bluuebunny/crossref_metadata_2025 huggingface dataset:
Photochemistry of Propynal in the Gas Phase Following S1(nπ*) ← S0 Excitation
Authors: Opitz Joachim
Published: July 2012

Following excitation of the S1(nπ*) ← S0 transition the photochemical decomposition of propynal (HCCCHO) and propynal α‐D (HCCCDO) is analyzed. Quantum yields for the main products CO and acetylene are reported for excitation wavelengths 382 nm ≥ λ ≥ 308 nm. Depending on the wavelength two photochemical pathways seem to occur leading to product formation with ϕ < 1 for λ ≥ 343.5 nm and ϕ > 1 for λ < 343.5 nm respectively. For the pathway leading to ϕ < 1 a mechanism is proposed which is based on a dissociation into molecular products from the excited ground state S0 by a concerted reaction.
Kinetics of Diabatic and Adiabatic Electron Exchange in Organic Systems Comparison of Theory and Experiment
Authors: Grampp Günter , Jaenicke Walther
Published: July 2012

The rate constants ket of electron self exchange between neutral molecules and the corresponding radical ions, measured by ESR line broadening, are discussed for seven organic ϕ‐systems in 18 aprotic solvents of a wide range of relaxation times, τL (0.2 < τL/ps < 10), and polarities, γ(0.05 < γ 0.53) in terms of the theoretical approaches of Marcus and Sumi and of Jortner and Bixon, both valid for comparable magnitudes of inner and outer reorganization energies. (γ = < γ = 1/n2‐1/ε; n = refractive index; ε = dielectric constant.) The electron transfer is diabatic for four substituted p‐phenylenediamines, it is adiabatic relaxation overdamped for tetracyanoquinodimethane (TCNQ), tetrathiafulvalene (TTF) and tetracyano‐ethylene (TCNE). By changing the solvents no transition between both mechanisms is found. To explain the results, the reactants are represented by ellipsoids. Their centre to centre distance in the transition state is derived from slopes of lnket τL γ−1/2 vs. γ (for adiabatic reactions) or of Infketγ1/2 vs. γ (for diabatic reactions). The mutual orientation of the reactants follows the minimum of electrostatic energy. The resonance splitting V for this orientation, calculated from the overlap integrals agrees well for all systems with the observed diabatic or adiabatic behaviour of the reaction, except for TCNE. The resonance splitting and the equilibrium constant of the precursor complex are derived experimentally from the temperature dependence of the electron transfer rate constant ket. Negative association energies of the complex are due to ion‐dipole interactions of the reactants. An additional reorganization term is observed for the aliphatic TCNE system in ethereal solvents. To describe the experiments quantitatively, both theories used are nearly equivalent.
The Superconductor/Ionic Conductor Interface at Low Temperatures
Authors: Lorenz W. J. , Saemann‐Ischenko G. , Breiter M. W.
Published: July 2012

The charge transfer across the interface superconductor/ionic conductor represents a relatively unknown field at present. This paper deals with the first electrochemical studies in this area. Both n‐type classical and p‐ and n‐type high Tc superconductors (HTSC) are considered. Different superionic conductors (Ag β‐alumina, Ag + ion conducting glass, and RbAg4I5) are used as solid electrolytes in experiments covering a temperature range down to 10 K. A transient technique in the time domain and Electrochemical Impedance Spectroscopy (EIS) in the frequency domain are used to study the silver deposition as Faradaic charge transfer process at these interfaces. The results show an admittance peak in transient measurements or a corresponding negative peak of the polarization resistance in EIS‐measurements at T ≈ Tc. These findings are attributed to an increase of the exchange current density around Tc. The effect is much less on an A15 compound than on HTSCs. The effect can only be interpreted as a quantumelectrochemical phenomenon caused by the contribution of Cooper pairs as correlated charge carriers crossing the electrochemical double layer. A proximity‐like phenomenon can be excluded.
Tracer Particle Diffusion in Crystal‐ and Fluid‐like Ordered Colloidal Suspensions
Authors: Härtl W. , Versmold H. , Zhang‐Heider X.
Published: July 2012

Static and dynamic light scattering experiments with crystal‐ and fluid‐like ordered colloidal suspensions are reported. The systems were composed of two electrostatically interacting particle species of similar size and effective particle charge but different refractive index. The refractive index of the abundant species was matched to the index of the dispersing medium. The incoherent scattering from the mismatched second species was used to investigate the self‐diffusion in the ordered suspension. Leakage of coherent scattering due to a slight mismatch was used to monitor simultaneously the structure factor S(Q) of the suspensions. – The self‐dynamic structure factor Fs(Q,t) at several ionic strength of the suspension is analyzed in terms of mean‐square displacements 〈R(t)2〉 and velocity autocorrelation functions v(0) v(t). The long time self‐diffusion coefficient is determined as a function of the effective hard sphere volume fraction Φ.
Neutron Scattering Experiments in the Neighborhood of the Glass Transition in Polybutadiene – a Test of Mode Coupling
Authors: Richter D. , Zorn R. , Frick B. , Farago B.
Published: July 2012

We review recent quasielastic and inelastic neutron scattering experiments taken in the neighborhood of the glass transition in polybutadiene. The experimental results are compared with predictions of the mode coupling theory. We specially emphasize experimental evidence for the existence of a dynamical transition above Tg. We present several experiments which from characteristic anomalies consistently obtain critical temperatures between 213 K ≤ Tc ≤ 220 K. Furthermore, we discuss experimental results for the dynamic structure factor S(Q,t) in the regime of the structural relaxation, showing striking similarities with the predictions of the mode coupling approach.
Dynamical Lightscattering of Pretransitional Phenomena in Liquid Mixtures
Authors: Schröer W. , Wiegand S. , Staude W. , Peters Th.
Published: July 2012

