression of chemical turbulence by global delayed feedback using, as an example, catalytic carbon monoxide oxidation on a platinum (110) single-crystal surface and carbon monoxide partial pressure as the controlled feedback variable. When feedback intensity was increased, spiral-wave turbulence was transformed into new intermittent chaotic regimes with cascades of reproducing and annihilating local structures on the background of uniform oscillations. The global feedback further led to the development of cluster patterns and standing waves and to the stabilization of uniform oscillations. These findings are reproduced by theoretical simulations.
335 citations
TL;DR: The high yields of styrene achieved suggest that a first industrial application of carbon nanofilaments in catalysis is possible, and this work is likely to be a first of its kind.
Abstract: Special carbon! Carbon nanofilaments differ from graphite and soot catalysts in their high stability during the oxidative dehydrogenation of ethylbenzene to styrene. The high yields of styrene achieved suggest that a first industrial application of carbon nanofilaments in catalysis is possible.
242 citations
TL;DR: Simulations on the basis of a reaction-diffusion model reproduce the experimental findings qualitatively well and reveals the limitations of this traditional approach to modeling spatiotemporal pattern formation in nonlinear dynamics.
Abstract: Scanning tunneling microscopy data revealed the atomic processes in propagating reaction fronts that occur in the catalytic oxidation of hydrogen on Pt(111). The fronts were also characterized on mesoscopic length scales with respect to their velocity and width. Simulations on the basis of a reaction-diffusion model reproduce the experimental findings qualitatively well. The quantitative comparison reveals the limitations of this traditional approach to modeling spatiotemporal pattern formation in nonlinear dynamics.
167 citations
TL;DR: In this paper, a third interaction between SDS and F127, which involves promotion of F127 micelles at concentrations up to 3 °C below the critical micellar temperature of pure F127 was identified and investigated.
Abstract: It has been established that sodium dodecyl sulfate (SDS) binds to the micelles and monomers of the block copolymer F127. SDS binds to the monomeric unassociated F127 in the form of polymer/bound SDS micellar complexes. SDS binds to F127 micelles first forming mixed micelles, which dissociate into smaller mixed aggregates and then to single F127 unassociated monomers. A third interaction of SDS, which involves promotion of F127 micelles at concentrations up to 3 °C below the critical micellar temperature of pure F127, was identified and is investigated in the present work. The formation of such SDS-induced mixed micelles was monitored using differential scanning calorimetry, light scattering, isothermal titration calorimetry, and a SDS selective electrode for electromotive force measurements. These investigations have shown how the different binding and aggregation processes between SDS and F127 involving induced micellization, growth of mixed micelles, breakdown of mixed micelles, and binding of SDS to m...
143 citations
TL;DR: In this article, the size effect for ethene adsorption is attributed to a redistribution between weakly bound π- and more strongly bound di-σ-ethene, with the di −σ -ethene molecule preferentially adsorbed on the larger particles.
125 citations
TL;DR: In this paper, the adsorption of CO on Pt(111) was studied by picosecond infrared−visible sum frequency generation (SFG) vibrational spectroscopy in a pressure range from 10-7 to 500 mbar and in a temperature running in a constant range.
Abstract: The adsorption of CO on Pt(111) was studied by picosecond infrared−visible sum frequency generation (SFG) vibrational spectroscopy in a pressure range from 10-7 to 500 mbar and in a temperature ran...
124 citations
TL;DR: In this article, stationary, nonequilibrium potential and adsorbate patterns with an intrinsic wavelength were observed in an electrochemical system with a specific type of current/electrodepotential (I-phi(DL)) characteristic.
Abstract: We report stationary, nonequilibrium potential and adsorbate patterns with an intrinsic wavelength that were observed in an electrochemical system with a specific type of current/electrode-potential (I-phi(DL)) characteristic. The patterns emerge owing to the interplay of a self-enhancing step in the reaction dynamics and a long-range inhibition by migration currents rather than by diffusion. Theoretical analysis revealed that this self-structuring of the electrode occurs in all electrochemical systems with an S-shaped I-phi(DL) characteristic in wide and well-accessible parameter ranges. This unusual pattern-forming instability in electrochemical systems has all the characteristics of the mechanism proposed by Turing in 1952 in the framework of an early theory of morphogenesis. Our finding might account for structure formation in certain biological systems that have gradients in the electric potential and may open new paths for fabricating patterned electrodes.
