bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Electronic Structure of Crystalline Lithium Hydride – A Reduced Density Matrix Approach
Authors: Asthalter Tanja , Weyrich Wolf 
Published: July 2012

AbstractThree directional Compton profiles J(q) of LiH were measured by means of 241Am γ‐ray scattering. The Fourier transforms (reciprocal form factors B(s)) were compared to the results from Löwdin‐orthogonalised wavefunctions and from a full solid‐state RHF calculation performed with the program CRYSTAL for various basis sets of different quality. The wavefunction that yielded best agreement with the experiment was then used to calculate two‐dimensional cuts through the one‐electron density matrix (ODM) in the main bonding directions both for the crystal and for clusters of variable size. From the off‐diagonal parts of the ODM it is possible to estimate the influence of small covalent contributions to the chemical bonding in LiH. The influence of different cluster orbitals is discussed as well as the question which cluster size already shows the main qualitative features of chemical bonding in the ODM of the crystal.
Investigation of Solid State Reactions and Solid‐Solid Phase Transformations with Time‐ and Temperature‐resolved X‐ray Powder Diffractometry
Authors: Epple M. , Cammenga H. K. 
Published: July 2012

AbstractAn X‐ray powder diffractometer has been equipped with a heatable sample holder which allows highly defined heating up to 250°C. A good temperature control permits isothermal as well as non‐isothermal runs. The applicability of time‐ and temperature‐resolved X‐ray powder diffractometry (TXRD) as a thermoanalytical method is demonstrated. Solid state reactions and solid‐solid phase transformations were investigated. As examples the phase transformation of phenanthrene and the dehydration of caffeine hydrate are presented. It is possible to extract the activation parameters for a solid state reaction from a single non‐isothermal run with a constant heating rate. The principles of the quantitative kinetic evaluation of time‐ and temperature‐resolved X‐ray powder diffraction data are outlined.
A High‐Temperature Mössbauer Study of Fayalite, Fe2SiO4: Cation Diffusion and Reactivity
Authors: Becker K. D. , Dreher S. , Wißmann S. 
Published: July 2012

AbstractResults are reported of a Mössbauer study of fayalite at elevated temperatures. At the highest temperature used in our study (1130°C), spectra are found to be affected by cation diffusion. The oxygen partial pressure dependent broadening of the Mössbauer lines is discussed in the context of the lattice structure of Fe2SiO4, which provides two non‐equivalent sites for diffusion of the ferrous ions. The kinetics of the formation reaction of Fe2SiO4 from its quasi‐binary components FeO and SiO2 has been studied by means of time‐resolved Mössbauer experiments.
Electrochemistry in Aprotic Solvents Containing Anhydrous Perchloric Acid: Electroreduction of Imidazoles
Authors: Pekmez Kadir , Özyöruk Haluk , Yildiz Attila 
Published: July 2012

AbstractThe electroreduction behavior of imidazole and some of its derivatives on a Pt electrode in acetonitrile was investigated using cyclic voltammetry and controlled potential electrolysis. In a solution containing TBAP a broad reduction peak was observed whereas no reduction process was detected in LiClO4 solution. In the presence of a strong proton donor another reduction peak was observed at more positive potentials that was assigned to the catalytic reduction of protons through the protonated imidazoles. The effects of hydrogen bonding and the pKa values of the imidazoles on the reduction process are discussed.
Resonant Behaviour of the Si/Fluoride Interface: A method for testing the uniform accessibility of an electrode system
Authors: Chazalviel J.‐N. , Ozanam F. 
Published: July 2012

AbstractThe p‐Si/fluoride interface exhibits a resonant behavior in the anodic potential region. The resonance frequency is proportional to the interface current density. It is shown that the response of the interface to a potential step excitation provides a direct means for accessing the current distribution at the interface. When the current density is under mixed (mass transport + kinetic) control, this gives a simple test for the uniform accessibility of the electrode. This method is tested on a circulation cell, where the current distribution can be varied by changing the geometry. The obtained current distributions are qualitatively consistent with a numerical calculation of the current‐density map.
Fiber‐Optic Quasielastic Light Scattering in Concentrated Latex Dispersions: The Performance of Single‐Mode vs. Multimode Fibers
Authors: Wiese H. , Horn D. 
Published: July 2012

