bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Diffusion in Crystalline Binary Compounds with Narrow Range of Homogeneity – I. A New Experiment for the Determination of the Heat of Transport
Authors: Janek J. 
Published: March 2014

AbstractThe formal analysis of the coupling between diffusional matter and heat transport shows that diffusional matter fluxes are driven by both temperature and composition gradients, and that matter fluxes are always connected with heat fluxes. An important concept in the description of this coupling is the introduction of so‐called heats of transport. The heats of transport, being combinations of phenomenological transport coefficients, denote the relation between individual matter fluxes and related heat fluxes for isothermal systems. For the case of mixed ionic/electronic conducting binary compounds with narrow ranges of homogeneity, A1+δXV, a new experiment for the determination of the reduced heat of transport of metal A is proposed and discussed with respect to a possible realization. The experiment is based on the direct measurement of the flux of the metal component in a temperature gradient, under special boundary conditions for the composition of the sample, and gives direct access to the (reduced) heat of transport, Q*A. Alternative ways for the determination of the heat of transport are summarized and compared with the proposed experiment.
Mixed Carbon Dioxide‐Krypton Solids: A New Diluted Quadrupole System
Authors: Langel W. , Fleger H.‐W. , Knözinger E. , Schuller W. 
Published: March 2014

AbstractMixtures of carbon dioxide and krypton gases were codeposited from the gas phase. The resulting solids were studied by X‐ray powder diffraction and IR absorption. Molecular dynamics simulation was applied to the system.Under equilibrium conditions phase separation occurs. If diffusion is suppressed, solids with extremely short coherence lengths were found in the concentration range of 30–70 mol% Kr. The simulation allows to reproduce this disorder. It is due to internal distortions rather than to grain size effects. The addition of krypton reduces the quadrupole‐quadrupole interaction. This leads to orientational and to centre‐of‐gravity disorder. The properties of CO2: Kr are discussed in comparison with the well known quadrupole glass N2: Ar. For the molecular dynamics simulation a flexible model of the CO2 was adopted. This allowed to reproduce the influence of the local environment on the band shape of the bending mode v2.
Viscosity of the System KF–KBF4–K2TiF6
Authors: Silný A. , Danêk V. , Nguyen D.K. 
Published: March 2014

AbstractThe viscosity of the melts of the system KF–KBF4–K2TiF6 has been measured by means of the computerised torsional pendulum method.The viscosity of KF is higher than that of KBF4 at the same temperature, most probably due to the substantial overheating of KBF4. In the ternary system the viscosity increases with the increasing content of K2TiF6.Additivity of the logarithms of viscosity was adopted as the ideal behaviour of the mixture. Negative deviations from such additive behaviour were found in the binary system KF–KBF4 probably due to the breaks of the B‐F‐B bridges caused by the excess of F− ions. Positive deviations from the ideal behaviour were found in the binaries KF–K2TiF6 and KBF4–K2TiF6 due to the formation of larger TiF3−7 anions caused by the reaction

Statistically significant ternary interaction confirmed that the above chemical reactions take place also in the ternary system.
Electrochemical Characterisation of Oxide Layers on Single Grains of a Polycrystalline Ti‐Sample
Authors: Kudelka S. , Michaelis A. , Schultze J.W. 
Published: March 2014

AbstractElectronic properties of passive films (d≤20 nm) on single grains of polycrystalline Titanium were investigated by micro‐ellipsometry and electrochemical methods using photoresist microelectrodes with defined areas. A number of experimental improvements are reported here: i) The minimisation of the electrochemical active area down to 3×10−6 cm2, ii) the determination of the crystallographic orientation of single grains by anisotropy microellipsometry, as well as iii) the determination of local film thicknesses under potentiostatic control by in‐situ micro‐ellipsometry. iv) The capacity C of the microelectrodes was measured applying a new droplet technique. Anodisation of Ti single grains up to the same potential U yields different oxide thicknesses, anodic charges, donor densities and oxygen evolution. Thin passive layers need less anodic charge qOx for the oxide formation and have a higher donor density Nd. The great extent of oxygen evolution at these grains can be explained by an increased tunnel probability for the transition to the conduction band. The properties vary with the substrate orientation in a systematic manner, indicating a change of the properties at the (0111) orientation.
Determination of Rate Constants and Product Branching Ratios for the Reactions of CH3O2 and CH3O with Cl Atoms at Room Temperature
Authors: Jungkamp T. P. W. , Kukui A. , Schindler R. N. 
Published: March 2014

AbstractReactions of CH3O2 and of CH3O radicals with Cl atoms have been investigated at 300 K using a discharge flow system with LIF and mass‐spectrometric detection.

