bluuebunny/crossref_metadata_2025 huggingface dataset:
High Pressure O‐17 Longitudinal Relaxation Time Studies in Supercooled H2O and D2O
Authors: Lang E. W. , Lüdemann H. ‐D.
Published: July 2012

The spin‐lattice relaxation times T1 of the oxygen‐17 isotope in light and heavy water have been measured at 13.56 MHz in the temperature range 457 K to 238 K and up to pressures of 250 MPa. Below 300 K all isotherms exhibit maxima of T1 which become most pronounced at the lowest temperatures measured. A marked isotope effect is seen in going from light to heavy water. The ratio [T1(H217O)/T1 (D217O)]T,p is temperature dependent and increases with decreasing temperature. Furthermore the isotherms in D2 17O exhibit a stronger pressure dependence than the isotherms in H2 17O. The correlation times τθ derived from 2H‐T1 and 17O‐T1 in heavy water are identical at all pressures and temperatures and demonstrate the isotropic nature of the orientational fluctuations of the molecules in liquid water. The temperature dependence of τθ can at low pressures (p < 150 MPa) be described by a fractional power law with a singular temperature Ts, whereas at high pressure (p > 150 MPa) the isobars can only be fitted by the VTF‐equation with the ideal glass transition temperature T0. Ts as well as T0 are found to be higher in heavy water compared to light water.
Laser‐Blitzlichtphotolytische Untersuchungen zur Druckabhängigkeit der Reaktion ClO + NO2 + N2 → ClONO2 + N2
Authors: Dasch W. , Sternberg K.‐H. , Schindler R. N.
Published: July 2012

The kinetics of the reaction ClO + NO2 + N2 → ClONO2 + N2 was investigated at room temperature in the pressure range 28 < p < 824 mbar by ClO‐absorption measurements. As source for ClO radicals Cl2O was used. The reaction was initiated using monochromatic light pulses from a KrF*‐excimer laser at λ = 248.5 nm. A Xe‐high pressure lamp and a pulsed Mg‐hollow cathode lamp respectively were used as analytic light sources. The atomic emission of the hollow cathode source at λ = 285.2 nm coincides with the 8. vibrational state of the ClO absorption. The results are discussed and compared with data obtained in other experimental studies as well as in model calculations.
Interaction of CFCl3 with an Fe(100) Surface Part I: Adsorption and X‐Ray Induced Effects at 90 K
Authors: Dowben P. A. , Grunze M.
Published: July 2012

We studied the interaction of CFCl3 with an Fe(100) surface over a temperature range from 90‐700 K using surface sensitive techniques. In the first part of our communication we describe adsorption at temperatures below 300 K. Initial adsorption on the clean Fe(100) surface at 90 K is dissociative and is followed by molecular adsorption up to 6 molecular monolayers. Multilayer formation is not expected from the heat of condensation of CFCl3. The adsorption of molecular layers therefore indicates a long‐range stabilization by the substrate of the adsorbate phase. This observation is of general significance of the understanding of extrinsic precursor states in adsorption. We further observe X‐ray induced processes in the adsorbed layer which can be distinguished from thermally induced dissociation.
ESR Studies on the Interaction of Molecular/Atomic Oxygen and Ethylene with Silver Zeolites
Authors: Hermerschmidt D. , Haul R.
Published: July 2012

Paramagnetic Ag2+ centres are formed by interaction of O atoms with dehydrated AgA and AgX as studied by in situ ESR measurements in a flow system. Interaction of molecular oxygen with the reduced, silver loaded zeolites leads to O−2 adsorbed on an “oxidized” surface. No indication for adsorbed O− was found. The conduction electron ESR signal of small Ag particles serves as a probe for chemisorption of O2 C2H4, C2H4O and H2O; it is not affected by CO2. – Reaction of C2H4 with Ag2+ results in a radical, while no paramagnetic intermediate is detectable in the immediate reaction with O2−.
Temperature and Hydrogen Concentration Measurements by CARS in an Ethylene‐Air Bunsen Flame
Authors: Müller‐Dethlefs K. , Pealat M. , Taran J.‐P. E.
Published: July 2012

Local temperatures and hydrogen concentrations in an ethylene‐air Bunsen flame have been determined from CARS measurements of the Q(0) to Q(4) [υ = 1 ← υ = 0] Raman transitions in hydrogen. A crossed beam, BOXCARS, technique of high spatial resolution including non‐resonant background cancellation is employed. The linewidth correction is taken into account for the limit of Doppler broadening. The results agree well with thermodynamic equilibrium calculations.
Temperature Dependence of the Chemiluminescent Reaction (1), NO + O3 → NO2(2A1; 2B1,2) + O2, and Quenching of the Excited Product
Authors: Schurath U. , Lippmann H. H. , Jesser Barbara
Published: July 2012

The title reaction (1) was studied at very low total pressures. The activation energy of the chemiluminescent pathway (1a) depends on the wavelength range in which emission is detected. Measurements at 1.27 μ, close to the maximum of the emission spectrum, yield 16.2 kJ mol−1 which presumably equals the activation energy E1a of the chemiluminescence integrated over all wavelengths. The absolute quantum yield at 290 K was determined to be k1a/k1 = 0.20, using the infrared atmospheric band emitted by known concentrations of O2(1Δg) as intensity standard. These results are combined with temperature dependent rate constants of the bulk reaction to yield separate Arrhenius equations, k1a = 2.90 · 10−12 exp(‐1951 K/T) cm3 s−1 for the electronically excited product, and k1b = 2.27 · 10−12 exp(‐1475 K/T) cm3 s−1 for the dark component of reaction (1). The half‐quenching densities of the chemiluminescence were found to be both wavelength‐ and temperature dependent, following approximately a T0.5 dependence for M = N2.
Statistical Treatment of Data of Excess Chemical Potential of Organic Binary Mixtures
Authors: Gioia Lobbia G. , Vitali G. , Berchiesi M. A. , Berchiesi G.
Published: July 2012