AbstractResults of fiber‐optic quasielastic light scattering from two monodisperse latex dispersions (particle diam. 135 and 270 nm, concentration range 1 – 30 wt%) are compared for single‐ and multimode fibers, respectively. For the 135 nm latex dispersions it is shown both by theory and experiment that the two types of fibers give identical results which can be interpreted in terms of the diffusional motion of the latex particles. Evidence is given that in the case of the multimode fiber the speckle pattern, i.e. the inhomogeneous illumination of the particles in the scattering volume, and the dependence of the mode excitation on the position of the scatterer do not give rise to additional intensity fluctuations on the delay time scale of the measurements. Discrepancies observed between the results obtained with the two fibers for the 270 nm latex dispersions, are shown to be due to multiply scattered light affecting the multimode fiber data.
A Kinetic Investigation of the Reaction between F Atoms and Cl2O
Authors: Vogt R. , Schindler R. N. 
Published: July 2012

AbstractUsing a fast flow system with mass spectrometric detection the rate constant at room temperature for the title reaction was determined to be k(4) = 7.5 (±0.8) · 10−11 cm3 molecule−1 s−1. The reaction appears to constitute a convenient dynamic ClO‐source.
On the Mechanism of Methanol Oxidation Sensitized by Anthraquinone
Authors: Kúti Z. , Gál D. 
Published: July 2012

AbstractThe mechanism of photosensitized oxidation of methanol in acetonitrile was investigated in the presence of anthraquinone. Among the main stable products formaldehyde, formic acid, hydrogenperoxide and hydroxymethylhydroperoxide has been found. Their accumulation was measured in the range of 30–60°C. Specific experiments were carried out to prove the existence or negligibility of reactions proposed in the literature. The computer simulation based on literature data and on our results combined with estimation of certain rate coefficients as parameters resulted in good agreement with experimental product accumulation curves. The estimated value of monomolecular decomposition of hydroxymethylperoxyl radical (k325°C ≈ 3 s−1) is in favour of the lowest values that can be found in the literature. In the overall termination process the Russell‐type termination step generally accepted in reactions between peroxyl radicals has decreasing importance with increasing temperature.
The Temperature and Concentration Dependences of Diffusion Coefficients of the Systems Ne–O2, Kr–O2, Xe–O2 and He–NO
Authors: Dunlop Peter J. , Bignell C. M. 
Published: July 2012

AbstractDiffusion coefficients have been measured for the systems Ne–O2, Kr–O2, Xe–O2 and He–NO at 10 K intervals from 280–320 K. The results differ by as much as 6% from literature values.
Study of the Equation of State of Cyclopentane from 193 to 298 K and Pressures up to 104 MPa
Authors: García Baonza V. , Alonso M. Cáceres , Delgado J. Núñez 
Published: July 2012

AbstractAn expansion apparatus has been used to measure the density of liquid cyclopentane, from 193 to 298 K and pressures up to 104 MPa. The experimental results have been correlated in terms of the Strobridge equation of state, which has been used to estimate several properties of the compressed liquid. Other semitheoretical and theoretical equations of state have been used to predict high pressure results as well as vapor‐liquid equilibrium and second virial coefficients. Comparisons with experimental data are reported in all the cases.
Thermodynamic Investigation of the Pt—Pb Binary Alloys
Authors: Amzil Abdelhamid , Castanet Robert 
Published: July 2012

AbstractThe enthalpy of formation, hf, of the Pt—Pb alloys was measured in the 923–1316 K temperature range with respect to composition by direct reaction calorimetry (drop method) with the help of high temperature Calvet‐type calorimeters. Furthermore we determined also some phase boundaries from the breaks of the hf(x) curves. — The thermodynamic behaviour of the melts is characterized by moderate negative deviations to ideality suggesting some chemical short‐range order (h = −15.88 kJ · mol−1 at 923 K for χPt = 0.53). The associates are very sensible to temperature since the excess heat capacity is positive with a maximum of about 10.2 J · K−1 · mol−1 near χPt = 0.71. Such a behaviour differs strongly from that of the Pd‐Pb system which shows a strongly negative enthalpy of mixing (h = −38.4 kJ · mol−1) without any temperature dependence.
H Atom Formation on Azoethane Pyrolysis
Authors: Klatt M. , Schad I. , Gg. Wagner H. 
Published: July 2012

AbstractThe decomposition of azoethane and the formation of H atoms during its decomposition were measured in shock waves for temperatures between 900 and 2100 K and very low azoethane concentrations. Around 1000 K the formation of H atoms amounts to about 30% of the H atoms expected if azoethane would only dissociate into two ethyl radicals and N2. Towards higher temperatures the H atom yield increases. This can be taken as an indication that the thermal decomposition of azoethane in the temperature range covered cannot only lead to ethyl radicals and N2 but that at least one further reaction channel leading to stable hydrocarbons and N2 must contribute to the reaction.
Reductions of Nitrite and NO on Pt Single Crystal Electrodes in Alkaline Solution
Authors: Ye S. , Hattori H. , Kita H. 
Published: July 2012

