bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of Thermal Unimolecular Reactions in the Fall‐off Range. I. Strong Collision Rate Constants
Authors: Troe J. 
Published: July 2012

Abstract(k0/k∞)‐reduced strong collision fall‐off curves of thermal unimolecular reactions are analyzed. They are represented by the Lindemann‐Hinshelwood expression multiplied by strong collision broadening factors FSC. The factors FSC are approximated by fully empirical representations of RRKM theory. Compact expressions suitable for modeling are proposed. Their quality is demonstrated by comparison with exact RRKM calculations for 20 molecular systems.
Theory of Thermal Unimolecular Reactions in the Fall‐off Range. II. Weak Collision Rate Constants
Authors: Gilbert R. G. , Luther K. , Troe J. 
Published: July 2012

AbstractThe master equation of thermal unimolecular reactions in the fall‐off range has been solved for a number of representative molecular systems. Weak collision broadening factors FWC(k0/k∞) are derived and represented empirically. Weak collision efficiencies βc for the low pressure range are calculated for very high temperatures. Combined with earlier representations (part I) of strong collision broadening factors FSC(k0/k∞), compact empirical expressions for the rate coefficient in the full fall‐off range are proposed. These expressions are useful for data representation and modeling of complex reaction systems which involve isomerization, dissociation and recombination reactions.
Computer Coupling of Phase Diagrams and Thermodynamics
Authors: Pelton A. D. 
Published: July 2012

AbstractIn recent years there has been much progress in the coupling of thermodynamics and phase diagrams. The development of solution models, of analytical and numerical techniques, and of computer software has now advanced sufficiently that it is possible to express the Gibbs energies of a wide variety of phases as functions of the state variables and to calculate multicomponent phase diagrams therefrom with good precision for many systems. This approach presents several advantages. Thermodynamic data and phase diagram measurements for a system can be critically assessed simultaneously. Once a set of thermodynamic functions has been compiled for a system, these can be extrapolated to calculate phase diagrams outside the ranges of T, P, composition, partial pressures, etc. of the measurements, or to compute metastable phase boundaries. N‐component phase diagrams can be estimated from the properties of their (N – 1)‐component sub‐systems. Solution models can be tested or, conversely, used to predict or extrapolate phase diagrams.
Non‐Linear Model of Structures and Phase Transitions of the SiO2 Crystal Family
Authors: Behnke G. , Bilz H. , Büttner H. 
Published: July 2012

AbstractThe polymorphism and the phase transitions of the silica family are explained in terms of a quasi‐one dimensional lattice model. The origin of the different SiO2‐structures is found in two microscopic potentials. The first potential describes the covalent bonding due to the tetrahedral (sp3) silicon coordination and the twofold (pσ) oxygen coordination. The second potential is a local double‐well potential due to the non‐linear polarizability of the non‐bonding (p π) electrons at the oxygen site. This potential is equivalent to a fourth‐order electron‐lattice interaction which may be responsible for the low‐symmetry modifications of the SiO2‐crystals. It turns out that the different crystals with 1,2,3,4 and 6‐fold screw axes correspond to possible commensurate static solutions of the potential. The model also includes incommensurate states which may be interpreted as the vitreous structures of the silica.
On Diffuse Phase Transitions and Hybrid Crystal Formation
Authors: Burggraaf A. J. 
Published: July 2012

AbstractA review and short discussion has been given of a particular type of phase transition called a diffuse phase transition and of microstructures which may give rise to it. Special attention has been paid to microdomains and hybrid crystal formation. Experimental evidence from literature has been reviewed. Results on some ferroelectric and ion conductive materials from the authors laboratory are summarised and discussed into more detail.
Vorstadien der Entmischung in Alkaliboratglasschmelzen
Authors: Würz U. , Chan S. K. , Döpkens J. 
Published: July 2012

AbstractThe coupling of the concentration field to the strain field may lead to the occurrence of stable modulated structures near to the top of the miscibility gap. This has been demonstrated through a Landau type theory and verified experimentally in some alkaliborate glass melts.
Stress‐Induced Transformations in Composite Zirconia Ceramics
Authors: Rühle M. , Kriven W. M. 
Published: July 2012