119 citations
TL;DR: Raman characterization revealed that the Keggin anion structure of H 4 PVMo 11 O 40 is inherently unstable upon heat treatment and loss of water as mentioned in this paper, and the absence of water during heat treatments stabilizes the intermediate defective structures.
Abstract: Raman characterization revealed that the Keggin anion structure of H 4 PVMo 11 O 40 is inherently unstable upon heat treatment and loss of water. Vanadyl and molybdenyl species are expelled from the Keggin cage and defective Keggin structures are formed. These defective structures further disintegrate to presumably Mo 3 O 13 triads of the former Keggin. These Keggin fragments oligomerize at later stages to molybdenum oxygen clusters comparable to hepta- or octamolybdates. The final disintegration and structural reorganization product is MoO 3 . This disintegration and recondensation process seems to be strongly affected by the heating rate and hence the presence of water in the sample. Only partial expulsion of V occurred under moderate dehydration conditions. The absence of water during heat treatments stabilizes the intermediate defective structures. Raman spectroscopy proved that free polyacids are unstable under catalytic partial oxidation conditions. Therefore, it can be suggested that intact Keggin anions are not the active species within an operating partial oxidation catalyst. From this Raman spectroscopy study it may be inferred that the structurally reorganized intermediates are relevant for the catalytic action. The Raman investigations of the HPA decomposition additionally revealed a dependency of the decomposition process on the reactive atmosphere and the presence of Cs. The presence of Cs led to a partial stabilization of the structural disintegration products of PVMo 11 and to the formation of the thermodynamically stable, but catalytically inactive Cs 3 -salt. Cs also inhibited the condensation of MoO 3 -type oxides. O 2 present in the gas phase also led to stabilization of the structural reorganization intermediates. Importantly, the presence of water did not lead to a stabilization of the intact Keggin structure. In contrast, hydrolysis of the Keggin anions seemed to be enhanced compared to the water-free situation. This observation is of high importance because water is added to the feed in industrial partial oxidation reactions. Hence, under industrial conditions, HPA-derived catalysts are inherently unstable and cannot contain intact Keggin anions at their active surface. Catalytic partial oxidation conditions even led to a more pronounced structural reorganization and amorphous suboxides of the MoO 3− x type seemed to be formed. Hence, heteropolyacids have to be understood only as defined molecular precursor compound.
117 citations
TL;DR: This work presents the first ab initio prediction of localized electronic excited states in a periodically infinite condensed phase, a heretofore intractable goal and lays the foundation of a microscopic understanding of photochemistry and spectroscopy on metal surfaces.
Abstract: We present the first ab initio prediction of localized electronic excited states in a periodically infinite condensed phase, a heretofore intractable goal. In particular, we examined local excitations within a CO molecule adsorbed on Pd(111). The calculation allows a configuration interaction treatment of a local region, while its interaction with the extended condensed phase is described via an embedding potential obtained from periodic density functional theory. Our work lays the foundation of a microscopic understanding of photochemistry and spectroscopy on metal surfaces.
TL;DR: Femtosecond time-resolved photoemission of photoexcited electrons in highly oriented pyrolytic graphite (HOPG) provides strong evidence for anisotropies of quasiparticle (QP) lifetimes and a pronounced anomaly in the energy dependence of QP lifetimes between 1.1 and 1.5 eV.
Abstract: Femtosecond time-resolved photoemission of photoexcited electrons in highly oriented pyrolytic graphite (HOPG) provides strong evidence for anisotropies of quasiparticle (QP) lifetimes. Indicative of such anisotropies is a pronounced anomaly in the energy dependence of QP lifetimes between 1.1 and 1.5 eV---the vicinity of a saddle point in the graphite band structure. This is supported by recent ab initio calculations and a comparison with experiments on defect-enriched HOPG which reveal that disorder, e.g., defects or phonons, increases electron energy relaxation rates.
TL;DR: The interaction between the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) and the Pluronic triblock copolymer F127 was investigated in this article.