AbstractThe reductions of nitrite and nitric oxide (NO) on platinum single crystal electrode were investigated by voltammetric method in alkaline solution. The reductions are very much structure sensitive and proceed exclusively in a potential region of 0.3‐0.5 V (RHE) at pH > 8. Spectrochemical analysis of the electrolyte shows the formation of ammonia with an efficiency of more than 80%. Thus, the overall reaction is concluded as: NO + 5H2O + 6 → NH3 + 7OH−. The present results are discussed in comparsion with other electrochemical results reported.
Kinetic Salt Effects on the Outer‐sphere Electron‐transfer Reaction between Hexacyanoferrate(II) and Pentaammineaquocobalt(III)
Authors: Galán M. , Jiménez R. , Sánchez F. 
Published: July 2012

AbstractThe kinetic salt effects in sodium nitrate solutions, up to 5 mol dm−3, on the reaction between hexacyanoferrate(II) and pentaammineaquocobalt(III) have been studied. The experimental trends of the association constant of the reactants, KIP, and the electron transfer rate constant, ket, can be explained within the framework of dielectric continuum models. – To further support this explanation, the KIP and ket values of the reaction between octacyanomolibdate(IV) and pentaammineaquocobalt(III) in a 0.5 mol dm−3 solution of sodium perchlorate have been determined. – The methodology employed in the present work could be used as a general method for analyzing medium and salt effects on electron transfer processes, when one of the reactants shows irreversible behaviour, from the electrochemical point of view.
Quantum Correlations and Topological Quantum Numbers in the Fractional Quantum Hall Effect
Authors: Brändas Erkki J. 
Published: July 2012

AbstractIt is demonstrated that the fractional Hall plateaux, experimentally observed in some nearly ideal samples at very low temperatures, are manifestations of strongly correlated objects explicitly connected with Coleman's extreme case and Yang's concept of off‐diagonal long‐range order (ODLRO). This interpretation yields (n – 1)/(2n – 1), n = 2,3,… the most stable fractions. The appearance of large even fractions is considered together with a possible explanation of the recently observed fractional Hall states with even numerators in bilayer two‐dimensional electron systems. The present quantum correlations theory also suggests a theoretical analysis of the observed variations in wire‐wound reference resistors.
An Alternating Current Battery
Authors: Schneider Friedemaan W. , Hauser Marcus J. B. , Reising Joachim 
Published: July 2012

AbstractWe built a true alternating current (a.c.) battery that periodically reverses value and sign of its electromotive force (e.m.f.). This a.c. battery is an electrochemical concentration cell that consists of two coupled half cells in which identical oscillating Belousov‐Zhabotinskii (BZ) reactions take place isothermally at 28.0°. The homogeneous BZ oscillations are phase shifted in order to create a potential difference between both half cells. With an increasing load the phase shift between the two half cells decreases (i.e. both oscillations tend to synchronize), consequently the amplitude of the alternating current decreases while the amplitudes of the individual BZ‐oscillators remain unaffected. The e.m.f.‐current diagram of the a.c. battery is analogous to that of direct current batteries. Although the present frequency (period of ∼58 s), current (∼±2.5 μA), e.m.f. (∼±50 mV) and maximum power produced (∼10−7 W) are low it should be possible to construct a.c. batteries with improved performances by the use of other chemical oscillators.
Dependence of the Protonation Constants of β‐Alanine on the Ionic Strength in KNO3 According to Pitzer's Formalism
Authors: Herrero R. , Brandariz I. , Sastre De Vicente M. E. 
Published: July 2012

AbstractIn this work we carried out a simple mathematical analysis of the functions describing the dependence of the stoichiometric acid‐base constant on application of Pitzer's formalism to the activity coefficients of the species involved in two common monoprotonation equilibria. Simulated pK* vs ionic strength plots for two typical acid‐base equilibria AH+2 ⇆ AH + H+ and AH ⇆ A− + H+) are compared with experimental data for the two pK*i of β‐alanine in KNO3 at 25 °C.
Comparison of the Effects of Anionic and Cationic Surfactant on the Precipitation of Calcium Oxalates
Authors: Škrtić D. , Filipović‐Vinceković N. , Bišćan J. 
Published: July 2012