AbstractA martensitic transformation may be induced in confined tetragonal zirconia particles by the stress field in front of a crack tip, resulting in an increase in toughness. The microstructure, transformation mechanisms, elastic strain distribution, and in‐situ studies of the interaction of the confined particles with the stress field of the crack tip have been studied by means of high voltage transmission electron microscopy techniques. Facetted particles below a critical size dc are retained metastably down to room temperature. — The transformation is predominantly controlled by a nucleation barrier. A model of nucleation by inhomogeneity of internal strains is postulated, in which the total resolved strain must exceed 0.25 of the unconstrained transformation strain over the volume of the nucleus for initiation of the martensitic transformation. The “critical size effect” may then be explained in terms of irregular‐shaped particles inducing an inhomogeneous internal strain field which scales with particle size and has a well‐defined dc. In contrast, regular‐shaped spherical particles have a homogeneous strain field with no well‐defined critical size.
Irradiation‐Driven Phase Transformations in Alloys
Authors: Wollenberger H. 
Published: July 2012

AbstractEnergetic particle irradiation produces supersaturation of vacancies and interstitials. The migrating defects annihilate at internal sinks and surfaces forming fluxes to the annihilation sites. Such defect fluxes may cause atomic redistribution in alloys due to an inverse Kirkendall effect. Local instability of the solid solution and precipitation may result. This mechanism is not confined to defect annihilation at sinks but might operate also for vacancy interstitial recombination. — An entirely different mechanism of phase transformation is induced by the atomic mixing effect occurring within the irradiation produced atomic collision cascades. Long range ordered precipitations can be dissolved that way.
Raman Spectra and Structural Phase Transitions of the Perovskite‐Type Layer Compounds RbAlF4 and NH4AlF4
Authors: Couzi M. , Loyzance P. L. , Mokhlisse R. , Bulou A. , Fourquet J. L. 
Published: July 2012

AbstractThe low frequency (0–600 cm−1) Raman spectra of RbAlF4 and NH4AlF4 single crystals have been studied at different temperatures ranging from 20 K to 600 K, in their various structural modifications. It is concluded that the transition of NH4AlF4 occuring at ∼150 K is purely an order‐disorder transition, governed by the reorientational dynamics of the NH ions. For RbAlF4, the observed phase transitions at 553 and 282 K are both related to displacive mechanisms, as evidenced by the observation of soft‐modes, but also to disordering processes probably connected with the AlF6 octahedra, and which result in a breakdown of the K = 0 selection rules in the tetragonal D and D phases.
Stability Behaviour of Mixed Conducting Solids after Applying Electrical Potential Differences — Measurements with Point Electrodes on Ag2S and Cu2S
Authors: Rickert Hans , Wiemhöfer Hans‐Dieter 
Published: July 2012

AbstractThe decomposition of the mixed conducting low temperature phases of Ag2S and Cu2S by applying electrical potential differences between two metal electrodes has been investigated. The experimental method is based on the use of a chemically inert point electrode. It is demonstrated that the electrical resistance of mixed conducting solids measured at point electrodes is a sensitive quantity for the detection of the deposition of components or other phases with different stoichiometry during the decomposition process. — The results on Cu2S and Ag2S show a large difference in the stability behaviour of the two substances. The deposition of copper on Cu2S occurs at critical voltages which are up to 250 mV higher than expected from thermodynamic data. On the other hand, silver or sulfur respectively are deposited on Ag2S approximately at the expected voltages.
Cooperative Phenomena: A Simple Model for Phase Transitions in Solid Electrolytes
Authors: Bunde A. 
Published: July 2012

AbstractThe influence of cooperative effects on the transitions of ionic crystals to a highly conductive solid electrolyte state is investigated within the framework of a simple model describing one type of ions as a lattice gas in a vibrating cage formed by the other type of ions. The formation of a solid electrolyte is interpreted as an order‐disorder phenomenon among the lattice gas ions. At low temperatures these are localized at certain lattice sites, while at high temperatures they are distributed over numerous interstitial sites. According to the number of equivalent and nonequivalent interstitial sites and, in particular, depending on the mutual interactions among the ions, the following transitions to the solid electrolyte state may occur: (I) gradual transitions, (II) one transition of first order, and (III) two successive transitions of first order. In addition, due to the coupling between the mobile ions and the vibration of the cage ions, the order‐disorder phase transition may be connected with a change of the equilibrium sites of the cage ions, the corresponding phonon branch becoming soft under certain conditions. Altogether, the experimental situation is in principle correctly described by the present model.
Orientierungsfehlordnung komplexer Kationen und Anionen in Hochtemperaturphasen von Ionenverbindungen ‐ Ergebnisse dreidimensionaler Elektronendichteberechnungen aufgrund von Röntgendaten
Authors: Berthold H. J. , Bäthge H.‐G. , Hölscher Brigitte G. , Kienert H.‐J. , Ludwig W. , Molepo J. M. , Wartchow R. 
Published: July 2012

