bluuebunny/crossref_metadata_2025 huggingface dataset:
Die Reduktion halogenierter organischer Verbindungen durch hydratisierte Elektronen
Authors: Köster R. , Asmus K.‐D.
Published: March 2014

Es wurden pulsradiolytische und γ‐strahlenchemische Versuche zur Reduktion von halogenierten organischen Verbindungen durch hydratisierte Elektronen durchgeführt. Dissoziativer Elektroneneinfang setzt aus verschieden chlorierten Methanen, äthylenen sowie fluorierten Benzolen Halogenionen frei. Diese wurden mit Hilfe von Leitfähigkeitsmessungen bei der Pulsradiolyse und mit Ionen‐sensitiven Elektroden bei den γ‐Versuchen quantitativ nachgewiesen. Die Geschwindigkeitskonstanten der Reaktion des eaq− mit den mehrfach halogenierten Verbindungen sind praktisch ausschließlich durch die Diffusion der Reaktionspartner zueinander bestimmt. Bei den wenig halogenierten Substanzen verläuft die Reaktion langsamer, was mit der größeren Stabilität der Halogen‐Kohlenstoffbindung in Einklang steht. Die primären Reaktionsprodukte sind Halogenionen und neutrale, kurzlebige Radikale, die keinerlei optische Absorption im Wellenlängenbereich von 250–800 nm aufweisen.

Alkohol‐ und Ätherradikale übertragen ein Elektron auf CCl4. Dies stimmt mit der Tatsache überein, daß die Halbstufenpotentiale für die Oxidation dieser Radikale negativer sind als dasjenige für die Reduktion des CCl4. Die theoretisch ebenfalls mögliche Elektronenübertragung vom CO2−‐Radikalion auf Tetrachlorkohlenstoff findet nicht statt, da offensichtlich eine zu hohe Aktivierungsenergie für diese Reaktion vorliegt.
Thermoelectric Power of solutions of Sodium and Potassium in Liquid Ammonia
Authors: Damay Pierre , Chieux Pierre , Lepoutre GÉRard
Published: March 2014

We have extended the experimental study of the thermoelectric power of metal‐ammonia solutions to the intermediate concentration range.

We have also determined the temperature coefficients of the thermoelectric powers.

Abnormal behaviors show up between 1 and 2.5% MPM (mole fraction of metal). They are interpreted by the formation of isolated unstable clusters within the bulk of the solution. These clusters become interconnected between 2.5 and 4%, and, beyond 4%, they provide entirely interconnected metallic paths for the transfer of electrons.
Contribution to the Problem of Electron Trapping in Non‐polar solids
Authors: Magat Michel
Published: March 2014

The trapping of electrons in non‐polar solids is discussed in the light of the polaron model and the bubble model. Comparison between semiquantitative theory and some experimental data suggest that the bubble model is the better model for explaining the properties of trapped electrons.
Electron‐Hole Pairs in the Mechanism of the Radiation Chemistry of Non‐Polar and Polar Liquid Systems
Authors: Weiss Joseph J.
Published: March 2014

It has been shown previously that after absorption of radiation leading to ionisation, in general, the electrons are at first captured in an expanded orbit around the positive ions. In media of low dielectric constants, the resulting charge‐transfer excitons are relatively long lived and they can react themselves with suitable electron or hole scavengers. If one takes into account that such electron‐hole pairs diffuse in the medium after their creation one can derive the experimentally observed dependence of the yield on the square root of the scavenger concentration. In polar media e.g. water, such electron‐hole pairs are very short lived and tend to dissociate into electrons and holes in times of the order of picoseconds. The experiments of Hunt et al. have been discussed and it has been shown that the observed dependence of the initial yields of the solvated electrons on scavenger concentration can be accounted for if one takes into account also that in the presence of scavengers, the formation of esolv− is only possible if, statistically speaking, a scavenger molecule is not sufficiently close to a radiation produced electron‐hole pair to enable it to react with it.
The Reaction of Metals with Weak Acids in Liquid Ammonia and Methylamine
Authors: Dewald Robert R.
Published: March 2014

Kinetic data for the reactions of sodium with water, ethanol, and t‐butyl alcohol in liquid ammonia are consistent with the mechanism: magnified image Analysis of the data for these reactions yields values for k1 and k2/k3. k3 has been measured directly at ‐35°C by reacting solutions of sodium and ammonium bromide in liquid ammonia using the stopped‐flow technique. Rate data for the reaction of cesium with water in ethylenediamine have been analyzed on the assumption that two parallel second‐order reactions are operative. Kinetic data for the reaction of cesium with water in methylamine at ‐70°C could best be explained in terms of Equation (1) and (2) where NH3 is replaced by CH3NH2. The reaction of sodium with water in methylamine was found to be consistent with observed second‐order kinetics. Recent data for the metal‐ammonia‐alcohol reduction of benzene suggest that a steady‐state concentration of ammonium radicals is established.
solvent Dependence of Optical and Kinetic Properties of solvated Electrons in Water‐Ammonia Mixtures
Authors: Olinger R. , Schindewolf U.
Published: March 2014

The absorption spectrum and the lifetime of solvated electrons was determined in water‐ammonia mixtures with special consideration of the temperature‐ and pressure dependence. The solvated electrons were produced by pulseradiolysis.

With increasing ammonia content the light absorption maximum of the solvated electrons is shifted to longer wave lengths. – The lifetime of the solvated electrons, restricted by the reaction with water, increases almost exponentially with the ammonia content whereas the activation energy and the activation volume decrease down to negative values.

