bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport and Magnetic Properties of Assemblies of one Dimensional Metallic Particles Produced by Irradiation of Organic Conductors
Authors: Zuppiroli L.
Published: July 2012

Organic conductors are molecular crystals composed of conducting stacks of molecules. Their electronic properties are quasi‐one‐dimensional. Submitted to irradiation by ionizing particles, these assemblies of parallel metallic chains are transformed in assemblies of metallic segments, bounded by strong defects. The transport and magnetic properties of a large variety of irradiated organic conductors have been measured; all these experimental results are interpreted very simply within the framework of models based on the electronic properties of one‐dimensional metallic particles: the magnetic susceptibility reveals the presence of unpaired spins on a half of the metallic segments, as expected; the longitudinal and transverse conductivities of such assemblies are dominated by the hopping of electrons between metallic segments, controlled by the differences in the level structure between neighbouring segments of different lengths; the electron spin resonance linewidth decreases exponentially with the lengths of the segments due to the confinement of spins within the metallic particles. – It is demonstrated that most of the electronic properties of the non magnetic metallic clusters, which are difficult to observe experimentally in three dimensional clusters, are very easy to study in one dimension.
Experiments on Simulated Circumstellar Clusters
Authors: Donn Bertram
Published: July 2012

Solid grains in a gas cloud ejected from a star condense in a hot gaseous medium with all elements present in their cosmic abundances. A study of this phenomena requires knowledge of the initial clusters that form from a multielement refractory system. Experiments on SiO, Mg + SiO and Fe + SiO clusters in a nitrogen matrix have been performed. Much of the results for the first two systems have been reported. These will be summarized and the iron silicate experiments described. A flow system with a quadrupole mass spectrometer detector has been built to study the temperature dependence of clusters in the gas phase. The systems to be studied are various combinations of Si, O, Mg, Fe and ultimately Ca and C. These six elements constitute the major fraction of refractory cosmic species.
Raman Measurements of Matrix‐Isolated Small Metal Clusters
Authors: Froben F. W. , Schulze W.
Published: July 2012

Small clusters of Group Ia, Ib, IIIa, IVa and Va homonuclear metals are measured in rare gas matrices. The results for Lix, Nax and Kx and problems concerning the identity of the species are discussed together with some theoretical predictions.
ESR‐Spectroscopic Investigation of the Homogeneous Electron Transfer Reactions between Substituted p‐Phenylenediamines and Quinonediimines, and the Validity of Marcus' Theory. II. Temperature Dependence and Activation Parameters
Authors: Grampp Günter , Jaenicke Walther
Published: July 2012

Using ESR‐line broadening the rate constants of electron self exchange between five substituted p‐phenylenediamines, semiquinonediimines, and quinonediimines in six aprotic solvents are measured in the temperature range 230 K < T < 360 K. A linear dependence of ln k on the solvent parameter γ = 1/n2 ‐ 1/ϵ (n = refractive index, ϵ = permittivity) is observed for each temperature as expected from Marcus' theory, also a linear dependence of ln kT−1/2 on T−1 for each solvent. The experimental surface ln k(γ, T), however, is not in agreement with Marcus' theory, the resulting activation energies and ‐entropies being proportional to γ and increasing from negative values at low γ (extrapolated) to positive at high γ. The deviations are explained by a temperature‐dependent reaction distance and a preceding association between the radical cations and the counterions which increases strongly with decreasing polarity of the solvent.
A LEED and RHEED Investigation of Cu on Au(111) in the Underpotential Region
Authors: Nakai Y. , Zei M. S. , Kolb D. M. , Lehmpfuhl G.
Published: July 2012

The structure of Cu adsorbates, deposited electrochemically up to one monolayer onto Au(111) at underpotentials, has been investigated using LEED and RHEED after transfer of the gold electrode from the electrochemical cell into an UHV chamber. Before electrochemical deposition, the gold surface was thoroughly cleaned in the UHV‐chamber by argon bombardment and subsequent annealing. The Cu adsorbate is then found to yield a (√3 × √3)R30° superstructure at medium coverages, which is in clear contrast to the growth behaviour for Cu evaporated in UHV onto a bare Au(111) surface, where pseudo‐morphic growth is observed from the very beginning.
Thermal Desorption and Photoelectron Spectroscopy of NO Adsorbed on ZnO(1010)
Authors: Zwicker G. , Ranke W. , Jacobi K. , Pöss D.
Published: July 2012

Exposure of the ZnO(1010) prism face to NO at 90 K leads to two molecularly adsorbed NO species. The weakly bound form desorbs at 110 K and the strongly bound form desorbs at 420 K for low exposure and at 300 to 450 K for high exposures. Adsorption of the strongly bound form is activated and slower than of the weakly bound NO. Simultaneously, NO reacts partly to N2O at 90 K. N2O desorbs at 140 K, oxygen desorption is not observed and it is concluded that the oxygen formed during the NO to N2O conversion diffuses into the substrate. After annealing to 190 K, the weakly bound NO and N2O desorb. After several cycles of reexposing and annealing to 190 K, N2O formation is completely suppressed due to accumulation of either oxygen or the strongly bound form of NO or both. The strongly bound NO increases, the weakly bound NO decreases the electron affinity χ. After saturation with the strongly bound form, the final increase of χ amounts to 1.2 eV.
A Laser Temperature Jump Investigation of the Interaction between Proflavine and Calf‐Thymus Deoxyribonucleic Acid at Low and High Ionic Strength Avoiding Electric Field Effects
Authors: Marcandalli B. , Winzek C. , Holzwarth J. F.
Published: July 2012