AbstractThe crystal structures of the orientationally disordered cubic high‐temperature phases of NaClO4, RbClO4, CsClO4, AgClO4, and Co(C5H5)2ClO4 have been investigated using single crystal X‐ray diffraction data. In the case of NaClO4 and AgClO4 the ClO4‐tetrahedra occupy 6 orientations, characterized by the fact that in each orientation only one of the three 4‐axes of the tetrahedra lies parallel to the cubic crystal axes. In RbClO4 and CsClO4 the orientational disorder comprises 2 orientations of the ClO4‐tetrahedra. In both of them all three 4‐axes simultaneously point into the directions of the cubic crystal axes. The space group in all cases is Fm3m, Z = 4. Co(C5H5)2ClO4 transforms at 376 K from the tetragonal room‐temperature structure (space group 14/mcm, Z = 16) into a primitive cubic structure (space group Pm3m, Z = 1), in which the sandwich‐like Co(C5H5)‐cations and the ClO‐anions are orientationally disordered. The electron density distribution around the Co‐atom proves that the cations occupy statistically three different orientations with the fivefold axis parallel to the x‐, y‐ or z‐direction. The electron density distribution around the chlorine atom reveals 6 maxima forming an octahedron and can be interpreted, if one assumes orientations of the ClO4‐tetrahedra with one of their threefold axes lying parallel or approximately parallel to the cubic crystal axes. The three oxygen atoms, which are not situated on the threefold axis, are rotationally disordered and hence in the electron density map not resolved. In NOCIO4 at 150 K the NO+‐cations have orientations perpendicular to the mirror planes of the space group Pnma. However, a disorder with respect to the direction of the NO+‐cations (NO or ON) is probable. At 298 K the cations are orientationally disordered. While approximately 60% of the NO+‐cations still have orientations perpendicular to the mirror planes, about 40% have orientations with both nitrogen and oxygen lying in the mirror planes.
Molecular Motion, Defect Structures and Phase Transitions in Oligomer Crystals
Authors: Strobl G. R. , Schwickert H. , Trzebiatowski T. 
Published: July 2012

AbstractDefect structures in the high temperature modifications of oligomer crystals can generally be discribed as a superposition of chain rotations, longitudinal shifts of the molecules and the occurrence of conformational defects. Applying a suitable combination of experimental techniques it is possible to discriminate between the different components of disorder. This is demonstrated in a discussion of results obtained on n‐alkanes, cycloalkanes and perfluoro‐n‐alkanes.
Phase Transition and Vibrational Spectra of I‐Leucine
Authors: Bougeard D. 
Published: July 2012

AbstractA phase transition was observed at 80°C in crystalline 1‐leucine. The transition heat was estimated to 170 J/mol by a DSC measurement. The analysis of the IR‐ and Raman spectra and some MNDO conformational analyses show that the transition is purely of conformational type without disorder effect, mostly localized in the alkyl side chain and nearly without effect on the double layer structure.
Birefringence Study of a Phase Transition in TGS Crystals
Authors: Kusto Wlodzimierz J. 
Published: July 2012

AbstractAccurate measurements of the optical birefringence over the temperature range 20–80°C have been made for the uniaxial ferroelectric triglycine sulfate (TGS) along the ferroelectric b‐axis. An anomaly at the Curie temperature is clearly seen. A slight deviation from Landau‐like behaviour is observed in the temperature range 0°C ≤ T – Tc ≤7°C, which is in agreement with recently obtained results on the dielectric, thermal and elastic properties.
Experimental Determination of Diffusion Coefficients, Viscosities, Densities and Refractive Indexes of 11 Binary Liquid Systems
Authors: Baldauf W. , Knapp H. 
Published: July 2012

AbstractDiffusion coefficients in 11 binary liquid mixtures were determined as a function of temperature and composition with the dispersion method. Simultaneously the density, the cinematic viscosity and the refraction index were measured.
Ein Näherungsmodell für die Äquivalentleitfähigkeit mizellarer Seifenlösungen
Authors: Kohler Hans‐Helmut 
Published: July 2012

AbstractA half‐quantitative cell model of micellar surfactant solutions is used to give a physical explanation for the increase of the equivalent conductivity, as it is observed at high concentrations in many paraffin‐chain salt solutions. The increase of the equivalent conductivity is found to result from the finite size of the micelles which, with increasing concentration, leads to an overlap of the counterion clouds and thus to an increase of the partial conductivity of the counterion. Spherical micelles with constant aggregation number and constant degree of dissociation are assumed. By fitting the theoretical curves to experimental data of different alkylsulfates, the degree of dissociation of the respective kinetic micelles is estimated.
Surface Tension Measurements for the n‐Alcohols in the Temperature Range from −40°C to + 40°C
Authors: Strey R. , Schmeling T. 
Published: July 2012

