bluuebunny/crossref_metadata_2025 huggingface dataset:
Noble Gas Immobilization in Zeolites
Authors: Penzhorn R.‐D. , Schuster P. , Leitzig H. , Noppel H. E.
Published: March 2014

It was discovered that the noble gases Ar, Kr and Xe can be trapped firmly in type A zeolites as well as in mordenites and chabazites when the molecular sieves are hydrothermally vitrified at temperatures between 340 and 650°C in the presence of pressurized gas. The occurrence of trapping in an amorphous nonzeolitic species was demonstrated by X‐ray diffraction, neutron scattering and electron scattering. The change in structure of loaded zeolites is also manifested by a substantial loss in sorption capacity for water as well as an almost complete disappearance of the specific surface area. – The gas release rates at temperatures below 550°C were found to be extremely low. The activation energies for the diffusion of Kr through amorphous Ca and Mg exchanged 5 A zeolite were determined to be 209 ± 15 and 187 ± 16 kJ/mol respectively. The estimated diffusion coefficients are exceedingly small. The trapped gas is neither liberated by hot water nor by liq. Rb at 150°C.
Solubility of Gases in Liquids. 15. High‐Precision Determination of Henry Coefficients for Carbon Monoxide in Liquid Water at 278 to 323 K
Authors: Rettich T. R. , Battino Rubin , Wilhelm Emmerich
Published: March 2014

The solubility of carbon monoxide in pure liquid water was measured in the pressure range 60 to 110 kPa and the temperature range 278 to 323 K with a high‐precision apparatus of the Benson‐Krause type. These data are used to derive Henry coefficients H2, 1(T, Ps, 1), the temperature dependence of which is accounted for by both a Clarke‐Glew type fitting equation and a power series in T−1. The imprecision of our measurements is characterized by an average deviation of H2, 1(T, Ps, 1) from these smoothing equations of about ±0.04%. From the temperature variation of H2, 1(T, Ps, 1) the partial molar quantities pertaining to the solution process (such as standard changes in enthalpy and heat capacity) are obtained. In addition, Ostwald coefficients are given in tabular form at rounded temperatures. Experimental results are compared with values calculated via scaled particle theory.
Solubility of Hydrogen in β‐Ti1 ‐ yRey
Authors: Bressel Burkhard , Weiss Alarich
Published: March 2014

Cubic body centered β‐phase alloys Ti1 ‐ yRey were studied by X‐ray diffraction, mass density measurements, and by measurements of their hydrogen solubility. In the pressure range 0.005 ≦ p(H2)/bar ≦ 1 the solubility of hydrogen decreases strongly with increasing mole fraction of Re. Typical equilibrium values for (Ti1 ‐ yRey)Hx are at T = 650°C: y = 0.18, x = 0.48; y = 0.27, x = 0.23; y = 0.33, x = 0.006. The lattice constants of the alloys increase slightly with increasing hydrogen content. Also the relative partial molar enthalpy at infinite dilution, \documentclass{article}\pagestyle{empty}\begin{document}$ \Delta \bar H_H^0 $\end{document}, increases with increasing Re‐content.
Flüssigkeitsähnliche Struktur in Suspensionen von Sulfonlatexkugeln
Authors: Härtl W. , Versmold H. , Wittig U.
Published: March 2014

By emulsion polymerization of styrene and vinylbenzene sulfonic acid monodisperse latex particles with sulfate and sulfonate surface groups were prepared. After careful cleaning, solid‐ and liquid‐like ordered suspensions of different particle concentration were obtained. Static and dynamic light scattering as well as electron micrographs were used to determine the particle size. Further, pH and conductivity experiments were carried out for the determination of the latex particle charge. For liquid‐like ordered suspensions of different concentrations the structure factor S(Q) and the radial distribution function g(r) are presented. These two quantities are discussed in terms of the rescaled mean spherical approximation (RMSA) of Hansen and Hayter.
Sterische Stabilisierung und Flockung von wäßrigen TiO2‐ und SiO2‐Suspensionen durch Polymerenadsorptionsschichten
Authors: Christakos G. , Hofmann U. , Weick B. , Joppien G.
Published: March 2014

The effect of adsorbed polymers on the stability of aqueous TiO2 and SiO2 suspensions was studied by a centrifugation technique in combination with spectrophotometric particle concentration determinations. TiO2 suspensions showed a marked resistance against sedimentation following the adsorption of polyvinyl alcohol) at higher concentrations and room temperature. The sedimentation velocity was lowest at pH = 5.9. An increase or decrease of the pH or of the adsorption temperature brought about destabilization. Aqueous SiO2 suspensions could be stabilized by adsorbed poly(oxyethylene) at pH 6.8 and 7.3 but were destabilized after adsorption of this polymer at lower pH values via the formation of a viscoelastic gel structure. The observed effects are interpreted as steric stabilization in the TiO2 and SiO2 adsorption systems and as bridging flocculation in the SiO2 system at low pH. They are correlated with adsorption isotherms of the polymers established by a turbidimetric concentration determination method.
Zur physikalisch‐chemischen Wirkungsweise von Waschmittel‐Gerüststoffen
Authors: Große J. , Nielen H.‐D.
Published: March 2014

The physicochemical properties of detergent builders are discussed with special respect to pentasodium triphosphate, Na5P3O10 (NTPP). The builder action can be interpreted in terms of colloidochemical theories. — Laboratory screening tests concerning calcium binding capacity, dispersing action and “threshold” effect of typical builder components are presented. — Detergent builders are also characterized by means of polyelectrolyte titration. Zeta potential data obtained on cotton fabrics are also included. — The results of the various experiments — screening tests as well as electrokinetic measurements — are discussed and verified by means of model washing tests.
Der Einfluß von pH, Elektrolytkonzentration und Mischverfahren auf die Flockung von gefällten und pyrogenen Silikahydrosolen durch Polyethylenglykol
Authors: Killmann E. , Gütling N. , Wild Th.
Published: March 2014

