bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polarized Absorption Studies on Ba[Pt1‐xPdx(CN)4]·4H2O and Ba[Pt1‐xNix(CN)4]·4H2O Mixed Crystals
Authors: Holzapfel W. , Gliemann G. 
Published: July 2012

AbstractPolarized single crystal absorption spectra of Ba[Pt1‐xMx(CN)4]·4H2O with M = Pd, Ni and 0 ≤ x ≤ 1 at T = 80 K are reported. The structure of the spectra depends on the concentration x. This effect is interpreted by the variation of the relative concentration of different cluster types.
Rotational, Internal Rotational, and Translational Motion of Liquid i‐Propanol
Authors: Frech T. , Hertz H. G. 
Published: July 2012

AbstractDeuteron magnetic relaxation rates of the following isotopically substituted i‐propanols (CH3)2CHOD, (CH3)2CDOH, and (CD3)2CHOH have been measured as a function of the temperature and the frequency. Thus the present investigations were performed in the dispersion range. We have attempted to interpret these relaxation rates within the framework of the Woessner theory of internal rotation. The success was not satisfactory, the quadrupole coupling constants were smaller than expected. Proton magnetic relaxation rates of the two i‐propanols (CD3)2CDOH and (CH3)2CDOD have also been measured as a function of the temperature and the frequency. Separation of intra‐ and intermolecular contributions was performed by usual isotopic dilution technique. With the intramolecular relaxation rates again difficulties to describe internal rotation appeared. The dipole‐dipole coupling constant came out too small. The intermolecular relaxation rates could be related to intermolecular configurations fairly satisfactory, although dynamical descriptions still leaves open questions.
A Molecular Dynamics Study of Liquid Chloroform
Authors: Dietz W. , Heinzinger K. 
Published: July 2012

AbstractMolecular Dynamics simulations of liquid chloroform with 200 molecules in the basic cube have been performed at 295 and 325 K. The interactions were described by a rigid five‐site model with (12/6) Lennard‐Jones spheres and partial charges at the atom positions. At room temperature four simulation runs have been carried out. Three of them differ in the method with which the Coulomb forces have been truncated at the cut off distance. For the fourth one the charges have been removed in order to study their influence on the MD results. The intermolecular structure functions have been calculated from the simulation and are found in good agreement with results from an x‐ray measurement and with four out of five structure functions from neutron diffraction studies with isotopic substitution. Strong disagreement between simulation and experiment exists, however, for the six atom‐atom radial distribution functions. The origin of this discrepancy is traced back to the difference in one of the five neutron structure functions (CH37Cl3); because of the consistency of the simulation results with each other and with the other experimental data, it can be attributed to uncertainties of the neutron scattering experiment. It is also shown that the expansion of the molecular pair correlation function in terms of spherical harmonics does not converge rapidly enough for the calculation of the first five so called g‐coefficients with a sufficient degree of reliability from five neutron diffraction measurements. The self‐diffusion coefficients have been calculated for 295 and 324 K, respectively, and found in good agreement with experimental results. Rotational diffusion coefficients, the spectral densities of hindered translations and of the librations are reported. Various reorientational correlation functions have been calculated, which reproduce satisfactorily the corresponding experimental results. The MD calculations show clearly that the description of the dielectric relaxation needs a multi‐particle correlation function, whereas the far infrared absorption is due to single‐particle motion.
Studies on the n‐GaAs Photoanode in Aqueous Electrolytes. 1. Behaviour of the Photocurrent in the Presence of a Stabilizing Agent
Authors: Vanmaekelbergh D. , Gomes W. P. , Cardon F. 
Published: July 2012

AbstractThe competition, at the n‐GaAs/Fe2+ photoanode, between the anodic decomposition of the semiconductor, the anodic oxidation of Fe2+ ions and surface recombination was studied as a function of the light intensity, the electrode potential, and the Fe2+ concentration by means of the rotating‐ring‐disc electrode technique. The results are interpreted on the basis of a reaction scheme, in which the competing processes are linked through the intermediates of the decomposition reaction. Numerical calculations, based upon this reaction scheme, of the relationship between the stabilization ratio and the photocurrent density, between the stabilization ratio and the electrode potential, and between the photocurrent density and the electrode potential are in good agreement with the experimental data.
Measurements of the Solubility of Carbon Dioxide, Ethylene and Methane in N‐Methylpyrrolidone and in its Aqueous Solution
Authors: Wu Z. , Zeck S. , Knapp H. 
Published: July 2012