We report measurements of the scattering intensity and of the autocorrelation function of the pseudo binary mixture guaiacol/glycerol‐water as a function of temperature and water content. The guaiacol glycerol ratio was kept constant 1:1, while the mass ratio of water/glycerol varied between 0.4% <x< 1.4%. The system shows a closed solubility loop ifx> 1.17%. A phenomenological model for the temperature dependence of the interaction parameter is used in order to describe the scattering intensity and the diffusion coefficient as function of temperature.
Ellipsometry on Anisotropic Langmuir‐Blodgett Films
Authors: Geiß G. , Hickel W. , Lupo D. , Praß W. , Scheunemann U.
Published: July 2012

Multiple angle null ellipsometry has been used to obtain information about the optical anisotropy of multilayer Langmuir‐Blodgett films. The data are evaluated with a simplified uniaxial (or biaxial) model system. The optical constants of films made of 22‐tricosenoic acid have been determined to nx,y = 1.51 and nz = 1.54 with a monolayer thickness of 3.2 nm. The data are compared with results from waveguide mode spectroscopy. Phenylhydrazone films have been measured in the spectral region between 420 nm (λmax) and 700 nm. The resulting data imply a tilt of the chromophore dipole direction greater than 45° with respect to the surface normal.
Thin Layers of Phospholipids with Branched Chains: Thermodynamic Analysis and Comparison
Authors: Brezesinski G. , Förster G. , Rettig W. , Kuschel F.
Published: July 2012

Monolayers and bulk phases of glycerophosphocholines with a branched fatty acid chain in 2‐position of the glycerol backbone were investigated. In the bulk the frustration caused by the drastic change of the molecule shape within the homologous series influences the structures of the gel and liquid‐crystalline phases in a different way. Gel phases with interdigitated chains and non‐bilayer liquid‐crystalline phases were found. All of the lipids investigated form stable monolayers at the air/water interface. The analysis of the temperature dependence of the compression isotherms leads to the characteristic temperature Tc (critical temperature of the monolayer). The comparison with the main‐transition temperature Tm of the bulk phases can be used as an indicator for structural differences between monolayers and bilayers.
Langmuir‐Blodgett Mono‐ and Multilayer Assemblies of Amphiphilic Liquid‐ Crystalline n‐Alkyl‐4′‐n‐alkoxybiphenyl‐4‐carboxylates. I
Authors: Decher G. , Sohling U.
Published: July 2012

Five n‐Alkyl‐4′‐Alkoxy‐biphenyl‐4‐carboxylates were investigated as Langmuir monolayers at the air/ water interface and as Langmuir‐Blodgett (LB) films on solid supports. All five compounds form stable monolayers at the air/water interface and can be transferred onto solid supports yielding LB‐films, whose structures and kinetic behavior strongly depend on the headgroup. The structures of the LB‐films were investigated by means of optical textures and X‐ray diffraction and compared with the structures of the corresponding bulk phases which were investigated by means of Differential Scanning Calorimetry and X‐ray powder diffraction. The LB‐films of the acid and the two methyl esters exhibit bilayer lamellar structures which are very similar to the bulk crystalline phases at room temperature. The two ethyl esters show a mixture of two phases after transfer, a monolayer and a bilayer phase, the percentage of bilayer phase decreasing with time. For these two compounds the bilayer phase is a deposition enforced phase, which has not been observed in bulk material.
Influence of Thin Superstrate Films on Evanescent Waves in Surface Waveguides
Authors: Gauglitz G. , Ingenhoff J.
Published: July 2012

Surface waveguide structures in glass substrates arranged as Mach‐Zehnder interferometers allow the measurement of slightest influences on a superstrate coated on one arm of the integrated optical device. The refractive indices of the substrate's, the waveguide's, and the superstrate's material determine the characteristics of the modal field in the interferometer arms. For this reason, any influence on the effective refractive index in the superstrate can be monitored with high sensitivity. By use of the wave theory of light, the amplitudes and the phase correlation of the interfering waves can be calculated for any given combination of the materials mentioned above. To prove these considerations, one arm of the Mach‐Zehnder interferometer is coated with polysiloxane as a thin superstrate film (0,5–2 μm). If organic hydrocarbons are passed over the superstrate, the molecules penetrate this interface and change its refractive index in dependence on the gas concentration. This experimental arrangement allows to compare measurements and calculations. Furthermore, the set‐up can be used to monitor physical and chemical effects taking place in the thin superstrate layer. Therefore, besides a verification of the theory, the Mach‐Zehnder chip can be used as a sensor. It can be shown that multi‐wavelength measurements increase the information obtained.
Adsorption Kinetics of Dye Molecules on Polymer Membrane Filters
Authors: Kost S. H. , Breuer H. D.
Published: July 2012

e kinetics of the adsorption of dye molecules on membrane filters made of cellulose nitrate have been studied. In order to obtain thermodynamical data the temperature has been varied from 283 K to 333 K. Because kinetic laws of 1. or 2. order cannot describe the experimental results two different theories were applied. In addition to a classical concept a new equation based on the fractal theory has been checked and has proved to be suitable for adsorption data. We have shown that obtained fractal parameters, fractal dimension Ds and fractal dimension Df, are in excellent agreement with other fractal kinetics experiments.
Prediction of the Isothermal Expansion Coefficient of Electrolyte Solutions Containing Dissolved Gases
Authors: Vogt H.
Published: July 2012