With a laser photosedimentometer one obtaines parameters which enable characterization of the turbidity and of the sedimentation in the Silica suspension flocculated by the adsorption of Polyethyleneglycols. By continuous addition of the polymer solution to the silica suspension the influences of the time of addition, stirring time, stirring intensity, polymer coverage, concentration of silica, pH and ionic strength on the flocculation state can be quantified. In contrast to pyrogenic silica precipitated silica is only flocculable by decreasing the pH below pH 3.5 or by addition of salt above 10−2 mol/l. The flocculation of pyrogenic silica is markedly dependent on the mixing conditions at high pH and without salt. At high salt concentrations and pH <3.5 the flocculation of precipitated and pyrogenic silicas becomes independent of mixing conditions.
Kalorimetrische Untersuchungen zur Adsorption von Tensiden an Mineralen
Authors: von Rybinski W. , Schwuger M. J.
Published: March 2014

A process for the separation of finely disseminated ores is the selective agglomerate flotation. In this technique surfactants are adsorbed at the mineral particles making their surface hydrophobic. In a second step the particles are tumbled in an aqueous solution containing an unmiscible bridging liquid which causes their selective agglomeration. The interaction between the adsorbed surfactant molecules and the mineral surface is decisive for high selectivity and recovery of the agglomeration process. This could be shown by calorimetric measurements of the heat of adsorption of sodiumoleate and sodiumhexadecylsulfate at scheelite and calcite. In adsorption of surfactants from aqueous solution at mineral surfaces effects as solubility of the minerals and the precipitate formation of surfactants with polyvalent ions have to be taken into account. By means of calorimetric measurements it could be distinguished, whether there is interaction between the mineral surface and adsorbed surfactant molecules, double layer adsorption or precipitate formation.
Direct Investigation of the Reaction CH2(X̃3B1) + O(3P) with the LMR
Authors: Böhland T. , Temps F. , Wagner H. Gg.
Published: March 2014

The reaction

has been studied at room temperature in an isothermal discharge flow reactor. Methylene‐radicals and oxygen‐atoms have been monitored with a Far‐Infrared Laser Magnetic Resonance spectrometer. The rate constant of reaction (1) was evaluated from the pseudo first order decay of CH2in the presence of a large excess of O‐atoms. The influence of side and consecutive reactions has been investigated in a computer simulation of the reaction system. — The final result for the rate constant of reaction (1) is

The experimental value is compared to theoretical predictions for the high pressure recombination rate constant of CH2and O.
Calculation of Isothermal Compressibilities of Mixtures. The Example Acetone + Chloroform
Authors: van Nhu Nguyen , Bhat Subray N. , Kohler Friedrich
Published: March 2014

From measured values of excess volumes vE at normal pressures, and from molar volumes and isothermal compressibilities of the pure components, compressibilities of the mixtures can be calculated by means of a generalized van der Waals equation of state. Similarly, excess volumes at elevated pressures can be calculated. This is shown for the example of the mixture acetone + chloroform, where newly measured values of vE and of isothermal compressibilities are presented. The agreement between calculation and experiment is within the experimental accuracy. The equation of state calculations give even reasonable agreement to vE‐measurements by Kulka and Schneider at 150 MPa.
Chemical Potential Measurements on Nonhydrostatically Stressed Solids
Authors: Durham W. B. , Schmalzried H.
Published: March 2014

Gibb's hypothesized dependence of chemical potential upon state of stress has been qualitatively confirmed by direct measurement, using solid‐state electrolytes both to transmit nonhydrostatic load and to measure (through a change in electrical potential) a corresponding change in chemical potential. Quantitative agreement with Gibbs predictions may not be possible because of the inevitable presence of nonideal chemical heterogeneities near the surfaces of solids.
Vapour Pressure of the AlCl3‐POCl3 System
Authors: Brockner Wolfgang , Grande Knut , Øye Harald A.
Published: March 2014

The vapour pressure and vapour compositions have been determined for the molten AlCl3‐POCl3 system in the composition range 50–64 mol% AlCl3 and for temperatures in the range 170–270°C using a boiling point method and analyzing the boiled‐off vapour after direct condensation. Knudsen effusion cell measurements of the solid AlCl3 · POCl3 compound have also been carried out. The melts are considered as molecular liquids consisting of Al2Cl6, Al2Cl6 · POCl3, AlCl3 · POCl3 and POCl3 molecules, respectively. The vapour species are Al2Cl6, AlCl3 · POCl3 and POCl3, A semiempirical thermodynamically based melt model has been developed explaining the vapour pressure minimum of acidic AlCl3‐POCl3 melts and the published azeotrope at 51.5 mol% AlCl3. Thermodynamic data have been calculated.
An infrared‐spectroscopic study on the state of water in alcohols and in inverted micelles
Authors: Rosenholm Jarl B.
Published: March 2014

