bluuebunny/crossref_metadata_2025 huggingface dataset:
Conformational Equilibrium and its Influence on the Dielectric and Thermodynamic Behaviour of Cyclohexane, or Benzene + 1,2‐Dibromoethane
Authors: Perez Fascual , Florian Asuncion , Lazaro Ana , Gracia Mariano , Losa Celso Gutierrez , Valero Jose
Published: July 2012

Static permittivities (ϵ), excess enthalpies (HE), and excess volumes (VE) of Cyclohexane or Benzene + 1,2‐Dibromoethane, and the densities and refractive indices of the pure components, at 288.15, 298.15, 308.15 and 308.15 K, were measured. The dielectric measurements allowed the study of the conformational equilibrium and the calculation of the equilibrium constant and the conformational enthalpy. We have found that HE is practically independent of T in the range studied by us, and an explanation of this result is proposed. The influence of the temperature on VE is small and negative. HE and VE data were correlated in terms of Flory‐Patterson's theory.
Prediction of Gas Solubilities by a Modified UNIFAC‐Equation
Authors: Nocon G. , Weidlich U. , Gmehling J. , Onken U.
Published: July 2012

The design of absorption processes requires the knowledge of gas solubility data. Because experimental data are often not available, an estimation method must be used. Various methods for the prediction of gas solubilities have been published in the literature. It is shown that none of the described methods provides satisfactory prediction results. Therefore a new method – the modified UNIFAC method – is proposed. This modification of the UNIFAC method takes into account free volume effects. The method has been used successfully for the estimation of carbon dioxide, methane, oxygen and ethylene solubilities in aliphatic hydrocarbons and alcohols at 1 atm.
Relations between Velocity Correlation Coefficients and Phenomenological Transport Coefficients in Multicomponent Mixtures
Authors: Schönert H.
Published: July 2012

By introducing the concept of tracer transport into the equations of thermodynamics of irreversible processes it is possible to link unequivocally the phenomenological transport coefficients of irreversible thermodynamics to the velocity correlation coefficients of the linear response theory. The equations derived are valid for neutral and/or ionic constituents or species.
An Improved Formula for the Partition Function of a Single Free Internal Rotation and Its Consequences Regarding Evaluation of Thermodynamic Functions
Authors: Slanina Zdenêk
Published: July 2012

Conventional partition function of free internal rotation shows incorrect limit behaviour for low temperatures and small values of reduced moment of inertia. Consequences of transition to the new formula with correct limit behaviour regarding calculations of thermodynamic functions have been studied for CH3NO2, C6H5NH+, C6H5, – C6H5, CIF, HF · HF CIF, CF3H · OH2, CCl3H · OH2 · C3H6 OH2, (H2)2, and (H2O)2. In the case of association of HF and CIF the thermodynamic characteristics of the overall process have also been recalculated in the terms of the newly suggested approach. It has been shown that application of the new formula can cause substantial changes in H and S values in the region of not only low but also moderate temperatures. Corrections of values of the thermodynamic characteristics which are required by this improved procedure can be more significant than or comparable with the values of corrections with respect to deviations from behaviour of rigid rotator or harmonic oscillator. As a side product the study points out a number of numerical errors and non‐reproducibilities of the earlier reported values based on the conventional formula.
Theory of Thermal Unimolecular Reactions in the Fall‐off Range. I. Strong Collision Rate Constants
Authors: Troe J.
Published: July 2012

(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

The 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

In 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

The 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

A 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

The 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

A 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

Energetic 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

The 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

The 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

The 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

The 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.
Phase Transitions in Discotic Liquid Crystals
Authors: Blinc R.
Published: July 2012

The phase diagram of a columnar discotic liquid crystal is evaluated within a Landau theory and the results are compared with the data obtained from 13C NMR measurements on hexapentoxy‐triphenylene.
Molecular Motion, Defect Structures and Phase Transitions in Oligomer Crystals
Authors: Strobl G. R. , Schwickert H. , Trzebiatowski T.
Published: July 2012