Density data of solutions of electrochemically generated gases such as hydrogen, oxygen, chlorine, carbon dioxide in water and electrolyte solutions are not available even from comprehensive data compilations. The same applies to the isothermal expansion coefficient due to varying concentrations of dissolved gases. These data, however, are necessary for calculations of natural convective mass transfer at gas‐evolving electrodes. An equation for prediction of the expansion coefficient is proposed and compared with some available data obtained experimentally.
The Formation of O and H Atoms in the Reaction of CH2 with O2 at High Temperatures
Authors: Dombrowsky Ch. , Hwang S. M. , Röhrig M. , Gg. Wagner H.
Published: July 2012

The formation of O and H atoms in the reaction of CH2 with O2 was investigated behind incident shock waves at temperatures between 1000 K and 1700 K and at total densities between 5 · 10−6 and 1 · 10−5 mol/cm3 by means of Atomic Resonance Absorption Spectroscopy (ARAS) at 130.5 nm and 121.6 nm, respectively. The contribution of O and H forming channels was found to be about 20%. The rates of formation of O and H atoms in this reaction were determined to be

k1a = (4 ± 2) · 1010 cm3/mol · s

k1e = (5 ± 2) · 1010 cm3/mol · s

In the temperature range investigated an over all rate constant can be represented by k1 = (5 ± 3) · 1011 cm3/mol · s. A comparison with low temperature data leads to a change of the apparent energy of activation of the overall reaction in the temperature range between 300 and 1000 K.
Study of Homogeneous Reactions with on Line Mass Spectrometry and Potentiometry: The Belousov‐Zhabotinsky‐Reaction
Authors: Schmidt V. M. , Vielstich W.
Published: July 2012

Potential oscillations of the Ce3+/Ce4+ redox couple in the Belousov‐Zhabotinsky reaction has been followed using a smooth and a platinized Pt electrode. The same potential oscillations are observed when applying a smooth Pt and a reference (RHE). With a platinized Pt electrode and a RHE as pair of electrodes however, only weak signals are obtained. This effect is due to the slow potential equilibration in a porous metal structure. — A more detailed study of the reaction steps can be made via simultaneous registration of the Ce3+/Ce4+ potential and the oscillations in CO2 formation rate using a PTFE membrane as an interface to a mass spectrometer. The CO2 formation follows the potential oscillation. The maximum rate of CO2 production occurs in the moment of highest Ce4+ concentration with a certain delay of time.
Cationic Self‐Diffusion in the Highest‐Temperature Solid Phases of Ammonium Chloride and Bromide Studied by 1H NMR
Authors: Tansho Masataka , Furukawa Yoshihiro , Nakamura Daiyu , Ikeda Ryuichi
Published: July 2012

Ionic motions in the highest‐temperature solid phases (Phase I) of NH4Cl and NH4Br having the NaCl‐type cubic structure were investigated by measuring 1H NMR spin‐lattice and spin‐spin relaxation times (T1, T1ϱ and T2). A long T2 of ca. 1 ms observed at 750 K in Phase I of both salts was attributed to the excitation of the rapid cationic self‐diffusion and isotropic rotation suggesting the plastic nature of this phase. The observed relaxation times could be explained well using the monovacancy‐diffusion model proposed by Sholl. The activation energy of self‐diffusion was determined as 120 kJ mol−1 for both salts, which value is much larger than those observed in ionic‐plastic phases with the CsCl‐type cubic structure. The diffusion mechanisms of the NH4+ ions in Phase I, and Phase II having the CsCl‐type structure, were compared.
Photochemical Decay Reactions of N2O5, HNO3, CINO3 and BrNO3 in the Energy Range 10–20 eV
Authors: Jochims H.‐W. , Denzer W. , Baumgärtel H. , Lösking O. , Willner H.
Published: July 2012

The photochemical behaviour of gaseous N2O5, HNO3, CINO3 and BrNO3 has been investigated in the energy range 10–20 eV by photoionization mass spectrometry using monochromatized synchrotron radiation. The decay reactions are analyzed using the photoion yield curves of fragment ions and their appearance energies. Hitherto unknown photochemical reactions and thermochemical data have been evaluated.
How Random are Regulatory Signals in RNA Replication? Evolutionary Constraints do not Play a Decisive Role
Authors: Fernández Ariel
Published: July 2012

We propose a kinetically‐controlled Monte Carlo simulation to investigate the search in configuration space of an RNA molecule which folds onto itself as it is being assembled by sequential incorporation of nucleotides. The results are specialized to the template‐directed synthesis of MDV‐1RNA performed by Qß‐replicase. The theoretical predictions are compared with existing experimental results obtained by pulse‐chase electrophoresis. The simulation reproduces satisfactorily the observed variable rate of chain elongation and specifically enables us to establish that the rate of growth out of a pause site is identical to the rate of the refolding event which has induced the pause. Moreover, our results reveal that the extent of functionally‐relevant secondary structure does not differ appreciably from that of a randomly generated sequence. This result suggests that the transient structures whose formation induce regulatory signals have not been selected by evolution.
Electrochemical Color Change of 1,4‐Diketo‐3,6‐Diphenyl‐Pyrrolo‐[3,4‐c]‐Pyrrole
Authors: Mizuguchi Jin , Rochat Alain Claude
Published: July 2012