The shifts of the antisymmetric stretching vibration bands of water (σ3) and of the ionized carboxylate group (σcoo) in the fundamental infrared region has been used to investigate the properties of water when mixed with pentanol or decanol and when engaged in the association to inverted micelles in the same solvents at 298 K. The systems studied were water + sodium n‐octanoate in pentanol and decanol, respectively. In order to identify the states occupied by water a method was developed to resolve the observed average wave number into the contribution of the different states. The Boltzmann‐distribution is utilized to give a rough estimate of the amount of water present in each state. When water is dissolved in pentanol it is initially bound to strong complexes with the alcohol molecules. In the high concentration range a part of the water seems to be dispersed free in the solvent. Diluted in decanol all the water seems to be engaged in intermolecular complexes characterized by strong hydrogen bonds. Present as hydration water of the ionic groups of the surfactant monomers the water is bound with an average strength resembling that of liquid water. The micellization seems to be initiated in all solutions investigated when the amount of hydrated surfactant is sufficiently high. Independent of the relative amount of water present the sodium ions seem then to be partly released from the strong ionic interaction found in the premicellar solutions. On the other hand, the fraction of water available is of prime importance for the state of the carboxylate group.
Fluorescence excitation spectra of hydrogen‐bonded cresol‐isomers in supersonic free jets
Authors: Appel I. , Kleinermanns K.
Published: March 2014

Free o‐, m‐ and p‐cresol and their complexes with H2O, CH3OH and cresol were cooled in pulsed supersonic nozzle beams and analyzed by fluorescence excitation spectroscopy. Results on the cis‐/trans isomerism of the OH group with respect to the CH3substituent and on the hindered internal rotation of the CH3 group were obtained. All the solvents studied induce red shifts of the cresol absorption between 230 and 420 cm−1, reflecting a strong increase in the hydrogen bond dissociation energy upon electronic excitation. Progressions of intermolecular cluster stretching and bending frequencies and their combination bands with intramolecular cluster vibrations were observed. From the red shifts and the break‐off points of the fluorescence signals in the high energy region of the cluster spectra, lower limits of the hydrogen bond energies in the electronic ground (S0) state were obtained. — The experimental results are compared with semiempirical quantum chemical calculations at the Hartree‐Fock level. Monomer and cluster structures and intermolecular stretching and bending frequencies were calculated. The comparison points to several stable conformations of the 1:1 complexes.
Hydrogen equilibrium separation factors in metal/hydrogen systems, a synopsis on the basis of the localized harmonic oscillator model
Authors: Andreev B. M. , Sicking G. H.
Published: March 2014

The isotopic equilibrium separation factor between gas phase hydrogen and hydrogen in metals is calculated for H‐D mixtures and H‐T mixtures between 150 K and 1000 K. Parameter for the calculations is the vibrational energy of hydrogen in interstitial lattice positions. The interstitial hydrogen isotopes are treated as localized Einstein‐oscillators of three‐fold degeneracy. The influence of lower point‐symmetries of interstitial positions is discussed by way of the Ta/hydrogen system as an example. The separation factors evaluated relate to tracer conditions as established with vanishing concentrations of deuterium (tritium). It is shown, how the separation factor for optional deuterium (tritium)‐concentrations in the gas phase is obtained from the tracer separation factor in question. — Special attention is drawn to the fact that metal/hydrogen systems, which dissolve hydrogen in tetrahedral interstitial positions, invert the direction of the isotope effect at a certain temperature. Inversion temperatures are given as a function of the local mode energy. Systems with H in octahedral (tetrahedral) positions are discussed with respect to technical utility. — The calculations are examined by means of experimentally determined separation factors and in the light of recent neutron vibrational spectroscopy work on metal/hydrogen systems.
Characterization of highly repeated sequences in eukaryotic DNAs by scanning microcalorimetry
Authors: Klump Horst H.
Published: March 2014

Our observation indicates at least four satellite DNAs in the calf, three in the human placenta, and none in chicken erythrocytes. We estimate that these satellites DNAs comprise up to 25% of the total calf genome and 12. 6% of the bulk human DNA. The individual repeated sequences show up in the experimental thermal transition curve from the scanning microcalorimeter as sharp peaks on top of a rather broad denaturation of common gene pool sequences of eukaryots. The individual satellite DNAs can be characterized by the position of the peak maximum on the temperature axis. The transition temperature Tm can be correlated to the base composition of each repeated sequence (40% GC for bulk calf DNA, 40%, 44%, 48%, 55%, and 62% for the satellites). The comparison with the transition curve of DNA that lacks satellites such as from chicken erythrocytes allows to determine the fraction of the individual satellites in the gene pool of the species.
Modelization of the electrical double layer: Structure of an lon‐dipole mixture near a wall
Authors: Rosinberg M. L. , Russier V. , Badiali J. P. , Boudh'hir M. E.
Published: March 2014

We present a statistical mechanical study of the structure of a hard sphere ion‐dipole mixture in the vicinity of a hard plane wall. We investigate the orientation ordering of the dipoles, the influence of an adsorption potential on the potential drop and the modifications of the ionic solvation.
The jellium/hard sphere electrolyte interface
Authors: Henderson Douglas , Leiva Ezequiel , Schmickler Wolfgang
Published: March 2014

A model of the metal/electrolyte interface in which the ions and solvent molecules are represented as charged hard spheres and hard spheres with imbedded point dipoles, respectively, and the metal is represented as a “jellium” is formulated and applied. In some of the calculations a pseudopotential is used to represent the metal ions. Two families of trial functions are used to obtain the electronic profile. Near the point of zero charge (PZC) the mean spherical approximation is used to obtain electrolyte properties. Away from the PZC a phenomenological extension of the mean spherical approximation is used. The results are in good agreement with experiment. The electronic density is found to be the key metallic parameter. The pseudopotential seems to be particularly important for fourth and fifth column sp metals.
Interfacial electrodynamics of interacting colloidal particles. Geometrical aspects
Authors: van Leeuwen H. P. , Lyklema J.
Published: March 2014

