bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and Catalytic Aspects of Functional Micelles. Ester Hydrolysis by Hydroxamic Acids bound to Cationic Surfactants
Authors: Brown John M. , Lynn Jesse L.
Published: July 2012

Hydroxamic acids (1b) and (2b) are effective catalysts for the hydrolysis of p‐nitrophenyl hexanoate (3) in mixed micelles with cetyltrimethyl‐ammonium bromide. Both surfactants show complex buffer‐dependent ionisation behaviour but their catalytic reactivity is dependent only on the concentration of conjugate anion. The concentration‐dependence of catalytic ester hydrolysis by (1b) and (2b) in the absence of added surfactant is different, the former being much more effective in very dilute solution. Mixed micelles of (1b) and (2b) and the surfactant histidine (6) react with (3) or with phenylalanine esters (7) by separate, non‐cooperative mechanisms.
Solubility Behaviour of Defective Fluorapatite and Fluorhydroxyapatites
Authors: Verbeeck R. M. H. , Thun H. P. , Driessens F. C. M.
Published: July 2012

Fluorhydroxyapatites were synthesized by solid state reaction at 1000°C. They contain vacancies in the OH sublattice and are, in this respect, a good model for tooth enamel mineral. The presence of fluoride at the 0.1 to 1 ppm level reduced the solubility of these defective apatites with a factor 8 in the caries relevant range 4 < pH < 5. The simultaneous presence of Ca2+ ions, till a level similar to that in saliva, together with the F− ions in the physiological range 6.5 < pH < 7.5 suppressed the eventual decrease in solubility of these defective apatites caused by the presence of F− ions alone. Thus, the combined effect of Ca2+ and F− ions on the solubility behaviour of defective apatites is supposed to be relevant to the caries process and the caries reducing capacity of extra F− additions.
NMR Studies of the Reorientational Motion in Methanol and Methanol‐Water Mixtures
Authors: Versmold H.
Published: July 2012

Deuteron nuclear magnetic relaxation rates 1/T1have been measured as a function of temperature for the labelled methanols CH3ODand CD3OH in the neat liquids and in mixtures with H2O and D2O. It was possible to supercoole the mixtures to sufficiently low temperatures to observe relaxation rate maxima. The data are discussed in terms of a rotational diffusion model for the overall and the internal rotation. — A rather slow reorientation is performed by the hydroxyl group of methanol. This motion is strongly coupled to the fluidity of the liquids and is markedly slowed down (at constant temperature) with increasing water content. On the other hand, the methyl group performs a rather free rotation which is not influenced by the mixture composition. — A short discussion of the fast methyl rotation in terms of an “extended” internal diffusion model is given.
A Proton and Oxygen‐17 Nuclear Magnetic Resonance Study of the Aquo Beryllium(II) Nitrate System
Authors: Frahm J. , Füldner H.‐H.
Published: July 2012

Kinetic measurements of proton and oxygen exchange of the aquo beryllium(II) ion in concentrated solutions of beryllium(II) nitrate are reported. These measurements have been performed by means of 1H spin‐echo NMR and by 17O FT‐NMR using natural abundance 17G and europium(III) nitrate as a shift reagent for the 17O bulk water line. The combination of both methods allows one to separate the contributions from protolysis and water exchange. The data obtained for water exchange are k298ex = 1.8 · 103 sec−1 (rate constant for one water molecule), ΔH+ex = 41.5 kJ mol−1, and ΔS+ex = ‐44 JK−1 mol−1. Protolytic dissociation of the aquo beryllium(II) ion is found to be approximately one order of magnitude faster than water exchange: k298d = 8 · 104 sec−1 (rate constant for the tetra aquo beryllium(II) ion). ΔH+d = 31.2 kJ mol−1, and ΔS+d = −45 JK−1 mol−1 for beryllium concentrations up to 0.2 molal.
Die Reaktionen von Acetaldehyd, Ethanol und Essigsäure an einem Rhodium/Kieselsäure‐Katalysator
Authors: Bos U. , Herzog W. , Leupold E.‐I.
Published: July 2012

Durch Thermodesorption mit massenspektrometrischer Analyse werden die Reaktionen von CH3CHO, C2H5OH und CH3COOH an einem promotierten Rh/SiO2‐Katalysator untersucht, wobei die Auswertung der linienreichen Massenspektren durch eine Rechenanlage mit Hilfe eines hierfür erstellten Programms erfolgt. Der Katalysator erweist sich bei den Reaktionen des CH3CHO als bifunktionell, indem der Träger durch Aldolkondensation die Bildung von Crotonaldehyd, Hexadienal und Oktatrienal katalysiert, während das Edelmetall den Zerfall des CH3CHO in CO und CH4 sowie den des Crotonaldehyd in CO und C3H6 verursacht. Der Träger katalysiert auch die Cyclisierung des Hexadienal zu Benzol. Verglichen mit CH3CHO erweisen sich C2H5OH und CH3COOH als wesentlich stabiler. Bei C2H5OH geht eine Dehydrierung zu CH3CHO mit anschließendem Zerfall zu CH4 und CO vonstatten. CH3COOH spaltet CO ab, wobei sich CH3OH bildet, das zu CO und H2 zerfällt.
Calculation of a Binary Solidus from the Liquidus and Minimal Additional Thermodynamic Information
Authors: Pelton A. D.
Published: July 2012

