bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Analysis of the Amplitudes in the Relaxation Processes in Micellar Solutions
Authors: Teubner M. , Diekmann S. , Kahlweit M. 
Published: September 2012

AbstractIf the relaxation processes in aqueous solutions of Na‐Decylsulfate and Na‐Dodecylsulfate are investigated by means of a pressure‐jump apparatus and followed by conductivity measurements, the amplitude of the slow relaxation process, if plotted versus the surfactant concentration, intersects twice with the abscissa, being negative in between. – Ananalysis of this result permits a decision between two alternative approximations used in the theory of micellation in favour of that made by Aniansson and Wall, at least for these systems. – The first zero is caused by the fact, that although the slow relaxation process takes place, its amplitude becomes indetectable because the changes of the contributions to the conductivity by monomers and micelles, respectively, compensate each other at this particular concentration. At the second zero the slow process itself vanishes, as there the change of the total number of micelles during the relaxation process changes its sign. Thus, at this particular concentration only the fast process takes place. – The results permit an independent determination of the width of the size distribution and the reaction volumes.
Solubility of Hydrogen in CuTi, CuTi2, PdTi2, and Cu0.5Pd0.5Ti2. Reactions of Titanium Alloys with Gaseous Hydrogen)
Authors: Kadel Rainer , Weiss Alarich 
Published: September 2012

AbstractCuTi2, PdTi2, and Cu0.5Pd0.5Ti2are isotypic (MoSi2‐structure type). The solubility of hydrogen in these alloys and in CuTi was measured by means of a volumetric method in the range 0.01 bar ≤ PH2≤ bar and 250°C ≤T≤ 850°C. The thermodynamic data were derived from the absorption isotherms found. The relative partial molar enthalpies of solution at infinite dilution ΔHH0increase in the following order: α‐Ti (‐45.5kJ/mol H); Cu0.5Pd0.5Ti2(‐40.5kJ/mol H); CuTi (‐37.5kJ/mol H); PdTi2(‐37kJ/mol H and ‐33.5 kJ/mol H at 600850°C and 400700°C respectively); CuTi2(‐33kJ/mol H). ‐ From the excess entropies and enthalpies it is concluded that the number of available interstitial sites for the H‐atoms is reduced in the alloys compared with α‐Ti, thus indicating a preferred occupation of interstices which are tetrahedrally surrounded by Ti‐atoms only. ‐ CuTi, CuTi2and Cu0.5Pd0.5Ti2show decomposition reactions by which titanium hydrides and other intermetallic compounds are formed. For the systems CuTi‐H and CuTi2‐H the decomposition steps could be analysed thermodynamically and roentgenographically up to the end products (copper and γ‐titanium hydride). ‐ The experimentally determined enthalpies of formation of CuTi and CuTi2, are compared with calculated ones. ‐ PdTi2dissolves hydrogen gas up to the composition PdTi2H2which can be explained by a complete occupation of the interstices formed by Ti‐tetrahedrons.
Temperature Dependence of the Intrinsic Pitch in Induced Cholesteric Systems
Authors: Finkelmann H. , Stegemeyer H. 
Published: September 2012

AbstractBased on the molecular‐statistical theory of Goossens a model has been developed to explain the temperature dependence of the intrinsic pitch in cholesteric systems induced in nematic host phases by chiral guest molecules. In the case of a rotational symmetric distribution function around the long axis of the chiral molecule the helix inducing dipole‐quadrupole interaction forces level out. Consequently, only a hindered long‐axis rotation causes the helical structure whose pitch increases with increasing temperature. The theoretically predicted value of the relative temperature gradient of reciprocal pitch 1/p−1(dp−1/dT) are in good agreement with the presented experimental data. The influence of structure of the chiral guest molecules on the helical twisting power as well as that of the nematic host phases also can be understood in terms of the proposed model.
Optical Properties of the Isotropic Mesophase Formed by Cholesteryl Esters
Authors: Bergmann K. , Stegemeyer H. 
Published: September 2012

