bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physikalische Chemie — Schnittstelle zwischen Naturwissenschaft und Technik
Authors: Felcht Utz‐Hellmuth 
Published: July 2012

AbstractPhysical chemistry appears on the surface to be an abstract science having only little direct relation to the chemical industry. On closer examination, however, it is very soon apparent that the laws developed within the field of physical chemistry to describe mass systems and mass transformation, as well as energy transfer and energy conversion, are of fundamental importance particularly to industrial chemistry. The application of these laws permits the theoretical treatment and elaboration of chemical processes and thus forms the basis for the realization of these processes on an industrial scale. Thermodynamic and kinetic studies of the chemical reaction are naturally of central importance, but the description of basic operations and measuring systems for process control and safety engineering, too, is only made possible by the application of physico‐chemical laws. This basic role of physical chemistry is described by means of examples from widely differing fields of the chemical industry.
Theoretische Chemie: Hilfe bei der Modellbildung oder Alternative zu Experimenten
Authors: Peyerimhoff Sigrid D. 
Published: July 2012

AbstractA short historical introduction shows a few stations important for the field of theoretical chemistry whose appearance occurred 100 years ago under the term of mathematical physics or mathematical chemistry primarily in the area of physical chemistry. Present possibilities of the field are discussed in a number of examples: today quantumchemical calculations, computer simulations and modelling are a convenient and universally applicable instrument in many areas of chemistry for the interpretation of mechanisms as well as for quantitative prediction.
Reaktionen an Festkörper‐Oberflächen
Authors: Ertl G. 
Published: July 2012

AbstractChemical processes at solid surfaces form the basis for heterogeneous catalysis whose scientific investigation and industrial application were initiated at the beginning of this century. Despite early formulation of significant concepts, studies of the elementary steps on atomic scale started only during the past few decades in parallel to the development of powerful experimental tools. The present status will be illustrated by means of selected examples.
Stability constants of silver(I) complexes with diaza‐18‐crown ethers in polar solvents
Authors: Burchard T. , Cox B. G. , Firman P. , Schneider H. 
Published: July 2012

AbstractThe stability constants of Ag+ complexes with macrocyclic diaza‐crown ethers of constant ring size [18], but with different donor atom distributions in the ligand bridges, are strongly dependent upon solvent. The effect of solvent, however, is essentially independent of the ligand involved, and this extends even to bicyclic cryptand ligands. Thus, the stability constants of any one ligand are linearly related to those of the other ligands across a wide range of polar solvents. A more detailed analysis of the results in terms of the free energies of solvation and transfer of the species involved in the complexation reaction shows that, although the dominant influence is normally the solvation of Ag+, specific solvation of either the complexed cation or the free ligand can influence complex stabilities in some cases. Effects due to the former, although relatively weak, are evident in complexes of monocyclic diaza‐ligands in strongly coordinating solvents, such as dimethylformamide and dimethyl sulfoxide, and the latter is quite marked in solvents possessing acidic hydrogen atoms, such as water, methanol, and nitromethane.
Determination of candidate structures for Lennard‐Jones‐crystals through cell optimisation
Authors: Schön J. C. , Jansen M. 
Published: July 2012

AbstractWe show at the example of noble gases, using the Lennard‐Jones potential to approximate the interactions between the atoms, that the global minimisation of the energy through variation of both the basis vectors of the simulation cell and the relative positions of the atoms within the cell leads to structures that are good candidates for the actual structure of the material. During this optimisation, no restrictions were imposed on size, shape, or symmetry of the simulation cell.
Nuclear magnetic resonance of 69Ga in CdGa2Se4 and other defect chalcopyrites
Authors: Breuer A. , Siebert D. 
Published: July 2012

AbstractBy pulse FT‐NMR we investigated the resonance of the 69Ga isotope with nuclear spin I = 3/2 in single crystals of CdGa2S4, CdGa2Se4, HgGa2S4, and powders of CdGa2S4, CdGa2Se4, ZnGa2S4, ZnGa2Se4, HgGa2S4, and HgGa2Se4. Only the signal of the transition mI= ‐ 1/2 to mI= + 1/2 was analyzed by its second order shift. In case of crystals we used angular variation to obtain the electric field gradients (EFG). For CdGa2Se4 a small difference of the chemical shifts of about 70 ppm was revealed due to the different Ga positions. A characteristic twinning of many crystals was confirmed. Line broadening was different for annealed and quenched crystals and depended very strongly on the orientation of the crystals. This could be assigned to a partially disordered cation sublattice.
Hamilton‐Jacobi dynamics for the solution of time dependent quantum problems II. Wave packet propagation in two dimensional, nonlinearly coupled oscillators – exact and time‐dependent SCF‐solutions–
Authors: Gunkel Thomas , Bär Hans‐Jürgen , Engel Michael , Yurtsever Ersin , Brickmann Jürgen 
Published: July 2012