In a binary system, if the liquidus has been measured, if the thermodynamic properties of the liquid phase are known, and if the entropy of the solid phase is known or may be assumed to be ideal, then an exact thermodynamic calculation of the solidus as well as of the enthalpy of the solid can be made. The equations are derived and sample calculations are made for several systems. General relationships between binary phase diagrams and the thermodynamic properties of the phases are then developed. It is shown that a knowledge of any four of the following six quantities is sufficient to permit the other two to be calculated exactly: the solidus, the liquidus, enthalpy of the liquid, entropy of the liquid, enthalpy of the solid, entropy of the solid.
Diffusion of Isotope Tracers in Binary Liquid Solutions
Authors: Hawlicka E. , Karolczak S. , Reimschüssel W.
Published: July 2012

The behaviour of isotope tracers in diffusion processes was investigated. In systems of organic binary solutions gradients of chemical concentration were present. Using the capillary method the tracer and the mutual diffusion coefficients were determined. It was found that the tracer diffusion coefficient is equal to the mutual one if the tracer moves in the same directions as the unlabelled part of component and the ratio of both parts of component is time independent. When both conditions are not justified the tracer diffusion is due to the simultaneously mutual and self‐diffusion processes.
Schwingungsspektren und Kraftkonstanten von teilweise und vollständig deuterierten Trimethylphosphitboranen (CH3O)3PBH3
Authors: Hassler K.
Published: July 2012

Die Infrarot‐ und Raman‐Spektren von (CH3O)3PBH3, (CH3O)3PBD3, (CD3O)3PBH3 und (CD3O)3PBD3 im flüssigen Zustand wurden aufgenommen und zugeordnet. Eine Normalkoordinatenanalyse unter Annahme von C3v‐Symmetrie erbringt für die Phosphor‐Bor‐Valenzkraftkonstante den Wert von 2,88 · 102 N/m. Die Aufspaltung einiger Grundschwingungen läßt auf die Anwesenheit mehrerer Rotamerer schließen.
Dissociative Electron Attachment to CCl4, CHCl3, CH2Cl2 and CH3Cl
Authors: Scheunemann H.‐U. , Illenberger E. , Baumgärtel H.
Published: July 2012

Resonance dissociative attachment of monoenergetic electrons in the energy range from 0.0 eV to 10 eV to CCl4, CHCl3, CH2Cl2 and CH3Cl has been studied using a trochoidal electron monochromator and a quadrupole mass filter. The following fragment negative ions as a function of electron impact energy could be observed: Cl−, Cl2−, CCl2− and CCl3− from CCl4; Cl−, HCl2 and CCl2− from CHCl3; Cl−, Cl2− and CCl2− from CH2Cl2 and Cl− and CH2Cl− from CH3Cl. — The attachment cross section decreases rapidly as H replaces Cl. Appearance potentials for the negative fragments and for CCl3 and CCl2 electron affinities in the limit of the excess energy are given.
A New Estimate of the H+ Ion Concentration in Pure Water. Part 1: A Critical Analysis of Current Treatments
Authors: Hertz H. G.
Published: July 2012

It is shown that attempts to determine the H+ concentration in pure water involve a search for a species which is not analytically well‐defined; thus appears the problem of what is the nature of the physical statements now available from pertinent measurements? Furthermore, it is demonstrated that both the conductance and the EMF determination of Kw erroneously involve an extrapolation from an aqueous solution to the pure solvent, water. Kw is not a strictly measurable quantity. Configurational definitions of the H+ and OH− ions are given which, using an intramolecular proton distribution function, essentially converts a statement concerning the distortion of a water molecule to species concentrations. The temperature dependence of the conventional Kw is also incorporated in the characterization of non‐analytical H+ and OH− ions.
Another New Estimate of the Hydrogen Ion Concentration in Pure Water (With Some Results for Methanol and Ethanol)
Authors: Hertz H. G.
Published: July 2012

From the study of nmr line shapes the mean life time of a water molecule with respect to proton exchange in pure H2O is known. The life time is connected with the mean flux of protons passing through the surface of the water molecule. The flux is the product of a velocity and a concentration. Estimates of the velocity yields the proton concentration. The numerical value of cH+ found in this way is fairly close to K1/2w. The same method is applied to water at 60 °C and to methanol and ethanol. There is fair agreement in all cases with K1/2s. The physical reason for the agreement is shown.
A Comparative Study of Photovoltaic Effects with Silver‐Silver Halide Electrodes
Authors: Clear J. M. , Corish J. , Feakins D. , Sidebottom H. W. , Waghorne W. E.
Published: July 2012

The photovoltaic effect produced by silver‐silver halide electrodes in a cell of the type Ag | AgX(dark) | Electrolytic solution | AgX(illuminated) | Ag has been investigated under well‐defined experimental conditions where X = Cl, Br, and I. The principal results concern the effect of varying the wavelength and intensity of the illumination; the thickness of the silver halide layer on the illuminated electrode and the pH and pAg values of the electrolytic medium. The time‐dependence of both the development and decay of these photoeffects and the influence of the adsorption of the dye Rhodamine 6G to the electrode surface have also been investigated. A mechanism is proposed for the photovoltaic effect on the basis of these observations. The photopotentials are considered to be developed through the movement of photo‐generated electrons and holes from their point of generation in the halide layer to the metallic silver of the electrode under the influence of an electrical field at the electrode‐solution interface.
Isotope Selective Photoaddition of Iodinechloride to Acetylene
Authors: Stuke M. , Marinero E. E.
Published: July 2012

The isotope selective photoaddition of ICl (A3 Π1) to acetylene giving highly chlorine‐enriched 1,2‐C2H2ICl, with enrichment factors of one hundred and purities better than 97% in a single step, was studied and its dependence on buffer gas, pressure and excitation wavelength determined. The relative amounts of the cis‐ and trans‐isomers are dependent on the excitation wavelength. Up to 70 mg of >91% chlorine‐labeled compounds were produced in a photochemical reactor.
Relation between Photochromism of Chromophores and Free Volume Theory in Bulk Polymers
Authors: Eisenbach Claus D.
Published: July 2012