The liquid‐solid equilibrium temperatures of organic binary mixtures are treated in order to have the excess chemical potential. This thermodynamic quantity is statistically treated following the groups interaction theory and the interchange parametres are derivated.
The Independent Molecular Interaction Sites Model I. A New Reference System for the Thermodynamic Perturbation Theory of Molecular Fluids
Authors: Naumann Karl‐Heinz , Lippert Ernst
Published: July 2012

A new reference system for the treatment of molecular fluids within the framework of thermodynamic perturbation theory is presented. The basic ingredient of our approach is a potential transformation which allows us to view molecular liquids and gases as mixtures of formally independent molecular interaction sites (IMIS model). Some relations between our method and the RAM theory are discussed.
Homogene Kondensation von übersättigtem Eisendampf. Kinetische Untersuchungen mit einem Stoßwellenrohr
Authors: Steinwandel J. , Dietz Th. , Joos V. , Hauser M.
Published: July 2012

Iron vapor was produced by unimolecular decomposition of Fe(CO)5 in the front of a planar shock wave giving supersaturation in a wide range. The condensation of these systems has been detected by time resolved absorption spectroscopy using the collision broadened Fe I‐Resonance line 385.991 nm. The initially produced atomic iron densities were 2 to 5.1014cm−3 in the temperature range between 1700 and 1000 K; the degree of supersaturation is 2 ≤ In p/p∞ ≤ 20. ‐ A pre‐equilibrium with condensation, according to classical nucleation theory, can be excluded within experimental limits of accuracy, even if supersaturation is low.
Solid State Chemical Model for the Solubility Behaviour of CaCO3  MgCO3 Solid Solutions
Authors: Driessens F. C. M. , Verbeeck R. M. H.
Published: July 2012

Mg‐calcite can contain up to about 6 mol‐% MgCO3, dolomite between 40 and 51%. Solid solutions of CaCO3 and MgCO3 are unstable between 20 and 30 mol‐% MgCO3. The thermodynamic stability of dolomite with respect to calcite and magnesite amounts to about ‐6.8 kJ mol−1. It is shown that both the thermodynamical properties and the solubility behaviour of these solids can be explained with a solid‐state chemical model based on the theory of subregular solid solutions. Evaluation of the parameters of the model resulted in a critical cluster size of about one unit cell for the dolomite structure. The fact that normal sea water is close to equilibrium with both calcite and dolomite means that the concentrations of Ca2+, Mg2+ and CO32‐ ions in sea water are restricted by fixed sclubility relations.
Fluide Grenzflächen und Lamellen in der Technik
Authors: Nassenstein H.
Published: July 2012

At first a survey of the different types of interfaces: fluid/gas, fluid/fluid, and fluid/solid and their technical applications is given. Following techniques for coating solids with thin liquid filmes are treated and as an example the production of photographic materials is described.
Investigation of Electron Transfer Reactions of Metal‐Porphyrin Complexes in Micellar Solutions
Authors: Eck V. , Marcus M. , Stange G. , Westerhausen J. , Holzwarth J. F.
Published: July 2012

We have used the “Stopped‐Flow”‐ and the “Continuous Flow”‐methods to investigate the electron‐transfer behaviour of silver‐porphyrin complexes in aqueous and micelle containing solutions. Using IrCl62‐or Os(dipy)33+as the electron acceptor compound and silver(II) complexes of tetraphenylporphyrin tetrasulfonic acid (TPPTS), protoporphyrin (PP) or mesoporphyrin (MP) as the electron donor, second‐order rate constants between 104M−1s−1and 1010M−1s−1could be measured.—In aqueous solutions all three porphyrin complexes showed a complex kinetic behaviour because of dimerisation or the formation of higher aggregates. Only Ag(II)TPPTS was monomeric at low ionic strength.—In the presence of surface active substances such as sodiumdodecylsulfate (SDS), dodecyltrimethylammonium chloride (DTAC) or cetyltrimethylammonium chloride (CTAC) in concentrations above the cmc, where micelles are formed, all silver‐porphyrin complexes could be incorporated as monomers into the hydrophobic core of the micelles. In this way it was possible to investigate the kinetics of electron‐transfer of monomeric porphyrin complexes and to compare these with the behaviour in aqueous surfactant‐free solutions. Special attention was paid to measuring the activation barrier for an electron‐transfer from porphyrin complexes in the hydrophobic part of the micelles to redox ions in the surrounding solution. By varying the ionic strength of the solution and adding different types of surfactants, pure electrostatic effects could be separated from barriers which are created by an electron‐transfer through the surface of the micelles.—The mechanisms of these reactions are explained quantitatively to demonstrate the possibilities of influencing such electron‐transfer reactions.
Elektronenmikroskopische Untersuchungen von Mizellen
Authors: Bachmann L. , Dasch W. , Kutter P.
Published: July 2012