AbstractSolubilities of CO2, C2H4 and CH4 in NMP and H2O‐NMP mixtures were determined at 25°C in a low pressure apparatus at atmospheric pressure. The data are used to obtain Henry and Ostwald coefficients as a function of solute‐free solvent composition. In addition densities of the H2O‐NMP system were measured with an oscillating U‐tube instrument. Experimental results are compared with literature data.
The Hydration of Aliphatic Aldehydes and Pyruvic Acid in Mixed Solvents
Authors: Knoche Wilhelm , Arturo Lopez‐Quintela M. , Weiffen Joachim 
Published: July 2012

AbstractIn water/dioxane mixtures and aqueous electrolyte solutions the hydration reaction has been studied. The formation of the gem‐diol of aliphatic aldehydes is associated with the binding of 3 water molecules to the carbonyl group, whereas for pyruvic acid 6 or 7 water molecules are involved in this reaction. Rate and equilibrium constants of the reactions have been determined. The hydration equilibria may be used to measure conveniently the local water activity in the aqueous and non‐aqueous regions of micellar solutions and microemulsions. The reaction rate indicates the local proton activity in these systems.
Neuere Konzepte und Ergebnisse zur Struktur von Polymernetzwerken
Authors: Burchard Walther 
Published: July 2012

AbstractTrends in the research of rubber elasticity in the last decade are shortly reviewed. Scientists are presently concerned mainly with the questions, to which extent are cycles relevant for the elastic modulus, and whether a certain affineness is still a necessary requisite for a polymeric network? After a discussion of the state of theories recent experimental results are presented. These show: (i) Cycles are formed already in the pre‐gel state, and in realistic networks many of these are not elastically effective. (ii) Small angle neutron scattering from long labled chains incorporated in the network show clearly that affineness on stretching the network is not obtained even for long chains of about 3000 monomer units in length. (iii) Deuterium NMR from stretched rubbers in the dry as well as in the swollen state disclose segmental orientation which is more pronounced for segments near a junction point. Again this behavior is not predicted by current theories.
The Polymerization of Diacetylenes on Solid Surfaces
Authors: Klauck W. , Breuer H. D. 
Published: July 2012

AbstractThe influence of solid surfaces on the polymerization of diacetylenes has been studied using 3,5‐octadiyn‐1,8‐diol as a model compound. The first molecular layers on polar surfaces are adsorbed by hydrogen bonds. Their relative orientation hinders the polymerization of these molecules. Subsequent layers can be polymerized by UV radiation. After the unreacted monomer has been extracted a highly stable polymer film remains on the surface.
Morphological Stability in the Course of Solid State Reactions: The System Fe3O4 ‐ Mn3O4 ‐ Cr2O3
Authors: Backhaus‐Ricouit M. , Schmalzried H. 
Published: July 2012

AbstractWe have investigated experimentally and theoretically the problem of morphological stability of interfaces in a nonequilibrium two‐phase ternary system while it equilibrates. The system chosen for this study was Fe3O4 ‐ Mn3O4 ‐ Cr2O3 at T = 1400 °C. Depending on the spinel reactant and the sesquioxide reactant, the initially planar interface is either unchanged, or develops nonplanar morphologies of different kind. The theoretical analysis starts with the independent flux equations and the appropriate boundary conditions and investigates whether or not small perturbations of the planar interface will grow or decay in the course of time. A critical parameter can be defined which is negative for stable and positive for unstable interfaces. This parameter is a complicated function of all the transport coefficients, the starting compositions and the chemical potentials of the components in both phases and can in principle be calculated, as long as local equilibrium prevails during the reaction.
A Neutron and X‐Ray Diffraction Study of the Binary Liquid Aromatic System Benzene‐Hexafluorobenzene II. The Mixtures
Authors: Bartsch E. , Bertagnolli H. , Chieux P. 
Published: July 2012