AbstractOptical rotatory dispersion (ORD) and selective reflection spectra (SR) of the isotropic so‐called “blue‐phase” (BP) of cholesteryl myristate and nonanoate have been studied. The anomalous ORD effect as well as the SR band is sharply separated from the corresponding effect of the cholesteric phase and positioned at longer wavelength. The sign of the ORD curve and the reflection of left circularly polarized light indicate any left‐handed helical arrangement in the BP. The refractive index of the isotropicBPis found to be related to that of the birefringent cholesteric phase by the Vuks formula. Requirements of structural models for theBPare discussed in terms of the experimental results.
ESR and PMR Studies of Alcohols Hydrogen Bonded with Nitroxide Radical
Authors: Kolodziejski Waclaw , Kecki Zbigniew 
Published: September 2012

AbstractThe ESR and PMR spectra of the solutions of 2,2,6,6‐tetramethylpiperidine nitroxide radical in the series of alcohols from methanol through ethanol, normal and branched propanols, butanols to pentanols were used to determine the 14N and the OH proton hyperfine coupling constants and to discuss trends of their changes. The dependence of the OH coupling constant on temperature was determined for four alcohols and explained in terms of oscillator anharmonicity of the radical‐alcohol hydrogen bond.
The Oxidative Dehydrogenation of 1‐Butene over Unsupported Vanadium Pentoxide Catalyst
Authors: Hauffe K. , Abd El‐Salaam K. M. 
Published: September 2012

AbstractThe gas phase oxidation of 1‐butene over unsupported V2O5 catalyst has been investigated with reference to the consumption of oxygen from the catalyst surface causing a deviation from the stoichiometry. Therefore, measurements of the weight change by an electromicrobalance in a flow system have been carried out. Simultaneously, electrical conductivity, the infrared absorption and catalytic oxidation in a microflow reactor in the range of 200500 °C were studied. In the overall reaction both the chemical reaction at the surface and the diffusion of oxygen through the lattice of the solid play a role in the rate of reaction. A kinetic model comprising these two steps is applied. The steady‐state composition of the catalyst at 350 °C which has the highest selectivity is V2O4.8. It is proposed that 1‐butene chemisorbed interacts with oxygen ions by donation of electrons to the catalyst surface as detected by the increase of the conductivity and the deviation from stoichiometry.
Reactivity of Silver Atoms in Aqueous Solution II. A Pulse Radiolysis Study
Authors: Tausch‐Treml R. , Henglein A. , Lilie J. 
Published: September 2012

AbstractFree silver atoms were produced by reducing Ag+ with hydrated electrons or hydrogen atoms. AgH+ with a lifetime shorter than 10−8 s is postulated as an intermediate of the H atom reaction. Organic free radicals cannot reduce Ag+ in a single electron transfer process. CO2− reduces Ag+ in a complex manner. The rate constants of reactions of both Ag0 and Ag2+ with a number of inorganic and organic compounds were measured. Both particles were found to be electron donating agents with approximate standard redox potentials of ‐1.8 V (Ag0) and ‐1.2 V (Ag2+). Ag2+ reacts faster in the presence than absence of ammonia.  Ag2+ radical cations react with 2k = 3.0 ·108 M−1 s−1 (or 5.0 · 109 M−1 s−1 in the presence of ammonia) to form dimeric silver. Ag2+ whose standard reduction potential is approximately −0.5 V is reduced by 1‐hydroxyalkyl radicals; the reaction with CH2OH proceeds through the complex Ag2CH2OH+ (life time: 3.3 · 10−4s). 2‐hydroxyalkyl radicals oxidise Ag2+ ‐ Dimeric silver whose standard redox potential for two‐electron transfer is about − 0.9 V is strongly complexed by Ag+ ions to yield Ag42+. Ag0, Ag2+, and Ag42+ absorb in the near UV, the maximum of the band shifting towards shorter wavelengths in this order. Ag42+ disappears by reaction with another Ag42+ (2k = 1.1 · 107 M−1 s−1 or reaction with colloidal silver particles (produced by preirradiation). In the presence of small sulfate concentrations, the reaction between two Ag42+ particles is accelerated. Sulfate also catalyses subsequent agglomeration processes. Colloidal particles with an agglomeration number of about 200 are present after a few milliseconds. They strongly absorb at 390 nm. Larger particles which still absorb close to 390 nm but cause much stronger scattering of red light are present after a few seconds. Free radical reactions can be influenced by the presence of colloidal silver particles; several examples are discussed. – The hydrogen yield from γ‐irradiated silver solutions (25 to 130°C) is equal to the yield of 0.6 molecules/100 eV known as direct molecular yield. It is concluded that the smaller silver aggregates formed in the reduction of Ag+ do not react with water in spite of their negative redox potentials.
Translational Energies of CH3+, CHO+, CH2OH+, and CH3CO+ Ions from Oxygen‐Containing Molecules
Authors: Kumakura Minoru , Sugiura Toshio 
Published: September 2012