The optical data indicate that there is a smooth transition from hydrated to ammoniated electrons and that the molare volume of the electrons increases continuously with the ammonia content. The kinetic data can be explained on this basis and under the assumption that the entropy of the solvated electrons is the bigger the higher their volume.
Electrochemical Effects Produced by Light‐induced Electron Emission
Authors: Barker G. C.
Published: March 2014

Direct evidence for light‐induced deposition of electrons in the solution near a mercury cathode is obtained by studying the coulostatic photopotential produced by a short duration light pulse. Similar studies permit the evaluation of rate constants for electron scavenging and the diffusion coefficient of the OH radical. The mechanisms of the photo‐currents produced by NO3−, No2− and H3O+ are discussed.
Über die Geschwindigkeit spontaner intramolekularer Umlagerungsreaktionen: II. Pseudorotation trigonal bipyramidaler Moleküle
Authors: Brickmann J.
Published: March 2014

Spontane Pseudorotationsraten trigonal bipyramidaler Moleküle werden am Beispiel von PF5 und AsF5 untersucht. Die intramolekulare Reaktion wird dabei als Bewegung einer effektiven Masse entlang der Reaktionskoordinate beschrieben. Der Einfluß des Tunneleffekts auf die Temperaturabhängigkeit der Pseudorotationsraten wird diskutiert. Die numerischen Ergebnisse liegen innerhalb der durch die charakteristische Meßzeit von NMR‐ und IR‐Untersuchungen gegebenen Grenzen.
Ermittlung der Zusammensetzung der Oberfläche von Korrosionslöchern auf Eisen während des Lochfraßes mittels der Elektronenmikrosonde
Authors: Strehblow H. H. , Vetter K. J. , Willgallis A.
Published: March 2014

Zur Aufklärung der Vorgänge bei der Lochfraßkorrosion wurde die chemische Zusammensetzung der Oberfläche von Korrosionslöchern auf Eisen mit einer Elektronenmikrosonde auf Chlorid‐ und Sulfatschichten untersucht (nc1 = 2,1 · 1015 Cl‐Atome/cm2 bzw. ns = 2,5 · 1015 S‐Atome/cm2 pro Impuls/sec). Es wurde eine Präparationsmethode ausgearbeitet und getestet, die es gestattete, die Probe aus dem Elektrolyten in das Vakuum der Sonde unter Erhaltung des korrosionsaktiven Zustandes der Löcher zu überführen. Der Lochfraß erfolgte in chlorid und sulfathaltigen Lösungen vom pH‐Wert 5,0 (Phthalatpuffer) bzw. pH = 8,0 (Boratpuffer) unter potentiostatischen Bedingungen.

In kleineren Löchern von 5 bis 10 μ Durchmesser, in denen noch keine Konzentrationsfällungen auftreten können, wurden trotzdem Chloridmengen gefunden, die Eisenchloridschichten von einigen 10 Å Dicke entsprachen (1 Imp/sec entspricht 7,4 Å FeCl2, Untergrund 10 Imp/sec), größere entsprechend länger gewachsene Löcher enthielten wesentlich mehr Chlorid, was hier auf Konzentrationsfällungen zurückzuführen ist. In bereits im Elektrolyten repassivierten Löchern war kein Chlorid nachzuweisen. Bei Anwesenheit von Sulfat im Elektrolyten wurden auch bei größeren Löchern nur kleine Chloridmengen gefunden. Dagegen waren unter den gewählten Versuchsbedingungen große Sulfatanreicherungen entstanden (1 Imp/sec entspricht 22 Å FeSO4). Bei kleinen Löchern wurde gefunden, daß der übergang von polygonalen zu runden Formen mit der Bildung von starken Sulfatschichten verbunden ist, die auf Konzentrationsfällungen zurückgeführt werden. Derartige Schichten sind offenbar für das anisotrope Wachstum der runden Korrosionslöcher verantwortlich.
Leitfahigkeitsmessungen an Polystyrylnatrium in Dimethoxiäthan (DME) und Tetrahydrofuran (THF)
Authors: Chmelí M. , Schulz G. V.
Published: March 2014

An Polystyrylnatrium werden in zwei polaren organischen Lösungsmitteln Leitfähigkeitsmessungen über einen größeren Temperaturbereich ausgeführt. Aus der Temperaturabhängigkeit der Dissoziationskonstante ergibt sich, daß die undissoziierte Verbindung in zwei Formen, dem Kontaktionenpaar (I) und dem solvatgetrennten Ionenpaar (II), vorkommt. Enthalpie‐ und Entropiedifferenz beim übergang von I nach II, sowie die entsprechenden thermodynamischen Parameter der Dissoziation von II werden ermittelt. Der effektive Ladungsabstand im solvatgetrennten Ionenpaar beträgt etwa 7 Å.
Elektronenspektren von Hexacyanochromaten
Authors: Schläfer H. L. , Wagener H. , Wasgestian F. , Herzog G. , Ludi A.
Published: March 2014

Die Hexacyanochromate(III) von Li+, Na+, K+, Rb+, Cs+, NH4+, [(C4H9)4N]+, [(C6H5)4P]+, [(C6H5)4As]+ und Tl+ wurden präpariert und röntgenographisch vermessen. In den Remissionsspektren wurde eine bisher unbekannte Elektronenüberführungsbande bei 45 kK gefunden, die in einigen Fällen eine Schwingungsstruktur besitzt. Die Phosphoreszenzintensität hängt stark von der Art des Kations ab. Die Bandenlagen in Emission und Remission unterscheiden sich bei den einzelnen Komplexsalzen nur geringfügig.
A Kinetic Model for Fluorescence solvatochromism
Authors: Rapp W. , Klingenberg H.‐H. , Lessing H. E.
Published: March 2014

A simple kinetic model is presented that describes the frequency‐time‐behaviour of the fluorescence of molecules showing an anomalous Stokes shift. A discrete and a continuous description of this model are given. Results are compared with an earlier formulation given by Bakhshiev [4].
Chemical Relaxation of a Basic Cooperative Binding Mechanism for Linear Polymers
Authors: Schwarz Gerhard
Published: March 2014