Defect 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

A 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

Accurate 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

Diffusion 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

A 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

The 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

Mixtures 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

Electroluminescence 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

SeS(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

Values 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

A 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

Based 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

The 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

The 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

Mixtures 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.
Photoelectron Spectroscopic Study of the Adsorption and Co‐adsorption of Hydrogen and Carbon Monoxide on Iron Films
Authors: Wedler G. , Ertel J.
Published: July 2012

The adsorption of carbon monoxide and of hydrogen on evaporated iron films is studied by means of ultra violet photoelectron spectroscopy (UPS) and X‐ray photoelectron spectroscopy (XPS). Both methods indicate that carbon monoxide begins to decompose at 298 K. At 423 K the decomposition is complete. UP spectra of co‐adsorbed hydrogen and carbon monoxide confirm the existence of an interaction between these two gases in the adsorption layer at 298 K. The results are used to correlate earlier thermodynamic and kinetic studies with known literature data about photoelectron spectra of the systems Fe/H2, CO and to discuss the influence of crystal orientation and surface structure on the adsorption of H2 and CO on Fe.
Hydrogen Trapping in β‐NbHx by Lattice Defects
Authors: Baden Wolfgang , Weiss Alarich
Published: July 2012

1H NMR was studied in thin foils of β‐NbHx (0.71 ≦ x ≦ 0.86). Three 1H NMR signals, A, B, and C have been observed. Their chemical shift depends on the hydrogen concentration x. The separation of the signals is several ten ppm. A strong dependence of the signal intensity from the pretreatment of the metal foil is found. It is shown that the signal A is most probably due to hydrogen atoms trapped at dislocations and domain boundaries. Signal B belongs to the 1H NMR in the undisturbed lattice of β‐NbHx. Finally signal C is possibly due to hydrogen trapped at interstitial oxygen impurities.
Kinetic Influences on Reaction Processes in the Quasiternary System HgkCd(1‐k)TelSe(1‐l)
Authors: Leute V. , Schmidtke H. M. , Stratmann W. , Kalb A.
Published: July 2012

Kinetic aspects of the solid state reaction between the binary semiconductors CdTe and HgSe as well as the topochemistry of the reaction zone are investigated by an electron microprobe and by optical microscopy. The reaction path is markedly influenced by intrinsic doping of the binary reaction components. Pronounced regions of uphill diffusion of chalcogens or of metals are essential features of the reaction behaviour in this semiconductor alloy system.
Defects and Cation Diffusion in Magnetite (V): Electrical Conduction, Cation Distribution and Point Defects in Fe3‐δO4
Authors: Dieckmann R. , Witt C. A. , Mason T. O.
Published: July 2012

Electrical conductivity in magnetite has been studied experimentally as a function of temperature and oxygen activity between 560 and 1400°C. The results indicate that above TC (=575°C) an octahedral site small polaron mechanism is dominant over the entire temperature range (Ea = 0.1136 eV). By comparing data on electrical conductivity and thermoelectric power, a second (small polaron) mechanism (Ea = 0.714 eV) is detected at elevated temperatures. Additionally, equilibrium constants for the cation vacancy formation are derived from fitting the conductivity isotherms as a function of oxygen activity. These agree well with values determined thermogravimetrically.
Electron Impact Induced Excitation Processes Involving the Sulfur Clusters S2 to S8
Authors: Rosinger W. , Grade M. , Hirschwald W.
Published: July 2012

Ionization efficiency curves of the gaseous sulfur species Si (i = 2–8) in equilibrium with solid red HgS were obtained by electron impact ionization. Analysis of fine structure of the curves yields energy levels of ground and excited ion states. — For S2 and S8 the experimental values are in good agreement with independent photoionization and photoelectron spectroscopic data from the literature. In the case of S3 to S7 numerous appearance potentials were determined which reflect processes such as direct ionization, autoionization, fragmentation, and predissociation. Extended Hückel calculations were performed for verification of the experimental energies and for spectroscopic assignment of states. — By the second and third law methods the heats of the gas phase reactions Si(g) = i/2 S2(g) (i = 3–8) and average bond energies of the sulfur species were determined.
Internal and External Oxidation of Nonmetallic Compounds and Solid Solutions (I)
Authors: Schmalzried H.
Published: July 2012

