bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adsorption of Water Vapor on the MgO(100) Single Crystal Surface
Authors: Heidberg Joachim , Redlich Britta , Wetter Dirk 
Published: March 2014

AbstractThe adsorption of H2O on the MgO(100) surface prepared by cleaving a single crystal in situ under ultrahigh vacuum has been studied. For the first time Low Energy Electron Diffraction (LEED) has revealed an ordering of the H2O monolayer with a c(4×2) translational symmetry at 150 K, highly sensitive Polarization Fourier Transform Infrared Spectroscopy (PIR) has shown a strong, very broad polarized absorption from ∼3050–3500 cm−1 in the spectral range of the symmetric and antisymmetric H2O stretching vibration v1 and v3. The peak absorption is less than 0.1%, the integrated absorption 0.07 cm−1 and 0.11 cm−1 for p‐ and s‐polarization, respectively, indicating that the molecular plane is nearly parallel to the surface. This broad polarized band is assigned to the ordered, nearly planar H2O monolayer with all OH groups participating in strong O–H ⃛O bonds between nearest neighbor H2O molecules. In the ordered monolayer no dangling OH groups have been found. Additionally a sharp, p‐polarized absorption at 3680 cm−1 has been observed, attributed to dangling OH bonds of the adsorbate on steps. At temperatures above 190 K three sharp, polarized absorptions at 3672, 3626 and 3513 cm−1 with integrated absorptions in the range from 4·10−4 to 5·10−3cm−1 and their disappearance above 240 K have been detected. They are ascribed to isolated H2O molecules on steps (3672 cm−1) and terraces, respectively. For D2O on MgO(100) all corresponding absorptions have been measured.
Dynamics of the Cyclohexadienyl Radical Adsorbed in Porous Silica and NaZSM‐5
Authors: Roduner Emil , Schwager Martina , Tregenna‐Piggott Philip , Dilger Herbert , Shelley Mee , Reid Ivan D. 
Published: March 2014

AbstractAvoided level crossing muon spin resonance spectra are reported for the muon substituted cyclohexadienyl radical which is formed on irradiation of benzene adsorbed on porous silica and in NaZSM‐5. The shapes of the resonances are discussed in terms of the reorientation dynamics of the adsorbed radical and of freezing of the pore‐confined benzene.
Quantum Theory of Photodesorption of Neutrals from Metals: Ab Initio Calculations and Active Control
Authors: Saalfrank Peter , Klamroth Tillmann 
Published: March 2014

AbstractIn continuation of previous work, two aspects of the ultraviolet laser‐induced desorption of NO from Pt (111) and ammonia from Cu(111) are investigated using different, quantum mechanical tools. First, for NO/Pt(111) it is shown with the help of simple, ab initio electronic structure cluster calculations, that previously introduced phenomenological two‐ and multiple‐state models are consistent with the more refined quantum chemical picture. Within this picture, the finite lifetime of a resonance state (“quenching”) is microscopically a consequence of the non‐adiabatic coupling of the resonance state to the metal electronic excitations. Further, both for NO/Pt(111) and ammonia/Cu(111) the possibility to actively control the desorption yields is investigated. For this purpose, time‐dependent wave packet propagations based on the nuclear Schrödinger equation are used. The proposed control mechanisms are (i) thermal and (ii) optical preparation of vibrational states of the adsorbate/substrate complex. The latter strategy, which is also supported by IR transition probabilities, is found to be much more efficient.
Rotational Alignment of D2 Desorbing from Pd(100)
Authors: Wetzig D. , Dopheide R. , David R. , Zacharias H. 
Published: March 2014

AbstractThe rotational alignment of D2 molecules desorbing from a Pd(100) single crystal surface is measured by laser‐induced fluorescence via the \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm B}^{\rm 1} \Sigma _{\rm u}^ + \leftarrow {\rm X}^{\rm 1} \Sigma _{\rm g}^ + $\end{document} Lyman bands around λ = 106 nm and 110 nm. Different rotational states in the vibrational ground state υ″ = 0 are probed. For low rotational states, J″ = 2, an isotropic distribution of the J vector is found. For higher rotational states J″ ≥ 3 a preference of the desorbing molecules for helicoptering over cartwheeling motion is observed, in agreement with recent theoretical predictions.
Atomic‐Scale Imaging of Catalytic Surface Reactions
Authors: Block J.H. , Drachsel W. , Ernst N. , Sieben B. , Gorodetskii V. 
Published: March 2014