We have used our very fast “Iodine‐Laser Temperature‐Jump” technique with a time resolution between 10−10 and 100 s to investigate the intercalation of proflavine into calf thymus DNA. Salt concentrations between 10−2 and 1 M and temperatures from 290 to 320 K were used. The DNA concentration ranged from 10−3 to 10−5 M and was always in large excess of the proflavine concentration to avoid aggregation of the dye in solution as well as on the surface of DNA. Under all experimental conditions only a single relaxation time which varied between 10−4 and 10−3 s could be detected. This result is in contrast to all temperature jump experiments performed so far using “Joule‐heating” equipments. The reason for this behaviour is that our technique is the only one which avoids the electric field effects inevitably associated with the “Joule‐heating” T‐jump arrangements.
205Tl NMR in Molten TlCl ‐ Tl2S Mixtures
Authors: Nakamura Yoshio , Baba Kazuhiro , Shimoji Mitsuo , Shimokawa Shigezo
Published: July 2012

NMR shifts and spectral linewidths of 205Tl in molten TlCl ‐ Tl2S mixtures have been measured as a function of composition. With increasing Tl2S content the chemical shifts increase toward the paramagnetic direction and the lines become broader. At the Tl2S‐rich end, no resolvable spectra were obtained due to anormally broad linewidth or rapid relaxation rate. This rapid relaxation rate may be attributed to the formation of the paramagnetic center Tl2+; their concentration and lifetime have been estimated from the present NMR data and electronic conductivity data.
Thermal Conductivity of Ammonia in a Large Temperature and Pressure Range Including the Critical Region
Authors: Tufeu R. , Ivanov D. Y. , Garrabos Y. , Le Neindre B.
Published: July 2012

Using a coaxial cylinder apparatus, the thermal conductivity coefficient of ammonia was measured up to 80 MPa along nine quasi‐isotherms in the supercritical regime and one quasi isotherm below the critical temperature. The thermal conductivity in the critical region was carefully investigated. The results are compared to previous data. A semi empirical equation is proposed to correlate the data in the supercritical regime.
Nonequilibrium Phase Transitions with Hysteresis in Solid Catalysts. The System Copper‐Oxygen‐Propene
Authors: Greger M. , Ihme B. , Kotter M. , Riekert L.
Published: July 2012

The rates of formation of acrolein, CO2and CO from propene and oxygen on oxides of copper as catalysts have been investigated atp= 50 mbar, 4 mbar ≤p≤ 200 mbar in a differential reactor at 645 and 735 K. Oxygen contents of the catalysts have been determined in situ by titration with H2at 713 K. Selectivity and rate of oxygen consumption at steady state of the catalyst arenotsingle valued functions of gas phase composition. Mainly the selectivity of acrolein formation follows a closed hysteresis‐loop over a finite interval ofp. This phenomenon can be understood as due to hysteresis in the phase transition between CuO and Cu2O under nonequilibrium conditions, which has been predicted by Wagner [1] on the basis of theoretical considerations. The results demonstrate that the steady state of a solid catalyst can be indeterminate for a given initial condition and a complete set of intensive variables describing the surroundings.
Infrared Spectrum of Isoselenocyanic Acid, HNCSe
Authors: Vogt Jürgen , Winnewisser Manfred
Published: July 2012

The preparation of gaseous isoselenocyanic acid, HNCSe, first reported by Landsberg [10] in 1979, has been considerably improved. This unstable molecule decays in the gaseous phase according to a second‐order reaction. In the infrared region the vibrational spectrum of HNCSe was measured in the gaseous phase and in an argon matrix at low resolution. The combined analysis of the vibrational spectra of HNCSe yielded the assignment of the A fundamental vibrations. From the gaseous phase absorptions v4 = 3535 cm−1, v2 = 1957 cm−1 and v3 = 625 cm−1 could be assigned. The bands in the gas phase spectrum at 760, 583, 521 and 419 cm−1 cannot be considered as band centers. They are the result of the superposition of the subband structures of the bending modes v4, v5 and v6 exhibiting quasilinear behaviour. This can be deduced from the wavenumber positions of v4 = 508 cm−1 and v5 = 419 cm−1 observed in the argon matrix spectra. Due to the rapid H/D exchange the infrared spectrum of DNCSe could not be measured.
Direct Determination of the Rate Constant for the Reaction CH2 + O2 with a LMR‐Spectrometer
Authors: Böhland T. , Temps F. , Wagner H. Gg.
Published: July 2012

The reaction

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was studied at room temperature in an isothermal discharge flow system. CH2‐radicals were produced either in a microwave discharge of CH2CO highly diluted in Helium or via the reaction O + CH2CO → CH2 + CO2. The CH2‐concentration was measured by laser magnetic resonance. From the pseudo first order decay of CH2 in the presence of a large excess of oxygen the rate constant for reaction (1) was found to be

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Thermodynamics of Polydimethylsiloxane‐Solutions III. Experimental Results and Theoretical Calculations of Solvent Activities
Authors: Dolch E. , Glaser M. , Heintz A. , Wagner H. , Lichtenthaler R. N.
Published: July 2012

Solvent activities of seven organic solvents in mixtures with PDMS (Polydimethylsiloxane) of different molecular weights have been measured at 298.15 and 313.15 K using the vapor sorption technique. The results have been used for testing the thermodynamic consistency of an extended version of Flory's theory. In this theoretical approach a more detailed expression of the combinatorial entropy is used and found to be superior to the common Flory‐Huggins expression.
Dielectric Relaxation Study of Dynamic Properties of Hydrated Phospholipid Bilayers
Authors: Enders A. , Nimtz G.
Published: July 2012