A linear Ising lattice of N> equivalent binding sites is used as a model system. The general theory predicts a spectrum of 4 N‐5 relaxation times. However, a substantially simpler situation is encountered in those cases of great practical interest where cooperativity is strong and N is sufficiently large. Under these circumstances only a single relaxation time controls the binding process at smaller values of the polymer to ligand ratio. For higher values of this quantity three relaxation times occur. It is shown that in studies of ligand aggregation on the polymer (e.g. dye stacking) only two of these relaxation times are significant. Since they differ little in magnitude the mean relaxation time τ* is more useful from an experimental point of view. This important kinetic quantity is therefore discussed in more detail. It is shown to reflect the opposing effects of growth and redistribution of bound ligand aggregates resulting in a minimum at medium polymer to ligand ratio.
Spectra of Cu(II)‐Complexes in Aqueous Solutions at High Temperatures and Pressures
Authors: Scholz B. , Lüdemann H.‐D. , Franck E. U.
Published: March 2014

The influence of pressure, temperature and chloride‐concentration on the optical spectra of copper(II)ions in aqueous solution has been investigated.

The measurements could be extended to 400 °C at a pressure of 2000 bars. In dilute aqueous solutions of copper(II)chloride the hexaquocopper‐ (II)complex is prevailing. With increasing temperature and concentration of chloride the copper(II)tetrachlorocomplex is formed via some intermediate compounds. The composition of some of the intermediate compounds was deduced from the spectra obtained.
Diffusion Isotope Effects in Isotope Mixtures
Authors: Bonn B. , Gans E. , Sicking G. , Wicke E.
Published: March 2014

The tracer diffusion of deuterium and tritium in the β‐phase of PdHn has been measured by means of special techniques, the time lag method with mass spectrometer or counter tube as detector, and the decay function of isotope exchange. It has been found that D atoms as tracer in β‐PdHn, i.e. surrounded by H atoms, reveal a smaller mobility than in PdDn, where they are surrounded by their own species. T atoms in the β‐phase of PdHn showed about the same mobility as can be estimated — from results of α‐phase measurements ‐for PdTn.

An explanation of this unexpected bevavior can be given by the assumption of displacement jumps as a particular type of correlation effect: by this the mobility of the tracer atoms becomes dependent on the mobility of the surrounding isotope species in the lattice.
Determination of Interstitial Deuterium Locations in Niobium by Channeling
Authors: Carstanjen H. D. , Sizmann R.
Published: March 2014

Channeling provides a new technique for determining the lattice positions of deuterium atoms in single crystals at low concentrations. In the present investigation the D(d,p)T reaction yield was measured around the 〈100〉 and the 〈111〉 incidence directions of a 300 keV deuteron beam penetrating through niobium loaded with 2 atomic percent deuterium. In combination with flux and energy distribution calculations of the channeled deuterons the conclusion was reached that at 150 K the dissolved deuterium atoms are located at tetrahedral lattice sites. Measurements at room temperature indicate that deuterium at 295 K occupies the same sites.
Verweilzeiten von adsorbierten Kohlenwasserstoff‐Molekülen an Pyrexglas aus Molekularströmungs‐Versuchen
Authors: Großmann W. , Haul R.
Published: March 2014

Die nicht‐stationäre Molekularströmung von Methan, Neopentan und n‐Pentan durch eine Pyrexglas‐Kapillare wurde mit einem Omegatron‐Massenspektrometer unter UHV‐Bedingungen gemessen. Aus den Strömungsversuchen wurden Adsorptions‐Isothermen auch bei niedrigen Bedeckungsgraden ermittelt, die durch eine Freundlich‐Gleichung dargestellt werden können. Aus der Temperaturabhängigkeit der differentiellen Verweilzeiten werden Aktivierungsenergien für die Desorption und zugehörige vorexponentielle Faktoren τ0 erhalten. Die auffallend große Variation der τ0‐Werte (10‐12 bis 10‐16 sec) kann durch statistisch‐mechanische Überlegungen unter Berücksichtigung der Oberflächen‐Heterogenität gedeutet werden.
Isotopieeffekt im zwischenmolekularen Potential von Methan
Authors: Gainar I. , Strein K. , Schramm B.
Published: March 2014

Der Temperaturverlauf der Differenz der zweiten Virialkoeffizienten von CH4 und CD4 wurde zwischen 200 und 510 K gemessen. Es wird gezeigt, daβ der Beitrag des Translationsquanteneffektes nur einen geringen, dem gemessenen Effekt entgegengesetzten, Einfluß auf den Unterschied im Virialkoeffizienten hat. Den Hauptanteil liefert der durch Substitution von Wasserstoff durch Deuterium auftretende Unterschied im zwischenmolekularen Potential. Die in dieser Arbeit gefundenen Änderungen der Potentialparameter werden mit denen aus anderen Meßgrößen und der Theorie [1 ‐7] verglichen. Eine eventuelle Anisotropie der zwischenmolekularen Kräfte des Methans scheint sich, im Gegensatz zu den Vermutungen in [8], nicht bemerkbar zu machen.
Investigations of the cis‐trans‐Isomerization of Benzylidene Aniline II. Kinetic Parameters of the cis‐trans‐Isomerization in Different Solvents [1]
Authors: Geibel K. , Staudinger B. , Grellmann K. H. , Wendt H.
Published: March 2014

The thermal cis‐trans‐isomerization of benzylidene aniline was investigated in the aprotic solvents cyclohexane (ϵ = 2), and acetonitrile (ϵ= 37) and the protic solvents ethanol (ϵ = 25) and methanol (ϵ= 36), and also in 98% H2SO4.

Whereas the isomerization in the organic solvents proceeds via an inversion mechanism this reaction is drastically hindered or even blocked in 98% H2SO4.