Abstract: The interaction between the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) and the Pluronic triblock copolymer F127 was investigated. F127 is a nonionic surfactant with structural formula EO97PO69EO97, where EO represents the ethylene oxide block and PO represents the propylene oxide block. A combination of experiments involving a TTAB selective electrode (electromotive force), isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), and light scattering have shown that TTAB binds to both monomeric and micellar F127. TTAB forms a polymer/micellar TTAB complex with monomeric F127. In addition, TTAB binds to F127 micelles leading to the transformation of the aggregated F127 into mixed micelles followed by a breakdown of these aggregates into smaller mixed F127/TTAB aggregates as more TTAB is added. This process continues until all the aggregated F127 is dissociated. DSC measurements have also shown that small amounts of TTAB (typically 10-4 mol dm-3) can decrease the ...
TL;DR: It is shown that such parameters as solvent polarity, current density, charge flow, distance between electrodes and temperature can be used to control the size of the Pd nanoparticles in the range 1.2-5 nm.
Abstract: A detailed study concerning the size-selective electrochemical preparation of R4N+Br- -stabilized palladium colloids is presented. Such colloids are readily accessible using a simple electrolysis cell in which the sacrificial anode is a commercially available Pd sheet, the surfactant serving as the electrolyte and stabilizer. It is shown that such parameters as solvent polarity, current density, charge flow, distance between electrodes and temperature can be used to control the size of the Pd nanoparticles in the range 1.2-5 nm. Characterization of the Pd colloids has been performed using transmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and X-ray powder diffractometry (XRD) evaluated by Debye-function-analysis (DFA). Possible mechanisms of particle growth are discussed. Experiments directed towards the size-selective electrochemical fabrication of (n-C6H13)4N+Br- -stabilized nickel colloids are likewise described. Finally, a new strategy for preparing bimetallic colloids (e.g., Pt/Pd nanoparticles) electrochemically is presented, based on the use of a preformed colloid (e.g., (n-C8H17)4N+Br- -stabilized Pt particles) and a sacrificial anode (e.g., Pd sheet).
TL;DR: This study provides the detailed analysis of the assembly and structural organisation of such an interface within a phage having a long tail and proposes that it is the interaction of gp6 with other viral morphogenetic proteins that drives its assembly into the 12-mer state.
TL;DR: In this paper, the authors investigated the thermal activation of a nanocrystalline Mo5O14-type Mo0.64V0.25W0.09Ox catalyst in inert atmospheres and found that it leads to enhanced catalytic performance in the partial oxidation of methanol, propylene and acrolein.
Abstract: Thermal activation of a nanocrystalline Mo5O14-type Mo0.64V0.25W0.09Ox catalyst leads to enhanced catalytic performance in the partial oxidation of methanol, propylene and acrolein. This thermal activation process was invest igated by X-ray diffraction, transmission electron microscopy and Raman microspectroscopy. Ther mal activation of the nanocrystalline Mo0.64V0.25W0.09Ox precursor oxide in inert atmospheres induces partial crystallization of a Mo5O14-type oxide only in a narrow temperature range ending at 818 K. The Raman spectrum of the crystalline Mo5O14 oxide was identified by statistical analysis and by comparison with XRD and TEM results. The observed Raman bands in the M=O stretching mode regime were attributed to the different Mo=O bond distances in Mo 5O15. A fraction of the precursor oxide remains nanocrystalline after activation as shown by Raman spectroscopy. HRTEM identified amorphous surface layers on top crystalline cores. Above 818 K, the Mo5O14-type structure disproportionates into the stable phases MoO 2 and MoO3. This disproportionation occurs via an intermediate state which is formed by bundles of molybdenum oxide chains exhibiting structural order in only one dimension as shown by HRTEM. These results from the combined structural analysis suggest that the improvement of the catalytic performance of the MoVW oxide catalyst in the partial oxidation of methanol is related to the formation of the Mo5O14 type mixed oxide.
TL;DR: In this article, infrared-visible sum frequency generation (SFG) surface vibrational spectroscopy was applied to monitor CO stretching vibrations on Ni(100) and Pt(111) in the range from submonolayer coverages up to 200 mbar.