Aqueous micellar solutions of the following surfactants were freeze‐etched and investigated by electron microscopy: eicosyl‐ and docosylsulfate, docosyl‐pyridiniumbromide, hexadecyl‐N‐glycine, sucrose‐monomyristate and ‐palmitate. Micellar weight, aggregation number and critical micellar concentration can be determined by counting the number of micelles per area. Within the investigated range (up to 20 times the cmc) the aggregation number is not influenced by the concentration of the surfactant. The data obtained by electron microscopy are in accordance with those found in the literature.—The size and the shape of the micelles were measured with a particle size analyser. All micelles appeared spherical with a diameter of more than 8 nm. Even if the particles appear too large due to the preparation techniques, the real diameter of the hydrated micelles should always be larger than 6 nm.—This technique is particularly good for the investigation of surfactants with a very low cmc (≤ 10−5 molar) in saltfree solutions. Its most interesting aspect is the investigation of systems containing particles of various sizes and shapes.
Mass and Charge Transfer across the Organic/Aqueous Phase‐Boundary in Electrolysis Processes using Two‐Phase‐Emulsion Mixed Electrolytes
Authors: Feess Hans , Wendt Hartmut
Published: July 2012

Four different process‐techniques are distinguished of how to conduct the electrochemical conversion of sparsely water‐soluble substrates in aqueous solutions in the form of two‐phase emulsions. Based on detailed experimental investigations these techniques are discussed with respect to (a) the underlying principles of mass and charge transfer across the organic/aqueous phase boundary (b) their technical implications and their applications.
Molecular Liquids
Authors: Kohler Friedrich
Published: July 2012

The essential aspects of a microscopic description of atomic liquids are reviewed, with emphasis on geometric features of the hard sphere model assembly. Before dealing with some microscopic modifications caused by the non‐spherical symmetry of polyatomic molecules, the deviations of molecular liquids from the law of corresponding states are discussed. Then the influences of electric moments are considered in some detail, especially the interference between effects of dipole moments, quadrupole moments and anisotropic molecular shape. Finally, recent perturbation theories for molecules with anisotropic molecular shape are discussed which use hard non‐spherical bodies as reference system.
Einfache Modelle für kalorische Eigenschaften der Flüssigkeiten
Authors: Luck Werner A. P.
Published: July 2012

An efficient hole‐model of unpolar liquids is described. Deviations of the theorem of corresponding states are corrected by one factor, which is caused by the type of package. The possibility of distance independant pair‐potentials of the hole‐model is explained by the summation of Lennard‐Jones‐potentials. The temperature independant position of the first maximum of radial distribution curves is interpreted.—H‐bonded liquids are described by an orientation defect model, which gives the caloric properties quantitatively.
Molecular Theory of Liquids and Liquid Mixtures
Authors: Rowlinson J. S.
Published: July 2012

This paper reviews the present position of statistical or molecular theory of simple liquids and their mixtures, with particular emphasis on the quantitative success of perturbation theories. It is shown that the limits to our present understanding are provided not so much by imperfections in the statistical mechanics as by our ignorance of the precise form and strength of the intermolecular potentials for all molecules except the noble gases and their mixtures.
A Statistical Mechanical Equation of State and the Applicability to Fluid Phases
Authors: Peters C. J. , Lichtenthaler R. N.
Published: July 2012

In this paper the practical applicability of the statistical mechanical virial equation of state will be discussed. Therefore a new method to utilize the advantages of perturbation theory as well as the integral equation method is proposed. Also a suitable numerical technique is introduced to fit experimental pVT‐data to the virial equation of state.
Die Flüssigkeit an ihren Grenzflächen
Authors: Fischer J.
Published: July 2012

The liquid‐gas and the liquid‐solid interface are investigated for a model fluid with Lennard‐Jones interaction starting from the Born‐Green‐Yvon equation. For the liquid‐gas interface the coexisting densities, the surface tension, the density profile and the surface thickness are obtained and compared with results of computer simulations and experimental results on Argon. For the case of the liquid‐solid interface the structure of the liquid close to the wall is shown for different densities and temperatures.
Molecular Structure of Expanded Liquid Selenium up to 1400 °C
Authors: Edeling M. , Freyland W.
Published: July 2012

The static structure factor, S (Q), and the pair correlation function, g (R), of liquid selenium have been investigated by neutron diffraction in the temperature range from 600°C to 1400°C at pressures up to 300 bar. Within this temperature range the intramolecular bond length increases slightly from 2.37 Å to 2.38 Å and the coordination number of nearest neighbors decreases from 2.0 to 1.8. From these findings and especially from the detailed analysis of the shape of the first peak of g (R) we conclude that the structural data give no indication for the existence of a significant concentration (≥ 1019 cm−3) of threefold coordinated sites (branched chain molecules) in liquid selenium at elevated temperatures. For the intermolecular distance distribution in the range 2.8 ≤ R ≤ 4.4 Å a continuous decrease up to a minimum around 1200°C is observed. This indicates a denser packing of small linear chain molecules with increasing temperature.
Self‐Diffusion and Reorientational Motion in an Aqueous LiI Solution. A Molecular Dynamics Study
Authors: Szász Gy. I. , Heinzinger K. , Riede W. O.
Published: July 2012

It is concluded from a molecular dynamics simulation of a 2.2 molal aqueous LiI solution that in all three subsystems – bulk water, hydration water of Li+ and I− – the self‐diffusion is decreased and the rotational correlation time is increased compared with pure water. This result is a consequence of the existence of a second hydration shell of Li+. The usefulness of molecular dynamics simulations for the interpretation of macroscopic properties of aqueous electrolyte solutions on a molecular level is demonstrated.
Brillouin Light Scattering and Structural Relaxations in Ionic Solutions
Authors: Breitschwerdt K. G. , Polke E.
Published: July 2012

The hypersonic velocity and the hypersonic absorption have been measured in aqueous solutions of alkali halides in the temperature range between ‐170 and +20°C by Brillouin light scattering techniques. Both the dispersion of the hypersonic velocity and the frequency dependence of the reduced hypersonic absorption indicate the existence of structural relaxations in the frequency range 3–24 GHz. At temperatures down to −40°C the structural relaxation may be described by a simple rate process of Debye‐type. Below temperatures of about −40°C the ionic solutions exhibit viscoelastic behavior.
Light Scattering Studies of Pentanediols in Liquid and Supercooled Liquid State
Authors: Fytas G. , Dorfmüller Th.
Published: July 2012

