bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of molecular shape on the excess volumetric properties of cycloalkane + n‐alkane mixtures
Authors: Siddiqi M. A. , Kohler Friedrich 
Published: July 2012

AbstractExcess volumes vE are reported for mixtures of cis‐ and trans‐1,4‐dimethylcyclohexane + n‐heptane, n‐decane, and n‐tetradecane at 293.15 and 313.15 K. The measurements were performed using a vibrating tube densimeter. As expected from previous measurements on methylcycloalkanes, mixtures of the more planar trans‐1,4‐dimethylcyclohexane exhibit a more negative vE than those of the cis‐compound. This effect increases with the chain length of the alkane.
Zur Dynamik des Aggregationsverhaltens zweikettiger ionogener Tenside
Authors: Bauernschmitt D. , Hoffmann H. , Platz G. 
Published: July 2012

AbstractThe micelle formation in aqueous solutions of p‐(6′‐Dodecyl)‐benzenesulfonate (LBS) with the counterions Na+, H2N(CH3)2+, H2N(CH2CH3)3+ and H2N(CH2CH2CH3)2+ was investigated with the aid of relaxation measurements. The existence of small and probably spherical micelles in a concentration range above a first critical micelle concentration could be shown. At higher concentrations the association leads to larger aggregates or mesophases. In the system H2N(CH2CH2CH3)2‐LBS the second cmc approaches to the value of the first cmc. — The small micelles have a narrow distribution variance σ. The reaction volumes are positive but much smaller than the values which were found on surfactant systems with a single alkyl chain. With the exception of the system H2N(CH2CH2CH3)2‐LBS negative reaction volumes are found in the oligomer region. The values for the relative distribution variance σ2/n were obtained from the concentration dependence of the short relaxation time and from the analysis of the amplitudes of the slow process. The results from both methods are in a good agreement.
The thermal conductivity of binary mixtures of helium and methane at 27.5 °C and pressures up to 13 MPa
Authors: Fleeter R. , Kestin J. , Paul R. , Wakeham W. A. 
Published: July 2012

AbstractThe paper reports new, accurate measurements of the thermal conductivity of mixtures of helium and methane in the pressure range 1–13 MPa at 27.5 °C. The measurements have been carried out in a transient hot‐wire instrument and have an estimated uncertainty of ± 0.2%. — The experimental data as a function of density have been extrapolated to yield reliable values of the zero‐density thermal conductivity of the mixtures. It is found that these experimental data cannot be satisfactorily represented by the existing first‐order kinetic theory formulae using independently determined collision numbers for rotational energy relaxation, unless empirical adjustments are made to certain collision integral ratios occurring in the equations. A recently proposed scheme for the prediction of the density dependence of the thermal conductivity of the mixtures is found to correlate the observed density dependence satisfactorily.
Viskoelastische Tensidlösungen
Authors: Hoffmann H. , Platz G. , Rehage H. , Schorr W. , Ulbricht W. 
Published: July 2012

AbstractClassical and dynamic light scattering, electric birefringence, kinetic, surface tension, conductivity and rheological measurements were carried out on so called viscoelastic detergent solutions of Cetylpyridiniumsalicylate (CPySal). The results indicate that spherical micelles are formed in these solutions above the critical micelle concentration (cmc) = 1.5 · 10−4 M. From the cmc on the concentration of the micelles increases linearly with the total detergent concentration up to a second critical concentration (cmc11 = 4.5 · 10−4 M). Upon further increase of the total concentration, the concentration of the micelles remains constant and the globular micelles grow to rodlike micelles. The length of the rods increases linearly with the total concentration. The residence time of a detergent molecule in the rod is longer than in the globular micelle. The surface charge density of the rods is smaller than for the spherical micelles. In unstirred solutions the rods are randomly oriented but their center of masses are ordered. As a consequence the rods can rotate freely as long as their main axis is shorter than the mean distance between the aggregates but their translational diffusion is hindered by the existence of lattice like ordering. Shearing of the solution leads to large areas of a new metastable nematic type phase in which the rods are oriented with respect to each other. These oriented domains are the source for the apparent elasticity of the solutions. When the shearing of the solution is stopped, the elasticity decays with rather long time constants that can amount to several minutes. — The complete equilibration of the solution after the system was perturbed by dilution or a change in temperature takes up to several hours.
Relaxation Phenomena in Raman Spectroscopy
Authors: Versmold H. 
Published: July 2012