AbstractMethods for the approximate numerical integration of the time dependent Schrödinger equation with given initial conditions (the initial wave packet) are presented. The methods are based on the Schrödinger representation of the quantum dynamic system. The quantum dynamic equations are transformed into Hamilton‐Jacobi type equations of motion as they occur in multi particle classical dynamics, i.e. standard techniques in molecular dynamics can be applied for the integration. The dynamics of minimum uncertainty Gaussian wave packets in strongly non‐harmonic, nonlinearly coupled oscillators are studied as examples. The numerically exact solutions are compared to time dependent SCF approximations of the wave packet.
PVTx‐Properties and virial coefficients of the water‐n‐hexane system
Authors: Abdulagatov I. M. , Bazaev A. R. , Ramazanova A. E. 
Published: July 2012

AbstractPVTx‐data for the water‐n‐hexane system are reported in this paper. The data cover a temperature range from 523 to 623 K and pressure range from 2 to 16 MPa at different concentrations. The low pressure compressibility measurements were used to determine second and third virial coefficients for the water‐n‐hexane system. The values of the parameters in the square well potential are derived from virial coefficients data for pure components and binary mixtures water‐n‐hexane.
Determination of the product branching ratio in the reaction of NO3 with OCl at 300 K
Authors: Kukui A. , Jungkamp T. P. W. , Schindler R. N. 
Published: July 2012

AbstractThe relative importance of the product channels for OCl + NO3→ClOO + NO2 (1 a) and OClO + NO2 (1 b) have been reinvestigated at 300 K using discharge flow mass‐spectrometric technique. The ratio k1b/k1 = 0.32±0.1 has been obtained observing the build‐up of calibrated OClO signals as well as from pseudo‐first‐order decays of NO3 and OCl in excess of OCl and NO3, respectively.
Stability of Diffusion Profiles in quasi‐binary Solid Solutions (Ag, Na)Cl
Authors: Schimschal‐Thölke S. , Schmalzried H. , Martin M. 
Published: July 2012

AbstractIn binary or quasi‐binary systems the superposition of chemical diffusion and field‐driven migration may lead to unstable diffusion fronts. This means that an initially one‐dimensional transport geometry may become three (two)‐dimensional. This concept is tested with the solid solution AgCl‐NaCl above T=200°C, which is above the critical point of the miscibility gap. Morphological instabilities of the concentration profile in the inter‐diffusion zone are found if an external electric field is applied. This field must exceed a critical value and the AgCl‐side must be anodic in order to induce an instability of the diffusion front. Numerical solutions of the transport equations and the given boundary conditions corroborate the experimental results.
High Pressure Combustion – Ignition Temperatures to 1000 bar
Authors: Steinle J. U. , Franck E. U. 
Published: July 2012

AbstractIgnition temperatures of gaseous mixtures of methane with oxygen or air at initial pressures between 50 and 1000 bar have been measured. Two cylindrical reaction vessels of 4 and 10 cm3 and one spherical vessel with 21 cm3 volume were applied which withstand dynamic pressures up to 6000 bar at 900 K (600°C). Most experiments used the “heat‐up” method with a high pressure gas mixture heated up inside and together with the reaction vessel until spontaneous rapid reaction began. Additional experiments were made with preheated empty vessels and with forced ignition by hot wires. Spontaneous ignition temperatures for stoichiometric methane‐air mixtures are around 870 K (600°C) at atmospheric pressure and decrease to 660 K (390°C) at 1100 bar ignition pressure. Semenov plots give straight lines for various reaction conditions. Effective activation energies could be derived. With the assumption of a global reaction order of 2, the activation energy for stoichiometric methane‐air is 359±4 kJ/mole, for stoichiometric methane‐oxygen it is 253±10 kJ/mol. Considering earlier experiments with “hydrothermal” supercritical flames, ignition with added high pressure steam were made.
Investigation of the Reaction of 3CH2 with NO at high Temperatures
Authors: Bauerle S. , Klatt M. , Gg. Wagner H. 
Published: July 2012