AbstractInfluence of anionic, sodium dodecyl sulfate (SDS) and cationic, dodecylammonium chloride (DDACl) surfactant, on spontaneous batch precipitation of calcium oxalate is investigated. A combination of particle number and size analysis, thermogravimetric analysis, X‐ray diffraction, optical microscopy, electrophoretic and adsorption measurements is used to characterize the processes involved. SDS and DDACl affect the precipitation process at different stages. SDS acts as a nucleation modifier. The action of both surfactants at the stage of primary particle formation exhibits a complex dependence of the rates and mechanisms of crystal growth and aggregation on the structure of aqueous surfactant solutions. Both surfactants inhibit crystal growth and aggregation by adsorption due to the charge and hydrophobic effects. Preferential DDACl sorption on oxalic faces changes the habit of calcium oxalate monohydrate crystals.
The Determination of the Transition State Structure from the J Dependence of the Dissociation Energy E0 (J): The Methane and Ethane Ion Dissociation
Authors: Weitzel Karl‐Michael , Mähnert Joachim , Baumgärtel Helmut 
Published: July 2012

AbstractA threshold photoelectron photoion coincidence experiment has been setup which allows to measure breakdown curves of energy selected ions at different sample temperatures. These studies reveal the rotational energy of the transition state in unimolecular reactions, which in turn is used as a probe for the transition state structure. According to a model recently suggested this should allow the distinction of tight and loose transition states. The breakdown curves of methane and ethane ions in the region of the lowest reaction channel have been measured at 300 K and close to 0 K. In the case of the H loss from methane ions the shift between these two breakdown curves reveals that the dissociation energy Eo varies significantly with the rotational temperature as expected for a simple bond fission (loose transition state). In the case of H2 loss from ethane ions the shift between the breakdown curves at 300 and close to 0 K shows that E0 (J) does not vary significantly with the rotational temperature. This is to be expected for a concerted elimination reaction (tight transition state).
Determination of Fractal Dimensions of Xerogels via Förster Energy Transfer
Authors: Schleicher J. , Rof M. , Schneider F. W. 
Published: July 2012

AbstractThe fluorescence decay of anthracene and 9,10‐diphenylanthracene in xerogels with various alkyltrimethoxysilane (alkyl = methyl, n‐propyl, n‐octyl) and tetramethoxysilane content is biexponential over a large parameter range. Decreasing degrees of cross linkage as well as lengthening of the alkyl chain lead to an increase of the value and amplitude of the short decay time and finally to a monoexponential decay. The “fractal dimension” of the doped xerogels with monoexponential 9,10‐diphenylanthracene fluorescence is determined via “Förster energy transfer” using rhodamine‐6G as the acceptor. Xerogels of low cross linkage (high content of n‐propyltrimethoxysilane or n‐octyltrimethoxysilane) are characterized by the dimension 3. Further aggregation of the primary silicate clusters leads to a “fractal‐like” network with the dimension of about 2.4.
Experimental Results and Aspects of Analytical Treatment of Vapour Pressure Measurements in Hydrated Melts at Elevated Temperatures
Authors: Boßmann E. , Richter J. , Stark A. 
Published: July 2012

AbstractVapour pressures of the hydrated melt systems NaNO3 + H2O, CsNO3 + H2O, (Na0.55,Cs0.45)NO3 + H2O, and (Rb0.40,Ag0.60)NO3 + H2O at 406K, 425 K, 452K, and 491K as a function of the ionic mole fraction are reported. The water activities and the water activity coefficients are computed. All systems investigated show a positive deviation from Raoult's law except the system NaNO3 + H2O which shows within the accuracy of the measurements the behaviour of an ideal mixing. The activity model of Pitzer which is based on the van Laar formalism shows a good representation of the water activity coefficients.
Calorimetric Investigations of Processes at the Solid/Gas Interphase
Authors: Wedler G. , Ganzmann I. , Borgmann D. 
Published: July 2012

AbstractAdsorption calorimetry, partially combined with thermal desorption spectroscopy and isotope exchange measurements, has been used to study the adsorption and coadsorption of gases on metal films under ultrahigh vacuum conditions. It has proved to be possible to get detailed information on both the primary adsorption step and the consecutive reaction in the adsorbed layer. Adsorption of CO and CO2 on Fe are treated as examples with subsequent decomposition reactions. In the case of the coadsorption of CO and O2 and of H2 and CO on Fe the mutual interaction of the gases including replacement processes are studied.
Surface Reactions of Molecular Hydrogen on Gas‐Phase Deposited Magnesium Oxide
Authors: Hofmann P. , Jacob K.‐H. , Knözinger E. 
Published: July 2012