The dynamical properties of hydrated di‐myristoyl‐phosphatidylcholin were studied at microwave frequencies. The relaxation frequency and the energy of bound water were determined: the properties of bound water vary quasi‐continuously with the amount of bound water. Water is stronger bound in the fluidlike than in the gel phase. For the first time we could measure directly the trans‐gauche isomerization rotation of the alcyl chains. It was observed that two mechanisms are separately operating at the phase transition of the hydrated bilayers: 1. a change of hydration coupled with a change of headgroup conformation and 2. the chain melting. The binding or release of water is preceding the chain melting or freezing by 1 K. It was found that hysteresis effects of the phase transition depend strongly on the rate of hydration.
Phase Equilibria in Liquid Crystalline Systems Part I. Synthesis and Liquid Crystalline Properties of Oligomers of the p‐Oxybenzoate Series
Authors: Ballauff M. , Wu D. , Flory P. J. , Barrall E. M.
Published: July 2012

Syntheses of the trimer (n = 3), tetramer (n = 4) and the pentamer (n = 5) of the p‐oxybenzoate series C6H5CO(–OC6H4CO)n‐2‐OC6H5 are reported. Densities and thermal expansion coefficients of the neat liquids were measured and phase transitions in the pure compounds and their binary mixtures were investigated by differential scanning calorimetry (DSC). The nematic‐isotropic transition is directly accessible only in the case of the tetramer (melting point 181°C, nematic‐isotropic transition temperature TNI = 254°); the trimer melts to an isotropic liquid at 136°C and the nematic‐isotropic transition of the pentamer (melting point 224°C) lies above the range of thermal stability. DSC results for the binary mixtures show the coexistence range of the nematic and the isotropic phases to be very small; it is obscured by pre‐ and post‐transition effects. In satisfactory approximation therefore, the binary mixtures can be treated as one‐component systems, and TNI may be identified with the maximum of the DSC peak. Values of TNI thus obtained are linear with respect to composition and may be extrapolated to obtain TNI = 100°C for the pure trimer and 464°C for the pure pentamer. As shown by conformational analysis, all conformers of a given homolog have virtually the same axial ratio. These compounds therefore can be treated as rigid rods.
Können flüssige Mischungen durch die Gittertheorie nach Guggenheim beschrieben werden?
Authors: Fischer Johann , Reschke Frank
Published: July 2012

By using perturbation theory it is shown that the lattice theory of Guggenheim applied to molecules of equal size makes good predictions for the excess Helmholtz energy aηE and the excess energy uηE for mixing at constant density. The differences of aηE and uηE to the excess quantities gpE and hpE for mixing at constant pressure, however, can be considerably large and are expressed analytically. These results are also essential for understanding new computer simulations. Finally, the applicability of the lattice theory to molecules of different sizes is investigated.
Thermodynamics of Solid Cu—Ni Alloys by Knudsen Cell Mass Spectrometry and Re‐Calculation of the Phase Diagram
Authors: Tomiska J. , Neckel A.
Published: July 2012

Solid Cu—Ni alloys have been investigated thermodynamically within the whole range of composition by Knudsen Cell Mass Spectrometry. The “Algebraic Intensity‐Ratio”‐method (A.I.R.) has been used for the determination of the thermodynamic mixing behavior. The thermodynamic activities aj show positive deviations from Raoult's law. The molar enthalpies of mixing HE and the molar excess Gibbs energies GE are positive over the whole range of composition. At 1350 K the maximum value of HE is 2420 J/mol (59.48 at‐% Ni), and the maximum value of GE is 3220 J/mol (53 at‐% Ni). The excess entropies SE are negative over the whole range of composition with a minimum value of — 0.719 J/mol · K at 36.71 at‐% Ni. The phase diagram has been re‐evaluated by using an analytical procedure which is based on the generalized Newton method for the numerical solution of equations. The calculations are based on the thermodynamic data obtained in this study, on the thermodynamic results from mass spectrometric studies on liquid Cu—Ni alloys, and on literature data for the heat capacities and the heats of melting of Cu and Ni.
Hydrogen‐Deuterium Atom Abstraction from Methyl Cyanide by CF3 Radicals
Authors: Pasteris L. , Oexler E. V. , Staricco E. H.
Published: July 2012

The reaction of CF3 radicals with CH3CN has been studied over the temperature range 298–623 K, using the photolysis of perfluoroacetic anhydride as a radical source. At temperatures higher than 473 K, the photolysis and the thermal decomposition of CF3I have also been used to generate CF3. — Arrhenius parameters for the reaction

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were measured relative to the CF3 recombination.

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The average value of the results from both sources of radicals gave the following parameters

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The high primary kinetic isotope effect and the non‐curved Arrhenius plot found confirm the absence of an addition reaction.
Photoelectrochemical Studies of Bis(triphenylphosphine)biquinoline Copper(I), Bis(biquinoline) Copper(I) and Bis(2,9‐dimethyl‐1,10‐phenanthroline) Copper(I) on SnO2 Electrodes
Authors: Breddels P. A. , Blasse G. , Casadonte D. J. , McMillin D. R.
Published: July 2012