The depolarized Rayleigh spectra of 1,5‐, 2,4‐, and 2 me‐2,4‐pentanediol have been measured in the temperature range of −40°C to +80°C using Fabry‐Perot interferometry. Additionally we report measurements of the correlation spectra of 2,4‐pentanediol in bulk and in solution and of neat 2 me‐2,4‐pentanediol in the temperature range of −75°C to −30°C using photon correlation spectroscopy. From the temperature and concentration dependence of the relaxing scattering intensities informations about the structure of these liquids have been obtained. The relaxation times of 1,5‐ and 2 me‐2,4‐pentanediol follow the change of the macroscopic viscosity with the temperature, in accordance to the Stokes‐Einstein‐Debye equation. This is not the case in 2,4‐pentanediol where we have to distinguish between a local and a macroscopic viscosity.
Inhomogene Schwingungsbandenverbreiterung aufgrund lokaler Konzentrationsschwankungen im flüssigen System Methyljodid‐Chloroform
Authors: Döge G. , Bien T. , Poßel M.
Published: July 2012

Some molecular vibrations bands of methyl iodide and chloroforme show drastic broadenings in mutual liquid mixtures at mean concentrations. This effect has been attributed to the existence of different microscopic environments of the vibrating molecules. Possibilities to get informations about structure of the liquid mixtures and molecular dynamics by studying this effect are discussed.
Equilibrium and Susceptibility Behaviour of the Pd/H2 System in the Critical and Supercritical Region
Authors: Wicke E. , Blaurock J.
Published: July 2012

Investigations of the palladium/hydrogen system about the critical point of demixing revealed surprising results in thermodynamic behaviour – i.e. ordering of the dissolved hydrogen – and in electronic effects, i.e. magnetic susceptibilities: Although the equilibrium hydrogen pressure increases with temperature smoothly and without irregularity from the two‐phase region through the critical point into the homogeneous supercritical phase – at constant (critical) concentration – the lnp – 1/T line exhibits a sharp curvature (“kink”) at the critical point.—The occurrence of the kink is shown to be a consequence of the unsymmetrical shape of the coexistence curve. This shape is related to a decrease in entropy that grows on quickly with rise of hydrogen concentration (third power), indicating a strong ordering tendency even in the supercritical phase. The Bragg‐Williams approximation, mostly applied in connection with mean‐field theory, is therefore not adequate, actually, to this system.—The supercritical phase enables investigation of electronic properties along broad ranges of continuously varying concentrations. Measurements of the magnetic susceptibility of PdHn in this range with 0 < n < 0.55 in comparison with Pd1‐xAgx alloys revealed higher values for PdHn at equal valence electron concentration (n = x). In this aspect the rigid‐band model, obviously, does not correlate the two systems.
An Attempt to Detect Higher Ion‐Ion Correlations (Microheterogeneity) in Aqueous Solutions of Rb and Cs Halides
Authors: Hertz H. G. , Mazitov R.
Published: July 2012

A set of inequalities is given as a formal definition of what we understand to be microheterogeneity. At the same time some known theoretical and experimental facts are mentioned representing already verifications of the criteria given. Experimental results for the87Rb,133Cs, and81Br nuclear magnetic relaxation rates in the respective aqueous halide solutions as a function of concentration and temperature are reported. These data are partly interpreted in terms of higher ion‐ion correlations, and partly a reduction of the first hydration number of the cations yields the explanation. The association parameterAis used to detect a feeble degree of water‐water association in the RbX and CsX solutions, X = Cl, Br, I. We conclude that we have evidence for microheterogeneity.
Photoelectrochemical Cells with Polycrystalline Cadmium Sulfide as Photoanodes
Authors: Neumann‐Spallart M. , Kalyanasundaram K.
Published: July 2012

A simple procedure for the fabrication of fairly efficient polycrystalline CdS electrodes from CdS powders is described (by coating a thin film of a paste formed with an aqueous solution of a surfactant and ZnCl2 on a Ti substrate and sintering at 670°C in Ar). Light conversion efficiencies of these thin film (‐20 μm) electrodes have been tested in two regenerative solar cells (with Fe(CN)63‐/4‐ and polysulfide redox systems) and ζsolar and ζ490nm have been found to be 0.37% and 4.4%, respectively for the former. The onset of the photoresponse was λ 520 nm with maximum efficiency at λ = 490 nm (2.53 eV). Photoelectrochemical cells of the type CdS/reductant//water/Pt for the visible light induced H2 generation from water have also been assembled and were found to produce H2 with a quantum yield of 5–16%.
Temperature Dependence of the Reaction OH + OH → H2O + O
Authors: Wagner Günter , Zellner Reinhard
Published: July 2012

Rate constants for the disproportionation reaction (1) OH + OH → H2O + O in the range 250–580 K have been measured by flash photolyzing H2O/N2 mixtures and monitoring the decay of OH using quantitative UV resonance spectrometry. The result k1 = (3.2 · 0.8) 10−12 exp (‐242/T) cm3/molecule · s, does not correlate with existing high temperature data and confirms previously suggested non‐Arrhenius behaviour for this reaction. On the basis of all available data the temperature variation of k1 over the range 250–2000 K is best represented by the empirical expression k1(T) = exp (‐27.73 + 1.49 · 10−3T) cm3/molecule · s. The extent of the Arrhenius graph curvature can be reconciled by a “close‐collision” model incorporating the energy variation of accessible product states.
Molecular Motion of Cations and Phase Transitions in Tetramethylammonium Hexachloroplatinate (IV), ‐tellurate (IV), and ‐stannate (IV) as Studied by CW and Pulsed 1H NMR and DTA Measurements
Authors: Prabhumirashi Laxman S. , Ikeda Ryuichi , Nakamura Daiyu
Published: July 2012