Abstract: Infrared–visible sum frequency generation (SFG) surface vibrational spectroscopy was applied to monitor CO stretching vibrations on Ni(100) and Pt(111) in the range from submonolayer coverages up to 200 mbar. Since SFG can operate in a pressure range from ultrahigh vacuum (UHV) to ambient conditions, it is particularly suited for in situ studies of adsorbates at elevated pressure or during a catalytic reaction. At high coverages, a compressed overlayer was formed on Ni(100) at 100 K that can be modeled by a coincidence structure. On Pt(111), terminally bonded (on-top) CO was the only species observed at 230 K, independent of gas pressure. At low pressure the SFG spectra were complemented by LEED, AES and TPD. The experiments were carried out in an SFG-compatible elevated pressure reactor that is attached to a UHV surface analysis chamber. After preparation and characterization in UHV, model catalysts can be transferred in vacuo into the reaction cell. The reactor is separated from the UHV chamber by an arrangement of differentially pumped spring-loaded teflon seals and can be pressurized to 1 bar without degrading the vacuum in the UHV analysis system.
TL;DR: Vibrational sum frequency generation (SFG) spectroscopy has been developed to a stage of surface sensitivity that is comparable to the classical surface science methods and has been successfully employed to study a variety of adsorbate-substrate interfaces and due to its surface-specificity it allows the study of ads absorbates from submonolayer coverages up to atmospheric gas pressure as mentioned in this paper.
Abstract: Vibrational sum frequency generation (SFG) spectroscopy has been developed to a stage of surface sensitivity that is comparable to the classical surface science methods. SFG has been successfully employed to study a variety of adsorbate–substrate interfaces and due to its surface-specificity it allows the study of adsorbates from submonolayer coverages up to atmospheric gas pressure. A number of case studies is presented including adsorption, co-adsorption and reactions on single crystal surfaces and supported nanoparticles. Studies of CO adsorption on Pt(111) and Pd(111) from 10−7 to 1000 mbar have shown that the high pressure adsorbate structures were comparable with saturation structures obtained at low temperature in ultrahigh vacuum. No evidence for pressure-induced surface rearrangements was found. However, pronounced differences in the CO adsorbate structure on supported Pd nanoparticles and on Pd(111) were detected. It
is further shown how polarization dependent SFG can be employed to determine molecular orientations of CO and NO and how SFG is carried out during ethylene hydrogenation. Broadband techniques allow the performance of time-resolved pump–probe SFG experiments and to take “snapshots” of the transient vibrational spectrum.
TL;DR: The dispersion of quantum-well resonances in ultrathin epitaxial Al films on Si(111) reveals energy- and wave vector-dependent reflection properties at the Al/Si interface, and the assumption of loss of parallel wave vector information upon reflection or transmission through a lattice-mismatched interface is challenged.
Abstract: The dispersion of quantum-well resonances in ultrathin epitaxial Al films on Si(111) reveals energy- and wave vector-dependent reflection properties at the Al/Si interface. The substrate electronic structure strongly influences the phase shift of the electron waves upon reflection at the interface. Thus the details of the substrate electronic structure need to be taken into account for a complete analysis of metallic quantum-well resonances. Furthermore, the assumption of loss of parallel wave vector information upon reflection or transmission through a lattice-mismatched interface is challenged. The changes induced in the electronic structure of the overlayer can be used to probe the ground-state substrate band edges.
TL;DR: In this paper, the adsorption and desorption processes of a rutile TiO molecule on a surface were investigated by means of synchrotron radiation photoemission spectroscopy.
Abstract: By means of synchrotron radiation photoemission spectroscopy, we have investigated the adsorption and desorption processes of the ${\mathrm{SO}}_{2}$ molecule on a rutile ${\mathrm{TiO}}_{2}(110)\ensuremath{-}(1\ifmmode\times\else\texttimes\fi{}1)$ surface. We have recorded the $\mathrm{S}2p$ core-level photoemission peaks for different ${\mathrm{SO}}_{2}$ exposures at a substrate temperature of 120 K in order to get information about the divers species formed on the surface. We have also recorded real-time photoemission spectra to study the adsorption from the early stages to large exposures and to follow the chemical transformations occurring with the adsorbed species as the temperature increases. We have seen that the first arriving molecules react with the oxygen atoms of the surface forming ${\mathrm{SO}}_{x}$ species, both at low and room temperature. Doses higher than the saturation dose (6 L) lead to the dissociation of the molecule generating adsorbed S. ${\mathrm{SO}}_{2}$ multilayer has been found for exposures higher than around 250 L. We have found a progressive reduction of the ${\mathrm{SO}}_{x}$ species with the temperature and the formation of sulphide as the most stable phase. We have not found any signature of molecular ordered species at the interface.