AbstractA series of X‐ray and neutron diffraction experiments has been performed on liquid benzene, hexafluorobenzene and their liquid mixtures in order to find out whether packing effects or electrostatic interactions are the structure determining factors. The results for the mixtures are reported together with a qualitative interpretation of the experimental data. By combined analysis of the X‐ray and neutron diffraction experiments it could be proved that a reorientation takes place from a L‐type pair geometry in the pure components to a nearly parallel alignment of the molecules in a 1:1 complex. In a second approach a new quantity ‐ a so‐called excess structure factor ‐ was defined, the analysis of which confirmed the deduced change of orientation. With a stacking distance of 3.7 Å and a separation of 7.6 Å between two consecutive hexafluorobenzene molecules the structure of the equimolar mixture in the liquid phase very closely ressembles the one obtained for the solid phase. It can be concluded that the quadrupolar interaction is the structure determining factor in the investigated liquid aromatic systems.
Excess Properties of Liquid Cyclohexane/Hydrocarbon Mixtures II. Excess Gibbs Energy Determined from Total Vapour Pressure Data
Authors: Wagner H. , Lichtenthaler R. N. 
Published: July 2012

AbstractResults of the composition dependence of the molar excess Gibbs energy GE determined from total vapour pressure data of mixtures of cyclohexane with saturated and unsaturated hydrocarbons at 298.15 and 313.15 K are reported. The results of the mixtures with the saturated hydrocarbons show a systematic behaviour of GE with respect to the chain length and the degree of branching of the molecules of the substances mixed. The results of the mixtures with unsaturated components extend the systematics taking into account the number and the location of multiple bonds within the molecules.
Electrochemical and Thermodynamic Studies on Copper‐Silver‐Selenium System
Authors: Mostafa S. N. , Selim S. R. 
Published: July 2012

AbstractWith the help of coulometric titrations, using the solid state galvanic cell Ag/AgI/(Cu,Ag)2+δSe/C, in the temperature region between 200 and 350°C, the following parameters: Point defect concentrations, effective mass of electrons and holes, width of band gap and the partial molar thermodynamic quantities of dissolution of one mole of silver in the mixed selenide were determined as a function of the metal/selenium ratio. The change of the thermodynamic quantities with the change of the stoichiometric composition can be explained by varying contributions of electrons and electron‐holes, depending on the fact whether the electrons, which are brought into the mixed selenide by the dissolution of silver, go into the conduction band (excess of metal) or. by destruction of electron‐holes into the valence band (deficit of metal). The band gap energy in the Ag1.188Cu0.812Se is 0.12 eV.
Scaled‐Particle Theory for Adsorbed Hard‐Core Molecules
Authors: Joshi Y. P. , Tildesley D. J. 
Published: July 2012

AbstractMolecular fluids such as N2 and CS2 adsorb on a graphite surface to form a variety of phases at temperatures below 200 K and sub‐monolayer coverages. To a first approximation, we can model the thermodynamic properties of the adsorbed fluid in terms of a two dimensional fluid of hard‐core molecules. However these systems are not strictly two dimensional, the molecules vibrate in the plane perpendicular to the surface and tilt at an angle to the surface. The tilt of the molecules can be included by projecting the three dimensional adsorbate onto the surface plane. For realistic fluids of linear molecules the two dimensional analogue is a mixture of hard convex molecules with a continuous distribution of bondlengths. This distribution is controlled by the distribution of tilt angles in the three dimensional precursor. In this paper we develop a scaled particle theory for this polydispersed mixture which predicts pressures and chemical potentials which are thermodynamically consistent. This hard‐core reference system can be used in perturbation theories to predict the spreading pressure and adsorption isotherms of realistic molecular fluids adsorbed on graphite.
Substrate Dependence of the 2D Gas‐Solid Phase Transition in Adsorbed Xenon Layers
Authors: Eder S. , Markert K. , Jablonski A. , Wandelt K. 
Published: July 2012

AbstractCoexisting 2D gas and 2D solid phases of adsorbed xenon can be distinguished by means of UV photoelectron spectroscopy. This is used to demonstrate the influence of the xenon/metal interaction strength on the 2D gas ⟷ 2D solid Xe phase equilibrium on Cu(111), Ag(111) and Ru(001).
Calculation of Interactions Between Adsorbates on Transition Metal Surfaces
Authors: Dreyssé H. , Tománek D. , Bennemann K. H. 
Published: July 2012