AbstractRecent experimental work is reviewed showing that a field ion microscope (FIM) can also serve as an in situ catalytic flow reactor. A platinum field emitter (model catalyst, grain diameter > 200 Å) exposes different small single‐crystal planes with well‐defined crystallographic orientations. The molecules reacting on the catalyst surface are also used as the FIM imaging gas. Due to preferential O2 field ionization on O(ad) layers, different surface sites (O(ad) and CO(ad)) can be discriminated in situ and in real time during the ongoing catalytic CO oxidation. The H2 oxidation on a Pt field emitter is distinguished by a preferential imaging of catalytically active sites with the product molecule H2O (desorbed mainly as H3O+). Isothermal, non‐linear dynamic processes of CO‐ and H2 oxidation reactions on Pt are investigated, involving the formation of face‐specific adsorption islands, mobility of reaction/diffusion fronts and the creation of chemical waves. The electric fields in the FIM (≈ 1.5 V/Å) appear to have a minor influence.
The Growth of Cobalt on a Rhenium (0001)‐Surface at 300 K
Authors: Parschau M. , Christmann K. 
Published: March 2014

AbstractWe report on combined LEED and scanning tunneling microscopy (STM) results of the initial growth of thin cobalt films on a Re(0001) surface at 300 K, whereby the coverage range 0 < ΘCo < 2 monolayers was investigated. At ΘCo ≈ 0.1 homogeneous nucleation of Co on the flat terraces of the Re(0001) surface and heterogeneous nucleation at defect (step) sites can be distinguished: Individual Co nuclei grow to dendritic islands with “arms” extending preferentially in the \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{\bar 12\bar 10} \right],\left[{2\bar 1\bar 10} \right] $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm \bar 1\bar 120}} \right] $\end{document} directions. At medium and high coverages kinetic limitations in the diffusivity of the impinging Co atoms provide additional growth in the second layer, while the first Co layer still remains incomplete: coalescence of individual first‐layer islands only occurs close to the monolayer coverage. Accordingly, we observe an incomplete layer‐by‐layer or ‘pseudo‐Frank‐van‐der‐Merwe’ growth for Co on the Re(0001) surface at room temperature.
The Growth and Properties of Pd and Pt on Al2O3/NiAl(110)
Authors: Bäumer M. , Libuda J. , Sandell A. , Freund H.‐J. , Graw G. , Bertrams Th. , Neddermeyer H. 
Published: March 2014

AbstractSmall metal particles have strongly size‐dependent properties, which – in the case of supported particles – are also influenced by the particle substrate interaction. We have investigated such effects for Pd deposited on a thin alumina film grown on NiAl(110) by probing the adsorption behaviour of CO. Structure and size of the metal islands were varied by employing different substrate temperatures during evaporation. We found that at 90 K small, disordered aggregates are formed, whereas deposition at 300 K results in larger crystallites with (111) facets. The CO thermal desorption spectra show a size‐dependent behaviour which can be attributed to a higher degree of CO coordination with decreasing particle size. The results are compared with the corresponding behaviour of Pt. In contrast to Pd, Pt leads to a strong interaction with the substrate at 300 K. This gives rise to a desorption feature of CO in a temperature range which is typical for transition metal oxides.
In Situ Controlled Promotion of Catalyst Surfaces Via Solid Electrolytes: The NEMCA Effect
Authors: Vayenas Constantinos G. , Yentekakis Ioannis V. , Bebelis Symeon I. , Neophytides Stylianos G. 
Published: March 2014

AbstractThe catalytic activity and selectivity of metal films interfaced with solid electrolytes can be varied in situ in a dramatic and reversible manner by applying currents or voltages (typically ± 1–2 V) between the catalyst film and a counter electrode also deposited on the solid electrolyte. Catalytic rates can thus be varied by up to a factor of 200. The induced steady‐state change in catalytic rate is up to five orders of magnitude larger than the steady‐state rate of electrochemical supply of ionic species from the solid electrolyte onto the catalyst surface. This novel effect termed Non‐Faradaic Electrochemical modification of catalytic activity (NEMCA) has been studied for over 40 catalytic reactions on Pt, Rh, Pd, Ag, Ni and IrO2 catalysts using a variety of solid electrolytes (O2−, F−, Na+, H+ conductors) and also, more recently, in aqueous alkaline solutions. Besides potential technological applications, this new effect allows for a systematic study of the role of promoters in heterogeneous catalysis. In this paper the main features of in situ controlled promotion are reviewed and the origin of the effect is discussed on the basis of recent XPS, TPD and cyclic voltammetric investigations.
Surface Characterisation and Modification by the Scanning Electrochemical Microscope (SECM)
Authors: Borgwarth K. , Ricken C , Ebling D.G. , Heinze J. 
Published: March 2014