The paper treats the effects of geometrical factors on the various double layer relaxation processes which may occur during interaction between colloidal particles. It is explained how the existing theory for interaction between flat plates can be extended to more involved geometries by taking into account the effective region of double layer overlap. Furthermore, the relation between particle interaction dynamics and the kinetics of electrodes of the same material is discussed in terms of the difference in geometry. Finally it is examined how the dielectric relaxation of a colloidal dispersion can be related to the electrodynamics of interaction between individual particles. Some conclusions are drawn on the occurrence of diffuse layer relaxation and interfacial transfer of exchangeable ions in the colloidal system.
Quantum‐mechanical model for surface (Un‐)enhanced resonance raman scattering of adsorbates at metals. Common effects in SERRS and SUERS
Authors: Pettinger B.
Published: March 2014

A recently developed quantum‐mechanical model for surface enhanced (resonance) Raman scattering (SERRS) has some implications for surface resonance Raman scattering (SURRS) in general: The molecule‐metal interaction for SURRS at any smooth metal surface is similar to that of SERRS except for the electromagnetic surface enhancement Hence, the total SURRS process consists of (i) a lossy coupling of an induced dipole to electron hole pairs, (ii) an increase of the resonance Raman contribution over the RRS gain of the unbonded species due to a suppression of molecular dephasing and relaxation caused by energy transfer molecule → metal and (iii) the usual resonance Raman contribution; the latter two mechanisms require some molecular resonance with the exciting photon energy (or CT resonance between adatom and adsorbate). In the case of molecular (pre‐) resonance, the loss (i) and the gain (ii) cancel each other. Thus, the overall photon scattering shows either a loss (process i) or an apparently unperturbed, (pre)‐resonance Raman enhancement (e.g. process iii).
The influence of the double layer field on the protonation equilibrium of adsorbed methyl orange
Authors: Schmidt P. H. , Plieth W. J.
Published: March 2014

The protonation/deprotonation of methyl orange adsorbed on a smooth platinum electrode has been investigated by modulated reflectance spectroscopy in the visible spectral region. The modulated reflectance spectra are mainly governed by the potential modulation of the protonation equilibria of methyl orange and the buffer (acetate/acetic acid), respectively. The pK values of the protonation equilibria within the adsorption layer change with the electrode potential E in the following way: dpK/dE = 0.8 V−1 and —1.0 V−1 for methyl orange and acetic acid, respectively.
The adsorption of carbon monoxide on platinum single crystals in alkaline medium
Authors: Leger J.‐M. , Beden B. , Lamy C.
Published: March 2014

The adsorption of carbon monoxide on low‐index platinum single crystals is studied in alkaline medium with a special computer potential‐time programme, which allows to control short adsorption times. — Two or three different adsorbed CO species are involved depending on the crystal planes, and on the adsorption time. At long adsorption times, apart linearly bonded species, bridge‐ or multi‐bonded CO species are still present on each surface, in contrast to the observation in acid medium. — On the other hand the behaviour of a polycrystalline Pt electrode is similar to that of Pt(100) at short adsorption times, and of Pt(110) at long adsorption times.
The electrochemical behaviour of n‐type silicon (111)‐surfaces in fluoride containing aqueous electrolytes
Authors: Gerischer Heinz , Lübke Margot
Published: March 2014

N‐type Si(111)‐electrodes have been studied in the dark and under illumination. A limiting current is found at modest anodic bias which increases with the fluoride concentration and is controlled by a chemical reaction. Near the open circuit potential where anodic oxidation and cathodic hydrogen evolution occur simultaneously a chemical reaction of surface atoms with water is involved. All processes in the dark seem to occur only at structural defects of the surface. — Reactions with holes control the current at anodic bias under illumination. The photocurrent doubling in fluoride solution could be confirmed. This effect disappears however with increasing pH if the photocurrent exceeds the rate of conversion of primary oxidic products into soluble silicon fluorides. A structural and energy model is presented in order to explain the results.
Reactions on colloidal semiconductor particles
Authors: Henglein Arnim , Fojtik Anton , Welter Horst
Published: March 2014

Inorganic colloids such as cadmium sulfide are often used as sensitizers and catalysts for photochemical reactions. In these reactions, which are described in terms of the concepts developed in electrode kinetics, electrons are transferred between the particles and molecules in the solution. Extremely small particles (Q‐particles) often have optical and catalytic properties different from those of the macrocrystals. These effects are due to the restriction in space of the charge carriers produced by light absorption (size quantization). CdS particles carrying an excess electron strongly change their absorption at wavelengths near the absorption edge. This effect is attributed to the influence of the excess electron on the optical transition leading to the lowest excitonic state in these particles.
Molecular dynamics study of raman scattering and infrared absorption of ferrous and ferric ions in aqueous solution
Authors: Halley J. W. , Hautman J.
Published: March 2014

Using a molecular dynamics computer model of water and ion water potentials we have used earlier to study electrolyte structure, we have calculated the infrared absorption and Raman scattering rates of ferrous and ferric ions in aqueous solution. Results for the Raman scattering from the ferric ion in solution are compared with experiments on molten Fe(NO3)3 · 28 H2O. The comparison suggests some new interpretations of the experiments.
Statistical Weights for Primary Structures of Inhomogeneous Polymer Chains
Authors: Fernández Ariel
Published: March 2014