The photoelectrochemical behaviour of Cu(PPh3)2biq+, Cu(biq)2+ and Cu(dmp)2+ has been examined. Here PPh3, biq and dmp denote triphenylphosphine, 2,2'‐biquinoline and 2,9‐dimethyl‐1,10‐phenanthroline, respectively. Thin films of these complexes deposited on a SnO2 electrode generate anodic photocurrents in a photoelectrochemical cell upon irradiation in their metal‐to‐ligand charge‐transfer absorption band. The stability of the photocurrents, however, is low and is due to photochemical decomposition of the dyes. The photoresponse is stabilized and enhanced by the addition of a supersensitizer, hydroquinone, to the electrolyte solution. The suppression of the photochemical decomposition is complete at hydroquinone levels of 10−3 M for each of the three Cu(I) complexes. The photocurrent quantum efficiencies in the presence of hydroquinone in the electrolyte solution have been measured. Peak values of 1%, 4% and 12% were attained for Cu(biq)2+, Cu(dmp)2+ and Cu(PPh3)2biq+, respectively. These quantum efficiencies are correlated with the lifetimes and redox potentials of the excited states of the complexes.
Eine einfache Methode zur Bestimmung von Dampfdrücken
Authors: Etzweiler F. , Senn E. , Neuner‐Jehle N.
Published: July 2012

Quantitative headspace analysis represents a simple method for the determination of vapor pressures. The method is based on the measurement of the substance concentration in the saturated vapor phase (headspace) which stays in equilibrium with the condensed phase. During the procedure the total amount of substance being present in a defined volume of vapor is collected on an adsorbent and quantified either by gravimetry or, after desorption from the carrier, by chromatography. The presented method delivers good results in a wide range of vapor pressures between 1 · 10−5 and 1 · 104 Pa.
Die Druckabhängigkeit der linearen Doppelbrechung eines cholesterischen Flüssigkristalls. Optische Rotation und Selektivreflexion einer Mischung von Cholesterylnonanoat und Cholesterylchlorid von 60‐−130°C und bis 3 kbar
Authors: Pollmann P. , Wiege B.
Published: July 2012

The pressure dependence of the linear birefringence of a cholesteric liquid crystal at constant temperature could be determined for the first time by combined measurements of the optical rotatory power and the selective light reflection up to 130°C and 3000 bar. From the birefringence data obtained in this way the corresponding pressure dependence of the order parameter η representing the degree of parallel orientation of the molecules was calculated fairly precisely. From these data follows that η at the transition point to the isotropic liquid phase is independent of the transition pressure.
An NMR Study of the Schlenk Equilibrium of tert‐Butylmagnesium Bromide in Tetrahydrofuran
Authors: Allen Peter E. M. , Hagias Stan , Mair Clyde , Williams Evan H.
Published: July 2012

A 300 MHz proton NMR determination of the thermodynamic parameters of the Schlenk equilibrium of tert‐butylmagnesium bromide in tetrahydrofuran is reported for the temperature range 285‐−330 K. In solutions where bromide is in excess over tert‐butyl groups other equilibria intervene below 285 K. However when the Grignard stoichiometry prevails concentrations are governed by the Schlenk equilibrium and its determined parameters to at least 260 K. — The Ashby assignments of the 1H resonances (low field: tBuMgBr, high field: tBu2Mg) are confirmed over the temperature range of our measurements but have been found to invert below 200‐−210 K. Resonances arising from impurities are assigned. — The 13C spectrum is assigned. The CH3 resonance of tBu2Mg occurs at a lower field than that of tBuMgBr. The equilibrium parameters determined from the 13C spectra over the temperature range 282‐−322 K agree with those determined from the 1H spectra though their precision is less.
Density and Pressure Dependence of the Critical Temperature near the Consolute Point of Isobutyric Acid (COOD)/Deuterium Oxide
Authors: Gansen P. , Woermann D.
Published: July 2012

Measurements of density of an isobutyric acid (COOD)/D2O mixture of critical composition (upper critical point; critical composition: xDA,c = 0.113; xDA: mole fraction of acid; critical temperature: Tc = 45.738°C) as function of temperature in the one fluid phase region are reported. The function p = P1 + P2t + P3t(1 ‐ α) is fitted to the data (p: density; P1, P2, P3: constants; t: reduced temperature difference (T–Tc)/Tc; α: critical exponent, α = 0.11). P3 has a positive value. Consequently, the coefficient dTc/dP (pressure dependence of critical temperature) has to be negative for thermodynamic reasons. This is confirmed by direct measurements. The experimentally determined values of P1, P3 and dTc/dP together with the value of the correlation length of local concentration fluctuations taken from the literature are consistent with the predictions of the amplitude relation of two‐scale factor universality. — For isobutyric acid/H2O, D2O mixtures of critical composition there exists a linear relation between the coefficient dTc/dP and the equivalent fraction of exchangeable protons Y (=nH/(nH + nD)). dTc/dP decreases from dTc/dP = −40.9 mK bar−1 for DA/D2O (Y=0) to dTc/dP = −55.0 mK bar−1 for HA/H2O (Y=1).
Ultrasonic Study of Nitro‐Benzene/Isooctane Mixtures near the Critical Consolute Point
Authors: Jaschull G. , Dunker H. , Woermann D.
Published: July 2012

The absorption and velocity of ultrasound are measured in a critical mixture of nitro‐benzene and isooctane (2,2,4‐trimethyl‐pentane) as function of the temperature difference (T–Tc) in the homogeneous phase region. The critical data of the system having an upper critical point are: critical temperature Tc = 29.16°C; critical composition ync = 0.525 (mass fraction of nitro‐benzene). The experiments are carried out in the temperature range 0.3 K ≤ (T–Tc) ≤ 21.8 K at seven frequencies between 9 MHz and 45 MHz. Four mixtures with off‐critical compositions and the pure components are also studied. — The sound absorption of the critical mixture is analysed in terms of the Bhattacharjee‐Ferrell theory. At the critical temperature the frequency dependence of ultrasound absorption is in agreement with the predictions of this theory. The data obtained at temperatures away from the critical temperature collapse on a single scaling curve when plotted as function of a reduced frequency given by the theory. Not all of the input data for the calculation of the temperature‐independent coefficient ω0 of the temperature‐dependent characteristic relaxation frequency are available for that system. Therefore, the coefficient ω0 is used as free parameter in a fitting procedure of the theoretical scaling function to the experimental scaling function. The best fit is obtained with ω0 = 15 MHz. The agreement between theory and experiment is good and supports the universality concept of the critical acoustic behavior.
A Two‐Fluid Theory for Liquid Mixtures with an Application to Poly(dimethyl Siloxane) Solutions etc.
Authors: Panayiotou Constantinos G.
Published: July 2012