AbstractThe translational energies of CH3+, CHO+, CH2OH+, and CH3CO+ ions from oxygen‐containing molecules have been measured by a new method in a time‐of‐flight mass spectrometer. The method is developed by which the energy can be readily determined from the analysis of the decay curve of ion. A relation between the translational energy of ions and the structure of source molecules was discussed.
Viscosity of Aluminium Chloride and Acidic Sodium Chloroaluminate Melts
Authors: Brockner W. , Tørklep K. , Øye H. A. 
Published: September 2012

AbstractThe viscosity of NaCl‐AlCl3 melt mixtures has been determined in the range 0.50 ≤ X ≤ 0.80, 160°C to 300°C. The viscosity of pure AlCl3 was measured over the temperature span 196°C to 286°C. A recently designed oscillating vessel viscometer was used. The method, which utilizes closed cylindrical cups subjected to vapour pressures exceeding 11 atm, is absolute and requires no calibration against reference liquids. Results are corrected for surface effects and for evaporation within the crucible. Applying Arrhenius temperature dependencies and the Arrhenius mixing rule, the viscosity is expressed as a function of temperature and composition with an overall standard deviation of 0.4% when the presence of AlCl−4, Al2Cl−7, Al3Cl−10, and Al2Cl6 is assumed.
The Viscosity of CaCl2 Solutions in the Range 20–50°C
Authors: Gonçalves F. A. , Kestin J. 
Published: September 2012

AbstractAs a continuation of an earlier paper concerned with the viscosity of aqueous solutions of NaCl and KCl, the present paper communicates the results of precise, relative measurements of the viscosity of aqueous solutions of CaCl2. The measurements covered the entire range of composition up to saturation, all at atmospheric pressure and at 20.00, 25.00, 30.00, 40.00, and 50.00°C ± 0.01°C. The reproducibility was of the order of several parts per ten thousand, and the accuracy is estimated to be one of 0.3% at worst. ‐ As a byproduct, we obtained an accurate correlation between molality, c, and density, p, for these solutions measuring at 20.00 and 25.00°C (± 0.01°C).
The Radial Pair‐Distribution Function of Liquid CHCl3
Authors: Hoheisel Claus , Zeidler M. D. 
Published: September 2012

AbstractThe spherically symmetric part of the static pair‐distribution function of liquid CHCl3 determined by neutron and x‐ray scattering experiments is compared with results of molecular dynamics calculations based on an (18‐6) Lennard Jones type potential. The agreement is sufficient with respect to the simplicity of the model involved.
Anomalie im Diffusionsverhalten von n‐Alkanen in NaMgA‐Zeolithen bei höheren Temperaturen
Authors: Roethe Klaus‐Peter , Roethe Annemarie , Fiedler Klaus , Gelbin David 
Published: September 2012

