bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion of Isotope Tracers in Binary Liquid Solutions
Authors: Hawlicka E. , Karolczak S. , Reimschüssel W. 
Published: July 2012

AbstractThe 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

AbstractDie 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

AbstractResonance 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

AbstractIt 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

AbstractFrom 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

Abstract1H 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

AbstractWithin 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

AbstractThe 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

AbstractProton 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

AbstractDurch 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

AbstractStarting 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

AbstractBy 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

AbstractThe 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

AbstractThe 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

AbstractSolid‐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

AbstractThe 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

AbstractRelative 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

AbstractA 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.
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

AbstractWith 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

AbstractAn 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

AbstractThe 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

AbstractThe 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.