bluuebunny/crossref_metadata_2025_split huggingface dataset:
Infrared Spectrum of Isoselenocyanic Acid, HNCSe
Authors: Vogt Jürgen , Winnewisser Manfred 
Published: July 2012

AbstractThe 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

AbstractThe reactionmagnified imagewas 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 bemagnified image
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

AbstractSolvent 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

AbstractThe 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

AbstractSyntheses 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

AbstractBy 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

AbstractSolid 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

AbstractThe 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 reactionmagnified imagewere measured relative to the CF3 recombination.magnified imageThe average value of the results from both sources of radicals gave the following parametersmagnified imageThe 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

AbstractThe 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

AbstractQuantitative 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

AbstractThe 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

AbstractA 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

AbstractMeasurements 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

AbstractThe 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

AbstractA 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

AbstractWith 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

AbstractDouble 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

AbstractThe 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

AbstractIn 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

AbstractThe 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

AbstractBy 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

AbstractA 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.