We analyze the distribution of configurational averages over an ensemble of primary structures. These primary structures are given by base sequences for linear polymers of fixed length N constructed randomly from two different kinds of monomers. The variance V(R2) of the thermally averaged square size of the random coil is calculated by defining a virtual ensemble of homogeneous polymers of length N. This ensemble is determined by effective short range two and three body interactions. We prove that V(R2) increases with the information content given by the length N. Specially, V(R2) ∼ N2.
On the Mechanism of Electroless Copper Deposition
Authors: Wiese Harm , Weil Konrad Georg
Published: March 2014

The mechanism of electroless copper deposition with formaldehyde from alkaline ethylenediamine‐tetraacetate (EDTA)‐containing solutions was studied. Oxidation and reduction could be investigated separately by use of a quartz microbalance in combination with fast solution exchange. It could be confirmed that the reaction is predominantly electrochemical, no indication for a direct electron transfer from a reducing agent to copper ions could be detected. In spite of this the oxidation and the reduction reaction are not independent. Formaldehyde oxidation on copper surfaces is enhanced when simultaneously copper ion reduction takes place. Formaldehyde, on the other hand, does not only act as an electron donor but also generates a catalyst for the copper ion reduction. We suggest that chemisorbed methanediolate anions catalyze the reduction. It can be shown that other substances, which either have a similar structure element as methanediolate or which are known to be specifically adsorbed on copper, also catalyze the copper ion reduction from alkaline, EDTA‐containing solutions.
The Ternary Systems H2O‐CH4‐NaCl and H2O‐CH4‐CaCl2to 800 K and 250 MPa
Authors: Krader T. , Franck E. U.
Published: March 2014

Experimental results are reported for the fluid phase equilibria of the ternary system H2O‐CH4‐NaCl and to a lesser degree of H2O‐CH4‐CaCl2. Measurements were extended to 800 K and 250 MPa. A “synthetic” method, described previously, was used, supplemented with an electrolytic indication. The high pressure autoclave with sapphire windows and variable volume together with its auxiliary equipment is described. Pressure‐temperature curves on the three‐dimensionalPTx‐surfaces at constant compositions,x, were obtained (“isopleths”). Data for 21 isopleths with NaCl‐concentrations of 0.6, 1.7 and 8 weight percent relative to water with CH4‐concentrations ranging from 6 to 71 mol percent are presented together with three isopleths for H2O‐CH4‐CaCl2mixtures. Molar volumes at the phase boundary surfaces are given. In comparison with the binary H2O‐CH4system, investigated earlier, the addition of only 0.53 mol% NaCl shifts the range of partial immiscibility to higher temperatures by more than 100 K (for example from 610 to 715 K at 100 MPa for 51 mol% CH4). The shift produced by CaCl2appears to reflect incomplete ionic dissociation at high temperatures. Encouraging results of computations of critical curves using pseudo‐binary approximations and a new equation of state based on defined interaction models are shown.
Cooperative Transfer of Excitation Energy and the Dynamic Structure of Micelles
Authors: Shahinian A. A. , Bagdasarian V. V.
Published: March 2014

The absorption and fluorescence spectra of aqueous solutions of amphiphiles, not containing highly conjugated systems of molecules and dyes, have been investigated in the presence and absence of electrolytes. Splitting of the UV absorption spectra of chromophore groups of amphiphile molecules and fluorescence sensibilization on micelle formation are observed. The presence of fluorescence concentration quench is connected to the quench caused by the decrease of intermolecular distance in the micelle. The fluorescence process is not accompanied by a change in the character of the absorption spectra. A hypothesis is made on the existence of flickering “well ordered” clusters in micelles, having a collective excitation energy (exciton) transfer mechanism. Using the fluorescence quench kinetics method it is shown that the average lifetime of the “well ordered” clusters in the micelle is 5 · 10−8‐10−7 s.
Osmotic Pressure of Aqueous Rod‐Like Polyelectrolyte Solutions with Mono‐ and Di‐valent Counterions
Authors: Bordi F. , Cametti C. , Di Biasio A.
Published: March 2014

Membrane osmometry has been used to measure the Donnan osmotic pressure of different salts of carboxymethylcellulose (Na+‐ Li+‐ NH4‐ Ca++‐ Mg++‐CMC) in aqueous solutions of simple chloride electrolytes. The results are analyzed in terms of cylindrical cell model for linear polyelectrolyte solutions, using the Poisson‐Boltzmann equation in order to calculate the counterion densities at the cell boundaries. Significant deviations with increasing polyion concentration have been found for all the counterions investigated.
Thermodynamics and Solubility of Oxygen in Liquid Bismuth‐lead and Bismuth‐antimony Alloys
Authors: Anik Sabri , Frohberg Martin G.
Published: March 2014

By means of emf technique the oxygen activities in the systems bismuth‐oxygen‐lead and bismuth‐oxygen‐antimony were measured at 1173 K. From the results and with the help of quenching experiments the unknown phase boundaries in the isothermal sections could be fixed. The miscibility gaps of the limiting binary systems extend far into the ternary systems. Isoactivity lines of oxygen in the homogeneous melts and conodes in the miscibility gaps were determined. The evaluation of the experimental data leads to important thermodynamic values as activity coefficients, interaction parameters and free enthalpies of oxygen in the liquid alloys bismuth‐lead and bismuth‐antimony.
A Proton NMR Study of the Deuterium‐Protium Fractionation in Aqueous Solutions of Some Organic Ions
Authors: El Seoud Omar A. , Kiyan Nilo Z. , Vieira Paulo C.
Published: March 2014