A free‐volume, two‐fluid theory for liquid mixtures is presented. It is based on Flory's equation‐of‐state theory. Two versions differing in the assumption concerning the relation between the reduced volumes of the hypothetical fluids are discussed. In both versions, two adjustable binary parameters are used, one related to the interaction energies and the other to segment core volumes. Correction for non‐randomness is, also, provided. The theory is tested against experimental data on heats of mixing, volumes of mixing and χ interaction parameters of five representative poly(dimethyl siloxane) solutions with satisfactory results. Relations with existing similar theories are discussed.
Thermodynamics and Solubility of Oxygen in Liquid Copper‐Lead Alloys at 1200°C from E.M.F. Measurements
Authors: Anik Sabri , Frohberg Martin G.
Published: July 2012

With the aid of the emf‐method the activity of oxygen in the total homogeneous region of copper‐lead alloys was determined at 1200°C. The logarithm of the activity coefficient of oxygen at constant alloy composition linearly depends on the oxygen concentration. The evaluation of the experimental data leads to the following values: magnified image. activity coefficients of oxygen (infinite dilute solution) magnified image.

For the solution reaction of oxygen in liquid lead and copper and their alloys the free energy of dissolution could be determined. For the pure metals the following values were obtained for 1200°C magnified image.

A statistically derived solution model for gases in liquid binary metallic melts was applied to this system and is in full agreement with the experiments also at higher oxygen concentrations.
Potential Dependence and Time Evolution of the Double Layer Structure and Topography of Silver Electrodes. Part I: Smooth Silver Films
Authors: Waser Rainer , Weil Konrad G.
Published: July 2012

Double layer capacity of evaporated silver film electrodes was studied as a function of potential and of time in solutions containing different strongly adsorbable species. The potential regime of specific adsorption of chloride, cyanide, thiocyanate, and sulfide ions is determined. From the time dependence of the double layer capacitance as well as from electron micrographs, it can be deduced that surface migration takes place which leads to a flattening of the surface. In the case of sulfide and thiocyanate ions an additional process leads to a marked decrease in the capacity, which at the same time becomes nearly potential independent. This observation is attributed to the formation of an adsorbed layer of complexes.
Fast Ionic Conductivity and Dielectric Properties of the Lithium Halide Spinels Li2MnCl4, Li2CdCl4, Li2MnBr4, and Li2CdBr4
Authors: Schmidt W. , Lutz H. D.
Published: July 2012

The lithium bromide spinels Li2MnBr4 and Li2CdBr4 exhibit fast ionic conductivity in the solid state as the corresponding chloride spinels. The specific conductivities of the bromide spinels, however, are slightly smaller than those of the chlorides, e.g. for the cadmium compounds 0.11 and 0.26 Ω−1 cm−1 at 400°C, respectively. Even Li2MnCl4‐−4xBr4x solid solutions do not show higher conductivity than pure Li2MnCl4. The activation energies for conduction decrease at higher temperatures, e.g. from 60 to 33 kJ mol−1 for Li2MnBr4, caused by disorder of the cation sublattice at elevated temperatures. The non‐ideal dielectric behaviour of the lithium ion conducting compounds shown by a characteristic inclination of the spurs and skewness of the semicircles in the impedance diagrams can be correlated to both structure changes (disorder at elevated temperatures) and the different polarizability of the halide ions.
Raman Scattering: Fast Axial Rotation of Methylhalides II
Authors: Gompf J. , Versmold H.
Published: July 2012

In extension of a previous study of liquid CH3CN, CH3I, CD3I, CH3Cl and CH3F, the density dependence of the degenerate methyl stretch Raman band of fluid CH3F at 50°C is investigated. The Raman bands are analyzed in the slow, intermediate and fast modulation limit of the Kubo model as well as in terms of the J‐diffusion model both with and without Coriolis interaction. A modification of the J‐diffusion model with decoupled collision frequency parameters for the reorientation of different spherical tensor components is also applied. Following theoretical arguments, the experimental correlation functions are decomposed into two partial correlation functions g1(2)(t) and g2(2)(t). The partial correlation functions g2(2)(t) are found to be systematically disturbed by non‐orientational, presumably collision‐induced effects. The behaviour of the partial correlation functions g1(2)(t) is in reasonable agreement with nuclear magnetic relaxation results. The J‐diffusion model in its simple form, characterized by only one collision frequency, is found to be incapable to simultaneously describe the spinning and tumbling motion of the molecules studied.
Absorption and Fluorescence Spectra, pKa Values, and Fluorescence Lifetimes of Monohydroxyflavones and Monomethoxyflavones
Authors: Wolfbeis Otto S. , Leiner Marc , Hochmuth Petra , Geiger Hans
Published: July 2012