It is shown that the experimental activation energy for the cis‐trans‐inversion is composed of three parts: 1. rehybridization energy E*rehyb, 2. difference between the dipole field energies of the cis‐isomer and the kinetic transition state due to different dipole moments of these species and 3. difference in the hydrogen bond solvation energies of the cis isomer and the kinetic transition state. It can be shown that the second dielectric term vanishes in solvents with high dielectric constants. By comparison of the activation energies of the cis‐trans isomerization in cyclohexane and acetonitrile we obtain μsp < μcis. By comparison of the activation energies as measured in acetonitrile and methanol the hydrogen bond solvation energy of the cis‐isomer in methanol is estimated to be approximately ‐ 2 kcal/mol. Additionally the cis‐trans‐isomerization of 10 substituted benzylidene anilines was investigated in cyclohexane.

The frequency factors for the reaction rates of the substituted benzylidene anilines are all within the narrow range from 4 · 1012 to 4 · 1013 sec‐1, whereas the activation energies vary from 14.6 to 18.8 kcal. The kinetic results agree qualitatively with those, obtained by Wettermark in ethanol. The equilibrium constant K and reaction enthalpy δ H° for the reaction trans‐benzylidene aniline ⇌ cis‐benzylidene aniline is estimated for the solvent chlorobenzene by combining appropriate kinetic data:

magnified image.
Elektronenanregungsspektren und Lumineszenzverhalten der Diazaphenanthrene
Authors: Bluhm Th. , Perkampus H.‐H. , Knop J. V.
Published: March 2014

Die ππ*‐Elektronenübergänge (Lagen, Intensitäten und Polarisationen) der Diazaphenanthrene, die einen Diazinring enthalten, werden durch Modellrechnungen nach der SCF‐CI‐ und der CNDO‐CI‐Methode gleich gut wiedergegeben. Die nach der CNDO‐CI‐Methode berechneten Lagen der nπ*‐Elektronenübergänge korrelieren annähernd linear mit den experimentellen Werten. Unter den ππ*‐Banden verborgene nπ*‐Banden ließen sich zum Teil durch Polarisationsgradmessungen lokalisieren.

Das vom Stickstoffabstand abhängige unterschiedliche Lumineszenzverhalten der Diazaphenanthrene erklärt sich in bekannter Weise aus der relativen Lage der nπ*‐ und nπ*‐Zustände. Zur Interpretation der Phosphoreszenzspektren werden unterschiedliche Spin‐Bahn‐Kopplungsmechanismen diskutiert.
Kinetik der Lumineszenz‐Thermochromie und Zuordnung der Tieftemperaturemission von Pyridino‐Kupfer(I)‐jodid
Authors: Radjaipour M. , Oelkrug D.
Published: March 2014

Lumineszenz‐ und Lumineszenzanregungsspektren sowie Lumineszenzabklingzeiten von CuJ · Pyridin wurden zwischen 300 K und 15 K gemessen. Bei Anregung zwischen 26 000 und 29 000 cm−1 beginnt die gelbe Zimmertemperaturlumineszenz (ṽmax = 17 000 cm−1) unterhalb von 120 K zugunsten einer schwach strukturierten blauen Bande (ṽmax = 22900 cm−1) zu verschwinden. Die Umwandlung ist bei etwa 50 K abgeschlossen. Bei Anregung über 29 000 cm−1 bleibt die gelbe Bande neben der blauen auch noch bei 15 K erhalten. Die blaue Lumineszenz mit einer Abklingzeit von etwa 3 · 10−5 sec wird der π* → π‐Phosphoreszenz des komplex an Cu(I) gebundenen Pyridins zugeordnet. Es wird ein kinetisches Modell aufgestellt, das die Farbänderung der Lumineszenz auf eine Energieübertragung zwischen zwei Termsystemen in CuJ · Py zurückführt. Der Übertragungsprozeß benötigt eine Aktivierungsenergie von 9,9 kJ/mol.
Digital Simulation of a Rotating Disk Electrode with Optically Transparent Ring
Authors: Dörr R. , Grabner E. W.
Published: March 2014

The numerical method of digital simulation has been applied to the rotating disk electrode with optically transparent ring which represents a new electrochemical system, developed recently by Debrodt and Heusler in order to detect directly intermediates of electrochemical reactions. The extinction has been calculated as function of the geometric arrangement of the electrode system and of the rate constant of a first‐order follow‐up reaction. By comparison of calculated working curves with absorption measurements kinetic parameters can be determined.
Microstructure Changes in Thin Silver Films
Authors: Henning Dietmar , Weil Konrad G.
Published: March 2014

Thin silver films, evaporated onto freshly cleaved mica sheets show an excess free energy density. In contact with solutions containing silver ions, these films relax and the excess free energy density approaches zero within a few hours. – As it can be assumed, that this excess free energy is due to the microstructure of the film, we investigated this microstructure in dependence on the evaporation conditions by electron microscopy. The same methods were used to observe the microstructure of relaxed films. – From the experiments it can be concluded, that domain boundary etching is the dominating process during the aging of epitaxial films. In case of discontinuous, nonepitaxial films, Ostwald ripening occurs in favour of bigger and better oriented crystals.
The Role of Phase Boundaries in Heterogeneous Solid State Reactions (II). Thermodynamics of Compounds with Small Deviations from Stoichiometry in the Region of Transformation
Authors: Schmalzried H.
Published: March 2014

The phase field of so called stoichiometric binary compounds in a temperature vs. mole fraction representation is calculated in the temperature range of a phase transformation. The concept of point defect thermodynamics is applied. The results are used to predict the shape of the two phase field for α/β‐Ag2S in the temperature range 170–180°C. These data are important for the discussion of the kinetics of the phase transformation.
Grain Boundary Segregation of Sulfur, Nitrogen, and Carbon in α‐Iron
Authors: Tauber G. , Grabke H. J.
Published: March 2014