AbstractThe reaction 3CH2 + NO was studied behind incident shock waves over the temperature range 1100–2600 K by following the H and O atom formation with Atomic Resonance Absorption Spectroscopy (ARAS) and the OH radical formation with Laser Absorption. In the temperature range from 1100 to 2500 K the rate constant of the H atom formation formally attributed to a reaction channel giving HCNO+H (1 h) obtained on the basis of the experiments reported here isk1h = 10(12.4 ± 0.2).exp (‐(25 ± 2) kJ mol−1/RT) cm3 mol−1 s−1.The rate constant of the channel leading to HCN + OH (1d) was determined to bek1d = 10(11.7 ± 0.3).exp (‐(12 ± 2) kJ mol−1/RT) cm3 mol−1 s−1.The evaluation of the experimental profiles by means of computer simulation leads to an overall rate constant of about k1 = (1 ± 0.5)·1012cm3mol−1 s−1 without any noticeable temperature dependence within the error limits in the temperature range from 1200 to 2600 K. The contribution of a reaction channel leading directly or indirectly to O (or N) atoms was found to be less than 15% of the overall reaction at temperatures below 2000 K.
A Kinetic Study About the Reactions of NH(X3Σ−) with Hydrocarbons Part 3: Benzene, 1,3‐Butadiene and Acetylene
Authors: Röhrig M. , Römming H.‐J. , Gg. Wagner H. 
Published: July 2012

AbstractThe reactions of NH in its electronic ground state with benzene (1), 1,3‐butadiene (2) and acetylene (3) were investigated behind incident shock waves using narrow line width absorption detection of NH(X3Σ). The experiments were performed with very low initial concentrations of HN3 which was used as NH(X3Σ−) source to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reactions of NH (X3Σ−) with these hydrocarbons directly. The following rate constants were obtained in the temperature range 1100 to 1500 K, resp. 1400 to 1700 K (acetylene):k1 = 10(14.2±0.3) exp (‐(76±8) kJ mol−1/RT) cm3/mol sk2 = 10(13.9±0.3) exp (‐(45±7) kJ mol−1/RT) cm3/mol sk3 = 10(14.7±0.3) exp (‐(59±9) kJ mol−1/RT) cm3/mol s
Kinetics of Photoinduced Electron Transfer Reactions of Some Anthraquinone Radical Anions with Various Inorganic Ions: Comparison with Marcus Cross‐Relation
Authors: Grampp Günter , Galán Manuel , Sacher Michael 
Published: July 2012

AbstractThe reactions of 2‐, 2,6‐ and 2,7‐anthraquinone (di) sulphonate radical ions with the paramagnetic ions Fe(CN)36, Cu2+, IrCl2‐6 and Fe3+ have been studied at different pH‐values at room temperature, in order to investigate the role of spin states on electron transfer. With 2‐anthraquinone sulphonate the rate constants are in the range 2.6 ‐ 7 × 108 mol−1 dm3 s−1, and for the other two anthraquinone derivatives the rate constants span over two orders of magnitude from 107 to 109 mol−1 dm3 s−1. The experimental rate constants have been compared with the predictions of the Marcus Cross‐Relation, taking also into account the contribution of the diffusion pathway in our calculations.The predicted values are systematically larger than the experimental values. This systematic deviation is justified in the present work as due to the spin‐forbidden character of the reactions studied. The need for suited corrections in the current electron transfer theories has been stressed.
High Pressure Supercritical PVT‐Data of Water‐Sodium Hydroxide Mixtures and of Liquid Sodium Hydroxide to 673 K and 400 MPa
Authors: Kerschbaum S. , Franck E. U. 
Published: July 2012

AbstractThe density of homogeneous fluid mixtures of water and sodium hydroxide has been measured from 293 to 673 K and at pressures from 10 to 400 MPa. Measurements were performed at eight compositions between 10 and 90 weight percent NaOH and with pure molten NaOH. At sufficiently high pressure complete miscibility of NaOH and H2O exists above the melting temperature of NaOH at 595 K. A differential autoclave with internal heating within a space filled with high pressure argon and with an internal nickel bellows cell for the H2O–NaOH mixtures is described. Immediate results are given as specific mixture volumes and molar volumes. Molar volumes in dependence of composition have distinct minima near 30 mole percent NaOH. All excess volumes are negative. A semiempirical equation is proposed on the basis of a hydration model to describe molar and excess volumes. Partial molar volumes and estimated activity coefficients are given for 673 K and pressures at 100 and 400 MPa.
Dynamic Light Scattering Experiments with Aqueous Solutions of Polyelectrolytes with Hydrophobic Side Chains in the Presence of Salt
Authors: Gröhn F. , Topp A. , Belkoura L. , Woermann D. 
Published: July 2012