The absorption and fluorescence spectra of all isomeric hydroxyflavones and methoxyflavones, except for the photolabile 3‐methoxyflavone, have been measured in organic solvents and in aqueous solutions of various acidity. With the exception of 5‐hydroxyflavone, all are found to be fluorescent in methanol and water solution. On the other hand, there is virtually no fluorescence observed in cyclohexane solution, a fact that is interpreted in terms of high intersystem crossing rates and the El‐Sayed selection rules. – Except for the 3‐hydroxy and 7‐hydroxy isomers, the anions of hydroxyflavones are non‐fluorescent, whereas the protonated forms exhibit strong fluorescence emission. Methoxyflavones have higher fluorescence quantum yields than the corresponding hydroxyflavones and have fluorescence decay times ranging from 1.3 to 6.9 ns in methanol at room temperature. – The ground state pKa values of the hydroxyflavones range from 7.8 to 9.8, except for the 5‐hydroxy isomer (11.6). The pKa's governing the protonation step range from – 1.22 to – 1.55, again with the exception of the 5‐hydroxy isomer (– 3.1). The dissociation constants of the first excited singlet state were calculated with the help of the Förster‐Weller equation. The results predict a reversal of the most basic and most acidic sites of the hydroxyflavones. In aqueous solutions, this should result in the formation of excited state tautomers which, however, could be detected only for the 3‐hydroxy and 7‐hydroxy isomers. Apparently, the lifetimes of the other isomers are too short to allow the establishment of excited state equilibria.
Calculation of Fluid‐Fluid and Solid‐Fluid Phase Equilibria in Binary Mixtures at High Pressures
Authors: Deiters U. K. , Swaid I.
Published: July 2012

By integrating an equation of state, an expression for the Gibbs energy of binary fluid mixtures is derived and used to define the thermodynamic conditions of phase equilibrium. These conditions are solved numerically for the equilibrium concentrations. The same equation of state is used for liquid and vapour phases. From additional solid density data and the sublimation/melting pressure, solid‐liquid and solid‐gas equilibria can be calculated, provided that no miscibility occurs in the solid state. ‐ Calculations of phase equilibria have been carried out for several binary mixtures of nonpolar substances (noble gases, CO2 hydrocarbons) for pressures up to 200 MPa, using the Redlich‐Kwong equation and our own equation of state, which has been published earlier [1]. ‐ The Redlich‐Kwong equation represents the experimental phase equilibrium data at low pressures only, whereas the other equation achieves good agreement over the whole pressure range. I f the molecules differ very much in size, deviations from one‐fluid theory can be accounted for by using the Leland‐Mansoori‐Carnahan‐Starling function for rigid sphere mixtures in the repulsion term of our equation of state.
Equation‐of‐State Predictions of Phase Equilibria at Elevated Pressures in Mixtures Containing Methanol
Authors: Peschel W. , Wenzel H.
Published: July 2012

A 1−4−12 association model for methanol is proposed and applied in the equation‐of‐state method to calculate high‐pressure phase equilibria. An equation of the van der Waals type is used. Tests are performed in systems containing methanol + methane, ethane, propane, butane, ethene, propene, nitrogen, carbon monoxide, hydrogen, carbon dioxide and hydrogen sulfide. One single adjustable parameter is used for a binary system; this parameter is temperature independent and is zero for mixtures of methanol with alkanes. The method yields satisfactory predictions except for carbon dioxide and hydrogen sulfide where association between unlike molecules should be taken into account. Critical pressures in binary systems are overestimated.
Phase Equilibria in Fluid Systems (Invited Lecture)
Authors: Schneider Gerhard M.
Published: July 2012

The present review considers some phase equilibrium phenomena that are important for fluid extraction, supercritical fluid chromatography (SFC) and other applications. The most important types of phase diagrams involving liquid‐gas, liquid‐liquid and gas‐gas equilibria are treated. Recent results are given for binary mixtures of a highly volatile (mostly supercritical) component 1 (e.g. CO2, N2, CHF3, SF6, propane) with a relatively involatile component 2 of very different molecular size, shape, structure and/or polarity (predominantly long‐chained and cyclic hydrocarbons); here mainly critical locus curves and pressure‐concentration isotherms are considered. Finally the determination of capacity ratios and binary diffusion coefficients from supercritical fluid chromatography (SFC) is shortly discussed and recent results are presented.
Solubility of Solids in Supercritical Solvents I. General Principles (Invited Lecture)
Authors: Koningsveld R. , Kleintjens L. A. , Diepen G. A. M.
Published: July 2012

Solubility of solids in supercritical solvents is not essentially different from equilibrium crystallisation/solubility behaviour in normal liquids, except for the highly non‐ideal nature of nearcritical fluid mixtures. It can be shown quite generally that interactions in the fluid phase play a predominant role both at the first and the second critical endpoints in a binary system. Further factors of importance, particularly at the second critical endpoint, are the solute's heat of fusion and the location of its triplepoint compared with that of the critical point of the solvent. In the separation of two solid components ternary critical endpoint behaviour and the location of the ternary eutectic further determine the selectivity of the extraction. The mean‐field lattice‐gas model provides a useful tool to describe and predict fluid phase behaviour around critical points.
Fluid Phase Equilibria in Binary Ethylene + n‐Alkane Systems
Authors: De Loos Th. W. , Poot W. , Lichtenthaler R. N.
Published: July 2012

Vapour‐liquid equilibria in binary systems of ethylene with n‐eicosane, n‐hexacosane and n‐tetracontane have been measured in the temperature range 325 to 450 K and at pressures up to 40 MPa. The results show a distinct influence of the molecular weight of the n‐alkanes on these equilibria especially in the critical region. Except for the critical region the fluid phase equilibria in this kind of systems can be represented reasonably well using the Peng‐Robinson equation of state with temperature dependent pure component parameters a and b and two binary interaction parameters.
Variable‐Volume Circulation Apparatus for Measuring High‐Pressure Fluid‐Phase Equilibria
Authors: Radosz M.
Published: July 2012