The segregation of sulfur, nitrogen, and carbon at surfaces and grain boundaries of α‐iron was studied by Auger Electron Spectroscopy (AES). Specimens of pure iron, doped with nitrogen or carbon by equilibria with gas mixtures were introduced into the UHV‐chamber and fractured by impact at about −130°C. Enrichment of nitrogen, carbon, or sulfur was observed on the intergranular fracture surfaces. Displacement equilibria exist between nitrogen or carbon and sulfur, which was present in the bulk material only as a trace impurity. The presence of sulfur decreases the cohesion of the grain boundaries, so that mainly intergranular fracture occurs. Obviously nitrogen or carbon reinforce the cohesion of grain boundaries, so that transgranular fracture prevails.
About SnF2 Stannous Fluoride V.: Conduction Characteristics
Authors: Ansel D. , Debuigne J. , Denes G. , Pannetier J. , Lucas J.
Published: March 2014

The electrical conductivity of the α and γ modifications of stannous fluoride SnF2 was studied by the complex admittance or impedance plot method on pellets. The activation energy is 0.52 eV for αSnF2 and 0.74 eV for γSnF2; the ionic conductivity rate is higher than 0.97. A study of the kinetics of the α r̊ γ phase transition is presented with a structural description of the three phases of SnF2.
Die Elektronenanregungsspektren der 1(Diazinyl)‐2‐(pyridyl)‐äthene — Triazastilbene —
Authors: Felbecker H. , Hollenberg D. , Schaaf R. , Bluhm Th. , Perkampus H.‐H.
Published: March 2014

Die Elektronenanregungsspektren der 18 isomeren Triazastilbene werden in Lösung bei Raumtemperatur und Tieftemperatur gemessen und im Zusammenhang mit CNDO/S‐Rechnungen interpretiert. Einige Gesetzmäßigkeiten bezüglich der Stellung der N‐Atome und der Aufspaltung der langwelligen Bande werden herausgestellt.
Polymer‐Film Covered Electrodes of Stable Electrochemical Performance
Authors: Doblhofer K. , Nölte D. , Ulstrup J.
Published: March 2014

The method of glow‐discharge polymerisation was applied to deposit highly cross‐linked polymer films of 100‐1000 Å thickness on steel, platinum, and glassy carbon electrodes. These films were characterized by electrical, electrochemical, and optical techniques and found to be stable during electrolysis in liquid solutions of both inert and redox electrolytes. Moreover, interesting correlations between the electrochemical properties of the film‐covered electrodes, studied by ac and dc techniques, and the conduction properties of metal‐film‐metal junctions using the same films, could be established. – Under suitable and well‐defined preparation conditions the films possess sufficiently high conductivity that their electrocatalytic properties can be exploited. Insertion of metal clusters or chelate polymers is likely to improve the electrocatalytic activity, and the film electrode systems are thus promising, e. g. in fuel cells and other practical applications.
Über approximative Chiralitätsfunktionen für den optischen Drehwinkel am Beispiel von [2.2]Metacyclophan‐Derivaten
Authors: Haase Dietrich
Published: March 2014

Unter Ausnutzung der algebraischen Theorie der Chiralitätsfunktionen nach Ruch und Schönhofer und einer quantenmechanischen Behandlung der optischen Aktivität wird die Gestalt approximativer Chiralitätsfunktionen für den optischen Drehwinkel diskutiert. Für eine Klasse von Molekülen mit C2h‐symmetrischem Gerüst werden geeignete Funktionen dieser Art angegeben. Die Systematik ihrer experimentellen Prüfung wird besprochen. Sie werden zur Beschreibung der molaren Drehwinkel von [2.2]Metacyclophan‐Derivaten verwendet.
Stoffbestand und Entwicklung des äußeren Erdkörpers
Authors: Wedepohl Karl Hans
Published: March 2014

The three major units of the earth are the core, the mantle and the crust. The material of the earth's mantle and core originated 4.6 billion years ago from condensation products of solar gases. The continental crust is on the average 40 km thick and varies in composition and age (≤ 3.8 · 109 years) while the present oceanic crust is about 7 km thick, composed mainly of basalt and less than 200 million years old. The renewal and the growth of the oceanic crust from partial melting of peridotites in the upper mantle is observable in the basaltic magmatism at mid‐ocean ridges and in the drift of the continents (˜ cm per year). The crustal growth is compensated by subduction of crustal plates into the mantle at some continental margins such as in the Circum‐Pacific. The oceanic basalts gain water through reactions with sea water and lose this during subduction (at about 900°C) to the overlying mantle materials (peridotites). Partial melting of mantle materials (and differentiation of primary melts) results in the formation of basaltic, andesitic or other magmas and contributes substantially to the growth of the continents. This direct or indirect origin of andesitic magmas from water containing peridotites is explained on the base of melting experiments and partition data of trace elements between melts and their potential source rocks. The majority of minerals in magmatic rocks are not stable under earth's surface conditions. They react with the degassing products of the earth's mantle (H2O, CO2, SO2, HCl) and with photochemically produced oxygen to form weathering and sedimentary minerals (OH containing silicates, CaCO3, CaSO4, NaCl etc.). Erosion, water transport and sedimentation control the material balance of elements near the earth's surface. The original sediments which contain water and other specific compounds are buried with time in deeper and warmer crustal levels. Their minerals reequilibrate at increasingly higher temperatures and pressures. Finally at 600–700°C, depending on the availability of water, they partially melt to form granitic magmas. The difference in density between the source rocks and the melts causes the uprise of granitic magmas. This process results in a chemical fractionation between the lower and the upper continental crust over long geologic time. – Summarizing the important observations of this report, water has controlled major processes in the outer shells of the earth.
Hydrothermal Solutions
Authors: Tödheide K.
Published: March 2014

A survey is given of recent results on the properties of pure water and binary and ternary mixtures at high temperatures and high pressures with emphasis on the geochemically important systems H2O‐CO2, H2O‐NaCl, and H2O‐CO2‐NaCl. Among the properties discussed are phase diagrams,PVTxdata, thermodynamic and transport properties, dielectric constant, electrical conductivity, and ionic equilibria. Concepts for predictive calculations of thermodynamic properties are briefly described.
Physical and Chemical Changes in Natural Fluids in Hydrothermal Processes and Mineral Deposition, Studied with Fluid Inclusions
Authors: Weisbrod Alain
Published: March 2014