AbstractThe surface tensions of the n‐alcohols from methanol through n‐octanol have been measured between about −40°C and + 40°C. The surface tension data can be represented within ± 0.5% by linear functions of temperature over the considered temperature range. The increase of surface tension with increasing chain length of the alcohol is in accord with the theorem of corresponding states.
Adsorption of Carbon Monoxide on Reduced Oxides of Iron and Manganese as well as on their Mixture
Authors: Lohrengel G. , Baerns M. 
Published: July 2012

AbstractMixtures of reduced iron and manganese oxide constitute potential catalysts for Fischer‐Tropsch synthesis. To contribute to a better understanding of the action of such catalysts the adsorption of CO was studied on the reduced oxides of iron and manganese as well as on their mechanical mixture (6.4 mol MnO2per mol Fe2O3) which were exposed to calcination before reduction. Adsorption was performed at temperatures between approximately 20 and 350°C and pressures up to 105Pa. Dissociation of CO which occurs rapidly on reduced iron oxide above 210°C and results in carbon deposition is hindered when manganese oxide is admixed. Also the coverage of the surface with CO is affected by the admixture of manganese oxide. The results indicate that surface interaction between iron and manganese oxide occurs.
Electroluminescence Transients at ZnO‐Electrodes by Hole Injection during Persulfate Reduction
Authors: Yamase T. , Gerischer H. 
Published: July 2012

AbstractElectroluminescence transients at the ZnO‐electrolyte interface have been studied during pulsed reduction of persulfate. The spectral distribution of the emitted light centers around the band gap energy and indicates hole injection from the intermediately formed SO4‐ radicals and consecutive radiative recombination with electrons. The decay in the photon emission during a cathodic current pulse is attributed to the formation of recombination centers by hydrogen evolution and cathodic crystal decomposition. Such centers can be structural defects, Zn‐atoms on the ZnO surface or H‐atoms adsorbed on the surface and possibly also incorporated into the crystal lattice.
Electron Impact Investigation of the Molecules SeS(g) and TeSe(g) Under High‐Temperature Equilibrium Conditions
Authors: Grade M. , Wienecke J. , Rosinger W. , Hirschwald W. 
Published: July 2012

AbstractSeS(g) and TeSe(g) molecules, produced by Knudsen‐cell vaporization of the mixed HB/VIA‐systems ZnS/ZnSe and CdSe/CdTe, were studied by energy‐dispersive electron impact ionization. Analysis of ionization efficiency curves yields energy levels of excited ionic states of the molecule ions SeS+(g) and TeSe+ (g). The energy levels correlate with corresponding states of S(g), Se(g) and Te(g) derived from independent photoelectron‐spectroscopic data. ‐ Thermodynamic analysis of the intensity data yields dissociation energies of the neutral and singly ionized species, standard enthalpies of formation, heats and equilibrium constants of the gas‐phase reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm XY}({\rm g}) = \frac{1}{2}{\rm X}_2 ({\rm g}) + \frac{1}{2}{\rm Y}_2 ({\rm g})\,({\rm X} = {\rm Se and Y} = {\rm S},{\rm Te} $\end{document} as well as total and partial pressures for the ZnS/ZnSe‐system.
Temperature Dependence of the Rate Constants of the Reaction O + NO + M → NO2 + M (M = He, NO, N2, CH4)
Authors: Schieferstein M. , Kohse‐Höinghaus K. , Stuhl F. 
Published: July 2012

AbstractValues of absolute rate constants of the termolecular reaction O + NO + M → NO2 + M were determined for different third bodies (M = He, NO, N2, and CH4) at temperatures ranging from 200 to 370 K, Small amounts of O atoms were generated in the H2‐laser photolysis of NO and were monitored by NO chemiluminescent emission. The temperature dependence of the rate constants can be expressed by k1,M = B x (T/K)−n with n = (1.10 ± 0.06) and B = 3.3 (+ 1.4; – 1.0) · 10−29 cm6s‐1 for M = He; n = (1.38 ± 0.06) and B = 3.3 (+ 1.2; – 0.9) · 10−28 cm6s‐1 for M = NO; n = (1.44 ± 0.10) and B = 3.2 ( + 2.5; – 1.4) · 10−28 cm6s‐1 for M = N2; and n = (1.55 ± 0.15) and B = 7.9 ( + 10.7; – 4.6) · 10−28 cm6s‐1 for M = CH4. These results are discussed and compared with previous experimental and theoretical work.
Anomalies in the Magnetic Circular Dichroism of Benzene in Cyclohexane?
Authors: Haberditzl Werner , Thiemann Wolfram , Jarzak Ute 
Published: July 2012