A formal analysis is given treating the phenomenon of internal and external oxidation of oxide solid solutions. Theoretically, two situations can arise if those oxides are brought in an environment of higher oxygen potential. (1) Demixing and subsequently the formation of an outer layer of the reaction product occurs. (2) The reaction product forms internally; the two‐phase front advances into the interior of the solid solution. Some analogies with the phenomenon of internal alloy oxidation are discussed. Normally, a parabolic reaction kinetics prevails. Depending on the composition of, and the transport coefficients in the solid solution, a change from an internal to an external reaction may occur, and a criterion for this change is deduced. Internal oxidation (and reduction) is a means to disperse a second phase into an oxide matrix. This process may alter electrical, chemical and mechanical properties of the solid in question and thus could be of interest for materials science as well as geochemistry.
ESR of Mn2+ Ions in ZnP2 and Structural Correlations
Authors: Frick B. , Siebert D.
Published: July 2012

In tetragonal ZnP2 paramagnetic Mn2+ substitutes for the Zn2+ ions that are all equivalent. The hyperfine structure constant A of the paramagnetic Mn2+ centre was determined to 53(2) · 10−4 cm−1. Measurements of the optical activity revealed a characteristic twinning of the red, plate‐like crystals. In monoclinic ZnP2 two different Mn2+ centres could be detected in accordance with two different Zn sites. A site assignment was possible by considering a pseudo‐orthorhombic unit. The same assignment was obtained by comparing the orientations of the centres' axes with calculated directions of the axes of crystal field tensors. The agreement of the A values of the two different centres in monoclinic ZnP2 among themselves and with the A value in tetragonal ZnP2 supports a structure without Zn‐Zn bonds for the monoclinic modification.
Improvement of Electrochemical Methods for Studying Metal‐Hydrogen Systems
Authors: Schöneich H.‐G. , Züchner H.
Published: July 2012

Correct diffusion measurements using electrochemical methods must be carried out under careful consideration of the boundary conditions. — It is shown that the diffusion of recombined H‐atoms from the metal surface into the electrolyte does not seem to be the main reason for a loss of hydrogen concentration, but the presence of oxidizing species (generally oxygen), solved in the electrolyte, which lead to an enhanced electrochemical oxidation of hydrogen. In order to avoid this source of systematic errors, deaerated H2SO4was used for measuring time lag curves of hydrogen diffusion in palladium. Measured time lag curves, obtained by the current pulse method, agree very well with theoretical curves, evaluated from the solution of Fick's second law. — When determining diffusion coefficients by measuring the break‐through time one has to take into account the ratio of the amount of hydrogen, discharged on the entry side of the diffusion foil, to the content of hydrogen within the sample from precharging runs.
The Trimethylsulfonium Ion, [(CH3)3S]⊕, in Hexachlorometallate(IV) Complexes, [(CH3)3S]2MCl6 (M = Pt, Se, Te, Sn). 1H NMR, 35Cl NQR, and X‐Ray Diffraction Studies
Authors: Ikeda Ryuichi , Nakamura Daiyu , Kadel Rainer , Weiss Alarich
Published: July 2012