The title compound (DPP) is a red pigment based on the diketopyrrolopyrrole chromophore. DPP is, however, transparent in solution and appears slightly greenish‐yellow. It has been found that DPP turns red when electrochemically reduced (“electrochromism”). Electrochromic properties of DPP have thus been investigated in the presence of sodium ferrocyanide or ferrocene used as a sub‐redox system. Attention has been paid to the elucidation of the coloration mechanism by means of voltammetry and spectroscopy. The first reduction of DPP proceeds in a one‐electron process and is reversible, whereas the second reduction is irreversible. The electrochromic red color arises as a result of deprotonation at the NH group which follows the cathodic reduction. The mono and di‐deprotonation give absorption maxima at 582 and 620 nm, respectively.
Negative Ion Chemistry in Clusters
Authors: Illenberger Eugen
Published: July 2012

For the prototype system oxygen it is shown that electron attachment to clusters results in a variety of new processes which do not show up in the single molecule. These are (a) formation of molecular anions in their stable configuration, (b) population of electronic states not accessible in isolated molecules and (c) secondary reactions due to inelastically scattered electrons within one cluster.
Direct Absorption Studies of Jet‐Cooled Metal Dimers: Magnesium and Cesium
Authors: Lauterwald H. , Rademann K.
Published: July 2012

Optical absorption of diatomic magnesium and cesium molecules is investigated in a supersonic molecular beam. A vibronic band of Mg2, which is located at 270nm and assigned to a 1Πu ← 1Σg+ transition, is found to have remarkable fine structure. The vibrationally resolved spectrum and the spectroscopic constants of the excited state are reported here for the first time.
Highly Sensitive Infrared Spectroscopy: IR‐REMPI Double Resonance Experiments
Authors: Bahnmaier Albert H. , Schmid Reiner , Zhang Bing , Jones Harold
Published: July 2012

The first double resonance signals involving the use of a c.w. infrared laser and multiphoton ionization Spectroscopy using a pulsed UV laser has been observed in 15NH3. Despite the low duty‐cycle of such a combination, very strong double resonance signals were observed using a low power CO2 laser as infrared source. The observations indicate that such measurements should be possible with the extremely low power levels available from tunable diode lasers. Such a combination would allow high resolution infrared Spectroscopy to be carried out with the sensitivity of ionization Spectroscopy and allow application to molecular species such as clusters. Term values of 15NH3 have been calculated from the data.
Characterization of Silica Supported Transition‐Metal Oxide Catalysts by Luminescence Spectroscopy
Authors: Hazenkamp M. F. , Blasse G.
Published: July 2012

The luminescence properties of some silica‐supported transition‐metal (Mo, W, Nb, Re) oxide catalysts are reported under dehydrated conditions and at low temperatures. The luminescence results are used to identify the metal oxide species in the catalyst samples. UV/VIS reflection spectroscopy is used as an additional tool. The anomalously long decay times of the luminescence of the Mo/SiO2, W/SiO2 and Nb/SiO2 samples indicate that in these samples there are strongly distorted monomeric oxo‐transition‐metal species present. The luminescence of the Re/SiO2 sample is very weak. It is the first report of luminescence of a perrhenate complex. Finally, the possibilities to use luminescence spectroscopy to characterize supported transition‐metal oxide catalysts are evaluated.
Phase Transitions in Minerals: From Equilibrium Properties Towards Kinetic Behaviour Progress Report
Authors: Salje E. K. H.
Published: July 2012

Landau theory is derived from a simple atomistic model. The Gibbs free energy can be written in the displacive limit as magnified image where Ts = 1/2Θs is the saturation temperature due to quantum fluctuations. The coefficients A, B,… and degeneracies of the order parameter are determined by the conventional symmetry constraints. For T > Θs, G is the classic Landau potential. Solutions for non‐displacive systems and coupled order parameters are discussed. – The theory is applied to some model‐minerals such as quartz, Na‐feldspar, and calcite as typical examples. It is argued that the structural complexity of minerals is often related to several thermodynamic degrees of freedom. The transition leads to coupling phenomena, which are reviewed in some detail. – Non‐equilibrium features in crystals which are “nearly” in thermodynamic equilibrium are domain walls. It is shows that domain walls react very sensitively to small changes in the thermodynamic state of the material. New structural configurations are generated in the wall which do not exist in the bulk. – Kinetic processes with continuous order parameters can be analysed using a general rate equation which contains δG/δQ (G is often a Landau potential, Q is the order parameters) as a driving force. This theory draws, thus, a connection between the equilibrium Landau‐type theories and kinetic rate theories.
Electron Density and Chemical Bonding: The Shape of Independent Atoms in Molecules
Authors: Irie S. , Lin H. L. , Niu J. E. , Schwarz W. H. E.
Published: July 2012

Electron density distributions ρ(r) contain three types of features, which give rise to a new natural approach of analyzing ρ with respect to chemical bonding. These features are 1) the very large spherical atomic core densities, defining the geometric structure, 2) the small multipolar atomic valence densities, defining the orientation and population of partially filled p‐ and d‐shells of the “independent atoms” in the molecule or crystal, and 3) the very small density deformations due to the interatomic interactions. The valence shell parameters and the Chemical Deformation Densities are determined theoretically and experimentally for molecules and crystals. The features are brought in relation to intramolecular and intramolecular interactions.
The Transition from Molecular Units to Collective Structures in Complex Transition Metal Chalcogenides, Characterized by Magnetochemical Experiments Progress Report
Authors: Bronger W.
Published: July 2012