The part played by the fluid phase(s) in most geological processes is of primary importance. These fluids have been often trapped in usually microscopic “fluid inclusions” which are considered as good samples of the natural solutions that once “wet” the rocks, with a few exceptions that can be easily detected. Once it has been trapped, the bulk composition and the bulk density of the inclusion fluid remain constant. – The major purpose of a fluid inclusion study is to determine the nature and the physical and chemical properties of the trapped fluids, and then to fit these properties with relevant geochemical processes. This is largely obtained by microthermometry, which consists in measuring the temperature of all the phase transitions observed in the inclusions when heated from −150°C to 700°C or more. Because fluid inclusions are assumed to be isochemical‐isochore univariant systems in the TPVX space, the microthermometry data can be interpreted in terms of chemical composition and molar volume. These data can be completed by other analytical techniques, such as bulk chemical analyses and Raman Microprobe analyses. – The first example presented in this paper deals with the postmagmatic hydrothermal alteration of a pegmatite. Because of the density‐composition constraints derived from fluid inclusions study, the TP cooling path of the fluid can be estimated with a fairly good accuracy between 500 and 200°C. Taking into account this result and the bulk chemical analyses (Cl, Na, K, Mg, Ca), it is possible to calculate the whole mass transfer and the water/rock ratio all over the evolution. – The second example, very briefly summarized, concerns fluid unmixing in porphyry copper type deposits. Such a process yields highly saline brines of moderate density and diluted vapour with low density. It is responsible of part of the mineral deposition, as a consequence of the supersaturation of the “boiling” liquid with respect to chalcopyrite. – The last example is related to the fluid evolution in a tin and tungsten deposit associated with a shallow granitic intrusion from Central Morocco. It is shown, mainly from fluid inclusion study, that the original fluid composition (70% water, 24% CO2, 5% N2, 1% CH4, traces of C2H6 and H2S) is changed by mixing with a slightly saline (5 wt% NaCl) aqueous solution. The composition of the volatile part (relative amounts of CO2, N2, CH4) has been analyzed by Raman spectroscopy. – Ore deposition occurred during this mixing process. Because of the lack of accurate experimental data on the system H2O – CO2 – N2 – (CH4) – NaCl, the TP conditions of the evolution cannot be accurately estimated, and using the system H2O – CO2 – NaCl as an approximation yields irrelevant results. This last example clearly shows why the availability of relevant experimental data on the C – O – H – N electrolytes systems is crucial for geochemists that deal with the fluid‐rocks interactions.
Raman Spectra of Hydrothermal Solutions of CO2 and KHCO3 at High Temperatures and Pressures
Authors: Kruse R. , Franck E. U.
Published: March 2014

Raman spectra of H2O – CO2 mixtures (3 mol‐% CO2) and of 2 molal aqueous KHCO3 solutions have been measured to 300°C and 2000 bar, thus covering a range of geochemical interest. A high temperature, high pressure, corrosion resistant Raman cell with sapphire windows and auxiliary equipment is described. The C – OH stretching vibration υ5(A′) at 1017 cm−1 is particularly characteristic of H2CO3 and HCO3− species. Its frequency and intensity decrease with temperature. H2O – CO2 mixtures at room temperature and about 1000 bar show a small but distinct band at 1017 cm−1 which is considered as indicating the formation of 2 to 3 percent of carbonic acid from the dissolved CO2. This is in qualitative agreement with a reaction volume of −12 cm3 mol−1 for the hydration process.
Preparation and Some Properties of a New Solid Sodium‐Ammonia Compound Na(NH3)3
Authors: Winter R. , Schindewolf U.
Published: March 2014

The preparation of solid Na(NH3)3 from sodium ammonia solutions is described. The very slow rate of formation (even in the presence of nuclei for crystallization) is attributed to a high energy and entropy of activation, other factors contributing to it. This new blue compound crystallizes in a primitive cubic structure with a lattice constant of 5.1 Å; it is probably isotype with AuCu3. Thermodynamic data indicate that its stability with respect to decay into metallic sodium and liquid ammonia (or a concentrated sodium ammonia solution) decreases with decreasing temperature (ΔH0 und ΔS0 of formation from sodium and liquid ammonia being positive); however by fast cooling in liquid nitrogen it can be stored as a metastable state. In this state the compound is diamagnetic (perhaps antiferromagnetic) and has the conduction behavior of a semiconductor.
NMR Study of Molecular Motion and Rotational Tunnelling in Co(NH3)6Cl3
Authors: Germer Hildegard , Müller‐Warmuth W.
Published: March 2014

Molecular motions in hexammine cobalt chloride have been studied over a wide range of temperatures using wide‐line and pulsed 1H NMR techniques. From five well‐defined plateaus in the temperature dependence of the second moment and from four relaxation peaks information about various rotational processes has been obtained on the basis of the known crystal structure. Assignment of the data has been made to the one‐dimensional rotation or tunnelling of NH3 groups (activation energies 5.6 and 11 kJ/mol), respectively) and to the three‐dimensional rotation of four nonequivalent Co(NH3)3+6 octahedra (activation energies 19, 34, 41, and 47 kJ/mol, respectively). Rotational tunnelling of NH3 groups is discussed in some detail.
Electrotransport in Molten Tl – Te Alloys
Authors: Nakamura Yoshio , Kitazawa Yukiharu , Shimoji Mitsuo
Published: March 2014

The electrotransport in molten Tl – Te alloys has been studied at 500°C. The effective charge, electric mobility and diffusion coefficient of Tl have been determined for compositions TlTe2, TlTe, and Tl2Te. Tl atoms migrate always to the cathode and the observed effective charge is the largest at the composition Tl2Te, in reasonable agreement with the electrical and thermodynamic properties of this system.
Aerosole
Authors: Wagner P. E.
Published: March 2014