The measurements of 35Cl NQR spectra and X‐ray powder diffraction patterns were carried out in a series of the complexes of trimethylsulfonium hexachlorometallates(IV), (triMS)2MCl6 (M = Pt, Se, Te, Sn). For (triMS)2TeCl6 and (triMS)2SnCl6, 1H NMR second moments were determined at various temperatures between 77 K and 370 K. The temperature dependence of 1H NMR spin‐lattice relaxation times was observed for (triMS)2PtCl6, (triMS)2TeCl6, and (triMS)3SnCl6. From X‐ray powder patterns, it was found that the complexes studied are isomorphous with each other and form cubic crystals belonging to the space group T‐Pa3. The unit cell dimensions were determined. A single 35Cl NQR line was observed for all of the complexes in agreement with the crystal symmetry. From 1H NMR studies, two kinds of motions of (triMS)⊕, namely, the intracationic CH3 group reorientation and the reorientation of the whole cation about its C3 axis, were observed separately in the above three complexes. The activation energies of these motions were evaluated and compared with those of trimethylammonium ions in hexahalometallate(IV) complexes previously reported.
14N Nuclear Quadrupole Resonance in Simple Compounds Containing the Amino Group
Authors: Okuda Tsutomu , Ueda Akinobu , Mishima Kanae , Suzuki Toshinori , Negita Hisao
Published: July 2012

14N nuclear quadrupole resonance was observed in acetamide, CH3CONH2, and chloroacetamide, CH2ClCONH2, by pulse technique. The resonance frequencies in both compounds increase with raising from 80 K to 340 K. In acetamide the activation energy was calculated to be 17.6 kJ · mol−1 in the temperature range from 260 K to 320 K and 48.1 kJ · mol−1 above 320 K. The former is thought to be attributed to the reorientation of the amino group and the latter, to the torsional motion of molecule. In the case of chloroacetamide the echo signal is too weak to obtain the correct T1 value, but the relaxation mechanism seems to be similar to that of acetamide. The positive temperature dependence of resonance frequencies is due to the hydrogen bond.
Interaction of Ammonia with Metallic Copper, Nickel and Cobalt Catalysts Studied by Temperature Programmed Desorption
Authors: Baiker Alfons , Monti Daniele
Published: July 2012

The adsorption of ammonia on unsupported and alumina supported copper, nickel and cobalt catalysts was studied employing temperature programmed desorption. No ammonia desorption was observed in the experiments carried out with the unsupported metal powders. Nickel and cobalt showed desorption of nitrogen and hydrogen, whereas with copper only nitrogen desorption was observed. On the alumina supported metal catalysts the desorbing gases were ammonia, hydrogen and nitrogen with ammonia as major desorbing species. The investigations indicate that the adsorption of ammonia at 570 K leads to nitride formation on the metal surfaces. The amount of metal nitride formed increases in the sequence: copper, nickel, cobalt. Hydrogen suppresses the nitride formation. This is shown by comparative desorption experiments on catalyst samples which were exposed to hydrogen after exposure to ammonia. The rate of the metal nitride reduction is larger on nickel and cobalt than on copper. This is ascribed to the lower activity of the copper for hydrogen dissociation.
Rate Coefficients of Elementary Steps in the Inhibited Oxidation of Ethylbenzene, I. Interaction between Peroxy Radicals and Inhibitor Molecules
Authors: Lukács J. , Héberger K. , Gál D.
Published: July 2012

The inhibited oxidation of ethylbenzene has been investigated in the presence of 2,6‐di‐tert‐butyl‐4‐methyl‐phenol (ionol). 1‐Phenylethyl‐hydroperoxide was used as a source of radicals. The time dependence of oxygen consumption was measured at t = 120°C and simulated using a reaction mechanism consisting of 20 elementary steps. Simulation was carried out by changing the value of the rate constant of the reaction

Since the calculated curves are — at a constant rate of initiation — essentially influenced by the value of k5, simulation is a proper method for its determination. The best fit was achieved at k5 = 5 · 105l · mol−1 s−1. — The contribution of the various elementary steps to oxygen consumption has been also determined.
Kinetics and Mechanism of Hydrocarbon Formation in the System C2H2/O/H at Temperatures up to 1300 K
Authors: Homann K. H. , Wellmann Ch.
Published: July 2012