The relation between the relaxation behaviour of photochromic aromatic azo benzenes and spiropyrans in a series of amorphous polymers and the polymer properties has been investigated. The distinctive differences of the rate of thermal isomerization found below and above Tg and also compared to solution can be explained by molecular properties of the polymer matrix, i. e., the overall chain segmental mobility, particular chain segmental motions and free volume effects. — The temperature dependency of the relaxation of the photochromes can be described by a WLF‐equation, log aT = ‐C1(T ‐ Tg)/(C2 + T ‐ Tg). The numerical values of the constants C1 and C2 differ from the „universal”︁ values, but for a given family of polymers a single set of parameters is sufficient for both types of photochromes. The deviations in the constants are ascribed to an unequal distribution of the free volume through the matrix caused by the photochromic foreign molecules. — The anomalies in the thermal cis‐trans relaxation of the aromatic azo chromophores in glassy matrices are correlated with restrictions in the fluctuation of the free volume. A temperature T0 is determined at which the contribution of translational motions to the fluctuations in the free volume is widely frozen in.
Excess Enthalpies of Liquid Alkane Mixtures at Pressures up to 500 bar I. Experimental Results
Authors: Heintz A. , Lichtenthaler R. N.
Published: July 2012

The composition dependence of the molar excess enthalpy HE of eight alkane mixtures is reported at 298.15 K and at various pressures up to 500 bar. The data have been obtained using a high‐pressure‐flow‐calorimeter. The directly measured dependence of HE on pressure is compared with the result determined indirectly from the temperature dependence of the molar excess volume and thermodynamical consistency was found.
A Proton NMR Study on the Kinetics of Protolysis and Water Exchange in Mixed Solvent Systems, Beryllium(II) Nitrate in Water‐Dimethyl Sulfoxide(d6) and Water‐Acetone(d6) Mixtures
Authors: Frahm Jens
Published: July 2012

1H spin‐echo NMR techniques were used to study the kinetics of proton exchange in the systems Be(NO3)2 in mixtures of water‐dimethyl sulfoxide(d6) and water‐acetone(d6) as a function of temperature, solvent composition and beryllium concentration. With increasing mole fraction of the organic component the total rate is reduced due to the decreasing contribution of protolysis of the hydrated beryllium(II) ion. Water exchange between coordinated sites at the beryllium(II) ion and the bulk solution dominates the proton exchange rate for DMSO mole fractions greater than 0.4 and for acetone mole fractions greater than 0.6, respectively. The calculated rates are almost independent of the solvent composition and beryllium concentration. Their values as well as the activation parameters are close to previous results on water exchange in the pure aqueous beryllium system using 17O NMR measurements [1]. For a 0.2 molal solution of beryllium(II) nitrate in water‐DMSO a temperature dependent water coordination number was found in the DMSO rich region which can be explained in terms of the extensive hydrogen bonded structure of the bulk solvent and of preferential solvation of beryllium(II) ions by water in these solutions.
Irradiation Energy Dissipation in Disordered Condensed Matter as Revealed by Quantum Statistics. I. A Generalized Approach in the Linear Response Theory
Authors: Chatzidimitriou‐Dreismann C. A. , Lippert E.
Published: July 2012

Within the framework of linear response theory, an exact expression for the energy dissipation of irradiation in disordered condensed matter is derived. There it is made use of Kubo's formalism for the treatment of a mechanical disturbance. This approach delivers a generalization of the known fluctuation‐dissipation theorem, a novel relationship between the time autocorrelation functions of the quantities M and dM/dt (M: dipole moment operator), and an explanation of the anomalous temperature dependence of the far infrared absorption band shape, e. g. of dilute solution of acetonitrile. Several limiting cases are discussed, e.g. vanishing density.
Neutron Scattering Study on a Benzene Layer on the Basal Planes of Graphite
Authors: Monkenbusch M. , Stockmeyer R.
Published: July 2012

The structure and dynamics of adsorbed layers of benzene on the basal planes of graphite (Grafoil, Carbopack B) in the monolayer regime has been investigated by thermal neutron scattering. The structure has been determined by diffraction from a C6D6 layer. A phase transition from a solid √7 × √7 registered phase with the benzene ring parallel to the surface at low temperatures to a compressible fluid phase above 150 K has been observed. — The dynamics has been studied mainly at 100 K and 200 K by inelastic incoherent scattering on a C6H6 layer. The phononlike scattering intensity of the low temperature phase has been compared to results, from a lattice dynamical model of a 2–D molecular crystal with external potential. The fluid phase shows quasielastic scattering similar to that of liquid benzene at 288 K, which can be accounted for by a model for a dense gas with a collision time in the order of 3 ps.
Proton Conductivity of Simple Ionic Hydroxides Part I: The Proton Conductivities of Al(OH)3, Ca(OH)2, and Mg(OH)2
Authors: Freund Friedemann , Wengeler Heinz
Published: July 2012