AbstractWe present an electronic calculation of two‐ and three‐body interactions in chemisorbed layers. The interaction energies are obtained in a self‐consistent way within the tight‐binding formalism which includes electron correlations and interatomic pairwise repulsion terms. Numerical results for Re2 and Re3 on W(110) are compared with recent experimental data.
Halogen Overlayer Structures on Fe(110)
Authors: Mueller D. , Rhodin T. N. , Dowben P. A. 
Published: July 2012

AbstractThe overlayer structures formed with halogen adsorption on an Fe(110) surface have been investigated using LEED. The LEED patterns are described using variable, non‐coincident nets of halogen adatoms. The adlayer nets rotate and contract with increasing halogen coverage. The structural changes within the adlayer are consistent with an adatom model developed for the Cl2/Br2/I2 Fe(110) systems. The internuclear spacings and geometry of the halogen overlayers on Fe(110) are shown to be consistent with previous work on Fe(110).
Neutron Scattering Experiments with a Binary Critical Mixture for the Determination of the Critical Exponent ζ
Authors: Schwahn D. , Belkoura L. , Woermann D. 
Published: July 2012

AbstractSmall angle neutron scattering experiments are carried out with an isobutyric acid (COOD)/deuterium oxide mixture of critical composition. The scattering patterns are measured at small temperature differences (T ‐ Tc) ≦ 1.0 K above the critical temperature Tc. In his temperature range and for scattering vectors larger than 0.03 Å−1 the critical scattering was found to be independent of temperaure. From these data the experimental correlation scaling function gexp(x) is constructed for values of the scaling variable x in the range 4 < x < 540. The Fisher‐Langer approximation of the correlation scaling function and its asymptotic form for large values of x are fitted to gexp(x). In this way a value of the critical exponent η of η = 0.039 ± 0.009 is obtained. It is based on the analysis of the experimental correlation scaling function composed of five scattering patterns obtained at five different temperature differences (ΔT ≤ 1.0 K). The analysis of 4 individual scattering patterns (ΔT ≤ 0.08 K) gives η = 0.037 ± 0.006.
Observation of Rates of Sorption and Diffusion in Zeolite Crystals at Constant Temperature and Pressure
Authors: Prinz D. , Riekert L. 
Published: July 2012

AbstractAn experimental arrangement is described which permits to observe mass transfer in synthetic zeolite crystals of small size by gravimetry without interference from external mass transfer and heat transfer resistance.—Experimental results concerning the kinetics of sorption of 3‐methyl‐pentane, benzene and p‐xylene in pentasil‐zeolite are reported. These results indicate that not only diffusion but also other intracrystalline relaxation phenomena can influence the rate of sorption into zeolites.
Inelastic Neutron Scattering Studies of Water in Natural Zeolites
Authors: Fuess H. , Stuckenschmidt E. , Schweiss B. P. 
Published: July 2012

AbstractResults on the motion of water molecules in six natural zeolites (natrolite, phillipsite, harmotome, heulandite, stilbite and chabazite) from incoherent inelastic neutron scattering are presented. The spectra for five zeolite samples exhibit broad maxima and few resolved peaks. Only for natrolite with water molecules tightly bound to the alumosilicate framework a spectrum with well‐resolved peaks is observed. A detailed interpretation is attempted for the Ba‐zeolite harmotome where data were recorded at various temperatures and different amount of water.—Differential scanning calorimetry gave a broad dehydration peak for chabazite (T = 443 K) and a sharp single peak for natrolite (T = 633 K), whereas three maxima (T = 433, 523 and 673 K) were observed for harmotome.
Optische Aufheller als Laserfarbstoffe
Authors: Rinke Monika , Güsten Hans 
Published: July 2012