AbstractMethods of surface analysis and micromodification using the scanning electrochemical microscope (SECM) are described. An ultramicroelectrode (UME) is scanned in a liquid electrolyte a few microns above a sample's surface. The principles of SECM are explained. Local surface conductivity and reactivity can be imaged in the feedback and collector/generator mode. The same set‐up allows micromodification processes as well. The degree of doping of polyaniline deposited on a PETG film was increased locally. The generated structure formed an inter‐digital array consisting of doped and undoped polyaniline. Its local conductivity was successfully analysed in a second step. To fabricate a polymer microstructure the monomer 2,5‐bis(1‐methyl‐pyrrol‐2yl)‐thiophene was deposited by evaporation on an ITO substrate. Polymerisation was induced by the tip via an oxidation reaction. The remaining monomer was easily removed by organic solvents. A new method for the microdeposition of silver on a gold substrate is described. Silver cations were complexated in an aqueous solution of ammonia. Protons locally generated by the tip shifted the complexation equilibrium to create free silver cations. When the sample is held on an adequate potential they were deposited on the gold surface.
Fourier Transform Microwave Spectroscopy – An Improved Tool for Investigation of Rotational Spectra
Authors: Dreizler Helmut 
Published: March 2014

AbstractLike in other fields of spectroscopy, the introduction of Fourier transform techniques promoted microwave and millimeter wave rotational spectroscopy of molecular species. As the time scale is shorter than in nuclear magnetic resonance, the development had to wait for sufficiently fast instrumental components for this time domain spectroscopy. By investigation of static molecular gases in waveguide sample cells and of molecular species in a pulsed supersonic beam, the Fourier transform technique has greatly enhanced the potential of rotational spectroscopy. The field is still open for further improvements.The basic theory and the present state of the experiments will be given and illustrated by examples of investigated species.
HCN Clusters in Molecular Beams and Cryogenic Matrices
Authors: Beichert P. , Pfeiler D. , Knözinger E. 
Published: March 2014

AbstractCluster formation of hydrogen cyanide (HCN) was traced by mass spectroscopy in molecular beams and by FTIR spectroscopy in cryogenic matrices in which the clusters were embedded. Both experiments provided evidence for the presence of linear (n ≥ 2) and cyclic structures (n ≥ 3) which were predicted by ab initio calculations as comparably stable.The mass spectra clearly reflect a fundamentally different behaviour of the two types of clusters within the expansion zone: the linear species exhibit the cabability of cluster growth, while the cyclic ones do not. This leads to a characteristic size distribution with two marked maxima. During matrix deposition, considerable distortions of the clusters are created which may be healed out by annealing. The resulting sharp bands in the CH stretching region were assigned in agreement with ab initio calculations and previous IR studies aiming at small linear and cyclic species (n ≤ 3) in diverse liquid and solid environments.
Influence of Cholesterol and β‐Sitosterol on the Dynamic Behaviour of DPPC as Detected by TMA‐DPH and PyrPC Fluorescence: A Fluorescence Lifetime Distribution and Time‐Resolved Anisotropy Study
Authors: Bernsdorff C , Winter R. , Hazlett T.L. , Gratton E. 
Published: March 2014

AbstractFluorescence lifetime and time‐resolved anisotropy measurements on 1‐(4‐trimethylammonium‐phenyl)‐6‐phenyl‐1,3,5‐hexatriene (TMA‐DPH) and 1‐palmitoyl‐2‐[10‐(1‐pyrenyl)decanoyl]‐phosphatidylcholine (PyrPC) in lipid vesicles of 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphatidylcholine (DPPC) with and without cholesterol and β‐sitosterol, using multifrequency cross‐correlation phase fluorometry, are presented. We used TMA‐DPH and PyrPC as fluorescence probe for detecting rotational dynamics. Contrary to TMA‐DPH, which is tethered to the bilayer interface and therefore detects wobbling rotational dynamics in the interfacial and headgroup region, PyrPC senses the deeper acyl chain dynamics of the lipid bilayer. We have investigated the influence of sterol structure on the lipid dynamics. The experiments were carried out at two temperatures, one below and one above the main phase transition temperature of DPPC. Data were analyzed in terms of Lorentzian distribution functions for the fluorescence lifetime results and in terms of hindered rotation for the time‐resolved anisotropy results. We noticed, that addition of cholesterol and β‐sitosterol results in a distinct increase in average fluorescence lifetime of TMA‐DPH in both lipid phases. The rotational rates of TMA‐DPH depolarizing motions are only modestly increased in going from the gel to the liquid‐crystalline phase of DPPC. However, a marked increase in the contribution of fast rotational motions of TMA‐DPH is found as the temperature is increased through the main transition. No significant differences in rotational rates of TMA‐DPH exist between samples with embedded cholesterol or β‐sitosterol at T = 55°C. The rotational rate of TMA‐DPH in the gel state of the lipid bilayer at T = 35°C is slightly larger in the case of β‐sitosterol, however. Cholesterol and β‐sitosterol, then, have a similar effect on the contribution of fast rotational dynamics in the interfacial region of the bilayer. It decreases about 40% upon addition of 50 mol‐% sterol. The incorporation of either sterol into DPPC vesicles leads to an increase in fluorescence lifetime of PyrPC in both lipid phases. The rotational rates of PyrPC in the bilayer are an order of magnitude smaller than those of TMA‐DPH. Also the contributions of fast rotational motions significantly differ for the two fluorophores. The motional freedom in the deeper acyl chain region of DPPC in its fluid‐like state at T = 55°C is scarcely affected by addition of either sterol. However, differences in the rotational rates of the two sterols are observed for high sterol concentrations.
Subpicosecond‐Pulse‐Laser‐Induced Electron Emission from Mercury and Silver into Aqueous Electrolytes
Authors: Krivenko A.G. , Krüger J. , Kautek W. , Benderskii V.A. 
Published: March 2014