Depending on the stoichiometry the alkali metal‐transition metal‐chalogenides crystallize analogous to the silicates in structures with isolated groups, chains or layers. The formation of the framework structures is realized by linkage of anionic transition metal‐chalcogenide complexes. – The magnetic properties of the transition metal ions are used as an indicator for the changes in bonding properties at the transition from molecular units to the collective framework structures. Susceptibility measurements and neutron diffraction experiments show a reduction of the magnetic moments with an increasing degree of linkage in the anionic frameworks of these structures. Crystal field calculations, based on a point charge model, concerning the total atomic arrangement, show a strong correlation with the series of magnetic moments. For ternary phosphides, arsenides etc. corresponding relations exist.
Investigation of Sub‐Shell Occupation in Some Ba Compounds by LMTO‐ASA Calculations
Authors: Felser‐Wenz Claudia , Hohlneicher Georg , Andersen O. K. , Jepsen O.
Published: July 2012

Ba compounds behave very unusual in XPS‐studies as they exhibit only small and often negative binding energy shifts. Four different explanations have been given for these observation. To provide a more quantitative basis for these different models and to shed new light on the unusual behaviour of Ba compounds, we calculated total and 1‐projected densities of states for Ba metal and three Ba compounds. All four explanations given up to now are not in qualitative agreement with the obtained results. A different possible explanation is discussed.
Thermodynamics, Structure, and Structural Dynamics in Glass Progress Report
Authors: Ingram Malcolm D.
Published: July 2012

A common feature of glass is the thermodynamic instability which manifests itself in differences between Tg and To, and in the existence of many relaxation/memory effects. These latter are observable by DSC, by crystallisation studies and by mechanical spectroscopy, and play an important rǒle in relation to such ubiquitous phenomena in “ionic” glasses as the conductivity dispersions and the mixed alkali effect. The concept of strong and fragile liquids provides a useful way of comparing the behaviour of glass‐forming systems, and for observing the influence of chemical bonding on the structural dynamics. It is the existence of the wide spectrum of structural relaxations, however, which seems to be the distinctive feature of the glassy state, rather than the presence of any special kind of chemical bonding or structural units.
Spinodal Decomposition in Solutions of Ternary Oxides
Authors: Burkert N. , Grüne R. , Schmalzried H. , Rahman S.
Published: July 2012

A miscibility gap exists in the quasi‐binary solid solution Co2TiO4 – CoAl2O4 as verified by experimental investigations and theoretical calculations. The critical temperature is ca. 1700 K. Spinodal decomposition was observed in this two‐cation‐sublattice system, if the spinel solid solution had been undercooled into the region of the coherent spinodal at T = 973 K. Simultaneous ordering occurs in certain regions of the crystal. The growth‐rate of the spinodal wavelength λ varies linearly in time. This unusual quasi‐ripening process is discussed in relation to the characteristic features of diffusion in (semiconducting) oxides.
Computerunterstützte Thermodynamik fester Ni–Pd Legierungen über die Knudsenzellen‐Massenspektrometrie und Berechnung des Zustandsdiagrammes
Authors: Kopecky K. , Belegratis M. S. , Neckel A. , Tomiska J.
Published: July 2012

Solid Ni–Pd alloys have been investigated thermodynamically by means of the computer‐aided Knudsen cell mass spectrometry. Thermodynamic evaluation has been performed by applying the enlarged “Algebraic Intensity‐Ratio”‐method (A.I.R.). The thermodynamic excess properties can be described algebraically by means of T.A.P.‐series (Thermodynamically adapted power series) with three adjustable parameters (C = [8757.5–11.2810 T/K] J/mol; C = [–18573.3 + 5.1073 T/K] J/mol; C = [3908.0–0.4558] J/mol). – At higher temperatures solid Ni–Pd alloys are characterised by negative molar excess Gibbs energies GE, and slightly positive molar excess entropies SE. At 1500 K the minimum GE‐value is –3270 J/mol (57 at.% Pd), and the maximum SE‐value is 2.25 J/mol·K (43.7 at.% Pd). Ni–Pd alloys with Pd contents with less than 50 at.% Pd show endothermic molar heats of mixing HE (maximum value: 835 J/mol at 21.5 at.% Pd), whereas Ni–Pd alloys with more than 50 at.% Pd show slightly exothermic HE‐values (minimum value: –575 J/mol at 79.5 at.% Pd). The thermodynamic Pd‐activities aPd exhibit at 1500 K over the whole concentration range slightly negative deviations from Raoult's law. The thermodynamic Ni‐activities aNi of the Ni‐rich solid alloys (xPD < 0.25) show at 1500 K nearly ideality, Ni–Pd alloys with higher Pd contents than 25 at.% Pd were found to show slightly negative deviations from ideality. – The phase diagram has been computed by means of a generally applicable procedure for the calculation of the equilibrium compositions of coexisting phases. The calculations were based upon the results of this work, the thermodynamic data from mass spectrometric studies on the liquid phase, and literature data for the heat capacities and enthalpies of Ni and Pd.
A.C. Impedance Studies of Glassy and Crystalline Lithium Aluminosilicate Compounds
Authors: Munro B. , Schrader M. , Heitjans P.
Published: July 2012

A.C. impedance spectroscopy was used to characterise the electrical conductivity behaviour of polycrystalline β‐LiAlSi2O6, β‐LiAlSiO4 and the corresponding glasses with identical stoichiometric compositions. Two bulk conduction processes with different activation energies were detected for β‐LiAlSiO4. The dispersion in the conductivity of the samples, the non‐Debye conductivity relaxation and the frequency dependence of the a.c. activation energies are discussed. The problem of how best to compare data from impedance measurements with results obtained from NMR relaxation experiments is addressed. It was found that diagrams of log resistivity against reciprocal temperature, plotted for individual frequencies, are suitable for comparing directly with NMR data.
Observation of Two Relaxation Processes in an Ion Conducting Glass Yields New Structural Information
Authors: Cramer C. , Funke K.
Published: July 2012