AbstractDynamic light scattering experiments are carried out with aqueous solutions of poly(4‐vinylpyridine) completely quarternized with dodecyl bromide and ethyl bromide in varying ratios in the presence of salt (KBr; αd + αe = 1; 0.010 ≤ αd ≤ 0.192; αd is the degree of quarternization by dodecyl bromide and αe that with ethyl bromide). Apparent diffusion coefficients Dapp (αd,c̄p) are calculated from the data (c̄p is the polymer concentration expressed in g dm−3). They are plotted as function of the reduced concentration variable λ = (cp*/cs) as well as of the degree of quarternization by dodecyl bromide αd at constant values of λ (cp* is the molar volume concentration of the repeating unit forming the polymer backbone; cs is the molar volume concentration of the added salt). The resulting curves indicate a characteristic change of the diffusive properties of the systems: For λ<< 1 one apparent diffusion coefficient is observed whereas for λ>> 1 a fast and a slow diffusive mode are detected. At a constant value of λ (λ ≈︁ 2.0) the appearance of a slow diffusive mode is induced by decreasing systematically αd (αd ≤ 0.192; αd + αe ≈︁ 1). It is predicted that the location of the “transition” on the λ‐axis is a function of αd.
In‐situ Optical Investigation of Oxygen Diffusion Profiles in SrTi03
Authors: Denk I. , Traub U. , Noll F. , Maier J. 
Published: July 2012

AbstractThe time evolution of oxygen stoichiometry profiles in Fe‐doped SrTi03 single crystals has been detected and analyzed in‐situ using an optical absorption technique. The profiles can be fitted according to Fick's second law by a constant chemical diffusion coefficient. The data obtained are in good agreement with earlier results from integral detection techniques and can be quantitatively understood by including the influence of internal coupling reactions to bare ambipolar transport via short range interaction.
Thermodynamic Properties for Solution of Hydrogen in Palladium‐Based Binary Alloys
Authors: Sakamoto Y. , Chen F. L. , Ura M. , Flanagan T. B. 
Published: July 2012

AbstractThe thermodynamic parameters for solution of hydrogen at infinite dilution and the (a+B) plateau thermodynamic properties for hydrogen absorption at moderate temperatures for a series of Pd‐based f.c.c binary alloys with relatively low solute metal content have been correlated from the viewpoint of whether the alloy lattice is expanded or contracted to parent Pd lattice. Newly determined data for Pd‐Zn, Pd‐Sb, Pd‐Bi, Pd‐Cr, Pd‐Mo and Pd‐Mn alloys are included. When alloys with solute metals in the same groups are compared, the lattice parameters of Pd binary alloys with the 4 d and 5 d transition elements are, in general, larger than those with the 3 d elements. The relative partial molar enthalpy, ΔH0H, at infinite dilution becomes more exothermic with an increase of lattice parameter for the lattice‐expanded alloys with the exception of Pd‐Pt alloys. Conversely, for contracted alloys, with the exceptions of Pd‐Li, Pd‐Zn, Pd‐Al and low Ti content Pd‐Ti alloys, the enthalpy becomes less exothermic with increasing lattice contraction. The dilute phase solubility at the same temperature as reflected by the relative chemical potential of dissolved hydrogen at infinite dilution, Δμ0H, increases with increasing lattice expansion for the expanded alloys, with the exceptions of Pd‐Pt and Pd‐Nb (Ta), whereas for the contracted alloys, the solubility decreases with increasing lattice contraction, with the exception of the Pd‐Li alloys. The standard free energy change, ΔG0plat'for B‐hydride formation in the expanded alloys decreases with increase of lattice expansion with the exceptions of the Pd‐Pt, Pd‐Zr, Pd‐Sb, Pd‐Nb(Ta) and Pd‐Mn alloys. For the contracted alloys, the B‐hydride becomes less stable with increasing lattice contraction except for the Pd‐Li alloys. The isobaric hydrogen solubilities in Pd alloys at relatively high pressures may be attributed to the influence of the solute metal atoms on the Pd band structure and to the exclusion of H from site occupation due to solute atoms in the nearest neighbor shells; both of these effects are independent of the lattice expansion and contraction.
A Capacitance and Infrared Study of the Electrical Double Layer Structure at Single Crystal Gold Electrodes in Acetonitrile
Authors: Panzram E. , Baumgärtel H. , Roelfs B. , Schröter C , Solomun T. 
Published: July 2012