The temperature dependences of the 1H spin‐lattice relaxation time T1, at 20 MHz and of the second moment of 1H NMR absorptions were studied in tetramethylammonium hexachloroplatinate (IV), ‐tellurate (IV), and ‐stannate (IV), which are referred below as (tetMA)2PtCl6, (tetMA)2TeCl6, and (tetMA)2SnCl6, respectively. From the measurements of DTA and pulsed 1H NMR carried out below room temperature, four phases were found in (tetMA)2PtCl6 while two phases in both of the remaining complexes. The 1H NMR studies revealed that, with decreasing temperature, the most part of the rotational or reorientational freedom of tetMA cations freezes at almost the same temperature, but a small fraction of the motional freedom still remains even at lower temperatures. From the analysis of the shallow T1 minimum clearly observed for (tetMA)2TeCl6, this motion activated in this complex and also in (tetMA)2PtCl6 is unambiguously attributed to a small‐angle reorientation of four methyl groups in the cation around their staggered conformation. The mechanism of the phase transitions detected in these complexes is discussed in relation to the motion of tetMA cations.
DNMR‐kinetische Untersuchungen der Beweglichkeit von 1,4‐diacyl‐substituierten 1,4‐Dihydropyrazinen
Authors: Kollmannsberger Georg , Gottlieb Raphael , Pfleiderer Wolfgang
Published: July 2012

The AA'BB'‐part of the proton NMR spectra of the 1,4‐diacyl‐1,4‐dihydropyrazines 1‐4 reveals a strong temperature dependence resulting from the restricted rotation of both acyl groups around the C – N bonds. A dynamic model is postulated for the interconversion of the cis‐ and transforms which are in equilibrium. Activation enthalpies and activation entropies have been determined from the comparison of theoretical and experimental spectra. The results are discussed by use of HMO‐calculations.
Formation of an Inversion Layer in n‐Type MoSe2 Electrodes: Observation in the Presence of Highly Oxidizing Redox Systems
Authors: Jaeger C. D. , Gerischer H. , Kautek W.
Published: July 2012

The creation of an inverted surface region at an n‐type MoSe2 electrode is demonstrated by two different experimental techniques. In one technique the ac conductivity of a thin electrolyte layer in contact with a MoSe2 single crystal was determined where the surface of the MoSe2 behaves like a parallel shunt resistor. Injection of minority carriers by oxidized thianthrene induced a substantial increase in the surface conductivity of the MoSe2. In the second technique, the impedance of the MoSe2 electrode was determined over the frequency range of 100 to 50000 Hz. A plot of the impedance in the complex plane showed that the low frequency limit of the ohmic impedance component dramatically decreases in contact with oxidized thianthrene. This can also be interpreted as an indication for the formation of an inversion layer.
Temperature Dependence of Excess Thermodynamic Properties of Binary Mixtures of Organic Compounds
Authors: Koenen Hans‐Eckhardt , Gaube Johann
Published: July 2012

For calculations on distillation processes it is necessary to know the vapor‐liquid‐equilibrium (VLE) data at the desired temperature range. Very often data are available only for different temperature ranges. Therefore it is necessary to convert the VLE data from one temperature range to another.—The excess functions of the various types of mixtures have very different temperature dependence. Therefore we classified the mixtures according to the temperature dependence of the excess Gibbs energy and the excess enthalpy. The thermodynamic properties of the mixtures of organic compounds exhibit remarkable regularities.—In the case of non‐associated mixtures the excess Gibbs energy and the excess entropy are directly proportional to the excess enthalpy. Here simple expressions for describing the temperature dependence of the excess functions could be obtained

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The temperature dependence of the excess functions of the associated mixtures can be described by the Chemical Theory of Solutions.—The analysis of the available thermodynamic data shows that our classification serves a two‐fold purpose. First it is very useful for estimating the temperature dependence of excess functions. Second it shows how an analysis of the GE vs. HE(T) curves may enhance the general understanding of interactions in mixtures.
Small Angle Neutron Scattering Measurements on Ionic Detergent Solutions with Rodlike Micelles
Authors: Kalus J. , Hoffmann H. , Reizlein K. , Ulbricht W. , Ibel K.
Published: July 2012

Small angle neutron scattering (SANS) measurements have been carried out on aqueous solutions of Cetylpyridinium‐Salicylate (CPySal). The data show the existence of rodlike micelles with the length L and the radius R. The radius R of 21.5 A is independent of the detergent concentration while the L‐values increase with increasing concentration. For 10 mM solutions the micelles show considerable nearest neighbour order.
Soret Coefficients and Transported Entropies of Nonisothermal Liquid Alkali Nitrate + Silver Nitrate Mixtures
Authors: Fuchs W. , Richter J.
Published: July 2012