Proton conductivity is an outstanding feature of Al(OH)3, Mg(OH)2, and Ca(OH)2 powders between room temperature and their respective dehydration temperatures. It can be measured by using Pd‐black electrodes in H2 either by d.c. conductivity measurements, applying high injection voltages (> 104 V/cm), or by thermopotential measurements. Two conductivity mechanisms are observed which can be assigned to proton conductivity σ*H and defect proton conductivity σH'. The activation energies σ'H are 1.65, 2.0, and 2.2 eV for Al(OH)3, Mg(OH)2, and Ca(OH)2 respectively. The activation energies σH* are lower, ranging between 0.5–1.0 eV. σ'H occurs 20–60 K below the on‐set temperature of dehydration. It is enhanced by the adsorption of CH3COOH vapor and suppressed by NH3 vapor acting as proton donator and proton acceptor or traps respectively.
Kristalloptische Untersuchungen an Ga2S3 und ESR eingebauter Mn2+‐Ionen
Authors: Siebert D. , Westerkamp W.
Published: July 2012

Durch Untersuchungen mit dem Polarisationsmikroskop wurde die monokline Modification von Ga2S3 sichergestellt und durch kristalloptische Daten charakterisiert. Im Zusammenhang mit ESR‐Messungen konnte eine durch Stapelfehler bedingte typische Lagenfehlordnung festgestellt werden. — Die ESR ergab drei verschiedene Mn2+ ‐Zentren. Zwei davon wurden kristallographisch verschiedenen Kationenplätzen zugeordnet, das dritte Zentrum einem Mn2+‐Ion auf Kationenlücke.
Abnormal Influences of Temperature and Fluidity on Fluorescence Depolarization of Solute Molecular Rotors
Authors: Griebel R.
Published: July 2012

Starting from a theory by Chuang and Eisenthal [9], a qualitative discussion is given concerning the dependence of rotational depolarization of photostationary excited fluorescence of solute asymmetric rotors on temperature and viscosity of the solvent. — These qualitative expectations are verified by photostationary measurements on two rotors, p‐Terphenyl and 9,10‐Diphenyl‐Anthracene, which both are known to have S1‐lifetimes independent of temperature and fluidity of the solvent. — In turn, deviations from this „normal”︁ depolarization‐behaviour in the case of trans‐stilbene and some heteroanulated polymethines indicate the activity of T, η‐dependent relaxation‐modes influencing the S1‐lifetimes of these rotors. — However, T, η‐dependent lifetimes of exited rotors are not readily revealed by this method, if disturbances are introduced by hydrogen‐bridges between solvent and solute, dielectric friction and temperature‐induced shifts of bands with asymmetric polarization components. A trivial T, η‐dependence of lifetimes is caused by oxygen‐quenching. These influences are demonstrated by the abnormal depolarization of Rhodamine B, 6G, and 9,10‐Dibrom‐Anthracene.
Zur Diffusion der Kationen in den Kupfer(I)‐halogeniden. Ergebnisse von Kernresonanz‐ und Leitfähigkeitsmessungen im Vergleich
Authors: Hamann H. , Hoeppener U. , Richtering H. , Stratmann L.
Published: July 2012

By doping the copper(I)‐halides with foreign halogen‐ions it is achieved that the spin‐lattice relaxation of63Cu is almost exclusively determined by the quadrupole interactions originating from the diffusion of the Cu+‐ions. From the relaxation rates measured up to the transition temperatures from the γ‐ to the β‐phases mean jump frequencies of the Cu+‐ions are derived. On the basis of a vacancy or a non‐collinear interstitialcy mechanism specific conductivities are calculated from these jump frequencies. For CuCl and CuBr they are in good agreement with conductivities measured directly with the same substances. For CuI the same holds true with the conductivity data of Tubandt. A direct interstitial migration of the cations can be excluded.
Nitroxide radical as a probe for the study of collisional interactions
Authors: Kolodziejski Waclaw
Published: July 2012

The contact shifts of13C NMR signals in four aliphatic hydrocarbons in the presence of 2,2,6,6‐tetramethylpiperidine nitroxide radical were determined and explained by collisional interactions. Earlier results for ethers are compared and the origin of the contact shifts is proposed.
The rate of the reaction of NH2 with O3
Authors: Hack W. , Horie O. , Wagner H. Gg.
Published: July 2012

The rate of the gas‐phase reaction of NH2 radicals with O3 was studied in the temperature range 250–358 K, and over the pressure range 4–20 mbar.

The kinetics of the reaction was followed in a discharge‐flow reactor by measuring the decay of [NH2] by laser‐induced fluorescence. The rate coefficient can be expressed as:

No significant dependence of k1 on pressure was observed. A numerical analysis of the [NH2] profiles suggests that the metathesis reaction to form NH2O and O2 is a plausible initial step, and that the NH2O radical can react further with O3 to regenerate NH2 radicals.
Solidification behaviour of addition compounds and eutectics of pure components and addition compounds
Authors: Rastogi R. P. , Singh N. B. , Dwivedi K. D.
Published: July 2012

Solid‐liquid equilibrium data for (i) o‐phenylenediamine‐β‐naphthol, (ii) resorcinol‐o‐phenylenediamine, (iii) o‐phenylenediamine‐α‐naphthol, and (iv) picric acid‐catechol systems, showing congruent melting points, have been recorded. The 1:1 addition compounds formed in these systems form eutectics with either of the components. The linear velocity of crystallization and heat of fusion for the addition compounds and the eutectics have been measured. Microstructural studies indicate that the addition compounds have a structure similar to that of the pure components, whereas the eutectics have fibrous, feather‐like, spherulitic and lamellar structures. The effect of impurities on microstructures has also been discussed. Diffusion coefficient measurements in lamellar eutectics show that Jackson‐Hunt theory of eutectic growth, based on a diffusion model, is applicable. Excess thermodynamic functions, gE, hE, and SE have also been calculated for eutectics.
Thermodynamics of the formation of aromatic radical anions and thermodynamics of solvated electrons in liquid ammonia
Authors: Gross W. , Schindewolf U.
Published: July 2012