The term aerosol designates a suspension of solid or liquid particles in a gas. The properties of aerosols have been investigated by many authors. The dynamics of aerosol particles is influenced by the interactions with the ambient gas, which are dependent on the Knudsennumber (mean free path of the gas molecules/particles radius). Presently many investigations are in progress dealing with diffusion and coagulation in ultrafine aerosols and the influence of electrical and van der Waals forces. For many applications the scattering of light by aerosol particles is important, which depends on the particle size parameter (particle circumference/light wavelength). Formation and evolution in time of aerosol particles are influenced by condensation processes. Particularly heterogeneous nucleation on ultrafine particles and homogeneous nucleation are presently investigated by many authors. Besides the investigations of the physico‐chemical properties of aerosols, a number of aerosol measuring techniques have been developed, which are of great practical importance particularly in view of the increasing problem of atmospheric air pollution.
Disperse Festkörper als Katalysatoren
Authors: Mroß W. D.
Published: March 2014

The activity of a catalyst increases as the degree of dispersion of the active component increases. In the case of supported catalysts it is possible to achieve dispersion right down to single active atoms. On the other hand, the smallest individual units of pure substances which can be obtained are generally 1 — 10 nm crystals. These finely dispersed systems can be stabilized by admixture with just small quantities of foreign substances. At temperatures above 600°C certain metal catalysts are capable of undergoing spontaneous dispersion under reaction conditions. — The degree of dispersion and the specificity of a catalyst are interrelated in a complex manner. Certain so‐called demanding reactions proceed most readily on finely dispersed systems (with low‐indexed crystallographic faces), others on coarsely dispersed active components (with predominantly highly‐indexed faces). — Although the selectivity of reactions taking place on model catalysts frequently correlates with the degree of dispersion, such a relationship has only seldom been observed in the case of technical catalysts.
Light Induced Viscosity Changes and Phase Transitions in Aqueous CTAB‐Solutions Containing Aromatic Molecules
Authors: Wolff Thomas , von Bünau Günther
Published: March 2014

Dynamic viscosities of aqueous solutions containing 0.25 M cetyltrimethylammonium bromide (CTAB) and small amounts of several aromatic compounds (anthracene, 9‐methylanthracene, 9,10‐dimethylanthracene, 9‐anthracene carboxylic acid, phenanthrene, 1‐methylphenanthrene, pyrene, fluorene, N‐methyldiphenylamine, naphthalene, 1‐methylnaphthalene, 2‐methylnaphthalene, acenaphthylene) were measured. Some compounds (9‐methylanthracene, 9‐anthracene carboxylic acid, phenanthrene, 1‐methylphenanthrene, pyrene, N‐methyldiphenylamine, naphthalene, 1‐methylnaphthalene, 2‐methylnaphthalene, acenaphthylene) enhance the viscosity of the CTAB‐solution while the others do not. A few of these Theologically effective substances (9‐methylanthracene, 9‐anthracene carboxylic acid, N‐methyldiphenylamine, acenaphthylene) can be converted photochemically to ineffective ones and vice versa. The influence of these substances on the position of the phase transition point isotropic solution/lyotropic liquid crystal was studied. Phase transition temperatures are altered upon addition of certain substances. Photochemical transformation of some additives may trigger the phase transition in both directions.
Fluorescent Dye in Soap Lamella as a Probe of the Electrical Potential
Authors: Fromherz Peter , Kotulla Reinhard
Published: March 2014

The electrical potential in a thin soap film stabilized by tetradecyltrimethylammoniumbromide is determined by a fluorescent dye. The fluorescence intensity exhibits a “beating” pattern as a function of the thickness of the lamella. This pattern is assigned to the interference of the exciting light and of the emitted light. The quantitative evaluation proves the localization of the dye in the surface layers of the lamella. The pH‐dependent fluorescence of the dye indicates a surface potential of 175 mV, corresponding to a dissociation degree of the ionic surfactant of 0.5. This potential is distinctly higher than the values determined on the basis of the DLVO‐theory.
Analysis of the Pathways for Cis ⇄ Trans Photoisomerization of 4‐Nitro‐,4,4′‐Dinitro‐, and 4‐Nitro‐4′‐methoxystilbene in Solution. XII1
Authors: Görner Helmut
Published: March 2014

Quantum yields for the direct trans → cis (Φl→c) and cis → trans (Φc→l,) photoisomerization of 4‐nitro‐,4,4′‐dinitro‐, and 4‐nitro‐4′‐methoxystilbene (NS, DNS, and NMS, respectively) were measured in solution at room temperature as a function of the concentration of quenchers (ferrocene, azulene, and oxygen). The results are in full agreement with a previously proposed reaction scheme for NMS, involving a triplet state as an intermediate in the trans → cis photoisomerization and both triplet and excited singlet states in the cis → trans photoisomerization. The branching ratios for decay of twisted configurations of the first excited singlet (1p*) and the lowest triplet (3p*) into the ground states and the yields for intersystem crossing from the first excited trans and cis singlet configurations to the lowest triplet state (Φlisc and Φcisc, respectively) were determined. Φlisc and Φcisc are large (0.45–0.86) for NS and DNS and significantly smaller for NMS in polar solvents. Since the trans triplet state (3t*) is in thermal equilibrium with 3p* it is this 3t* ⇄ 3p* equilibrium which is accessible for the influence of triplet quenchers and solvent properties in the cis ⇄ trans photoisomerization. At room temperature oxygen quenches mainly 3p* while at lower temperatures (between 0 and — 140°C) also3t* is quenched. The yields for the conversion 1t* → 1p* and for formation of 4a,4b‐dihydrophenanthrene (DHP) are small. From the kinetic analysis no indication was found for involvement of excited states of DHP in the cis → trans photoisomerization of 4‐nitrostilbenes.
Study of a Binary Critical Mixture of 2,6‐Dimethyl Pyridine/Water: Measurements of Static and Dynamic Light Scattering and Specific Heat Near the Lower Critical Point
Authors: Jungk M. , Belkoura L. , Woermann D. , Würz U.
Published: March 2014