The consumption of O atoms and the formation of CO, C3H4 (Propyne and Propadiene), C4H2 (Butadiyne) and other hydrocarbons in the system C2H2/O with and without added H atoms has been studied in the temperature range 295–1300 K, p = 2.7 mbar. Both the rate of formation and the yield of C3H4 in C2H2‐rich mixtures increases with higher temperature. The rate of C4H2 formation increases but the maximum concentration remains constant up to 500 K. The results can be described quantitatively through a slightly modified mechanism of 30 reactions that had been proposed previously for the reaction at room temperature.
Kinetics of the Reactions of OH‐Radicals with Benzene, Benzene‐d6 and Naphthalene
Authors: Lorenz K. , Zellner R.
Published: July 2012

Absolute rate constants for the reactions of hydroxyl radicals with benzene (1), benzene‐d6 (2), and naphthalene (3) have been obtained using excimer laser photolysis to generate OH and time resolved resonance fluorescence as its monitor. Reaction (1) was studied at total pressures between 1.5 and 112 mbar at 298 K using Ar as a diluent gas. k1 is found to increase with pressure up to –40 mbar, but to be essentially pressure independent at still higher pressures, k (298 K) = (7.0 ± 1.5) 1011 cm3/mol · s. The temperature variation of k1 as studied over the range 244 – 24 K. At temperatures below 330 K normal Arrhenius behaviour with k1 (T) = (3.8 ± 1.0) 1012 exp[‐(500 ± 50) K/T] cm3/mol · s is observed, corresponding to the addition reaction (1) OH + C6H6 → C6H6OH. Between 330 and 420 K a sharp decrease of k1 with increasing temperature is noted, which we attribute to reaction (1) becoming reversible. For the stabilization energy of C6H6OH we derive (79 ± 6) kJ/mol. Above 420 K a transition of k1 to a positive temperature dependence, corresponding to the abstraction reaction (1') OH + C6H6 → H2O + C6H5 is noted. Rate constants for the reaction of OH with benzene‐d6 (2) are essentially identical to those of reaction (1) except for temperatures above 420 K, where k2 falls considerably below k1. This isotope effect is a confirmation of the (1') abstraction route. Reaction (3) was studied at total pressures between 6 and 128 mbar (He) where it is found to be essentially pressure independent. Its temperature variation was studied between 337 and 525 K. Over this region the rate coefficient decreases from (8.8 ± 3.5) 1012 cm3/mol · s to (6.6 ± 2.6) 1011 cm3/mol · s, with the decrease with temperature being relatively weak up to 410 K, k1(T ≤ 410 K) = (2.2 ± 1.0) 1012 exp[(440 ± 50) K/T] cm3/mol · s, and stronger at still higher temperatures. This behaviour is interpreted as to correspond to the addition reaction (3) OH + C10H8 → C10H8OH and its equilibration. The stabilization energy of the OH‐naphthalene adduct is estimated to be (95 ± 6) kJ/mol.
Spectrum and Lifetime of NH(a1Δ → X3Σ'−) in Inert Gas Matrices
Authors: Esser H. , Langen J. , Schurath U.
Published: July 2012

Metastable NH(a1Δ) radicals were produced by the photolysis of matrix isolated HN3(HNCO) at 206.2 nm. The (0,0) and (0,1) bands of the forbidden transition to NH(X3Σ−) were observed in emission in the rare gases and in nitrogen, yielding Franck‐Condon factors, ΔG1/2 values, and matrix shifts. The line structure of the (0,0) band in Xe is due to nearly free rotation of the radical in the electronic ground state. Rotation in the other matrices is strongly inhibited or totally suppressed by the presence of the other photofragment N2 in or near the cage. Lifetimes of NH(a1Δ) in Ne, N2, Ar, Kr and Xe are 335 ms, 365 ms, 375 ms, 790 ms and 1020 ms. The strong temperature dependence of the lifetime in Xe is in quantitative agreement with a theoretical model of multiphonon induced inter system crossing to NH(X3Σ−, ν = 4), indicating a fluorescence yield near 80% in the low temperature limit. The shorter lifetimes in the other matrices are believed to be due to enhanced molecule‐medium coupling by the nearby N2 photofragment. Extrapolation of the Xe data yields an estimate of 3.3 s for the radiative lifetime of gaseous NH(a1Δ).
Coexistence Curve of the System Methanol/Carbon Disulfide in the Vicinity of the Critical Point
Authors: Oswald U. , Woermann D.
Published: July 2012