AbstractBei Diffusionsmessungen mit n‐Alkanen in NaMgA‐Zeolithen wurde zwischen 523 und 750 K ein Übergang von einem Niedertemperaturzu einem Hochtemperaturzustand beobachtet. Wir deuten diesen Vorgang als eine Änderung der Kationenkonfiguration im Hohlraum unter Beteiligung des Adsorptivmoleküls. In einem thermischen Gleichgewichtsprozeß sollten derartige Kationenpositionswechsel zur Blockierung der Eingänge zum großen Hohlraum und dadurch zur Änderung des Sorptionscharakters von 5 A‐ zu 4A‐ähnlich führen. Auffallende Abweichungen vom Arrheniusgesetz und der Abfall der Mikroporen‐Diffusionskoeffizienten Dz bie hohen Mg‐Gehalten und 673 K sind durch die Zustandsänderung erklärbar. Der schwankende Verlauf der Dz mit der C‐Zahl der n‐Alkane bei 673 K läßt sich mit unseren Modellgleichungen nachrechnen.
Vibronic Coupling via the Non‐Totally Symmetric C‐H Bending Mode in Pyrazine
Authors: Brickmann Jürgen 
Published: September 2012

AbstractThe absorption and emission data for the forbidden S0 → S1 transition of pyrazine in the vapor phase and in a benzene host are analyzed with the aid of an intensity‐borrowing mechanism which involves vibronic coupling of the 1B3u(n, π) and 1B2u(π, π) states via the non‐totally symmetric 10a mode. The vibronic coupling is discussed in terms of a non‐adiabatic model (NA) which takes static and dynamic interactions into account, as well as in terms of static Herzberg‐Teller coupling (HT). By variation of different model parameters all observed quantities can be reproduced within experimental error with the NA model, while this is not generally possible with the HT scheme. It is observed that the adiabatic frequency of the 10a mode in the S1 state is much lower than the ground state frequency; the NA model predicts that the frequency of this mode in the S2 state is approximately equal to the ground state value.
On the Coupling of Vibronic States in NO2
Authors: Gerloff M. , Russegger P. , Brickmann J. 
Published: September 2012

AbstractA model of indirect near resonance coupling of two vibronic states belonging to different excited Born‐Oppenheimer electronic states of a molecular system is presented. In the absence of direct coupling terms the two states can interfer via a third “messenger” state or via a manifold of such states. If the coupling is not too strong the messenger states act only in a seeming catalytic capacity, i. e. the two originally not coupled vibronic states seem to be coupled directly. The 5935Å laser‐excited fluorescence of NO2 is interpreted in terms of indirectly coupled 2B1‐ and 2B2‐vibronic states via highly excited 2A1 vibrational states. The Franck‐Condon factors are calculated within the rigid bender model of Hougen, Bunker, Johns, and Stone. Best agreement with experiment is obtained if one assumes that the fluorescent state is a linear combination of 2B1 (ν = 4) and 2B2 (ν = 7) vibronic states. The spectra calculated with a pure 2B1 or 2B2 initial vibronic state disagree with experimental material.
Vibrational Relaxation in Liquids. I: 1D‐Molecular‐Dynamics Studies of Mixtures of Bromine and Argon
Authors: Nehrkorn Christoph , Brickmann Jürgen 
Published: September 2012

AbstractVibrational energy relaxation in liquids is investigated using the molecular‐dynamics method. A one‐dimensional ensemble of liquid bromine and of mixtures of bromine and argon is simulated with different compositions and temperatures. The vibrational motion of the bromine molecules is described by a harmonic oscillator, and the intermolecular interactions are given by Lennard‐Jones (12, 6) potentials with the parameters being derived from different experiments. The observed energy relaxation times of initially excited bromine molecules decrease at higher temperature, and are longer in mixtures of bromine and argon than in the pure liquid. The effective collision strength is also calculated, the results disagree with the strong collision assumption used in reaction rate theories. It is demonstrated that the main aspects of vibrational energy relaxation in liquids can be adequately studied with the aid of one‐dimensional models.
The Shape of the Absorption Edge in Compressed Fluid Mercury Vapour
Authors: Popielawski J. , Uchtmann H. , Hensel F. 
Published: September 2012