AbstractThe singlet absorption, triplet absorption and the absolute fluorescence spectra together with the fluorescence quantum yields and fluorescence decay times as well as the laser performance (tuning range, conversion efficiency, photochemical stability) of nine fluorescent brightening agents have been measured in ethanol at room temperature. High fluorescence quantum yields of over 0.75 with short fluorescence decay times of well under one nanosecond have been obtained. With the exception of two fluorescent brightening agents the tuning ranges are in the violet‐blue region between 415 and 447 nm. The conversion efficiencies range from 1 to 15%. The photochemical stability of the optical brighteners in solution with energy half‐life values between 2 × 104 and 105 J/l, corresponding to average lifetimes of 75 to 200 photons per molecule, is poor in comparison to their known photochemical stability in the adsorbed state.
Experimental Evaluation of the B‐DNA → Z‐DNA Transition: Energetics of a Reversible, Thermally Induced Helix/Helix Transition of Poly dG‐m5dC in Physiological Mg2± Concentrations
Authors: Klump H. 
Published: July 2012

AbstractUV spectroscopic studies show that poly dG‐m5dC above 2 mM Mg2+ undergoes a reversible, thermally induced helix/helix transition from the B‐ to the Z‐DNA conformation. The observed cooperativity of the transition suggested to monitor the enthalpy change of the interconversion by means of an adiabatic scanning microcalorimeter. The transition is endothermic, the transition temperature at half conversion is 59°C (10 mM Mg2+), the transition enthalpy is 4.77 kJ per mole base pairs, the transition entropy amounts to 14.35 J · mol−1 K−1. From the slope of the absorbance/temperature scan at 280 nm as well as from the plot of the degree of transition/temperature ΔHvH is calculated (1078 kJ/mol). The ratio of the ΔHvH and the true enthalpy obtained by calorimetry gives the number of base pairs (226) which undergo the transition simultaneously. The Gibbs enthalpy of the B→Z transition yields 0.5 kJ per mole base pairs.
The System Water—Carbon Dioxide—Sodium Chloride to 773 K and 300 MPa
Authors: Gehrig M. , Lentz H. , Franck E. U. 
Published: July 2012

AbstractExperimental results are reported for fluid‐fluid phase equilibria of the ternary system H2OCO2NaCl. Measurements were extended to 773 K and pressures to 300 MPa. A “synthetic” method was used: Known quantities of the three components were filled into an autoclave at room temperature. The autoclave with a sapphire window and variable volume is described. Transition points to homogeneous one‐phase conditions could be determined from recordedp—T‐curves at constant volumes and from visual observation. From the transition pointsp—T‐curves on the three‐dimensional phase equilibrium boundary surface at constant compositions, “isopleths”, were obtained. Data for 20 isopleths with CO2‐concentrations between 0.2 and 85 mol% and with 6 weight YO of NaCl are presented together with a few additional results for higher salt concentrations. Molar volumes were measured at the phase boundary surface and within the one‐phase region. Excess molar volumes are given. In comparison with the binary H2O‐CO2system, the addition of NaCl shifts the range of partial immiscibility to higher temperatures by up to 100 K; for example from 573 to 673 K at 100 MPa for 48 mol% CO2. Results are in agreement with earlier data of Takenouchi and Kennedy. Considerations of the ternary phase diagram H2OCO2NaCl within a wide range of conditions are given.
Bestimmung der Geschwindigkeitskonstanten der Reaktion von 1CH2 mit Fluor‐ und Chlorethen
Authors: Simon F. G. , Heydtmann H. 
Published: July 2012

AbstractThe rate constants for the addition of 1CH2 to fluoroethene and chloroethene have been determined using the known rate constant for the reaction of 1CH2 with ketene. The experiments yielded the results
1H‐NMR Relaxation Study of Water in Binary Solvent Mixtures in the Absence and Presence of Electrolytes
Authors: Merboldt Klaus‐Dietmar , Frahm Jens 
Published: July 2012

AbstractNMR spin‐lattice (T1) and spin‐spin (T2) relaxation times are reported for water protons in aqueous solutions of deuterated HMPT, pyridine, and DMF in the absence and presence of electrolytes of different charge types. Measurements have been performed for a wide range of temperatures and for three different magnetic field strengths corresponding to 15, 60 and 270 MHz. Neglecting contributions from intermolecular interactions, water proton relaxation is described using a modified BPP‐theory that assumes an asymmetric distribution of correlation times. In binary solvent mixtures both shape and width of the distribution are shown to depend on the type of the solvent and its composition. The distribution parameters correlate with the strength of interaction between water and solvent molecules. In a similar way, the addition of electrolytes affects the distribution width as well as its dependence on solvent composition.