A new variable‐volume circulation apparatus is presented for measuring high‐pressure fluid‐phase equilibria. This apparatus was designed to handle liquid‐liquid, vapor‐liquid and vapor‐liquid‐liquid equilibria at temperatures from 10 to 260°C and pressures up to 35 MPa (5000 psia). Such versatility is useful for obtaining data for supercritical and subcritical extraction of chemicals where all these types of phase equilibria can be observed. The apparatus is an efficient and accurate engineering tool to generate equilibrium phase compositions needed to develop and design separation processes. Its capabilities are illustrated with phase equilibrium data obtained for the supercritical carbon dioxide‐isopropanol and carbon dioxide‐isopropanol‐water systems.
An Experimental Method for Measuring Solubilities of Solids in Supercritical Fluids
Authors: Kwiatkowski Jacek , Lisicki Zygmunt , Majewski Wieslaw
Published: July 2012

An experimental method has been developed for measuring solubilities of organic solids in supercritical fluids. These solubilities are determined by measuring the volume of gas passing through the equilibrium cell and the difference of the mass of pure solid samples placed in this cell. For mixtures of organic solids, the mass difference, the gas volume, and the composition of solid phase taken from the gas after expansion have to be determined. Special design of the equilibrium cell allowing the control of saturation has been proposed. This method has been successfully used for measuring solubilities of organic solids such as fluorene, anthracene, phenanthrene, carbazole. Solubilities of mixtures of two organic solids have also been determined.
Mass Transfer from Solid Material in Gas Extraction
Authors: Brunner G.
Published: July 2012

Extraction rates of substances from solid substrates by supercritical gases have been determined for coffee beans and for rape oil seeds. In case of the indestructed coffee beans an unsteady extraction process prevails, which is determined by the transport of caffeine in the solid material. An approximate solution of the differential equations and a steady state approach are applicable to the long time part of the extraction process. In case of the crushed seeds a steady state mass transfer prevails which can be calculated by mass transfer calculations.
High Pressure Extraction of Crude Montan Wax
Authors: Braun Gero , Schmidt Hans
Published: July 2012

The high pressure extraction of crude montan wax was investigated at 20 to 100°C and at 150 to 500 bar with CO2 and ethylene and also with the fluorinated hydrocarbons Frigen 13, 13 B1 and 23. – In some cases the acid numbers, saponification numbers and setting points of the extracts differed markedly from those of the starting material. Especially at low extraction temperatures and pressures, where however solubilities are relatively low mainly low‐molecular weight wax components, such as free wax acids, wax alcohols and paraffins, as well as low‐molecular weight resin components were extracted. The corresponding high‐molecular weight components remain preferentially in the extraction residues.
New Methods for Characterization of Supercritical Fluid Solutions
Authors: Yonker C. R. , Wright B. W. , Udseth H. R. , Smith R. D.
Published: July 2012

The dependence of the solvating power of a supercritical fluid on pressure allows this property to be continuously changed from that of a gas to approaching that of a liquid. This ability has led to the development of new analytical, separation, and extraction methods. These methods include open tubular capillary column supercritical fluid chromatography, direct fluid injection‐mass spectrometry, and the direct combination of these techniques. The direct fluid injection process enables the transfer of nonvolatile or thermally labile compounds to the gas phase allowing the use of mass spectrometry and other analytical techniques. In addition, the rapid development of capillary column supercritical fluid chromatography now allows the high resolution separation of complex mixtures. Several examples are given to demonstrate the application of these methods for the characterization of complex supercritical fluid solutions and extracted mixtures.
The Luminescence of Bismuth Molybdates
Authors: Blasse G. , Boon L.
Published: July 2012

The luminescence properties of Bi2MoO6, Bi2MO2O9, and Bi2(MoO4)3 are reported. Excitation bands peak in the violet, and emission bands in the red spectral region. The results are discussed in connection with the crystal structures and compared with those of the corresponding tungstates. The luminescence of γ'‐Bi2MoO6 suggests fourfold coordination for molybdenum in the phase.
Photolumineszenz und Energietransfer im mit Seltenen Erden aktivierten Perowskit Ca2Lao,5Na0,5WO6
Authors: Otto R. , Kemmler‐Sack S.
Published: July 2012

By activation of the new host lattice Ca2La0.5Na0.5WO6 with trivalent rare earth ions an emission in the visible (Ln3+ = Sm, Eu, Dy, Ho, Er, Tm) or near infrared region (Nd, Ho, Er, Tm, Yb) is observed. Energy transfer from Nd3+ to Yb3+ and Er3+, Tm3+, Yb3+ to Ho3+ has been found to occur. The excitation, emission and diffuse reflectance spectra are discussed and compared to the properties of the systems Sr2La0.5Na0.5WO6: Ln3+.
A Resonance Raman Investigation on the Degradation of Polyacetylene During Electrochemical Cycling
Authors: Wieners Gerhard , Monkenbusch Michael , Wegner Gerhard
Published: July 2012