The dependence of the proton chemical shift of water on the concentration of sodium methane sulphonate, tetramethylammonium bromide, and tetrabutylammonium bromide was measured in water and in water‐D2O mixtures. Chemical shift data were used to calculate the fractionation factors (ø) for the methane sulphonate anion, the tetramethylammonium‐, and the tetrabutylammonium cation. In agreement with the results of other studies the obtained fractionation factors (0.97 ± 0.03, 1.0 ± 0.05, 1.06 ± 0.05 for the above mentioned ions, respectively) indicate that the methane sulphonate anion decreases the structure of water (relative to that of bulk water) whereas the tetrabutylammonium cation is clearly a structure maker. The effect of the tetramethylammonium ion appears to be negligible.
Light‐Induced Hole Transfer Across a Langmuir‐Blodgett Double‐Layer Membrane with a Short Tunneling Barrier
Authors: Willig F. , Eichberger R. , Bitterling K. , Durfee W. S. , Storck W. , van Der Auweraer M.
Published: March 2014

Light‐induced hole transfer across a membrane has been investigated with time resolved methods. The membrane has been assembled with the Langmuir‐Blodgett technique from two monolayers, one containing a modified dye, N,N'‐distearyl‐2,2'‐phenylindolocarbocyanine, and the other a modified anthracene molecule, 7‐(2‐anthryl)‐1 heptanoic acid. An anthracene single crystal has been employed as electrode to measure injection of holes from the above membrane as time‐resolved photocurrent transient with 100ps time resolution. The fluorescence decay of the excited dye layer was measured with 10ps time resolution. Comparison of both signals shows that the reaction sequence involves energy migration to dye aggregates and from there hole transfer through a short alkane chain tunneling barrier to the anthracene monolayer.
The Low‐Temperature Phase of the Organic Conductor (Fluoranthene)2PF6
Authors: Dormann Elmar , Sachs Günter
Published: March 2014

Possessing single crystals of sufficient size and quality, we reconciled the informations available from the electrical conductivity and the magnetic susceptibility with the results of different magnetic resonance techniques for the low‐temperature phase of the organic conductor (FA)2PF6. The influence of localized paramagnetic defects and a bottleneck situation for the defect‐spin relaxation via the conduction electrons are crucial ingredients for an understanding of the ESR properties of this and related radical‐cation salts of arenes. We conclude from our analysis, that it is a decisive advantage for a “model system” of organic conductors, if it has a low‐temperature semiconductor phase that enables one to “switch off” the influence of the conduction electrons.
Electrochemically Prepared Radical Salts of BEDT‐TTF: Molecular Metals and Superconductors
Authors: Schweitzer D. , Gogu E. , Hennig I. , Klutz T. , Keller H. J.
Published: March 2014

The structural, electronic and superconducting properties of several electrochemically prepared BEDT—TTF radical salts are discussed.
Electronic Excitations in (BEDT‐TTF)‐Salts
Authors: Helberg H. W.
Published: March 2014

The indicatrix orientation, the birefringence, and the transmission spectra were measured in small crystals of the organic conductors α‐(BEDT‐TTF)2I3 and α‐(BEDT‐TTF)3(NO3)2 in the near infrared (NIR) and the visible (VIS) spectral range. The results are discussed with regard to the orientation of the BEDT‐TTF molecule axes and the arrangement of the intermolecular contact directions. — The principal polarizabilities are calculated by composing the polarizabilities along the BEDT‐TTF molecule axes and along the several contact directions. At high energies (Δ2 eV) in the VIS the orientation of the polarizability tensor is governed by the orientation of the stack forming molecules due to the intramolecular excitations. In the NIR the intermolecular excitations become dominant. — The transmission spectra are compared with calculations of the dipole interactions.
Ferroelectric Liquid Crystals – Properties of the Smectic C Phase and the Smectic A Phase of Compounds with High Spontaneous Polarization
Authors: Bahr Ch. , Heppke G.
Published: March 2014

A short introduction to the properties of ferroelectric liquid crystals is given. Some new results concerning the coupling between the tilt angle and the polarization are presented for the SmC‐ and the SmA‐phase of a compound exhibiting very high values of the spontaneous polarization. A submicrosecond electrooptical effect in the SmA‐phase of this material is demonstrated.
Classification of Higher Excited States in (4N + 2)‐Annulenes and Related π‐Electron Systems
Authors: Hohlneicher Georg , Börsch‐Pulm Birgitt
Published: March 2014

The nomenclature introduced by Platt [1] for the assignment of electronically excited states of cata‐condensed benzenoid hydrocarbons is reinvestigated and extended to higher excited states. The extension to higher excited states was prompted by the increasing amount of knowledge on such states that result from new experimental techniques. The reinvestigation includes a careful consideration of pairing symmetries which were not a part of Platt's original concept. Further, it is shown that the subindices a and b cannot be used for higher excited states. These subindices have been introduced by Platt to distinguish between states that are degenerate in an ideal annulene. To combine the simplicity and generality of Platt's nomenclature with the higher quantitaty predicting ability of more sophisticated methods a formalism is provided that allows the analysis of the results of more advanced calculations in terms of certain “zero order perimeter states”. The analysis allows us to determine if a perimeter based assignment is possible, and if it is it tells us how to assign specific bands.
Experimental and Theoretical Studies on the Redox Properties of Conducting Polymers
Authors: Heinze Jürgen , Störzbach Michael , Mortensen John
Published: March 2014