AbstractThe electrical double layer at Au(100) and Au(111) electrodes in acetonitrile containing tetraethylammoniumper‐chlorate (TEAP) was studied by means of differential capacitance and in‐situ FTIR spectroscopy measurements. For both surfaces, a preponderant capacitance maximum was observed at a positive charge of about 8 μC cm−2. Two types of acetonitrile molecules were identified in the interfacial infrared spectra. One of these concerns adsorbed acetonitrile with a strongly blue shifted vCN mode at 2337 cm−1. The potential dependence of the spectra provides a clear evidence for dielectric saturation of the solvent and specific adsorption of the ions at large electrode charges. The spectra also indicate that the maximum ability of the solvent to reorientate in the interfacial field is in an adsorption geometry with the molecular axis inclined with respect to the surface. The data are discussed in context of the current models of the double layer, and compared with the related literature data obtained in an aqueous electrolyte.
A Kinetic Study About the Reactions of NH2(X̄2B1) Radicals with Saturated Hydrocarbons in the Gas Phase
Authors: Hennig G. , Wagner H. G. G. 
Published: July 2012

AbstractThe reactions of NH2(X̄2B1) with the hydrocarbons methane (1), ethane (2) and propane (3) were investigated behind incident shock waves at temperatures between 1500 K and 2100 K. The decay of NH2 was measured by laser absorption. NH2 was formed by the thermal decomposition of hydrazine. The following rate constants were obtained for the temperature range mentioned:k1 = (1.2±0.6)·1013 exp(‐(63.4±3.4) kJ/mol/RT) cm3 mol−1 s−1k2 = (9.7±0.3)·1012 exp(‐(48.0±1.8) kJ/mol/RT) cm3 mol−1 s−1k3 = (1.7±0.4)·1013 exp(‐(44.6±2.0) kJ/mol/RT) cm3 mol−1 s−1.These measurements extend the results obtained at low temperatures by Demissy and Lesclaux (330 K–250 K) and by Hack et al. (400 K–1080 K) into the range of interest for combustion processes.The apparent energies of activation fit rather well into an Evans Polanyi plot. They correlate with the energies of activation of the corresponding reactions of OH(X2II)and those of CH3(X2A2) radicals.
Viscosity of N‐Pentane, N‐Heptane and Their Mixtures within the Temperature Range from 298 K up to Critical Points at the Saturation Vapor Pressure
Authors: Abdulagatov I. M. , Rasulov S. M. 
Published: July 2012

AbstractThe viscosity of n‐pentane, n‐heptane and their mixtures has been measured with a capillary flow method between 298 K and the critical temperatures at the saturation vapor pressure. The concentrations studied were 0.259, 0.419 and 0.745 mole fraction of n‐heptane. The maximal error of the experimental values of the viscosity is estimated to be ± 1.2% in the region far from the critical point and ± 5% in the immediate vicinity of the critical point. The viscosity obtained was compared to data by other authors with satisfactory agreement. The validity of the method has been confirmed by the measurement of the viscosity of standard liquids as water and toluene.
Surfactant Properties of Semifluorinated Alkanes in Hydrocarbon and Fluorocarbon Solvents
Authors: Binks B. P. , Fletcher P. D. I. , Thompson R. L. 
Published: July 2012

AbstractThe phase behaviour and aggregation of the semifluorinated alkane F‐(CF2)8‐(CH2)16‐H (abbreviated to F8H16) in hydrocarbon and perfluorinated solvents has been investigated. The variation of solubility with temperature for F8H16 in perfluorinated solvents shows highly non‐ideal behaviour and exhibits a sharp increase at a temperature a few degrees below the melting point of F8H16. The behaviour is similar to that in the region of the Krafft point of a conventional surfactant in water. With iso‐octane as solvent, the solubility shows only slight deviations from ideal behaviour. Vapour pressure osmometry (VPO) results confirm the near ideal behaviour of F8H16 in iso‐octane. For F8H16 in perfluorodecalin at 38 °C, VPO results show that aggregates are formed at concentrations above approximately 0.02 mole fraction. The aggregation number is 6 and is virtually independent of the SFA concentration. The results are discussed in terms of the antipathy between hydrocarbons and fluorocarbons as reflected in the values of the upper critical solution temperatures (UCST) of binary mixtures of hydrocarbons with perfluorinated solvents.
Thermodynamics of Aggregation in Droplet‐phase Water/AOT/Oil Microemulsions
Authors: Koper G. J. M. , Sager W. F. C. , Smeets J. , Bedeaux D. 
Published: July 2012

AbstractWe discuss the results of three experiments, namely dielectric permittivity, low shear viscosity, and electro‐optic birefringence measurements, that were designed to obtain quantitative information on the aggregation in droplet phase microemulsions. The data consistently yield a rather large binding free energy of −4 k T between two aggregated microemulsion droplets and we discuss possible explanations for this large value.