AbstractMgO samples with a specific surface area of up to 400 m2/g were prepared by chemical gas phase‐deposition. The resulting samples were used for H2 and D2 chemisorption experiments. IR spectroscopy clearly evidences that homolytic and heterolytic dissociation processes are effective. The corresponding surface centers are radicals (O− and Mg+) and ion pairs MgO respectively. In addition, two isotope exchange reactions on completely different time scales occur between D2 and isolated surface OH groups.
High Temperature in Situ Raman Spectroscopy of Working Oxidative Coupling Catalysts
Authors: Mestl G. , Knözingers H. , Lunsford J. H. 
Published: July 2012

AbstractOxidative coupling of methane is an important route to formation of ethane and ethylene. The reaction is catalyzed by a broad range of basic oxides, including lanthanum oxides, that are modified with group IA or group IIA ions. — Laser Raman spectroscopy has been used to characterize surface peroxide structures on La2O3 and Na‐ and Sr‐modified La2O3. These surface peroxide groups are formed on these catalysts by calcination in O2 at temperatures between 500°C and 800°C. By high temperature in situ Raman spectroscopy it was possible to follow the formation of these surface peroxides and their reaction with methane. Changes in the structure and concentration of peroxide groups on the surface of the working catalysts were investigated at elevated temperatures as high as 800°C by varying the partial pressures of the reactant gases. The results provide evidence for the role of peroxide ions for the activation of methane during the oxidative coupling reaction.
A FTIRAS Study of CO Adsorbed at Ni(100) Surfaces
Authors: Lauterbach J. , Wittmann M. , Küppers J. 
Published: July 2012

AbstractAdsorption of CO at Ni(100) surfaces has been studied with Fourier‐Transform Infrared Absorption‐Reflection (FTIRA) spectroscopy in the temperature range 121 K to 350 K. Up to a coverage of θ = 0.5 top site and bridge site bonded CO has been identified by absorption peaks in the frequency range 2016 to 2048 cm−1 and 1885 to 1949 cm−1, respectively. The site population is temperature dependent, top sites are preferred at high temperatures, bridge sites at low temperatures. Towards the saturation coverage, θ ≈︁ 0.67 the top site peak is replaced by a broad absorption structure between 2000 and 2100 cm−1, which contains at least 3 separate peaks. The bridge site related absorption remains a single peak but shifts upwards by 20 cm−1 to 1968 cm−1. This suggests that above a coverage of θ = 0.5 CO molecules are arranged in an incommensurate adsorption structure, in which a unique top adsorption site does no longer exist.
Kinetics of H2O Adsorption on Clean and Potassium Precovered Ni(111) Surfaces
Authors: Kuch W. , Schulze M. , Schnurnberger W. , Bohwin K. 
Published: July 2012

AbstractThe interaction of water with clean and potassium precovered Ni(111) was studied by X‐ray photoelectron spectroscopy (XPS) in combination with an H2O particle beam for K submonolayer coverages. Equilibrium measurements of the kinetic parameters of the water desorption were performed in the H2O partial pressure range up to 2 · 10−3 Pa. At temperatures between 155 K and 175 K the coverage dependent apparent Arrhenius parameters can be obtained. On the clean surface water adsorbs in a bilayer structure and no dissociation of the water molecules was observed, whereas for potassium covered surfaces a dissociation of approximately one water molecule perpotassium atom and a more complex adsorption behaviour was observed. The apparent Arrhenius parameters for the water desorption on the clean surface and for various potassium precoverages are presented. The different H2O layers are discussed and qualitatively compared with temperature programmed desorption (TPD) measurements.
In‐situ Investigations of the Conduction Mechanisms in Low‐Dimensional Organic Semiconductors and Metals
Authors: Schmeißer Dieter , Göpel Wolfgang 
Published: July 2012

AbstractWe characterize the electronic structure of polypyrrole films and (2,5‐DMe‐Dicyanoquinonediimine)2Ag, Rb single crystals using a combination of electrochemical preparation and electron‐spectroscopical techniques (XPS, UPS, HREELS). These studies allow to characterize the electronic structure, to conclude on the particular conductivity mechanisms for controlled order and structures, and to determine the strength of both, the electron‐phonon and the electron‐electron interactions.