Voltammetric measurements on selected polypyrrole (PPy) films and defined soluble oligomers belonging to the oligo‐p‐phenylene and the oligo‐p‐phenylenevinylene series provide new insights into the charging/discharging properties of conducting polymers. It turns out that the current response in the whole accessible potential range of conventional conducting polymers is mainly caused by faradaic charge transfer reactions rather than capacitive effects. This is supported by digital simulations which are based on a model of n‐fold electron transfers within a finite layer. In addition, from the data of defined oligomers it becomes clear that the number and energies of accessible redox states in such materials depend on the extension of conjugation in the monomeric unit and on the chain length of the polymer. In general, in systems such as PPy up to a charging level of approximately 20 – 25 mol% all redox states are degenerated. Then, the successive redox states are gradually shifted to higher energies in accordance with increasing Coulomb repulsion between the charges. The results show that the bipolaron model must be amended. Nevertheless, experimental data reveal that the charging steps in conducting polymers are coupled with structural relaxation processes; but they occur, in contrast to the theoretical predictions, already on the polaron state.
Kinetics and Mechanism of the Oxidation of N,N‐Diethyl‐p‐phenylenediamine by 12‐Tungstocobaltate(III)
Authors: Nickel Ulrich , Klein Boris , Hsin‐min Jen
Published: March 2014

The almost irreversible oxidation of N,N‐diethyl‐p‐phenylenediamine by 12‐tungstocobaltate(III) was studied by means of a multi‐mixing, stopped‐flow apparatus with optical detection. Both unprotonated and simple protonated p‐phenylenediamine are oxidized rapidly to form p‐semiquinonediimine. The reaction rate is dependent on the concentration of all ions present in the solution, as well as on the choice and concentration of the buffer. The rate constant varies from 3·104 M–1 s–1 to 1.4·106 M–1 s–1 at 25°C. The activation energy in all cases is very small.
An Ultrasonic Method for the Accurate Determination of the Melting Line: Data for Cyclohexane and Benzene
Authors: Sun T. F. , Kortbeek P. J. , Biswas S. N. , Trappeniers N. J. , Schouten J. A.
Published: March 2014

The p‐T melting curves of cyclohexane and benzene were measured accurately at pressures up to 85 MPa and 175 MPa respectively using an ultrasonic method. Important features of this new method are that the phase transition is studied by monitoring changes in the attenuation of ultrasonic echoes and that the measurements start in a non‐equilibrium two‐phase region, the partially solidified liquid, created by superpressing the liquid sample. The accuracy of the experimental melting temperatures for both liquids is about 0.03 K. The Simon‐Glatzel equation, fitted to the experimental data, can be extrapolated to 500 MPa without introducing large errors.
High Pressure NMR Study of the Molecular Dynamics of Liquid Methylfluoride and Deutero‐Methylfluoride
Authors: Lang E. W. , Prielmeier F. X. , Radkowitsch H. , Lüdemann H.‐D.
Published: March 2014

The 2D‐, 1H‐ and 19F‐spin‐lattice relaxation rates R1, have been investigated in fluid methylfluoride in the temperature range 150 K ≤ T ≤ 450 K and at pressures up to p = 200 MPa. In addition, the self‐diffusion coefficient D has been obtained with NMR techniques in the same p. T‐interval. — The latter are interpreted within the rough hard sphere model yielding a temperature independent RHS diameter d and a strongly temperature dependent rotation‐translation coupling parameter A. The total 2D‐, 1H‐ and 19F‐relaxation rates in CD3F and CH3F are decomposed into their respective quadrupolar, dipolar and spin‐rotation contributions. Furthermore orientational and spin‐rotational correlation times are estimated. It is shown that they are in good agreement with the predictions of the extended M‐diffusion model (EDM). Inertial effects influence the molecular dynamics in the whole p, T‐range investigated. The self‐diffusion coefficients and orientational correlation times are in excellent agreement with MD‐simulation data.
IR‐Chemiluminescence in the Reaction Systems F + CH3I and F + CH2I2
Authors: Schwanke U. , Heydtmann H.
Published: March 2014

Infrared chemiluminescence from HF is observed from the reactions of F atoms with CH3I and CH2I2in a fast flow apparatus under low pressure. The vibrational and rotational distributions for HF are determined for different nozzle configurations and changing reagent flows. The vibrational distributions forv= 1 – 3 are interpreted by proposing two microscopic channels for HF product formation in both reaction systems.
Laser Induced Thermal Diffusion
Authors: Scholz Malte
Published: March 2014

The concept of laser‐induced thermal diffusion was investigated by using a separation column in which a laser beam was aligned axially. This serves the same end as the heating wire normally employed in the Clusius‐Dickel method. The experimental runs used Ar‐SF6 mixtures to observe separation effects. The measurements showed a dependence on upward or downward direction of the beam and best results were obtained by changing the direction during the ran. Separation factors were measured as a function of pressure, beam diameter, radius of the column and laser power. Theoretical predictions could be confirmed within a factor of ≥ 5 as compared to a wire‐heated Clusius‐Dickel column.
2H‐NMR‐spectroscopic investigations of phospholipid bilayers
Authors: Hübner W. , Blume A.
Published: March 2014

2H‐NMR‐spectroscopy has been used to determine structure and dynamics in phospholipid bilayers composed of phosphatidylcholines (PC)

Abbreviations: PC, phosphatidylcholine; PE, phosphatidylethanolamine; DMPC, dimyristoyl‐phosphatidylcholine; DPPC, dipalmitoyl‐phosphatidylcholine; DSPC, distearoyl‐phosphatidylcholine; DMPE, dimyristoyl‐phosphatidylethanolamine; DPPE, dipalmitoyl‐phosphatidylethanolamine; DSPE, distearoyl‐phosphatidylethanolamine; DSC, differential scanning calorimetry.