In a thermocell containing two silver electrodes the stationary state of thermal diffusion in the systems of molten KNO3 + AgNO3, RbNO3 + AgNO3, and CsNO3 + AgNO3 is measured at 513 K, 533 K, and 563 K as a function of the composition of the mixture. These measurements provide the thermoelectric power ε∞ (of the steady state) which depend linearly on temperature at a given composition. Thus it is possible to combine the ε∞‐values, extrapolated to higher temperatures, with the published ε∞‐values (thermoelectric power of the initial state) at 633 K and to compute the transport quantities of non‐isothermal melts in the temperature range from 493 K to 633 K. The transported entropies of the two ion constituents, a linear combination of the heats of transport of the same constituents, and the Soret coefficients of the three liquid systems mentioned are discussed, in connection with the same quantities for the systems LiNO3 + AgNO3 and NaNO3 + AgNO3, evaluated in a previous paper, thus leading to a complete investigation of the alkali nitrate systems.
Molecular Dynamics of Liquid Argon: Collision Times and Durations
Authors: Samios J. , Samios D. , Mersch W. , Dorfmüller Th.
Published: July 2012

The mean collision time 〈τC〉 and the mean durations of collision 〈τD〉 in liquid argon were calculated by a molecular dynamics computer simulation. The calculations were performed from the triple point temperature of T = 83.81 K to T = 150 K. The collision rates Z were obtained under isothermal, isochoric and isobaric conditions and the corresponding derivatives

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as well as the isokinetic coefficient

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have been calculated for our model and for liquid cell models. The use of the coefficients thus introduced for the calculation of frequency factors in solution kinetics is discussed. A comparison with collision induced spectra shows that the calculated values of 〈τC〉 and 〈τD〉 are in agreement with experimental data in liquid argon.
Calculated Koopmans' Defects for Transition Metal Compounds in the Framework of an Effective Semiempirical Hamiltonian: Bis(π‐pentadienyl)dinickel
Authors: Böhm Michael C.
Published: July 2012

A variable semiempirical Hamiltonian of the INDO type is employed in order to investigate the magnitude of reorganization effects (Koopmans' defects) in the photoelectron (PE) spectrum of bis(π‐pentadienyl)dinickel (1). The dependence of the calculated reorganization energies as function of the resonance integral βμνAB and as function of the two‐center electron‐electron interaction integral γμνAB is studied in detail. βμνAB has the property of an inverse coupling constant enlarging calculated Koopmans' defects with reduced βμνAB values. For γμνAB an exponential formula with a variable range parameter has been used; reorganization effects are of stronger importance in the case of short‐range forces with large γμνAB gradients. In the long‐range limit a significant reduction of the calculated reorganization energies is observed. The theoretically determined Koopmans' defects are calculated via a renormalized approximation for the self‐energy part in the perturbational framework of the one‐particle Green's function formalism.
Osmoseeffekte beim Stofftransport durch flüssige Membranen
Authors: Draxler J. , Marr R.
Published: July 2012

The water transport through the membrane of a stable w/o/w‐emulsion has been investigated. It has been found that the surfactant SPAN 80, which is added to the emulsion as a stabilizing agent, is a good carrier for water molecules. The water transport from the outer water phase through the organic membrane phase into the inner water phase causes swelling of the emulsion and therefore several properties of the emulsion are changed. An admixture of various carriers to the membrane phase showed that nitrogen containing agents have less influence on the water transport than oxygen containing agents. Organic phosphoric or carboxylic acids enhance the water transport whereas emulsions containing anion exchangers (like ALIQUAT 336) show an almost ideal behaviour: the water transport by SPAN 80‐molecules is prevented without affecting the properties of the carrier.
Clustering of Liquid Molecules on Solid Surfaces
Authors: Lagaly G. , Witter R.
Published: July 2012

The strong self‐association of DMSO, FA, DMFA, H2O controls their adsorption by swelling systems, for instance, by vermiculite, a mica‐type layer silicate. Using this type of porous adsorbents the influence of the interlayer charges has to be reduced by replacing the interlayer cations by alkylammonium ions. In equilibrium with the liquids (DMSO, FA, DMFA, H2O, EtOH) the silicate layers are prized apart until distinct cavities for the sorption of the liquids are created. Their volumes are independent on the chain length of the alkylammonium ions.—The mutual influence between the clustered liquid molecules and the alkyl chain arrangements determines the interlayer structure. Therefore, substitution of alkylammonium ions by trimethyl alkylammonium ions not only changes the type of the liquid clusters but also the alkyl chain arrangement. Dimethyl dialkylammonium ions impede the formation of liquid clusters because of the strong van‐der‐Waals interactions between the chains, and only allow incorporating isolated guest molecules.—The surface excess isotherms describing competitive adsorption of DMSO and H2O show substantially linear sections. The DMSO/H2O ratio in the adsorbed phase is constant through most of the mole‐fraction range of DMSO in solution (mole fractions DMSO from x1 = 0.15 to 0.95). DMSO is preferentially adsorbed, the ratio DMSO/H2O being 4–5.
Dielectrical Relaxation Measurements in Binary Liquid Mixtures with an Upper Critical Point
Authors: Kaatze U. , Woermann D.
Published: July 2012

The complex (dielectric) permittivity of the systems isobutyric acid/water and butyric acid/water is measured as function of frequency (0.001 GHz ≤ v ≤ 38 GHz), concentration (1 mol · dm−3 ≤ c ≤ 5 mol · dm−3) and temperature (25°C ≤ T ≤ 35°C). Both systems have an upper critical point (isobutyric acid/water: ccrit = 4.36 mol · dm−3, Tc = 26.30°C; butyric acid/water: ccrit = 4.33 mol · dm−3, Tc = ‐ 3.0°C).—The temperature dependence of permittivity of isobutyric acid/water mixtures of critical composition shows no critical contribution near the critical temperature (0.01 K ≤ (T–Tc) ≤ 9 K) within the accuracy of the measurements (±1%).—Different relaxation functions based on different models of the solution are fitted to the measured dielectric spectra. The results of this analysis can be interpreted by assuming that butyric acid and isobutyric acid molecules form associates in solution even well below the critical concentration. On the basis of this assumption it is possible to understand:

(a) the concentration dependence of the main relaxation time of water in the Cole‐Cole‐distribution function;

(b) the concentration dependence of the number of water molecules per molecule of solute having relaxation times different from that of pure water;

(c) the concentration dependence of the relaxation time of hydration water.
Defects and Cation Diffusion in Magnetite (IV): Nonstoichiometry and Point Defect Structure of Magnetite (Fe3‐δO4)
Authors: Dieckmann R.
Published: July 2012

Nonstoichiometry and point defect structure of magnetite have been studied experimentally by thermogravimetry covering the stability range of magnetite between 900 and 1400 °C. A cation deficit is observed at high and a cation excess at low oxygen activities corresponding to cation vacancies and iron interstitials as the predominant point defects, respectively. An overexponential temperature dependence occurs for the defect concentrations in stoichiometric magnetite.
The Fluorescence Lifetime of Trans‐Stilbene and its Variation with Temperature
Authors: Good Hans P. , Wild Urs P. , Haas E. , Fischer E. , Resewitz E.‐P. , Lippert E.
Published: July 2012

The fluorescence lifetime of trans‐stilbene in solution was measured in the temperature range 300–80 K by three different methods. The decay was found to be mono‐exponential throughout, but prone to falsification by impurities, which may be responsible for the bi‐exponential decays reported by some authors. At room temperature τF is 80–130 ps, increasing to 1200–1400 ps at 77 K.
Chlorine NQR on Hemiacetals of Chloral, Cl3CCH(OH)OR
Authors: Hashimoto M. , Weiss Alarich
Published: July 2012

The 35Cl NQR spectra of 22 hemiacetals of chloral, Cl3CCH(OH)OR, were studied. Most of these hemiacetals with R = unbranched aliphatic group, show a three line 35Cl NQR spectrum having a regular splitting pattern; two lines around vL = 38.6± 0.1 MHz and the third line at vH = 39.0 ± 0.1 MHz. It is assumed that the difference between vL and vH is due to “chemical splitting”. Completely irregular splitting pattern are found for the hemiacetals carrying bulky branched aliphatic groups. Moreover the magnitudes of these splittings are relatively large. A deformation of the molecules due to intramolecular steric hindrance seems to be responsible for this large splitting. The frequency shift in these compounds due to the steric effect is estimated to be 1 MHz or less. A peculiar temperature dependence of the 35Cl NQR line intensity was found for chloral n‐butylhemiacetal. An intramolecular bifurcated hydrogen bond between CCl3 and OH groups is proposed to be responsible for the phenomenon. For p‐chlorobenzylalcohol at ca. 226 K a phase transition was observed.
Photoelectrochemical Investigations of Pyranthrone in Aqueous Electrolytes
Authors: Ahuja R. C. , Hauffe K. , Schumacher R. , Schindler R. N.
Published: July 2012

The present paper reports the results of investigations on the photoelectrochemical properties of pyranthrone. The used samples were of the type SnO2/pyranthrone/aqueous electrolyte and Au/pyranthrone/aqueous electrolyte. They were prepared by vacuum evaporation of pyranthrone on SnO2 and Au substrates. Under illumination, both samples showed anodic as well as cathodic currents. It was found that the potential at which the anodic photocurrent crosses over to the cathodic, depends on pH and additives introduced into the electrolyte. The magnitude of photocurrents is also dependent on pH, biasing conditions and the presence of additives. The results are discussed, treating the pyranthrone as photosemiconductor. The observed photocurrents thus arise, because of the reaction of photogenerated charge carriers with H+/OH− ions in the aqueous electrolyte. The pyranthrone layer was found to be stable especially under conditions where cathodic photocurrents flow. The observed quantum yield was ca. 10−3 e/incident photon. Using redox potential data, the position of energy bands of pyranthrone at pH 13 were determined to be: Ev = −5.35 eV and Ec = −3.40 eV with respect to the vacuum level.
Messungen dielektrischer Eigenschaften bei hohen Drücken und tiefen Temperaturen III: Die statische und komplexe Dielektrizitätszahl von Cyclopentanol
Authors: Würflinger A.
Published: July 2012

The static permittivity ε of liquid and solid cyclopentanol has been determined as a function of temperature (+ 50 to ‐ 80 °C) and pressure (up to 3 kbar). From these and PVT data the Kirkwood correlation factor g has been calculated. Plots of g as a function of temperature intersect at g = 2.6 and at the “cross‐over‐temperature” of 30 °C. The calculations have also been extended to the plastic phases (SI, SII) of cyclopentanol, because their permittivity (especially that for SII) exceeds that for the liquid considerably. There is a drastic decrease of ε to values about 2.5 at a lower SII/SIII transition. The increase of ε at the freezing point is larger as should be expected according to the Onsager equation. The temperature dependence of g at constant volume is negative. Also the dielectric relaxation has been studied for the plastic phases of cyclopentanol up to frequencies of 10 MHz. The complex permittivity has been evaluated with the help of the Cole‐Cole equation, showing only a small deviation from a simple Debye‐mechanism (α ≤ 0.05). The relaxation times τ about 1000 bar vary from 10−5 s (‐70°C) to 3 · 10−8 s (‐ 10°C) in solid cyclopentanol, τ being discontinuous at the SI/SII transition. Activation volumes (5–7 cm3 mol−1) and activation energies (40 kJ mol−1) have been derived from the pressure and temperature dependence if τ.
Theoretical Study of Intermolecular Proton Transfer between Equivalent Molecules in Solution: Diffusion Induced Tunneling
Authors: Klöffler Martin , Brickmann Jürgen
Published: July 2012