Static and dynamic light scattering experiments are reported for the system 2,6‐dimethyl pyridine/water to determine the critical amplitude ζo of local concentration fluctuations and the critical amplitude Ωo of the characteristic frequency ΩD to scale ultrasound absorption data. It is found: ζo = (2.7 ± 0.2) · 10−8 cm and Ωo/π = 2.9 GHz. Measurements of the temperature dependence of specific heat capacity at constant pressure lead to a critical amplitude A = (0.183 ± 0.002) J g−1 K−1. The two scale factor universality is tested by combining the values of ζ0 and A as well as the values of ζ0 and τ*0 and B* (B*: critical amplitude of the coexistence curve, τ*0 critical amplitude of turbidity). The two ratios of the critical amplitudes calculated from the experimental data are higher by about 15% than the highest theoretical predicted value.
Ion‐Solvent Interactions in Water‐Acetamide Mixtures from Volume Data
Authors: Woldan Marian
Published: March 2014

Densities of solutions of NaCl, NaI, KCl, KBr and CsI in mixtures of water + acetamide have been measured at 348.15 K using the magnetic float densimeter. The apparent molal volumes of the electrolytes calculated from the experimental data were extrapolated to infinite dilution by means of the Masson equation. The ionic partial molal volumes of alkali‐metal and halide ions have been estimated. The partial molal volumes of transfer of ions from water to water‐acetamide mixtures were separated into the two components: V̄0elect(tr) and V̄0disord(tr). The effect of acetamide and temperature on V̄0elect(tr) and V̄0disord(tr) in the temperature range 298.15 — 348.15 K is discussed.
Thermodynamics of Non‐Isothermal Coadsorption Processes
Authors: Keller J. U.
Published: March 2014

Physical adsorption processes from a multi‐component fluid phase to the internal, inert surface of a single pellet of an adsorbens are considered. — Using the formalism of a generalized thermodynamics of irreversible processes, originally development by Meixner, a set of differential and algebraic equations is established from which the masses of the various components of the adsorbate and its temperature can be calculated. Numerical examples referring to adsorption/desorption processes of an ideal gas mixture of N2/CO2 on active coal “Aerosorb LR4” are given and discussed. It is demonstrated that considerable differences between a non‐isothermal coadsorption process and its isothermal approximation can occur. Finally, we consider a pressure‐swing adsorption‐desorption process for removing CO2 from a mixture of N2/CO2. Within an optimization procedure for the process it turns out that thermal effects can be essential if not decisive for the performance of the process.
Static Dielectric Constant and Density of Supercritical Methane‐Methanol‐Mixtures to 200 MPa
Authors: Diguet R. , Deul R. , Franck E. U.
Published: March 2014

The static dielectric constant (permittivity), ε, and the molar volume of supercritical, homogeneous mixtures of methane and methanol were measured at 323 K and 398 K from 50 to 200 MPa over the whole composition range between pure methane and pure methanol. Both quantities were determined simultaneously with the same samples in one autoclave which served as high pressure dilatometer and capacitor. At 398 K and 200 MPa ε increases from 1.53 (methane) to 23.2 (methanol). The measured mixture ε‐values are always below the linear interpolation line. Excess volumes of the mixtures are negative. At constant composition and temperature, ε always increases linearly with increasing density. With the Onsager‐Kirkwood‐Fröhlich relation, dielectric correlation factors, g, have been derived. At constant T and P the g‐values as function of composition give an s‐shaped curve from methane (g = 1) to methanol (g ≈ 2.6). This polar‐nonpolar supercritical combination is one of the very few systems for which the dielectric behaviour in dependence of temperature, total density and the complete concentration range could be studied.
Photochemistry of semiconductor colloids. 17. Strong luminescing CdS and CdS‐Ag2S particles
Authors: Spanhel L. , Weller H. , Fojtik A. , Henglein A.
Published: March 2014

The luminescence of colloidal CdS in solutions containing sodium polyphosphate as stabilizer is activated by the addition of either Ag(ClO4) or colloidal Ag2S. The degree of activation depends on how strongly the CdS and Ag2S particles are attached to each other, and this attachment is controlled by the concentration of polyphosphate and added divalent metal ions which bind to polyphosphate. The CdS fluorescence in these solutions can be excited by light of wavelengths longer than the wavelength of the absorption edge of CdS. The results are explained in terms of an interfacial region in which anion vacancies and incorporated silver centers, which deliver electrons into the conduction band of CdS upon illumination with photon energies less than the bandgap energy of CdS, are present. The preparation of Q‐CdS sols which fluoresce with quantum yields close to 100% is also described. Strong fluorescence occurs when defect sites, at which radiationless recombination takes place, are blocked.
The analysis of the small‐signal AC‐response of bovine enamel membranes
Authors: Scholberg H. P. F. , Borggreven J. M. P. M. , Driessens F. C. M. , Schoonman J.
Published: March 2014

The ion permeability of bovine enamel membranes can be estimated from impedance spectroscopy. In this study the 6‐parameter model, a previously proposed operational description of the frequency dependence of the impedance of an enamel membrane is compared with a model which uses a Constant‐Phase‐Angle (CPA) element, and which is proposed as an onset to a more mechanistic description of enamel impedance spectra The model using the CPA element is shown to be a valid description for the measured impedance data. The parameter values for R0 and ωmax (the angular measuring‐frequency where the imaginary part of the membrane‐impedance is maximal) obtained using this model, confirm that these parameters can be employed as predictors for bovine enamel permeability.