Rate constants k1 = (1.15±0.3)·10−10 and k2 = (1.00±0.2)·10−10, in units cm3 molecule−1 s−1 have been obtained observing pseudo‐first‐order decays of CH3O2 and CH3O radicals, respectively. The branching ratio k1a/k1 = 0.51 ±0.09 has been found from the determination of OCl yields. Formation of the Criegee intermediate CH2O2 in reaction (1b) was inferred from CO2 generation. A lower limit of 0.8±0.5 was derived for the CO2 yield from unimolecular CH2O2 decomposition.Possible reaction pathways for steps (1a) and (1b) are suggested on the basis of ab initio model calculations. The calculations include the estimation of structures and energies of intermediate CH3O2Cl collision complexes and the decomposition of CH3OOCl to yield products.
Composition Dependence of the Liquid/Air Interfacial Tension of 2‐Butoxyethanol/Water Mixtures at Temperatures below the Lower Critical Temperature
Authors: Knecht B. , Woermann D. 
Published: March 2014

AbstractMeasurements of the liquid/air interfacial tension σα,βγ (α, vapour phase; (βγ), homogeneous liquid phase) of 2‐butoxyethanol (abbreviated C4E1)/water mixtures carried out as function of temperature (15°C≤T≤50°C) and composition (O≤x≤1; x, mole fraction of 2‐butoxyethanol) reveal the existence of extrema in the σα,βγ versus x curves measured at constant temperature. The location of the minimum on the composition axis xmin approaches the critical composition xc when temperature approaches the critical temperature Tc. For composition xc<x<xr (xr, mole fraction of C4E1 in the C4E1/water in the mixture forming the right boundary of the closed loop coexistence curve) the interfacial adsorption ΓC4E1(w) of C4E1 relative to water w calculated from the σα,βγ versus x isotherms has a negative value indicating the existence of a water‐rich layer at the α,βγ interface in this range of compositions. The extent of the depletion of C4E1 from this region increases if xc is approached from values x>xc. This could reflect the existence of a wetting transition from partial wetting of the α,γ interface by water‐rich phase γ to complete wetting of this interface by phase γ at a temperature very close to Tc. The existence of such a transition was presumed in the literature.
Dynamics of Molecular Hydrogen Interactions with Silicon Surfaces
Authors: Hasselbrink Eckart 
Published: March 2014

AbstractMolecular hydrogen exhibits an exceedingly low dissociative sticking coefficient on the (100) and (111) faces of silicon. This finding would suggest that the molecule experiences a large barrier (> 100 kJ/mol) when it attempts to adsorb. However the assumption of such a large barrier is in conflict with the known desorption activation energy and the estimated bond strength of hydrogen atoms to silicon surface atoms. In recent experiments it has been observed that the desorbing molecules do not carry away a large extend of excess energy as translational energy nor in their internal degrees of freedrom. This apparent contradiction can be resolved if one considers that the dangling bonds on the silicon surface are localized and that hydrogen adsorption induces significant alterations of the surface structure. Hence, hydrogen adsorption is expected to be activated in degrees of freedrom localized in the surface. This proposition has been substantiated by the observation of an increasing adsorption probability with increasing sample temperature. Recent total energy calculations lend theoretical confirmation to this model.
Analysis of the Hydrogen Formation at GaAs Electrodes by Impedance Spectroscopy Investigations
Authors: Uhlendorf I. , Reineke‐Koch R. , Memming R. 
Published: March 2014

AbstractThe kinetics of the hydrogen formation from protons as well as from water has been studied over a large potential range by measuring the interfacial current and the impedance spectrum in dependence of the electrode potential simultaneously. According to a quantitative analysis of the experimental data a semilogarithmic plot of the current j versus the potential across the space charge region ϕsc yielded a straight line of an ideal slope of 60 mV/decade. In addition it was found that the j‐ϕsc behavior at n‐GaAs electrodes can be described by the thermionic emission model, i.e., the electron transfer rate is controlled by the electron transport across the space charge region. From this result it has been concluded that the reduction of protons is an extremely fast process. The mechanism and the consequences of this surprising result are discussed in detail.
High Pressure Electrolyte Conductivity of the Homogeneous, Fluid Water‐Sodium Hydroxide System to 400°C and 3000 bar
Authors: Eberz A. , Franck E.U. 
Published: March 2014