AbstractNew optical absorption measurements near the absorption edge of dense supercritical mercury vapour are presented. An attempt is made to explain the shape of the edge on the basis of the model of the band‐state densities in disordered semiconductors suggested by Mott and others. It is shown that the shape of the edge can be explained with the assumption that it arises from electronic transitions between localized states in the band edge tails, the density of which is assumed to be a Gaussian function of the energy.
Zum Mechanismus der elektrokatalytischen Sauerstoffreduktion an Metallchelaten II. Metall‐Tetraphenylporphyrine
Authors: Behret H. , Clauberg W. , Sandstede G. 
Published: September 2012

AbstractDie kathodische Sauerstoffreduktion wurde an den Tetraphenylporphyrinen mit verschiedenen Zentralatomen auf glatten Metall‐ und Kohlenstoffelektroden sowie zum Vergleich auch an den unbedeckten Elektroden untersucht. Dabei wurde die Methode der rotierenden Scheibe‐Ring‐Elektrode verwendet, um das bei der Reduktion entstehende Wasserstoffperoxid quantitativ zu bestimmen. Nach Auswertung der Stromspannungskurven lassen sich die Parallel‐ und Konsekutivreaktionen des Umsatzes von Sauerstoff zu Wasser und/oder Wasserstoffperoxid (und evtl, weiter zu Wasser) durch Berechnung der Geschwindigkeitskonstanten bestimmen. ‐ Im Anschluß an die Ergebnisse mit Metall‐Dibenzotetraazaannulenen wurden die Messungen auf die Metalltetraphenylporphyrine ausgedehnt. Frühere Ergebnisse bezüglich der Abhängigkeit der Aktivität von den Zentralatomen der Porphyrine konnten bestätigt und erweitert werden. Sowohl in sauren als auch in alkalischen Elektrolyten entsteht Wasserstoffperoxid, das in sauren Elektrolyten am Eisen‐Tetraphenylporphyrin bei niedrigen Potentialen weiter reduziert wird. Das Hauptprodukt ist aber im Gegensatz zu den Tetraazaannulenen Wasser, das in direkter Reaktion entsteht. Lediglich an Kobalt‐Tetraphenylporphyrin entsteht mehr Wasserstoffperoxid als Wasser. An reinem Gold und reinem Pyrographit bildet sich in der Hauptsache Wasserstoffperoxid, an reinem Platin im mittleren Spannungsbereich ausschließlich Wasser.
Exzeßvolumina von Alkanmischungen aus Dichtepräzisionsmessungen. Vergleich mit flüssigkeitstheoretischen Berechnungen einer erweiterten Flory‐Theorie
Authors: Heintz A. 
Published: September 2012

AbstractEs wird über Meßergebnisse der Exzeßvolumina von Cyclohexan (c‐C6) mit einer Auswahl von n‐Alkanen (n‐C6 bis n‐C16) und verzweigter Isomere bei 298,15 K und 313,15 K berichtet. Die Messungen wurden mit einer Präzisionsdichtemeßzelle durchgeführt. die nach der Methode des schwingenden U‐Rohres arbeitet. Die Ergebnisse wurden zusammen mit weiteren Daten für Exzeßvolumina aus der Literatur mit den Voraussagen der Flory‐Theorie verglichen. Dabei auftretende Diskrepanzen bei Mischungen, die verzweigte Alkane enthalten, lassen sich durch Einführung eines verallgemeinerten van der Waals‐Modells im Rahmen der Flory‐Theorie teilweise beheben.
Gas Phase α,α Elimination of Hydrogen Halides from Halomenthanes. I. Thermal Decomposition of Chlorodifluoromethane, Trifluoromethane, and Trichloromethane Behind Shock Waves
Authors: Schug K. P. , Wagner H. Gg. , Zabel F. 
Published: September 2012