TL;DR: In this article, infrared spectroscopy of carbon monoxide as a probe molecule was used to characterize the structure and charge of ultrasmall metal aggregates and single metal atoms.
Abstract: Supported metal particles may exhibit properties fundamentally different from the corresponding bulk materials.To gain insight into principles underlying size- and structure-dependent phenomena, a structural characterizationof small aggregates at the atomic level is crucial, while far from straightforward. A long-standing questionin the study of supported clusters and metal-oxide interfaces concerns the extent of metal-oxide charge transfer.We show that infrared spectroscopy, utilizing carbon monoxide as a probe molecule, may provide valuableinformation on both structure and charge of ultrasmall metal aggregates and single metal atoms. To createsupported particles containing only few atoms or even a single atom, submonolayer amounts of the transitionmetals palladium, rhodium, and iridium were vapor-deposited onto a thin, well-ordered alumina film at lowsubstrate temperatures. Scanning tunneling microscopy served to characterize nucleation behavior and averageparticle size. Sharp, discrete features in the infrared spectra of adsorbed CO are due to uniform metal (M)carbonyls, most notably the mono- and dicarbonyl species MCO and M(CO)
TL;DR: In this article, experimental structure determinations for molecular adsorbates on NiO(100) reveal much shorter Ni-C and Ni-N bond lengths for adsorbed CO and NH3 as well as NO (2.07, 1.88, 2.07 A) than previously computed theoretical values.
Abstract: New experimental structure determinations for molecular adsorbates on NiO(100) reveal much shorter Ni-C and Ni-N bond lengths for adsorbed CO and NH3 as well as NO (2.07, 1.88, 2.07 A) than previously computed theoretical values, with discrepancies up to 0.79 A, highlighting a major weakness of current theoretical descriptions of oxide-molecule bonding. Comparisons with experimentally determined bond lengths of the same species adsorbed atop Ni on metallic Ni(111) show values on the oxide surface that are consistently larger (0.1-0.3 A) than on the metal, indicating somewhat weaker bonding.
TL;DR: In this article, a comparative study of the phonon features of an ultra-thin, well-ordered aluminum oxide film on NiAl(1/1/0) by infrared reflection-absorption spectroscopy (IRAS) and high-resolution electron-energy-loss (HREELS) was performed.
TL;DR: In this paper, a poly(ethylene oxide) derivative of polyethyleneimine behaves like a strong polyelectrolyte at pH = 2.5 and a neutral polymer at pH 10.
Abstract: A poly(ethylene oxide) derivative of polyethyleneimine behaves like a strong polyelectrolyte at pH = 2.5 and a neutral polymer at pH 10. Both the charged and uncharged versions of this polymer bind strongly to the surfactant sodium dodecyl sulfate (SDS) with no phase separation taking place. Binding isotherms were measured using a dodecyl sulfate electrode, and these data were complemented with isothermal titration calorimetry (ITC) measurements. Small-angle neutron scattering measurements were also carried out at some specific concentrations in the binding region at pHs 2.5, 5.5, and 10. With the exception of one measurement, bound micelles were detected and their aggregation numbers could be evaluated. For the SDS/polymer system at pH 10, the polymer/surfactant complex contains 6−8 bound SDS micelles per polymer molecule at the binding limit. In a solution of 6.5 mM SDS/0.5% w/v polymer at pH 10, bound SDS exists in a nonaggregated form. A detailed examination of the ITC data for the SDS/0.5% w/v polyme...
TL;DR: In this paper, the structure and stability of group-III nitride surfaces were analyzed based on density-functional theory and it was shown that surfaces are always metal-rich and nitrogen atoms on and in the surface layer are thermodynamically unstable.