AbstractAbove the melting temperature of 319°C the ionic fluid sodium hydroxide is completely miscible with dense water. The electrolyte conductivity of such a fluid “water‐salt”‐system has been studied from dilute aqueous solution to the ionic melt. Apparatus and procedure are described to perform conductance measurements from 25 to 400°C and from 100 to 3000 bar with eight NaOH‐mole fractions from 0.024 to 0.93 and with the pure NaOH‐melt. At 400°C and 2000 bar the specific conductance rises slightly from 2.09 ohm−1cm−1for the pure melt to 2.58 ohm−1at 64.0 mol% NaOH and reaches a maximum of 4.28 ohm−1cm−1at 30 mol%. Density measurements permitted the determination of molar NaOH conductivity isotherms at nearly constant molar concentration of 50 mol · dm−3. At 350°C and 400°C the isotherms ascend continuously from molten hydroxide to dilute aqueous solutions. A function is presented which describes the conductance over the whole composition range with a quadratic combination of the two limiting conductances, with a Debye‐Hückel addition and with two realistic adjustable parameters for viscosity and interionic approach.
Ligand‐Substitution Reaction of Cobalt(III) Complexes of [CoCl(N)5]2+‐type with Carbonate: Activation of Kinetic Processes by Steric Chelate Effect
Authors: Masuda Chié , Jitsukawa Koichiro , Masuda Hideki , Einaga Hisahiko 
Published: March 2014

AbstractKinetics and mechanisms of coordination by ligand‐substitution of HCO3− for Cl− on the cobalt(III) complexes of [CoCl(N)5]2+‐type having different (N)5 backbone chelate ring structures to form those of [Co(CO3)(N)5]+‐type have been investigated in a weakly alkaline aqueous 0.10 mol dm−3 sodium perchlorate solution at ambient temperatures, in order to elucidate any possibility for the fixation of atmospheric CO2 on the coordination sphere of the transition metal center in the form of CO2−3. The HCO3− in the aqueous solution easily and substitutionally coordinates to the cobalt(III) complexes in place of coordinated chloro ligand via two consecutive rate‐determining steps, the faster one with two parallel pathways of aquation and hydroxide‐anation and the slower one with a pathway of carbonate‐anation. Of these reaction pathways, the hydroxide‐anation was explained by a dissociative interchange mechanism via conjugate base (IdCB), whereas the carbonate‐anation was explained by a nucleophilic attack of coordinated oxygen atom on the central cobalt(III) atom to the carbon atom of HCO3− while maintaining the Co – O bond throughout the step by taking the result of an EHMO calculation into consideration. The (N)5 backbone chelate ring structure served to enhance the rate of coordination of HCO3− on the cobalt(III) center as well as that of preceding aquation and hydroxide‐anation steps chiefly by its entropy effect. The pentadentate tetren backbone structure was recommended for the rapid fixation of CO2 in the form of CO2−3 on the cobalt(III) complexes of [CoCl(N)5]2+‐type.
Excess Enthalpy HE of Binary Mixtures Containing Alkanes, Ethanol and Ethyl‐Tert. Butyl Ether (ETBE)
Authors: Mier W. , Oswald G. , Tusel‐Langer E. , Lichtenthaler R.N. 
Published: March 2014

AbstractThe excess enthalpies of all possible binary mixtures of n‐heptane, isooctane (2,2,4‐trimethylpentane), ETBE (ethyl‐tert. butyl ether) and ethanol have been measured at 298.15 K and 313.15 K and atmospheric pressure using a quasi‐isothermal flow calorimeter. The experimental excess enthalpies HE and published excess heat capacities CEP and excess volumes VE are used to test the applicability of the ERAS (Extended Real Associated Solution)‐model.
Influence of Charge Density and Concentration on the Dynamics of Aqueous Polyelectrolyte Solutions
Authors: Walkenhorst R. , Dorfmüller Th. , Eimer W. 
Published: March 2014

AbstractWe have investigated the dynamics of protonated poly(2‐vinylpyridine) (Mw = 135000) in aqueous solution by dynamic light scattering over a wide concentration range (0.5 ≤ cpe ≤ 100 g/l). The charge density on the polymer chain (degree of protonation α) was varied from 0.26 to 0.62 by hydrochloric acid. The reduced composition variable Λ = αcmpe/ with cmpe and cs the molar concentrations of the polymer repeat unit and salt, respectively, was constant for a given charge density.We always observed two well separated relaxation processes (a fast and a slow mode). At low charge density the diffusion coefficient of the fast mode reveals an increase‐maximum‐decrease pattern with concentration while the diffusion coefficient of the slow mode decreases with increasing concentration. The relaxation times of both modes as well as the ratio of their amplitudes were found to depend strongly on the degree of protonation of the polymer chains. Temperature‐dependent measurements at low polymer concentration (cpe = 2g/l) exhibit that both modes follow the Stokes‐Einstein prediction, except that we observed a significant non‐zero intercept for the fast mode. A possible influence of hydrophobic effects on the dynamics of protonated poly(2‐vinylpyridine) in aqueous solution is discussed.
HF Vapor
Authors: Suhm Martin A. 
Published: March 2014