AbstractHighly efficient superlinear electron emission from liquid mercury and polycrystalline silver electrodes into aqueous electrolyte solutions has been discovered. The effect is induced by visible subpicosecond‐laser pulses (300 fs) with a photon energy (h v ≈ 2 eV; 615 nm) less than the threshold of the linear photoeffect. The charge density q emitted from mercury by 615‐nm laser pulses increased from 10−9 to 10−5 C cm−2 in the intensity range 7 = 4–30 GW cm−2. At silver, 10−9 to 10−7 C cm−2 were generated in the range of I = 7–70 GW cm−2. The charge density grew with the concentration of electron acceptors (H3O+ and CHCl3) at I < 20 GW cm−2, because the capture of emitted electrons prevents them from returning to electrode surface. The subsequent slow electron reduction of the electron capture products (H‐atoms and CHCl2‐radicals, respectively) indicates the laser‐induced electron transfer across the interface. Ultraviolet 300‐fs‐pulses (h v ≈ 4 eV) at intensities I < 6 GW cm−2 lead to effective quantum yields corresponding to one‐photon emission. This emission disappeared at Hg when 6‐ps‐pulses were applied with the same energy, but still occurred at Ag. These results conform with theoretical predictions of charge‐intensity dependencies, pulse duration and electrode potential characteristics for thermoelectron emission of a nonequilibrium electron gas from metals into electrolyte solutions.
Festkörperelektrolytpotentiometrie an oxidischen Katalysatoren
Authors: Brück Johannes , Brust Monika , Lintz Hans‐Günther 
Published: March 2014

AbstractThe oxygen activity in the solid determines the phase composition which should be stable in the case of oxygen transfer reactions at oxidic catalyst. Its value results from the rates of the oxygen uptake by the solid and the oxygen transfer to an acceptor in the gas phase, e.g. a hydrocarbon or ammonia. This oxygen activity in the catalyst can be determined under reaction conditions with the aid of a potentiometric method based on the application of solid ion conductors. In that case the catalyst is simultaneously one electrode of an electrochemical cell, the oxygen activity and the reaction rate being measured simultaneously.The method has been applied during the investigation of the reduction of nitrogen monoxide by ammonia on copper oxide and a typical SCR catalyst on the basis of vanadia‐titania. The reaction was studied in the domain 300 <ϑ/°C < 390 at reactant concentrations up to 4000 ppm, the oxygen content in the gas phase being varied between 0 and 10 Vol.%.The results demonstrate unambiguously a correlation between oxidation state of the catalyst and the reaction kinetics. The rate increasing influence of oxygen is accompanied by the transition of V4+to V5+in the case of the SCR catalyst. In the case of copper oxide catalyst the reduction rate of NO is decreased at increasing oxygen concentration at the transition to Cu2+. In addition the increased N2O formation could be observed.In spite of the high oxygen excess a quasiequilibrium of oxygen chemisorption can be excluded in any case.
Electrochemical Study of Zircaloy‐4 in Aqueous Sulphate Solution
Authors: Al‐Abdallah M.M. , Göhr H. 
Published: March 2014

AbstractThe surface of zircaloy‐4 electrodes was studied in 0.5 M K2SO4 solution by using impedance measurement as a function of potential and by polarization curves. Parameters of the faraday impedance, charge transfer and properties of passivation film were obtained. Faradayic impedance shows clear dependence on the applied anodic potential as well as on the time of polarization.
Investigations of the Reactions of 1CH2 (ã1A1 (v = 0,1)) with H2O, D2O and HCl
Authors: Carstensen H.‐H. , Wagner H. Gg. 
Published: March 2014