The thermodynamic data of formation of aromatic radical anions from nine different aromatic hydrocarbons and solvated electrons in ammonia are determined by potentiometric titration with a suitable electrochemical cell without diffusion potential. As expected a linear relationship is obtained between ΔHR0 and ΔGR0 of the electron attachment reaction and the energy parameter of the MO‐theory for the hydrocarbons — Via a Haber‐Born‐cycle the solvation enthalpy and solvation entropy of the electrons are obtained under the assumption that the solvation effects of the aromatic hydrocarbons and their radical anions can be estimated as the electrostatic effects of charging a spheric particle in the dielectricum ammonia. Due to the structure breaking action of the solvated electrons ΔH0 = −89 ± 9 kj/mol ΔS0 = 175 ± 25 J/mol · K are appreciable more positive than for normal univalent ions in ammonia.
The solvent dependent fluorescence quantum yield of acridine as a probe for water in micelles and for the preferred location of acridine in micellar solutions
Authors: Wolff Thomas
Published: July 2012

Relative quantum yields of the blue fluorescence of acridine were measured in protic and aprotic homogeneous solvents of different polarity and in alkaline aqueous solutions of anionic, cationic, and nonionic surfactants above the critical micelle concentrations as functions of tenside concentrations. Measurable quantum yields were detected only in protic homogeneous and in micellar solutions. For high concentrations of anionic and cationic micelles the relative quantum yields approached constant values between 3 and 30% (depending on tenside) of those obtained in surfactant free solutions. The effect is due to protection of acridine from the bulk water which was found to be more efficient for more voluminous micelles. The results permit conclusions on water penetration into micelles and on the solubilization of acridine molecules in micellar solutions.
A triplet mechanism for magnetic field modulation of photochemical quantum yields
Authors: Steiner Ulrich
Published: July 2012

A mechanism is described whereby the influence of an external magnetic field on the sublevels of a triplet exciplex, subject to heavy‐atom‐induced sublevel‐selective deactivation, modulates the radical dissociation yield of the exciplex. A sublevel selection rule for the heavy atom effect on T1 — S0 intersystem crossing in the triplex exciplex is derived. The magnetic field influence is treated on the basis of an approximate solution of a stochastic Liouville equation, leading to a simple analytic expression for the magnetic field effect on the radical yield. The result is applied to explain a previously observed magnetic field effect. The mechanism described may induce magnetic field effects on any triplet reaction competing with sublevel‐selective deactivation.
Determination of elasticity and viscosity coefficients in a ferroelectric smectic c liquid crystal
Authors: Kuczyński W.
Published: July 2012

Experimental methods of determination of the twist elasticity and rotational viscosity coefficient in ferroelectric smectics C are described. Temperature dependences of the coefficients obtained for a typical smectic C liquid crystal are presented.
Model potentials for protonic orbitals in molecules
Authors: Goodfriend P. L.
Published: July 2012

A new approach to the problem of a proton in a molecule is developed. Plausibility arguments are given for the form of model potentials for protons in molecules. Model potential results are evaluated and a simple approach to a hydrogen bond is presented.
1H NMR‐spectroscopic studies on the dynamic behaviour of Co(15‐crown‐5) (L1) (L2) complexes
Authors: Dickert F. L. , Hellmann S. W.
Published: July 2012

With 1H NMR‐spectroscopy the complex formation of Co(II)‐ions with the crown ether 15‐crown‐5 was studied in methanol, dimethylformamide, and mixtures thereof. — Evidence is presented for a fluctuating structure of coordinated crown ether which behaves in our case as a four dentate ligand. At 298 K the solvent exchange rates of the remnant solvate molecules are reduced by coordinated crown ether in comparison to the pure solvent complexes. The activation parameters present information about the solvent exchange mechanism.
A new method for measuring the kinetics of repassivation of titanium
Authors: Brauer E. , Schurich B.
Published: July 2012

An apparatus has been developed which allows electrochemical measurements at freshly generated active metal surfaces. The principle of the method is the laminar flow technique. — The test of the equipment with respect to several parameters has confirmed its function and quality. — Some results are given concerning measurements with titanium: the sequence of repassivation of titanium is prewetting, wetting, dissolution, adsorption and formation of a surface oxide layer. The adsorption is influenced by anions. The repassivation time was found to be t ‐ 10 ms.
Temperature Dependence of the Deactivation Behaviour of Substituted Acridizinium Derivatives in Dilute Solutions
Authors: Bendig J. , Wagner J. , Buchwitz W. , Kreysig D.
Published: July 2012

The energies of the excited states which are involved in the deactivation, the quantum yields of fluorescence and intersystem crossing, and the fluorescence decay times were determined for acridizinium and seven substituted acridizinium derivatives. Taking into account a contribution of temperature independent intersystem crossing the temperature dependence of the fluorescence quantum yield can be described by means of the Arrhenius equation. The thermally activated isc‐process in acridizinium (kisc± = 6 · 108 s−1) which determines the radiationless deactivation, is equivalent to the S1 (1B2u) → T3 (3B3u) transition observed in anthracene. The level inversion of the energetic sequence of S1 and T2 which is known from the exocyclic substitution of anthracene, takes place during the endocyclic azinium‐substitution, too. — Depending on their nature and position, additional exocyclic substituents will influence the activation energy, resulting in the case of heavy atoms in a drastic acceleration of kisc± or the rate constant for the temperature independent isc‐process (kisc0).
Comparative Study on the Reactivity of Polycrystalline and Single Crystal ZnO Surfaces: Catalytic Oxidation of CO
Authors: Esser P. , Feierabend R. , Göpel W.
Published: July 2012