The mechanism of intermolecular proton transfer AH + A ⇋ A + HA in solution is studied in terms of a model in which the motion of the molecule A is treated as a classical random motion while the proton behaves quantum mechanically. The proton moves in a symmetrical double well potential which is stochastically time dependent. The energy splitting due to the coupling of the AH stretching vibration in different molecules is assumed to depend only on the distance between diffusing molecules but not on their relative orientation.—Using a first order perturbation approach the transfer rate is found to be inversely proportional to the diffusion coefficient. The proton transfer rates are calculated for two limiting cases corresponding to a WKB type and a Franck Condon type coupling term.
A Semi‐Empirical Investigation into the Trans‐Cis Photoisomerisation of Stilbene
Authors: Olbrich Gottfried
Published: July 2012

Potential curves of the eight lowest singlet and eight lowest triplet states for the isomerization reaction of stilbene have been calculated by CI including triply excited configurations. The CI was based on MO's evaluated by a CNDO method. A ground state activation energy of the isomerization of 259 k J/mol was calculated. The lowest excited singlet state has a minimum at the perpendicular geometry and an activation energy of 50 kJ/mol for the trans cis isomerization in this state was found. It is shown, that this activation energy originates from an avoided crossing with a higher lying singlet state. Isomerization in the triplet manifold should occur preferentially via the lowest triplet state.
A Proton Magnetic Resonance Study of Ligand Exchange on Tetrakis (N,N‐Dimethylacetamide) Beryllium(II) and its N‐Methylacetamide, and N,N‐Dimethylformamide Analogues
Authors: Lincoln Stephen F. , Tkaczuk Michael N.
Published: July 2012

A 1H (90 MHz) NMR study shows that ligand (L) exchange on [BeL4]2+ is characterised by the rate law: exchange rate = 4(k1 + k2[L]free)[BeL2+4] when L = O = CMe(NMe2), O = CMe(NHMe), or O = CH(NMe2) in the non‐coordinating solvents CD3NO2 and CD3CN, and also in CD2Cl2 in the case of O = CH(NMe2). The kinetic parameters observed for these systems are exemplified by those characterising [Be(O = CMe(NMe2))4]2+ in CD3NO2 solution which are: k1 (340 K) = 7.3 ± 0.7 s−1, ΔH#1 = 56.9 ± 1.5 kJ mol−1, ΔS#1 = −62.1 ± 4.6 J K−1 mol−1, k2 (340 K) = 10.5 ± 1.0 dm3 mol−1 s−1, ΔH#2 = 66.7 ± 2.6 kJ mol−1, and ΔS#2 = −30.1 ± 7.4 JK−1 mol−1. The k1 and k2 rate constants are interpreted in terms of dissociative (D) and associative (A) (or interchange (I)) ligand exchange mechanisms and are discussed in conjunction with previously reported data for other beryllium(II) systems.
Colloidal TiO2 Catalyzed Photo‐ and Radiation Chemical Processes in Aqueous Solution
Authors: Henglein A.
Published: July 2012

A number of free radical reactions was observed upon the illumination of TiO2 sols with light of the near UV. Cl−, Br−, and I− were oxidized to yield the radical anions Cl−2, Br−2, and I−2, respectively. Propanol‐2 was oxidized to yield the 1‐hydroxy‐1‐methyl ethyl radical. These intermediates were identified by their optical absorptions or their reaction with tetranitromethane or acrylonitrile. The quantum yields were measured as a function of the substrate concentration. The effects are explained by the formation of electron‐hole pairs in illuminated colloidal TiO2, rapid diffusion of these charge carriers to the surface of the colloidal particles, and reaction with adsorbed acceptors. Most of the charge carriers, however, disappeared by recombination, the largest quantum yield observed being 0.16. The lifetime of the charge carriers was less than 30 ns.—Acidic TiO2 sols containing propanol‐2 were also γ‐irradiated. In these sols, 1‐hydroxy‐1‐methyl ethyl radicals were formed which attacked the colloidal particles. The overall reaction consisted of the dissolution of the colloid. At short irradiation times, the sols became blue, and this color slowly disappeared upon further irradiation. The color centers had an absorption coefficient of 1 · 104 M−1 cm−1. They were very sensitive towards oxygen. Their formation is connected with the electron transfer from the organic radicals to the colloidal particles. A mechanism is proposed according to which the energy of dissolution of colloidal TiO2 is supplied by the overall disproportionation of the radicals.
Influence of the Solvent on the Electrochemical Stability of a Semiconductor Electrode
Authors: Sculfort Jean‐Lou , Gautron Jacques , Lemasson Philippe , Herlem Michel
Published: July 2012

The influence of the supporting electrolyte on the decomposition mechanisms of an electrode (n‐ZnSe) whose behaviour is well‐known in aqueous media has been investigated in liquid ammonia (‐60 °C) and in liquid ammoniate of sodium iodide (room temperature). In each case, the flat band potential of the ZnSe‐electrolyte junction was determined unambiguously giving the following values: −2.3 V/MSE in acidic aqueous medium; −2.2 V/SRE (‐60°C) in liquid ammonia and −2.2 V/SRE in neutral ammoniate. For low concentrations of residual water (CH2O ≤ 10−2 M), a cathodic mechanism of decomposition is evidenced. In liquid ammonia, it takes place below −2.0 V/SRE (‐60°C) and in neutral ammoniate below −2 V/SRE. In the latter solvent, when CH2O increases, this decomposition is changed for the reduction of water. At positive potentials, in the dark and under illumination, whereas the semiconductor decomposes in aqueous medium, in liquid ammonia and in ammoniate it is the solvent which decomposes, the electrode remaining unmodified.