AbstractThe reactions of 1CH2(ã1A1) in its vibrational ground state (1CH2(v = 0)) and with single excited bending mode (1CH2(v = 1)) with the reactants H2O (1), D2O (2) and HCl (3) were investigated with a LIF apparatus under quasistationary and first order conditions. 1CH2 was produced via ketene photolysis at 308 nm (1CH2(v = 0) and 1CH2(v = 1)) and at 336 nm (only 1CH2(v = 0)). The evaluation of the kinetic data of 1CH2(v = 0) gave different results for both wavelength. At λ = 336 nm obtained rate constants were in general higher compared to those at λ = 308 nm. The measurements at λ = 308 nm therefore seem to be influenced by secondary processes and they do not give the ‘real rate constant’.1CH2(v = 1) reacts faster with all three investigated reactants than 1CH2(v = 0) does. Vibrational deactivation with unusual high rate constants may explain these different reactivities of 1CH2(v = 0) and 1CH2(v = 1), but can only in part explain differences for the two 1CH2(v = 0) measurements.The following rate constants were measured at T = 295 K (in cm3·mol−1·s−1): k1(1CH2(v = 0)) = (1.45 ± 0,1)·1014, k1(1CH2(v = 1)) = (2.3 ± 0.2)·1014, k2(1CH2(v = 0)) ≈ 1.1·1014, k2(1CH2(v = 1)) = (1.75 ± 0.15)·1014, k3(1CH2(v = 0)) = (2.0 ± 0.2)·1014, and k3(1CH2(v = 1)) = (2.2±0.2)·1014.In the range from 255 K to 475 K the rate constants of the reactions of 1CH2(v = 0,1) with H2O and D2O show a significant dependence on temperature T which can be expressed by T−n with n = 0.6 to 0.8.The channel of the reaction of 1CH2 + H2O leading to CH3 + OH was found to contribute 50±15% to the total reaction, thus being the main channel at p ≤ 14 mbar. Formaldehyde could not be detected as a product of (1).
An Investigation by Diffusion Layer Imaging of Coupled Homogeneous Chemical Reactions of the Benzophenone Radical Anion in N,N‐Dimethylformamide
Authors: Walczyk K.R. , Popkirov G.S. , Schindler R.N. 
Published: March 2014

AbstractThe electrochemical reduction of benzophenone (BP) to its primary radical anion BP− with coupled homogeneous chemical reactions was investigated in N,N‐dimethylformamide. Protonation of BP− with benzoic acid and with o‐cresol, respectively, used as proton donors, and disproportionation of BP− in the presence of excess Li+ ions were studied by DLI technique. Rate constants for protonation and disproportionation as well as equilibrium constants for ion association were evaluated. Possible reaction pathways, and the effect of ion association on the kinetic behaviour are discussed.
Surface Enhanced Raman Scattering from Acridine on Copper Electrodes at Low Adsorbate Concentration
Authors: Niaura G. , Malinauskas A. 
Published: March 2014

AbstractSurface enhanced Raman spectra of acridine in a concentration range 6.7·10−9 to 3.6·10−3 M were obtained on a copper electrode in a chloride‐containing solution at pH 2.5. A conclusion was made that acridine adsorbs as an ion pair formed from acridinium cation and chloride anion. An adsorption isotherm for acridine on an activated copper electrode was obtained.
Rate Constants of the Reactions of CHCl (X̃1A′) with Ethylene, Propylene, and Acetylene
Authors: Carstensen H.‐H. , Rehbein C , Wagner H. Gg. 
Published: March 2014

AbstractThe rate constants of the reactions of CHCl (X̃1A′) with C2H2 (k4), C2H4 (k5) and C3H6 (k6) were measured as a function of temperature. Experiments were carried out under quasistationary conditions at around 18.5 mbar total pressure. It is shown that excimer laser photolysis of CF2 = CHCl at λPH = 193 nm is a suitable source for CHCl (X̃1A′) generation. The following rate constants were obtained from logarithm plots:
k4 = (4.2±0.1)·1012 (T/295K)−(0.79±0.06) cm3 mol−1 s−1
k5 = (3.2±0.2)·1012 (T/295 K)−(1.52±0.12) cm3 mol−1 s−1
k6 = (8.3±1.4)·1012 (T/295 K)−(1.39±0.05) cm3 mol−1 s−1
The reactivity of CHCl (X̃1A′) is compared to those of other carbenes.