The kinetics of the catalytic CO‐oxidation on both ZnO single crystal (1010) surfaces and ZnO polycrystalline samples were studied under ultra‐highvacuum conditions. — Single crystal results enable the first quantitative experimental verification of electronic charge transfer models to describe catalysis on semiconductor surfaces. — Results on polycrystalline samples are determined by contributions from nonpolar ZnO(1010) patches. Therefore, elementary steps of catalysis can be understood on the basis of single crystal studies if strong pore resistance is taken into account.
Old Tools Updated for New Problems: RAMAN Spectroscopic Studies on the Structure of Inorganic Compounds
Authors: Eysel Hans H.
Published: July 2012

The present paper gives a survey over applications of vibrational spectroscopy — especially RAMAN methods — in inorganic chemistry. The following topics are covered: analytical application for the characterisation of molecular compounds, their symmetry and structure, discussion of bond properties by means of Valence Force Field methods, effects of intermolecular interactions on the spectra of liquids and solids. The importance of intensity calculations for the check and improvement of force field calculations is briefly referred to. These different aspects of RAMAN spectroscopy are introduced using examples from recent literature and from the current work of the author.
Surface Enhanced Raman Scattering from Pyridine, Water, and Halide Ions on Au, Ag, and Cu Electrodes
Authors: Pettinger Bruno , Wetzel Herbert
Published: July 2012

The enhancement of Raman scattering for pyridine molecules on Au, Ag, and Cu and for water and halide ions on Ag and Cu electrodes has been investigated. — An enhancement has been found only in that spectral region where relative undamped surface plasmon polaritons (SPP) can be excited, showing a general increase for long wavelength excitation. — The electrochemical pretreatment of the metal surfaces. consisting in an oxidation/reduction cycle creates large scale roughness and adatom‐adsorbate complexes, both of which are necessary simultaneously in order to obtain intense SER scattering. — It is infered that the enhancement results from high density of SPP quanta created at rough or particularly shaped metal surfaces and the SPP scattering cross section being significant larger than that of photons.
Raman Spectra of Mercurimethanes CH4‐n (HgX)n at High Pressures
Authors: Kress Wolfram , Emmert Leonhard , Breitinger Dietrich K.
Published: July 2012

Raman spectra of the mercurimethanes C (HgX)4 (X = Cl, Br, and I), CH (HgCl)3, and CH2 (HgX)2 (X = Cl and Br) at high pressures up to about 6 GPa were studied. v (CH) and v (CHg) valence vibrations show strong and medium pressure dependences in the ranges (13.8 ± 2.7) and (7.6 ± 1.7) cm−1 · GPa−1, respectively. It is concluded that obviously anharmonic vibrations of light atoms with large vibrational amplitudes should exhibit high pressure sensitivities.
High‐Pressure Raman Studies of Scheelites and Related Solids
Authors: Breitinger Dietrich K. , Emmert Leonhard , Kress Wolfram
Published: July 2012

High‐pressure effects (up to 6.5 GPa) in Raman spectra of spinels Na2MO4 (M = Mo and W) and Ag2MoO4, of scheelites M″ MO4 (M″ = Ca, Sr, Ba, and Pb) and of scheelite‐type rhenates M'ReO4 (M' = Na, K, Rb, Ag, and NH4) were compared. For rhenates with high force constants f(ReO) the internal modes show small or medium pressure dependences, in contrast to the highly dependent lattice modes. The pressure dependences are correlated to vibrational amplitudes and anharmonicities.
Heterocyclic Ring Vibrations as Diagnostic Tools for the Differentiation of Metal Coordination Sites
Authors: Lippert B.
Published: July 2012

Ring stretching and ring breathing modes of (uracilato)ethylenediamineplatium (II) complexes have been examined by means of Raman spectroscopy at different pH values and compared with related complexes in order to establish typical Raman frequencies for the various binding modes possible.
Kinetic and Equilibrium Isotope Effects of Proton Exchange and Autoprotolysis of Pure Methanol Studied by Dynamic NMR Spectroscopy
Authors: Gerritzen Detlef , Limbach Hans Heinrich
Published: July 2012

The rate constants of the intermolecular proton exchange in pure methanol, i.e. the reciprocal proton lifetimes, τ0−1, have been determined as a function of the temperature by total lineshape analysis of the1H‐NMR spectra. Since CH3OH is an AB3spin system of high order the quantum mechanical density matrix formalism was employed for the simulation of the spectra. The neglect of high order effects as well as the presence of impurities had led to inconsistencies in previous studies. For the first time, the primary kinetic isotope effects were determined indirectly by simulation of the1H‐NMR spectra of CH3OD samples containing 1 vol‐% CH3OH. The results are given byfor CH3OH, andfor CH3OD, with a kinetic isotope effect of 3.2 ± 0.4 at 298 K. ‐ The data cannot be explained by a cyclic exchange mechanism. However, they can be quantitatively related to the autoprotolysis constant of methanol and to Grunwald's kinetic data on proton transfer in buffered methanol solutions. It is concluded that the proton lifetimes in pure methanol are determined by the natural amount of free solvated CH3OH2+and CH3O−ions generated by autoprotolysis. The observed energy of activation is then the sum of two terms, namely the energy of activation of the proton jumps between the ions and a methanol molecule, and half the enthalpy of methanol selfdissociation. In the presence of acid or basic impurities the second term becomes negligible. We propose a method for the quantitative determination of these impurities in the 10−9to 10−7mol 1−1range. From our results we derive an equilibrium isotrope effect of (KH/KD)298K = 6 ± 3 for the autoprotolysis of pure methanol, which has not been reported before. It is shown that the literature data on proton exchange in pure water and other protoc systems can be explained in a similar way. The mechanism of the neutralisation in water and methanol is discussed. For the neutralisation of solutions containing 1 mol of each ion it is found that the mean number of proton transfer steps necessary is 5.3 for water and 2.5 for methanol. These data correlate well with the molar solvent density.
Influence of Ion Pair Formation Kinetics in Diffusional Transport of Symmetrical Electrolytes
Authors: Turq Pierre , Orcil Louisiane , Chemla Marius , Barthel Josef
Published: July 2012