AbstractThe thermal decomposition of CHClF2, CHF3, and CHCl3 has been studied behind incident and reflected shock waves. The unimolecular decomposition was observed to proceed via the α,α elimination reactionsmagnified imagemagnified imagemagnified imagein agreement with previous work. The progress of reaction was monitored via time resolved absorption spectrometry of CF2 at 253 nm (for (1) and (2)) and of the secondary reaction product C2Cl4 at 230 nm (for (3)). The pressure dependence of k1, k2, and k3 was investigated over a pressure range of a factor of ∼ 100. From the experiments in the fall off region, low and high pressure limiting rate constants (k0 and k∞) were obtained by application of a modified Kassel theory. For k∞, the Arrhenius expressionsmagnified imagewere deduced. Excellent agreement with previous work is achieved for k1∞ and k2∞, provided that fall off is properly taken into account.
Effects of Pressure and Temperature on the Fluorescence of 9‐Methylanthracene and 9,10‐Dibromoanthracene in Solution
Authors: Hammerich B. , Schmidt R. , Brauer H.‐D. 
Published: September 2012

AbstractThe pressure and temperature dependencies of the fluorescence quantum yield of 9‐methylanthracene (MA) and 9,10‐dibromoanthracene (DBA) were investigated in heptane and toluene, respectively. The data were interpreted in terms of the Eyring transition state theory. ‐In the case of MA it was found that the activation enthalpy ΔH* of S1 → T2 intersystem crossing increases with increasing pressure, while for DBA no pressure dependence of ΔH* was observed. An increase in the fluorescence quantum yield at higher pressures was found for both compounds and was attributed to a positive activation volume S1 → T2, which inhibits S1 → T2 intersystem crossing.
On the Influence of the Surface Pretreatment on the Photocurrent‐Voltage Characteristics and the Spectral Response of the n‐GaAs/Electrolyte Interface
Authors: van Meirhaeghe R. L. , Cardon F. , Gomes W. P. 
Published: September 2012

AbstractA comparative study was made on the photocurrent of etched and mechanically polished n‐GaAs single crystal electrodes. The photocurrent was investigated as a function of voltage, light intensity and wavelength. The results indicate that polishing creates defects which act as recombination centres. Spectral response measurements yield information on the spatial distribution of the defects involved and on the diffusion length of the holes.
The Temperature Dependence of the Properties of Electrolyte Solutions. I. A Semi‐Phenomenological Approach to an Electrolyte Theory Including Short Range Forces
Authors: Barthel J. 
Published: September 2012

AbstractPair distribution functions f,ij(r1, r2) of a symmetrical ionophoric electrolyte compound Y Cz+ Az‐ in solution are determined with the help of a semi‐phenomenological method permitting to avoid a truncated series expansion of the Boltzmann factor exp [ — eo zj ψ i(r) k T] of Coulomb ion‐ion interaction in the vicinity of the i ion and to introduce the mean potential of short range forces. The appropriate chemical potential of the electrolyte component μY(p, T) and the relevant transport equations, especially of electrolyte conductance, are given. The concept of ion association is discussed within the framework of this approach.
Gas Sorption and Transport in Glassy Polymers
Authors: Paul D. R. 
Published: September 2012

AbstractGas sorption and transport in amorphous polymers above their glass transition temperature are adequately described phenomenologically by Henry's and Fick's laws. However, below the glass transition temperature an additional sorption mechanism develops which follows the Langmuir isotherm, and, thus, there are two populations of gas molecules which may be regarded to be in equilibrium with each other. The Langmuir mechanism evidently arises from the non‐equilibrium nature of the glassy state. Molecules sorbed by this mechanism have less diffusional mobility than molecules sorbed by the Henry's law mode. Because of these differences, the analyses of transient permeation experiments are more complex for glassy polymers compared to those used widely for rubbery polymers. A more comprehensive phenomeno‐logical model for transport of gases in glassy polymers is developed here which has been successfully used to interpret the observed dependence of the permeability coefficient and diffusion time lag on upstream gas pressure. The state of knowledge about gas sorption and transport in glassy polymers is reviewed and contrasted with that of rubbery polymers. It is seen that such observations provide a unique method to probe the physical structure of the glassy state and that knowledge in this area is increasing rapidly.