The frequency dependent ionic conductivity of the glass B2O3·0.56Li2O·0.45 LiBr has been measured from 1kHz up to 60 GHz, at temperatures up to 573 K. At first sight, the frequency spectra seem to conform with the so‐called “new universality”, i.e., with a σ(ω) ∝ ω1.0 power law at high frequencies/low temperatures. However, inspection of Arrhenius plots constructed at different frequencies clearly shows that two very well defined processes are superimposed, featuring different activation energies and different power‐law exponents. The latter are 0.67 and 1.30, respectively, while a genuine power law with exponent 1.0 does not exist. The two processes are identified with translational jump diffusion (including jump relaxation) and a non‐Debye localised reorientational motion of the ions within a given neighbourhood.
Alkali Intercalation into Layered Compounds: UHV in‐situ Preparation and Reactivity
Authors: Schellenberger A. , Jaegermann W. , Pettenkofer C. , Papageorgopoulos C. A. , Kamaratos M.
Published: July 2012

Li was adsorbed at room temperature (RT) onto UHV cleaved 2H WX2 (X = S, Se) and 1T TaS2 (0001) van der Waals surfaces. On TaS2 Li is intercalated in terms of the rigid band model leading to several phase transitions of the charge density waves. On WX2 Li is intercalated for low concentrations and leads to a decomposition reaction to Li2S and W0 for high concentrations. These experimental results and those of previously studied alkali/layered chalcogenide combinations and their reactivity are discussed in terms of thermodynamic, kinetic and electronic effects.
Defect Chemistry and Luminescence of ZnS: Cu, Au, Al
Authors: Bredol M. , Merikhi J. , Ronda C.
Published: July 2012

Present high quality CRT TV sets employ wurtzite–(Zn,Cd)S:Cu,Al phosphor or its Cd‐free variant sphalerite‐ZnS:Cu,Au,Al to generate the green primary colour. If prepared properly, both phosphors exhibit the desired emission properties. However, the Au‐codoped material tends to large variations of the emission as a function of the preparation procedure and thus is more demanding in terms of precise control of the manufacturing process. – This work aims at a better understanding of these peculiarities. Experiments are presented which demonstrate the large influence of the defect chemistry of the ZnS‐host on the Au‐related emission, whereas the Cu‐related emission is affected to a lesser extent. – Possible techniques for a fine‐tuning of the emission spectrum are discussed and evaluated according to the requirements of screen manufacture.
Formation of Aluminium(III)‐Monocarboxylates in Aqueous Solution
Authors: Pohlmeier Andreas , Thesing Ulrich , Knoche Wilhelm
Published: July 2012

By means of stopped‐flow experiments equilibrium and rate constants are determined for the weak complexation of the aluminium(III)‐ion with formate, acetate, chloroacetate and benzoate. For the innersphere complex formation both equilibrium and rate constants depend on the nature of the ligand, and a linear free energy relation is observed between rate constants and dissociation constants of the corresponding acids.
Volume‐Explicit Perturbed Hard‐Sphere Equation of State for Dense Gases at High Pressures
Authors: Nezbeda Ivo , Vörtler Horst L.
Published: July 2012

An attempt is made to construct an equation of state of dense gases at high pressures in a volume‐explicit form. The equation is a simple perturbed hard sphere equation and is based on the finding that the volume‐explicit equation of state of the fluid of hard spheres captures not only qualitatively but also, roughly, quantitatively the temperature‐ and pressure‐dependence of volume of non‐associating gases at these conditions. The equation is applied to geologically important species, H2, N2, CO, CO2, and CH4, at pressures greater than 1 kbar. The results are compared with existing purely empirical equations and clearly demonstrate the superiority of the proposed equation over the empirical ones.
Double and Triple Helices of Nucleic Acid Polymers, Studied by UV‐Resonance Raman Spectroscopy
Authors: Gfrörer A. , Schnetter M. E. , Wolfrum J. , Greulich K. O.
Published: July 2012

UY‐resonance Raman (RR) spectra with laser excitation at 260 nm and 220 nm were taken of the triple helix poly (U) · poly(A) · poly(U), the double helix poly(A) · poly(U) and a random copolymer poly(AU). The experiments were carried out both in H2O and in D2O as solvent. It is shown that by appropriate choice of excitation wavelength, structure‐spectra correlations can be established that allow these different conformations to be clearly distinguished. Whereas the formation of the double helix poly(A) · poly(U) results in both frequency and intensity changes, only minor frequency shifts are discernible when we compare the spectra of the double helix and the triple helix poly(U) · poly(A) · poly(U). As far as the uracil modes are concerned, no significant differences between the spectra of the triple and the double helices can be discerned. Therefore the RR‐spectra indicate a very similar base conformation of the two poly(U) strands in poly(U) · poly(A) · poly(U) and that in poly(U) · poly(A). However, there are considerable changes in the relative intensities of strong adenine modes with 260 nm excitation. For example, the intensity ratio of bands around 1480 cm−1 and 1338 cm−1 increases from 0.8 in poly(A), and 0.95 in poly(A) · poly(U) to 1.4 in poly(U) · poly(A) · poly(U). The spectra suggest that both the poly(U) strands in the triple helix are of quite similar structure, whereas the conformation of the poly(A) strands changes when triple helix is formed. With 220 nm excitation, no prominent marker bands or intensity patterns are found that would allow a distinction between double and triple helical conformations. The experiments demonstrate that UV‐Raman spectroscopy, with its possibility to choose an appropriate excitation wavelength adds a valuable degree of freedom in identifying different nucleic acid structures on the basis of intensity criteria.
On the Temperature Dependence of the Second Refractivity Virial Coefficient
Authors: Artym R. , Preiss U.
Published: July 2012