AbstractIR absorption spectroscopy of HF clusters in synchronized pulsed supersonic jet expansions and at thermal equilibrium is combined with a 1 +2 + 3 body decomposition scheme of the potential energy surfaces, different quantum chemical approaches and multidimensional vibrational quantum Monte Carlo calculations to characterize all major constituents (HF)n (n = 1–8) of the strongly associated HF vapor phase in terms of their structure, spectra, energetics, dynamics and abundance. From this data base, a microscopic quantum statistical model of HF vapor up to moderate pressures is constructed. Comparison to existing bulk thermodynamic data confirms that the model provides a globally correct and detailed microscopic description of this unique association phenomenon together with its explanation.
Fundamentals of Sorption Kinetics of Gas Mixtures in Porous Media under High Pressure Conditions
Authors: Micke André , Bülow Martin 
Published: March 2014

AbstractBased on the Volterra integral technique, a universal method to calculate the sorption uptake curves of multi‐component gas mixtures in porous solids under variable high pressure conditions with non‐ideal behavior of the gas phase has been proposed. It takes into account a non‐linearly behaving concentration dependence at the surface of the porous medium. The applicability of the introduced method presupposes an isothermic gas phase and a constant diffusivity matrix. For the description of the non‐ideal gas phase behavior, equations of state were utilized.
UV Absorption Cross Sections of Acetyl Peroxynitrate and Trifluoroacetyl Peroxynitrate at 298 K
Authors: Libuda H.G. , Zabel F. 
Published: March 2014

AbstractThe UV absorption cross sections of acetyl peroxynitrate (PAN) and trifluoroacetyl peroxynitrate (FPAN) were determined at 298 K in the wavelength ranges 220–325 nm and 230–305 nm, respectively. Both peroxynitrates were prepared from nitric acid and the corresponding peroxy acids in n‐tridecane solution. The UV spectra were measured in a large cell (v = 420 dm3) equipped with White mirror systems for the simultaneous detection of gas phase species by long‐path UV and IR absorption. Impurities in the samples were quantified by their IR and/or UV absorption, and the UV spectra were corrected for contributions from these impurities using appropriate reference spectra. Concentrations of acetyl peroxynitrate and trifluoroacetyl peroxynitrate were derived from their IR absorptions by application of Beer's law. IR absorption coefficients were determined based on pressure measurements of the pure compound (for PAN) or on the stoichiometric CO2 yield in the thermal decomposition of the peroxynitrate in the presence of NO and O2 (for FPAN). The resulting UV absorption cross sections of PAN are larger than literature values, leading to photolysis rate constants on the Earth's surface which are higher by a factor of 4 than previous values (Senum et al., 1984). The absorption cross sections of FPAN were measured for the first time and result in photolysis rate constants which are slightly higher than those of PAN, suggesting that CF3C(O)O2NO2 and, by analogy, other haloacetyl peroxynitrates have too short a lifetime in the upper troposphere to be of importance for the transport of halogens into the stratosphere.
Proton NMR Studies on the Structure of Water at Interfaces of Aqueous Micelles. Part 4: Effects of Cationic and Zwitterionic Headgroups
Authors: El Seoud Omar A. , Blaskó Andrei , Bunton Clifford A. 
Published: March 2014

AbstractFractionation factors, φM, of interfacial water at surfaces of cationic and zwitterionic surfactants were determined from the dependence of the 1H chemical shift of water on the isotopic composition of the solvent (H2O plus D2O). Values of φM are greater than unity, showing that interfacial water is more structured than bulk water, whose fractionation factor = 1, by definition. The structuring increases with increasing bulk of the headgroup, but is unaffected by the length of the cationic surfactant hydrophobic tail. The effect of zwitterionic sulfobetaine surfactants on the structure of their water of hydration is less than that of cationic surfactants that have otherwise similar headgroups. Values of φM for cationic micelles are: cetyldimethylphenylammonium chloride, 1.08; cetylpyridinium chloride, 1.06; and dodecyltrimethylammonium bromide, 1.06. Values of φM for sulfobetaine micelles are: 3‐N‐tetradecyl‐N,N‐di‐n‐butylammonio‐1‐propane sulfonate, 1.07, and 3‐N‐tetradecyl‐N,N‐diethylammonio‐1‐propane sulfonate, 1.03.
Anorganische und organische “Modell”‐Oberflächen für chemische Sensoren
Authors: Schierbaum Klaus‐Dieter 
Published: March 2014