Abstract: Recent results based on density-functional theory calculations concerning the structure and stability of group-III nitride surfaces are discussed. An analysis of the thermodynamically stable surface structures for this materials system reveals that the driving mechanisms behind surface reconstructions are fundamentally different to those in ‘traditional” (i.e. arsenic or phosphorus based) III–V semiconductors. Specifically, surfaces are always metal-rich and nitrogen atoms on and in the surface layer are thermodynamically unstable. This feature will be shown to have important consequences on surface morphology, adatom kinetics, growth, reactivity, and alloy formation.
TL;DR: In this paper, a SiO 2 film on a Mo(1/1/2) single crystal is reported, which results in a thin and crystalline SiO2 overlayer with a commensurate relationship to the substrate.
Abstract: A preparation is reported which, for the first time, results in a thin, crystalline SiO 2 film on a Mo(1 1 2) single crystal. The procedure consists of repeated cycles of Si deposition and subsequent oxidation, followed by a final annealing procedure. LEED pictures of high contrast show a crystalline SiO 2 overlayer with a commensurate relationship to the Mo(1 1 2) substrate. Surface imperfections have been studied by SPA-LEED and a structure model, consistent with the appearance of antiphase domain boundaries as preferential disorder, is proposed. AES and XPS have been used to control film stoichiometry. A spatial dependence of the Si 4+ core level shift with distance from the interface plane is observed and well explained by image charge interaction across the interface. Furthermore, the theoretically predicted insensitivity of the Si 4+ core level shift with respect to the degree of crystallinity is experimentally verified for the first time. The wetting of the substrate by the film has been investigated by XPS and TDS. The results prove that the film covers the substrate completely.
TL;DR: In this paper, the adsorption of CO molecules on the Cr-terminated (0, 0, 0, 1) surface plane of Cr2O3 is studied theoretically by means of quantum chemical cluster calculations and experimentally by thermal desorption spectroscopy and infrared reflection absorption spectra.
TL;DR: Using a scanning tunneling microscope, electron-stimulated photon emission spectra have been measured for individual Ag clusters on differently pretreated TiO 2 (1/1/0) substrates as mentioned in this paper.
01 Jan 2001
TL;DR: In this article, the use of infrared (IR) spectroscopy for characterization of vibration frameworks in zeolites has been explored, where the wave number of the corresponding IR bands depends on the nature of the cations as well as on their siting.
Abstract: Publisher Summary This chapter explores the use of infrared (IR) spectroscopy for characterization of vibration frameworks in zeolites. IR spectroscopy of self-supporting wafers and diffusive reflectance IR Fourier transform (DRIFT) spectroscopy of zeolite powders enable the investigation of cation vibrations in the far IR region. They are also used to employ heat treatment, to achieve complete dehydration and, if desirable, to admit probes. Also, the (thermal) stability of zeolitic materials against, for example, dehydration, dehydroxylation and interaction with sorbates, may be characterized by (in situ) transmission IR or DRIFT. In the far infrared region (200 - 50 cm-1) vibrations of cations against the framework occur. The wave number of the corresponding IR bands depends on the nature of the cations as well as on their siting. Extra-framework species such as aluminium-containing entities, which occur upon dehydroxylation, may be detected and quantitatively determined by IR spectroscopy when suitable probe molecules are employed as adsorbates. Hydroxyl groups attached to zeolite structures may be detected and characterized by IR spectroscopy as such due to their vibration modes or with the help of probe molecules. Investigation of the overtone and combination vibrations of hydroxyls via DRIFT spectroscopy is a valuable means for characterization of zeolite materials since it frequently reveals more detailed features than are obtained from the fundamental stretch region.
TL;DR: Having performed the first three-dimensional ab initio quantum dynamical study of photodesorption from solid surfaces, mechanistic understanding of the rotational alignment observed in the CO/Cr(2)O(3)(0001) system is gained.
Abstract: Having performed the first three-dimensional ab initio quantum dynamical study of photodesorption from solid surfaces, we gained mechanistic understanding of the rotational alignment observed in the CO/Cr{sub 2}O{sub 3} (0001) system. Our study is based on potential energy surfaces obtained by embedded cluster calculations for both the electronic ground and excited state of the adsorbate substrate complex. Stochastic wave packet calculations demonstrate the importance of the angular degrees of freedom for the microscopic picture of the desorption process in addition to the desorption coordinate.