It has been shown that the second refractivity virial coefficient bR vanishes at the Boyle temperature TB. A theory has been developed with account of change of sign of bR at TB, and analytical formulas have been derived. For the first time the temperature dependence of bR has been calculated for He at temperatures over the range 5 K to 800 K using the Woolley potential.
Formation of Metal Clusters in Zeolites Studied by Differential X‐Ray Scattering
Authors: Vogel W. , Sachtler W. M. H. , Zhang Z.
Published: July 2012

Pd/NaY catalysts, ex situ calcined at 500°C and in situ reduced at 200°C, contain mainly small palladium clusters which are identified by XRD as Pd13 icosahedra. A fraction of 20 wt% are larger than the supercage dimension and produce lattice damage of the NaY support. Admission of CO at room temperature partly transforms the particle structure to fcc. Depending on temperature and time of CO exposure, crystallites in the order of 100 Å in size are formed. Methanol exposure at 224°C for 75 min decreases the X‐ray dispersion from 84% to 54%.
Infrared Study of Supported Rhodium Catalysts Exposed to CO/H2 Mixtures at High Pressure and Temperature
Authors: Mcquire Mandy W. , Rochester Colin H.
Published: July 2012

Infrared spectra have been recorded of Rh/SiO2 catalyst exposed to CO/H2 mixtures at various temperatures (473–553 K), pressures (3–50 atm) and CO:H2 ratios (1:14 to 14:1). Information was gained about surface hydroxyl groups on the support, the formation of gaseous methane, adsorbed carbon monoxide on rhodium and surface species containing alkyl groups. The dominant observed products of reaction were methoxy and ethoxy groups on the silica support, methane and higher hydrocarbons consisting predominantly of methylene chains. Depending on reaction conditions selectivities could be widely varied to give product distributions including 100% methoxy/methanol, a high proportion of ethoxy/ethanol or 100% higher hydrocarbon. Methane became more favoured at higher temperature, methanol rather than ethanol was favoured at low temperature and high pressure and higher hydrocarbons were favoured by CO‐rich feedstock. — Reaction of CO/H2 over Rh/Al2O3 and Rh/TiO2 gave higher selectivity to methane than Rh/SiO2 and also led to adsorbed carboxylate species on the oxide supports. The products were in part formed by catalysis involving the oxide components of the catalysts.
Reaction of CO2/H2 on K‐Cu(100): RAIRS Studies at Ultrahigh Vacuum and Higher Pressures
Authors: Pritchard J. , Chadwick D. , Zheng K.
Published: July 2012

The reaction of CO2/H2 on clean and potassium dosed Cu(100) was investigated by in situ RAIRS using a high pressure gas cell. For clean Cu(100), exposure to 120 torr of CO2/H2 mixture in the RAIRS cell from 25°C to 200°C resulted in no clearly resolvable RAIRS bands. The result indicates that under the conditions used, the coverage of formate must be very low. A K predosed Cu(100) surface was exposed to CO2/H2 in the RAIRS cell at 120 torr. At temperatures lower than 70°C, weak RAIRS features were observed, the most prominent being at ∼1600 cm−1. At temperatures above 70°C, a RAIRS band was observed at ∼1550 cm−1 with the band at 1600 cm−1 disappearing. CO2 adsorption on N2O oxidized K/Cu(100) surfaces also produced a RAIRS band at ∼1545–1550 cm−1, suggesting that the surface was oxidized in CO2/H2 at elevated temperatures and reacted with CO2 to form a carbonate species.
Variation of the Binding Energy due to High Electrostatic Fields (NO on Rh(111))
Authors: Madenach R. P. , Abend G. , Kreuzer H. J. , Block J. H.
Published: July 2012

The influence of high electrostatic field strengths (V/nm to V/A) on the binding energy has been studied by pulsed field desorption mass spectrometry (PFDMS). For this purpose the equilibrium between adsorption and thermal desorption of NO on Rh(111) has been observed as a function of temperature and field strength. — We obtained 102.6 kJ/mol for the binding energy of NO on Rh(111) which is in good agreement with TPD measurements of Bugyi and Solymosi [1]. With a negative field strength of 3 V/nm the binding energy increases about 10%, and a decrease of about the same amount was observed for a positive field of 3 V/nm. — In an attempt to understand the effect of high field strengths on binding energy, calculations of the change in electron density due to various field strengths have been performed. These calculations were carried out within density functional theory using a nonlocal spin density approximation. The change of the electron density involved in the bonding will be shown.
Work Function Investigations on Nickel Surfaces in Dynamic Equilibrium with Water Vapor Covering the Pressure Range 10−3 — 10 Pa
Authors: Oertel M. , Schulze M. , Bradke M. V. , Schnurnberger W.
Published: July 2012

The interaction of water vapor with clean and oxidized surfaces of polycrystalline Nickel was studied at temperatures from 300 K to 430 K. — The changes of the work function Δθ were recorded as a function of the interaction time of water with these surfaces. Immediately after starting water exposure a steep decrease of the work function was observed at all temperatures studied. The amount of this initial decrease depends on the H2O partial pressure. The subsequently observed increase of the work function was found to be mainly temperature dependent with a typical time constant of a few minutes. — Determining the relative stability of the H2O molecules and their dissociation products the influence of the substrate temperature must be emphasized. Size and sign of Δθ in the equilibrium state change due to variation of the substrate temperature from 320 K to 435 K. — The observed time dependence of the work function was attributed to a two step dissociation process. Its slight increase was related to the dissociation of OHad and to the beginning of oxide layer formation. This work function increase is a thermally activated process with an activation energy of 61.8 kJ/mol and preexponential factor of 6.3 · 106 s−1.
Molecular Structure and Dynamics within Self‐Assembled Hexakisalkoxy‐triphenylene Monolayers and Alkane Wetting Films
Authors: Askadskaya L. , Boeffel C. , Rabe J. P.
Published: July 2012