AbstractA brief introduction is given on charge transfer reactions and inclusion reactions for oxide‐based and supramolecular compound‐based chemical sensors, respectively. TiO2 serves as inorganic “model” d0 oxide in the present study. By employing different surface spectroscopies and scanning tunneling microscopy, the formation and the role of intrinsic defects and Pt dopants at the thermodynamic most stable (110) surface is characterized with implications for the design of Schottky diode sensors and heterogeneous catalysts.Organic supramolecular compounds like calix[4]arene and resorcin[4]arendialkylsulfide form molecular recognition structures at surfaces which act as specific interaction sites for small organic molecules. Adsorption/desorption properties have been studied using quartz microbalance oscillators, thermal desorption spectroscopy and theoretical force field calculations.
Structural Aspects of Tetramethylthiourea Adsorption on Au(111) Electrodes Investigated by In Situ Scanning Tunnelling Microscopy
Authors: Bunge E. , Nichols R.J. , Baumgärtel H. , Meyer H. 
Published: March 2014

AbstractWe have examined tetramethylthiourea (TMTU) adsorption on Au(111) with capacitance measurements and in situ scanning tunnelling microscopy (STM). Capacitance measurements of the TMTU‐containing solution indicate that the organic molecule is adsorbed over a wide potential range. High resolution STM images at +20 mV are totally different to those in the absence of TMTU and point to an ordered structure of the organic adsorbate. Three distinctive bright spots are seen in the STM images. A model has been developed with the molecules lying near to horizontal on the surface, forming a (3×3) adlayer.
Dynamik der Wechselwirkung von Molekülen mit Oberflächen
Authors: Ertl Gerhard 
Published: March 2014

AbstractA multitude of methods from surface physics in combination with molecular beam and laser spectroscopic techniques provides detailed insight into the various aspects of the dynamics of interactions between molecules and surfaces, reaching from macroscopic kinetics over phenomena of spatiotemporal self‐organisation to the microscopic elementary process. The present state of our knowledge is illustrated by means of selected examples, concerning mainly single crystal surfaces of metals.
Multi‐Nuclear Solid‐State NMR Study of the Local Structure of SiOHAl Groups and their Interaction with Probe‐Molecules in Dehydrated Faujasite, Mordenite and Zeolite ZSM‐5
Authors: Hunger M. , Horvath T. 
Published: March 2014

AbstractStructural variations of Si–O–Al bridges in dehydrated zeolites have been studied by 29Si CP/MAS NMR and 27Al NMR spectroscopy. After deammoniation of zeolites Y (nSi/nAl = 2.6 and 8.0), mordenite (nSi/nAl = 8.0) and ZSM‐5 (nSi/nAl = 22.0) 29Si NMR high‐field shifts of Si(1 Al) signals of maximum 0.8 ppm and of about 2.7 ppm and 4.0 ppm, respectively, were observed. This is explained by a protonation‐induced increase in the mean Si–O–T bond angles of SiOHAl groups. Simultaneously, an increase in the aluminium quadrupole coupling constant from about 5.0 MHz to about 16.0 MHz was determined indicating a strong protonation‐induced shear strain of framework AlO4 tetrahedra. On the other hand, the proton transfer from Si–O–Al bridges to basic probe‐molecules causes a decrease in the aluminium quadrupole coupling constant which corresponds to a higher AlO4 symmetry. The high symmetry of AlO4 tetrahedra in zeolite HZSM‐5 loaded with one methanol molecule per SiOHAl group, the mobility of the hydroxyl protons existing in this sample and their chemical shift value observed at the temperature of T = 295 K by 27Al, 2H and 1H NMR, respectively, indicate a rapid exchange of hydroxyl protons between bridging OH groups, hydrogen‐bonded methanol molecules and methoxonium ions. At the temperature of T = 85 K methanol molecules are fixed at the zeolite framework by hydrogen bonds.
Structure and Reactivity of Small Metallic and Bimetallic Clusters Hosted in Molecular Sieves
Authors: Shpiro Efim S. , Jaeger Nils I. , Schulz‐Ekloff Günter 
Published: March 2014

AbstractThe relationship between the electronic structure of small metallic (Pt, Ir, Rh) and alloyed (Pt‐Cr, Pt‐Cu) particles and their chemical reactivity has been established using zeolite matrix and a set of physical techniques, such as XPS, XAES, HRTEM, electron microdiffraction, FTIR of CO and catalytic model reactions.