AbstractA magneto‐optical anomaly in the MORD of benzene dissolved in cyclohexane was reported by von Loewis in 1976; a similar “asymmetry” of MCD spectrum upon reversal of the magnetic field had been published by Komiyama and Miwa in 1979. Introducing a 20 mm thick iron plate to shield the CD stress modulator from stray magnetic field apparently eliminates this anomaly. Therefore the observed phenomenon seems to be an apparative artefact.
2‐(2‐Pyridinyl)‐1‐(3‐Pyridinyl)‐Ethanone – Photoinduced Proton Transfer and Isomerisation
Authors: Vogel J. , Knoth G. , Melzig M. , Cmiel E. , Schneider S. , Dörr F. 
Published: July 2012

AbstractBased on experimental evidence from UV‐absorption and emission, transient UV‐absorption (laser flash photolysis), and light induced changes in NMR‐spectra, the electronic relaxation pathways of 2‐(2‐pyridinyl)‐1‐(3‐pyridinyl)‐ethanone are discussed, including proton transfer and isomerisation in both the excited state and the ground state. It is found that the relaxation mechanism is dependent on the solvent properties.
Über die Reaktionen von F‐Atomen mit H2O, H2O2und NH3
Authors: Walther C.‐D. , Wagner H. Gg. 
Published: July 2012

AbstractThe reaction of H2O, H2O2, and NH3with an excess of F‐atoms was investigated in an isothermal flow system. The following rate constants were obtained\documentclass{article}\pagestyle{empty}\begin{document}$ \begin{array}{*{20}c} {k1({\rm F} + {\rm H}_2 {\rm O}) = (2.5 \pm 0.6) \cdot 10^{13} {\rm exp}\left({ - \frac{{(400 \pm 70){\rm K}}}{T}} \right)\frac{{{\rm cm}^3 }}{{{\rm mol s}}}243 < T < 369{\rm K}} \\ {k_3 ({\rm F} + {\rm H}_2 {\rm O}_2) = (3 \pm 1) \cdot 10^{13} \frac{{{\rm cm}^3 }}{{{\rm mol s}}}} \\ {k_5 ({\rm F} + {\rm NH}_3) = (1.5 \pm 0.8) \cdot 10^{14} {\rm exp}\left({ - \frac{{(650 \pm 150){\rm K}}}{T}} \right)\frac{{{\rm cm}^3 }}{{{\rm mol s}}}250 < T < 250{\rm K}.} \\ \end{array} $\end{document}A computer simulation of the measured concentration profiles of intermediates and final products allowed the determination of the rate constants of the consecutive reactions.
Model Calculations on Surface and Permeation Controlled H2 Absorption and Desorption of Oxide Coated Metals
Authors: Fromm E. , Uchida H. , Chelluri B. 
Published: July 2012

AbstractThe absorption and desorption kinetics of H2 is calculated for a system where dissociation or recombination of H2 molecules and permeation of H atoms through a surface layer are the rate determining steps of the reaction. The model yield rate laws ν(T, x), time laws x(t, T), and their dependence on p, T, and x. Two parameters introduced determine where simple equations for the limiting cases of surface or permeation control hold and where more complex relations for the transition region with two partial reactions as rate determining steps are valid. As rate laws for absorption ν ∝︁ pn with 0.5 < n < 1 and for desorption ν ∝︁ an with 1 < n < 2 are obtained. The change of the experimental activation energies between the values of the limiting cases is also described by the model.
Characterization of GU‐Base Pairing in Double Helical Polynucleotides by IR‐Difference Spectroscopy
Authors: Stulz J. , Ackermann Th. 
Published: July 2012

AbstractMixtures of poly (A,G) and poly U and of poly G and poly (C,U) are shown to form 1:1 complexes under appropriate conditions, where GU‐base pairs are involved in a double helical complex of normal Watson‐Crick base pairs. The infrared spectra of their D2O‐solutions could be obtained by standard methods, whereas FTIR‐spectroscopy was used to record the spectra of the strongly absorbing H2O‐solutions. By comparison with the spectra of poly A · poly U and of poly G · poly C the characteristic features of “pure” GU‐base pairs in the infrared spectra could be extracted. They show the typical differences to the spectra of unbound guanosine and uracil which are expected for base pairing.