Scanning tunneling microscopy (STM) has been employed to investigate two classes of ultrathin molecular layers on the basal plane of highly oriented pyrolytic graphite (HOPG). First, molecules with three‐fold symmetry were studied at solid‐fluid interfaces. Structure and dynamics within the first monolayer of hexa‐substituted triphenylenes with two different substitutions, —OC7H15 and —OC16H33, could be readily observed, since the molecules exhibit a strong contrast between the triphenylene cores and the alkyl side chains. While the dynamic disorder prohibited atomic‐scale resolution imaging, sub‐molecular resolution images were suitable to determine packing patterns together with a number of characteristic packing defects. No ordered monolayers could be observed from unsymmetrically substituted triphenylenes like triphenylene dimers, which in bulk materials do only exhibit glassy but no crystalline phases. Secondly, long chain alkanes have been observed, for the first time, in the vicinity of the edge of a solidified alkane‐melt drop. The data indicate frozen disordered lamellae at the drop‐edge, where the alkane phase is still many monolayers thick, while a columnar phase is found in a thin precursor layer some millimeter away from the drop‐edge.
A Computational Evaluation of Populations of Complexes under Atmospheric Conditions: The (H2O)2 and (CO2)2 Cases
Authors: Slanina ZdenĚK
Published: July 2012

Various van‐der‐Waals or hydrogen‐bonded complexes have been understood as significant components of the Earth's or other planetary atmospheres. The species can be characterized by computational‐chemistry techniques. Present possibilities are illustrated with the water dimer described by flexible potentials. It is shown that the dimer mole fraction in equilibrium with the monomer should be about 0.1 ‐0.2% close to the Earth's surface under saturation conditions. For sample atmospheric conditions about 3 km above the surface the mole fraction decreases to some 0.004‐0.005%. Another example is supplied with the carbon dioxide dimer in the Venus atmosphere, using the Stogryn‐Hirschfelder treatment within a Lennard‐Jones scheme and calculations based on recent quantum chemical data. The dimer mole fraction in equilibrium with carbon dioxide can be higher than 4% close to the Venus surface and the fraction should decrease with distance from the surface.
Extension of the Group‐Contribution Equation of State Parameter Matrix for the Prediction of Phase Equilibria Containing Argon, Ammonia, Propene and Other Alkenes
Authors: Pusch Jens , Schmelzer JüRgen
Published: July 2012

The Group‐Contribution Equation of State (GC‐EOS) by Skjold‐Jørgensen [1, 2] for predicting phase equilibria has been extended by groups (components) Ar and NH3 and olefin‐groups C3H6, CH2 = CH, CH2 = C, CH = CH and CH = C. It was necessary to determine parameters for pure groups and to adjust binary interaction parameters. By comparison calculations were made using the Schmidt‐Wenzel‐EOS [3] and the hole model of Smirnova and Viktorov [4].
Dielectric Studies of the Association of Strongly Polar Molecules
Authors: Kȩdziora P. , Jadž J. , Bonnet P.
Published: July 2012

The dipole‐dipole association of compounds of different shape with the CN terminal group has been studied by the static dielectric polarization method. The apparent dipole moment behavior of nematogen molecules (n‐pentylcyanobiphenyl) with comparison to non‐nematogen molecules (benzonitrile) has been discussed.
Behaviour of the Electroclinic Effect and the Soft Mode Rotational Viscosity in the Smectic A Phase of Ferroelectric Liquid Crystalline Polymer/Monomer Mixtures
Authors: Bennemann Dirk , Bömelburg Jan , Heppke Gerd
Published: July 2012

Measurements of the electroclinic effect in the smectic A phase of a chiral side‐chain polyacrylate, of a low molecular mass liquid crystal with very similar structure and of mixtures between these two compounds are reported. The ratio of the induced tilt angle and the electric field strength is found to be independent of the concentration, whereas the coupling constant between induced tilt and induced polarization decreases with increasing amount of polymer. This behaviour of the electroclinic effect implies a considerably lower tilt controlling susceptibility coefficient for the chiral polyacrylate than for the low molecular mass compound. The values of the soft mode rotational viscosity of the polyacrylate, which are obtained from the electrooptical measurements in combination with dielectric spectroscopy, are found to be three orders of magnitude larger than for the monomer.
Ultrasonic Properties of a Nematic Sidechain Polysiloxane in the 100 MHz—1 GHz Range
Authors: Deeg F. W. , Diercksen K. , Bräuchle C.
Published: July 2012

Liquid crystalline polymers exhibit a number of properties, e.g. the viscoelastic behaviour in the ultrasonic range, which are neither observed in low molecular weight liquid crystals nor in isotropic polymers. Acoustic waves in the 100 MHz‐1 GHz range have been generated in a nematic liquid single crystal sidechain polysiloxane elastomer through impulsive stimulated thermal scattering and their propagation characteristics have been studied. The experiments reveal a dispersion step for the speed of sound and a strong anisotropy for the acoustic attenuation constant in the investigated frequency range consistent with a recently proposed hydrodynamic model of a coupling of the elasticity to the nematic order parameter in this class of substances.