The coexistence curve of the system methanol/carbon disulfide is determined by observing the temperature of phase separation of 32 samples over a narrow range of composition close to the critical point (10−5≤t≤ 10−3;t= (Tc‐Tc)/Tc). The functional form of the difference in order parameter in terms of mass fraction, mole fraction, or volume fraction is consistent with the concept of universality of critical phenomena. The following critical data are obtained: mass fraction of carbon disulfideyc= 0.805 ± 0.005;Tc= (34.281 ± 0.002) °C; β = 0.329 ± 0.005.
The Independent Molecular Interaction Sites Model III. A Monte‐Carlo Study of the Reference Fluid for Hard Dumbbell Systems
Authors: Naumann K.‐H. , Bansal R. , Bruns W.
Published: July 2012

The site‐site pair distribution functions of the Independent‐Molecular‐Interaction‐Sites (IMIS) reference fluid for homonuclear hard dumbbell systems are evaluated by Monte‐Carlo simulation and from the Percus‐Yevick approximation. The good overall agreement with the “exact” pair correlation functions for these systems suggests that the IMIS model provides a reliable route to the structural properties of interaction site model fluids with short‐ranged site‐site potentials.
A Generalized van der Waals Equation of State I. Treatment of Molecular Shape in Terms of the Boublik‐Nezbeda Equation
Authors: Svejda P. , Kohler F.
Published: July 2012

A description is given how to construct hard convex bodies to resemble several hydrocarbon molecules. It is shown that this description, when inserted into a generalized van der Waals model, leads to very good agreement in the p‐p‐T properties at low temperatures and high densities. Furthermore, the attractive van der Waals parameters exhibit the property of additivity. The extension of this model to mixtures is presented, though the detailed comparison of some mixing properties is deferred to forthcoming publications.
Additional Comments on the Induced Optical Activity in the Charge‐transfer Complexes of Optically Active Ketones with Tetracyanoethylene
Authors: Tajiri Akio , Gonohe Narishi , Hatano Masahiro
Published: July 2012

The intermolecular electron donor‐acceptor complexes of the optically active ketones with tetracyanoethylene (TCNE) have exhibited circular dichroism (CD) and magnetic circular dichroism in the charge‐transfer absorption region. A possible geometry has been proposed in order to interpret the sign of the observed CD spectrum in each complex. A symmetry consideration for the observed Faraday B term has supported a local structure of the ketone‐TCNE complex where the TCNE plane is rotated around the carbonyl axis. A temperature variation spectrophotometry of the thermodynamic parameters for the selected systems has not given a conclusive evidence for the isomeric 1:1 complexes in these systems.
Recent Developments in the Experimental Determination of Thermodynamic Quantities of Metals and Alloys
Authors: Komarek Kurt L.
Published: July 2012

Recent developments of experimental techniques for the measurement of thermodynamic quantities of metals and alloys are reviewed. Special emphasis is placed on calorimetry of reacting and non‐reacting systems, emf methods with liquid and solid electrolytes, and the various Knudsen effusion methods.
Thermodynamics of Compounds with Narrow Ranges of Nonstoichiometry
Authors: Schmalzried H.
Published: July 2012

Thermodynamic functions of compounds with narrow ranges of homogeneity are calculated with the aid of the concept of defect thermodynamics. In doing so, the irregular structural elements of a crystal are formally treated as quasi‐particles in dilute solution on their respective sublattices. This concept is illustrated with binary and ternary ionic crystals (for example Fe3‐δO4; Ag2+δS; Co1‐δ; (Co,Mg)1‐δO; (Fe,Mg)2‐δSiO4). The nonstoichiometry δ of these compounds is calculated as a function of the independent thermodynamic variables and compared with experimental results.