The diffusional properties of an associated electrolyte are calculated accounting for the kinetics of pair formation. Chemical rate constants as well as individual particle diffusion coefficients are the fundamental parameters introduced in the calculation. Comparison with other transport coefficients such as mutual diffusion coefficients shows the specificity of the fluctuating mode and the importance of the departures from local equilibrium condition.
Radiation Emitted by a Slightly Ionized Nonideal High‐Pressure Plasma
Authors: Uchtmann H. , Popielawski J. , Hensel F.
Published: July 2012

The paper presents first measurements of the optical emissivity of a slightly ionized mercury plasma at a temperature T of 1600 °C in the pressure range from p = 400 bar to p = 1925 bar corresponding to a density range from d = 0.45 g/cm3 to about d = 4.1 g/cm3. For densities smaller than about 3 g/cm3 where a broad featureless emission band is observed in the visible spectral range the results can be explained in terms of absorption by excitonic states of large randomly distributed Hg‐clusters. The experimental data above 3 g/cm3 show additional strongly density dependent emission tails in the infrared spectral range. A comparison of these results with a recent computer study leads to the conclusion that the infrared emissivity is due to electrons localized in clusters of high atomic densities.
High Temperature Ultraviolet Absorption Spectra of Polyatomic Molecules in Shock Waves
Authors: Astholz D. C. , Brouwer L. , Troe J.
Published: July 2012

The ultraviolet absorption spectra of substituted cycloheptatrienes, toluene, p‐xylene, and of benzyl and methyl‐benzyl radicals have been measured in shock waves at temperatures between 700 and 1650 K. The temperature dependence of the spectra is compared with an analysis based on the deltafunction method in various approximations. The measurements allow for the prediction of the shape of microcanonically hot spectra of laser excited molecules.
Activities in Solid and Liquid Fe  Ni and Fe  Co Alloys Determined by Knudsen Cell Mass Spectrometry
Authors: Rammensee W. , Fraser Donald G.
Published: July 2012

The thermodynamic activities and heats of mixing of liquid and solid solutions in the systems Fe‐Ni and Fe‐Co have been measured by Knudsen‐Cell mass spectrometry using a newly designed molecular beam apparatus. The data obtained for the system Fe‐Ni agree very closely with previous results and confirm negative deviations over the whole concentration range. Results for Fe ‐ Co indicate negative deviations from ideality for all composition between XCo = 0.05 – 1.00 and positive deviations below XCo = 0.05. This supports calorimetric measurements and is in conflict with a previous mass‐spectrometric investigation reporting positive deviations from ideality.
Theoretical Equation of State for n‐Paraffin Liquids
Authors: Jain R. K. , Simha R.
Published: July 2012

Previous theoretical analyses of several n‐paraffins are extended to recent PVT measurements for n = 11 and 12. The results are combined with the earlier ones to obtain interpolation equations for the characteristic scaling and other parameters of the theory as functions of chainlength. This makes it possible to predict the complete equation of state of a n‐paraffin fluid. Finally we discuss the extension of these considerations to mixtures.
PVT Data for Water in the Ranges 20 to 600°C and 100 to 4000 bar
Authors: Hilbert R. , Tödheide K. , Franck E. U.
Published: July 2012

PVT data for pure water have been measured between 20°C. and 600°C. for pressures between 100 and 4000 bar using an internally healed pressure vessel. The accuracy of the measured specific volumes is 0.2 percent or better. The volume isotherms were fitted by the Tait equation with an average absolute deviation of the experimental points from the smoothed curves of 0.02% below and of 0.05% above 200°C.
Role of Solvation and Desolvation in Polymer “Catalysis” III. The Influence of High Pressures on the Alkaline Fading Reactions of Triphenylmethane Dyes Catalyzed by Macroions
Authors: Maruno Tohru , Okubo Tsuneo , Ise Norio
Published: July 2012

Alkaline fading reactions of ethyl violet and crystal violet were studied in the presence of polyelectrolytes under high pressure, and the significant role of the hydrophobic hydration effect in polyelectrolyte “catalysis” was demonstrated in terms of the volume of activation (ΔV#). Polyelectrolytes used are poly‐4‐vinylpyridine quaternized with n‐cetylbromide (5 mol‐%) and benzylchloride (95 mol‐%) (C16BzPVP), 3‐6 ionen polymer (polybrene), sodium polyethylenesulfonate (NaPES), and sodium polystyrenesulfonate (NaPSS). These four samples, respectively, enhanced, slightly retarded, retarded and strongly impeded the reactions. The influence of a cationic surfactant, cetyltrimethylammonium bromide, on the rates and the activation parameters was similar to that of C16BzPVP. These experimental findings indicate that the hydrophobic macrocations such as C16BzPVP facilitated the formation of the “ice‐berg” structure of water around the activated complex so that the complex and the macrocations are incorporated in the ice‐berg structure causing decrease in ΔV≠. On the other hand, the hydrophobic macroanions (NaPSS, for example) enhanced the ice‐berg formation around the reactants with resulting increase in ΔV≠. Correspondingly, addition of C16BzPVP decreased the enthalpy and entropy of activation (ΔH≠ and ΔS≠) whereas NaPSS increased both ΔH≠ and ΔS≠. These results can be reasonably accepted if we assume that the contribution of the electrostatic hydration term is much less important than that from the hydrophobic hydration.
The Influence of Crystallographic Anisotropy on Photocurrents at GaSe‐Electrodes
Authors: Gerischer Heinz , Lübke Margot
Published: July 2012