The degradation of a polyacetylene (PA) anode as proposed in PAy+ (ClO)y/LiClO4/PC type half cells has been investigated by resonant Raman scattering. – During electrochemical cycling, which modelled the operation of a PA/Li cell as a rechargeable storage battery, degradation becomes evident after only a few cycles. The charge regainable in the reduction steps after the seventh step is only 80 percent of the charge transferred in the preceding oxidation step. – The resonance Raman spectra have been analysed according to the method of Kuzmany which yields informations on the length distribution of conjugated segments in the sample. At the beginning of cycling a distribution of long segments and a distribution peaked at segment lengths around 5 double bonds have been found to coexist. After 7 cycles the long segments are already affected by the degradation and after a total of 27 cycles the Raman spectrum reveals the complete absence of conjugated segments longer than 10 double bonds.
Magnetic Susceptibility and Optical Absorption Studies of Rb – Au Alloys
Authors: Nicoloso N. , Freyland W.
Published: July 2012

The magnetic susceptibility of liquid Rb – Au alloys and the optical absorption of the solid and liquid equimolar alloy RbAu have been measured up to temperatures of 1000°C. The optical gap of solid RbAu shows Urbach type behaviour with E0 = 2.75 ± 0.1 eV. On melting it is reduced by about 1 eV: Eg(510°C) = 1.35 ± 0.1 eV. The magnetic susceptibility exhibits a strong diamagnetic minimum near the equiatomic composition yielding further evidence that liquid RbAu is semiconducting and predominantly ionic in bonding. The observed deviation from the expected susceptibility value for purely ionic RbAu and the high optical absorption in the near infrared suggest that localized paramagnetic electron states exist in the ionic liquid, possibly in equilibrium with free carriers. Like Cs – Au the alkali metal‐gold system Rb – Au thus closely resembles the alkali metal‐halogen systems the major differences arising from the reduced charge transfer and chemical ordering in these alloys.
Hydrogen Bonds in Hydrohalides of Amino Acids. A 79,81Br and 127I NQR Study
Authors: Fleck Silvia , Weiss Alarich
Published: July 2012

By 79,81Br− and 127I NQR the hydrobromides of glycine, l‐alanine, l‐leucine, l‐proline, semicarbazide and the hydroiodides of l‐leucine and semicarbazide were studied in the temperature range 77 ≦ T/K < decomposition point. Furthermore the compound diglycine sodium iodide monohydrate was investigated. A phase transition is observed for l‐leucine hydrobromide at 331.5 K, which is reversible and of small transition enthalpy, as shown by DTA. – 79,81Br NQR frequencies are strongly influenced by hydrogen bonds N+ – H…Br− and O – H…Br−. The 79Br frequencies can be grouped into two bands, one at 15 < ν/MHz < 19, the other at 24 < ν/MHz < 26. The high frequency group of compounds is characterized by N+ – H…Br− and O – H…Br− hydrogen bonds, whereas the bond scheme of the low frequency compounds is determined by bonds N+ – H…Br− only. This grouping of the amino acid hydrobromides according to frequency band and hydrogen bond scheme can be applied to the hydroiodides and to diglycine sodium iodide monohydrate, too.
Electron Transfer Reactions at n‐GaP (100) and (111) in Acetonitrile Solutions Facilitated by Cation Adsorption
Authors: McIntyre R. , Gerischer H.
Published: July 2012

Electron transfer reactions occurring at n‐GaP (111) and (100) electrodes have been investigated in acetonitrile solutions. In the presence of strongly oxidising cations, such as 10‐methylphenothiazine (10‐MP+·), Ferrocene (Cp2Fe+) and tetrathiafulvalen (TTF+·), it is shown that electron transfer proceeds directly from the conduction band to cations adsorbed at the semiconductor surface. Differential capacitance and photo/dark‐current measurements have been used to identify a considerable positive shift of the flatband potential (UFB) in the presence of the oxidising cation. This phenomenon is absent in the presence of a similarly oxidising neutral species. No evidence was obtained to support the model which proposes mediated electron transfer via surface states deep in the band gap.
The Concentration Dependence of the Eutectic Enthalpy of Transition in a Binary System with Application to the System Gelatin‐Water
Authors: Borchard W. , Luft B. , Reutner P.
Published: July 2012

Explicit formulae of general validity have been derived for the eutectic enthalpy of fusion of a binary system using the balance equations of masses and enthalpies for different coexisting phases. The formation of a compound‐like intermediate phase and the incomplete transition have been included which are essentially important for polymer solvent systems. A compound‐like intermediate phase has been stated in the system water‐gelatin at the eutectic temperature with a gelatin concentration of nearly 67% by weight. Nearly 10% of the binary phase does not transform in the concentration range from 10% to 40% weight of gelatin.
Investigation of CIDEP Effects of Hydrogen Radicals by Time Resolved ESR Spectroscopy
Authors: Beckert D. , Mehler K.
Published: July 2012

By means of time resolved ESR spectroscopy the CIDEP effects of hydrogen radicals produced by pulse radiolysis of aqueous solutions were investigated. The quantitative analysis of the ESR time profiles of both H atom hfs lines and of D atom hfs lines based on the modified Bloch equations allows us to determine the spin relaxation times T1 and T2, the chemical life time τH and the initial and recombination polarizations PA, PA. While the relaxation rates T and T and the reciprocal of the life time τH−1 are proportional to the H radical concentration the recombination polarization PR is independent on the H atom concentration but shows an asymmetric behaviour to the spectrum centre. This asymmetry can be attributed to the ST0‐ and ST−1‐polarization of F pairs. – The experimental polarization parameters were compared with the theoretical results obtained from the stochastic Liouville equation by Pedersen and Freed. By this comparison the following quantities can be determined:

The exchange interaction J(d) at the distance of closest approach of two H radical without recombination,

The distance d of closest approach without use of the Smoluchowski relation and

The number of radical pairs in the spur of water radiolysis including the probability of triplet and singlet precursors of direct produced H atoms in water radiolysis.