and phosphatidylethanolamines (PE) of different chain length. The phospholipids were all labeled at the 4‐position of the sn‐2 chain. In pure lipid bilayers PEs always display wider quadrupole splittings than the corresponding PCs indicating a more condensed liquid‐crystalline phase for the PEs. In binary mixtures of PE and PC gel state immiscibility is observed when the two components differ in chain length by 4 CH2‐groups. In the liquid‐crystalline state deviations of the quadrupole splittings from linear behavior as a function of composition indicate the occurrence of clusters of different composition being in rapid exchange.
Pulsed electron nuclear double and triple resonance schemes
Authors: Mehring M. , Höfer P. , Grupp A.
Published: March 2014

The following pulsed electron nuclear double (ENDOR) and triple resonance schemes are discussed: Population transfer ENDOR, TRIPLE resonance, coherence transfer ENDOR, spin echo double resonance (SEDOR) and stimulated echo double resonance.
Optically detected NQR on matrix‐isolated organic molecules
Authors: von Borczyskowski C.
Published: March 2014

During an optical pumping cycle involving electronically excited triplet states of organic molecules electron spin alignment can be transferred by the solid state effect to nuclear spin alignment. By this the sensitivity of NQR is enhanced by at least six orders of magnitude, which makes it possible to study low concentrated nuclear spin reservoirs. Applications to (1) photochemical reactions at defect site structures in molecular crystals, (2) doped organic glasses and (3) NQR on 33S in natural abundance will be discussed.
35Cl NQR spectra and crystal structures of 1,2,4,5‐tetrachloro‐3,6‐dinitrobenzene and of 1,3,5‐trichloro‐2,4‐dinitrobenzene
Authors: Wigand Silvia , Walz Leonhard , Weiden Norbert , Weiss Alarich
Published: March 2014

The crystal structures of 1,2,4,5‐Tetrachloro‐3,6‐dinitrobenzene and of 1,3,5‐Trichloro‐2,4‐dinitrobenzene were determined and the temperature dependence of the 35Cl NQR frequencies was investigated. 1,2,4,5‐Cl4‐3,6‐(NO2)2C6 crystallizes monoclinic, space group C32h‐C2/m with 2 molecules in the unit cell. The lattice constants are a = 990.4 pm, b = 923.4 pm, c = 573.5 pm, β = 92.721°. The plane of the nitro groups is perpendicular to the benzene ring. ‐ 1,3,5‐Cl3‐2,4‐(NO2)2C6H crystallizes monoclinic, space group C52h‐P21/c with 4 molecules in the unit cell. The lattice constants are a = 821.3 pm, b = 924.8 pm, c = 1300.0 pm, β = 92.39°. The nitro groups are tilted out of the ring plane (79.7° and 87.6°). — The 35Cl NQR spectra are in agreement with the crystal structures and in both cases no phase transition occurs in the temperature range 77 ≦ T/K ≦ melting point.
Application of photon count statistical measurements to the stationary fluorescence of fluoranthene
Authors: Degen Joachim
Published: March 2014

The broad S1 → S0 emission spectra of fluoranthene at room temperature in solution and in solid state down to T = 25 K have been recorded in a standard photon counting experiment. The wavelength dependence of the photon count statistics have been measured. In time scales of several microseconds deviations from poission statistics are found which exhibit a fine structure not or less resolved in the broad luminescence spectrum.
The calculated and observed vibrational spectra of the ordered phase of tris(hydroxymethyl)aminomethane
Authors: Schroetter S. , Bougeard D.
Published: March 2014

The ordered phase of Tris(hydroxymethyl)aminomethane can be described in terms of molecular layers with intermediate intralayer and weak interlayer hydrogen bonds. The results of a normal coordinate treatment prove the strong coupling of the OH and NH deformation modes with other internal vibrations. Except for the vibrations including the hydrogen bonded groups the calculations agree with the experimental data. In order to assign the OH and NH stretching vibrations polarized infrared spectra of an oriented polycrystalline sample have been used.
Nuclear quadrupole coupling and electronic structure of boron trihalide adducts with chalcogen ligands
Authors: Conrady R. , Müller‐Warmuth W. , Krebs B. , Schwetlik G. , Wienkenhöver M.
Published: March 2014

11B NMR spectra of several boron trihalide (X = Cl, Br, I) adducts BX3 Y(CH3)2 with Y = S, Se, Te and BX3 S(CH2)4 have been measured at 96 MHz. Analyses of the well‐resolved first order quadrupole splittings have yielded coupling constants and asymmetry parameters at various temperatures. Applying the semiempirical Townes‐Dailey theory relative atomicorbital occupation numbers have been obtained and linked with the bonding configurations around boron. The results give information about the electron density distribution, the donor‐acceptor strength of the boron chalcogen bond, and the effect of various ligands.
Catalytic Effect of Metal Ions on the In: SnO2/Aqueous Polysulfide Interface: Application for Polysulfide Based Photoelectrochemical Cells
Authors: Tenne R. , Braun M. , Braun R. , Kerfin W. , Koschel W.
Published: March 2014

Large surface area photoelectrochemical cells exhibit low fill factors mainly due to mass transport polarizations in the electrolyte. To avoid that problem transparent (and conductive) materials must be used either as substrate to the photoelectrode or as a counter electrode. — It is shown here that cobalt(II), can reduce the overpotential at the interface between the transparent electrode and polysulfide electrolyte, without loss in transmittivity, rendering those materials good counter electrode. Surface analyses reveal that the metal ions form some kind of a sulfide superstructure with typical grain size of few tens of angstroms. The binding to the oxide layer is briefly discussed.