Photocurrents have been measured at single crystalline p‐type GaSe electrodes under cathodic polarization where a Schottky barrier is formed at the contact to a suitable electrolyte. By using polarized light and varying the orientation between the c‐axis of the crystal and the light beam, the influence of the optical anisotropy and the anisotropic mobility of the electrons is exemplified by a varying quantum yield. The results can be explained by a theoretical model for the generation of the photocurrent at such a hetero‐junction, using two different values for the absorption coefficients and the diffusion lengths in the directions ∥c and ⟂c.
Entropieerzeugende Prozesse an Phasengrenzflächen
Authors: Hampe Manfred J.
Published: July 2012

A thermodynamic theory for the treatment of transport phenomena in multiphase and multicomponent systems is presented. Starting point is a field theoretical description of interfacial systems. The interface in its three dimensional structure is described by new thermodynamic variables, namely the structure vectors ak of the components k. This offers the possibility to analyse processes related with a change of the three dimensional structure by means of the methods of irreversible thermodynamics. Compared to the well known theory of irreversible processes in single phase and membrane systems there are differences regarding the balance equations for component masses and momentum; additionally a balance equation for the structure vector has to be introduced to treat changes of the interfacial structure. The linear constitutive equations obtained from the production term of the entropy balance equation describe transport processes at every point of a multiphase system.—It is shown that in the interfacial region of multiphase systems there are other processes producing entropy than in the bulk of a single phase system. E. g. in the region of an interface Fickian diffusion is not allowed to occur due to a stability criterion. Instead of this a tensorial transport phenomenon due to the structural change of the interface sets in which is possible only at interfaces. By means of a thermodynamic coupling of this tensorial process with the tensorial momentum transport a thermodynamic explanation and description of the Marangoni‐effect is obtained.—New expressions for entropy producing processes are also derived for generalized chemical reactions and transport of momentum. A discussion of potential interactions between fluxes shows that the same cross‐effects occurring in single phase systems cannot be supposed to occur in an interfacial region roo. This results in new aspects for the thermodynamic explanation of active transport.
Ellipsometrie—Eine Methode zur Charakterisierung dünner Filme
Authors: Haller W.
Published: July 2012

Ellipsometry is an optical non‐destructive method used to examine a surface or a thin film. The principle of measurement is a characteristic change in the state of polarization of elliptic polarized light reflected at a clean or a film‐covered surface. This surface may be on a solid or on a liquid. Normally the evaluation takes place with the aid of a computer. The results are the optical properties of the surface: refractive index and extinction coefficient, or thickness and refractive index of the film.
The Treatment of Ionic Solutions over the Entire Miscibility Range
Authors: Pitzer Kenneth S.
Published: July 2012

Conductance and thermodynamic properties are considered for several ionic systems continuously miscible from the fused salt to dilute solution in water or another polar solvent. Over most of the composition range, the activities of the respective components of the ionic systems show the same patterns of behavior and can be represented by the same equations that were developed for nonelectrolytes. Consideration is also given to ionic systems of large but finite solubility, including mixed electrolytes. The dominant factor in the behavior of these systems is the strength of ion solvation in competition with intermolecular forces in the solvent and direct interionic forces. Strong ion solvation yields negative deviations from ideal solution behavior and vice versa.
Mikrodynamische Vorgänge in Flüssigkeiten
Authors: Bertagnolli H. , Hertz H. G. , Posch H. A.
Published: July 2012

After a brief introduction with a discussion of the concept of the correlation function needed for the formulation of the problem, a progress report is given concerning our knowledge of microdynamic processes in liquids covering the fields of neutron scattering, IR‐absorption and light‐scattering, dielectric and nuclear magnetic relaxation as well as studies of diffusion and electric conductance.
Abweichungen im Konzentrationsverlauf scheinbarer Molvolumina und Viskositäten bei hochverdünnten Elektrolytlösungen
Authors: Härtling Christiane , Mecklenburg Thomas , Seidel Wolfhart
Published: July 2012

With the assumption of different subsystems in a liquid model can be shown that a perturbation of the molecular distribution in the liquid, caused by ions, may give rise to deviations in the concentration course of apparent molar volumes and of viscosities of very dilute solutions. Results of the qualitative model discussion are confirmed by some experiments.
Statistical Thermodynamics of Nonspherical Molecule Fluids
Authors: Boublik T.
Published: July 2012

Formalism to characterize the equilibrium behaviour of the convex molecule‐ and the ISM fluids is summarized and the unique description of both kinds of systems and the derivation of the equation of state of HCB and HD fluids is discussed.
The Blue‐Shift of the FIR‐Absorption Bands of Hydrogen Halides due to the Phase Transition Gas/Solution: A Quantum Statistical Interpretation
Authors: Chatzidimitriou‐Dreismann C. A. , Lippert E.
Published: July 2012

The physical principles concerning the far‐infrared absorption process in liquids are discussed. It is shown that the adiabatic approximation cannot be justified in this physical context. The basic ideas of the Kubo‐van Vliet linear response theory are discussed in connection with the FIR‐absorption process. As an application, the blue‐shift of FIR‐absorption bands of dipolar molecules due to the transition gas/solution is interpreted.