AbstractThe line shape of Raman bands and its relation to rotational and vibrational relaxation is the topic of the present contribution. First, rotational and vibrational correlation functions are introduced. Depending on the vibrational mode under study the rotational correlation functions contain information on rotations about different molecular axes. The discussion will be restricted to linear and symmetric top molecules, for the first of which “tumbling” and the latter “tumbling” and “spinning” reorientational motions are of importance. Experimental correlation functions for CO2, CH3J, and CH3CN of totally symmetric and degenerate bands are discussed. A comparison of the experimental correlation functions with those obtained from the rotational J‐diffusion model will be given. — Next, vibrational relaxation (dephasing) is considered. Several mechanisms may contribute to vibrational dephasing. The popular Kubo‐model for vibrational relaxation is introduced and the relaxation of the v2‐band of CH3J is discussed in terms of this model. — The paper closes with a brief discussion of interaction induced scattering. Interaction induced scattering contributes to the wings of depolarised Rayleigh (pure rotational Raman) and Raman scattering and therefore is a severe source of error for the short time behaviour of rotational and vibrational correlation functions. Different approaches to correct experimental spectra are considered.
Anomaler Verlauf der Lösungsenthalpien von CF3H und CF3Cl in aromatischen Kohlenwasserstoffen bei Molenbrüchen x < 0,001
Authors: Braun G. , Becker F. , Steiger A. 
Published: July 2012

AbstractComparative microcalorimetric measurements of the molar enthalpies of solution ΔHs (298 K, 0.1 MPa) of gaseous CF3H and CF3Cl in benzene, toluene, p‐xylene, and mesitylene have revealed an unexpected strong dependence of ΔHs on the mole fraction x of the solute at very low concentrations. In the range 10−5 ≤ x ≤ 10−3 an increase of ΔHs by 8 to 10 kJ mol−1 was observed. A detailed analysis of the experimental procedure which was adopted using a Wadsö differential heat flow microcalorimeter and dissolving the gases at very small flow rates in the unstirred liquids is given. The additional exothermic contribution to ΔHs at x < 10−3 is attributed to structure formation in the aromatic liquids induced by the dissolved gas molecules.
NMR Relaxation in Solutions of Six Fluorinated Benzenes Containing a Free Radical
Authors: Darges G. , Müller‐Warmuth W. 
Published: July 2012

Abstract1H and 19F NMR spin‐lattice relaxation times and dynamic nuclear polarization (DNP) enhancements have been measured at various temperatures in a magnetic field of 17 mT for solutions of six polyfluorinated benzenes containing free radicals. From the radical induced relaxation rates and DNP coupling factors, dipolar and scalar hyperfine coupling contributions have been separated. As a result, the dipolar fluorine and the total proton relaxation rates are more or less the same, and they are only controlled by the molecular motion. The scalar relaxation rates depend upon the chemical structure, but their temperature dependence is also given by the process of translational diffusion. The activation energies for molecular translation, and the scalar contact coupling intensity both increase as one goes from mono‐ to hexafluorobenzene. Coupling mechanisms and comparison with viscous flow and diffusion are discussed.
Molekulardynamische Rechnungen an fluiden Mischungen: Paarverteilungsfunktionen und lokaler Molenbruch für Komponenten sehr unterschiedlichen Volumens
Authors: Hoheisel Claus 
Published: July 2012

AbstractMolecular dynamics calculations (MDC) were performed for binary model‐mixtures on the basis of Lennard‐Jones potentials. The σ‐parameters of the components differed by a factor of two.—Pair‐correlation functions and local molefractions were obtained as function of the compositon.‐The MDC results show appreciably altered pair‐correlation functions compared to the those of mixtures with similar σ‐parameters. The local mole fractions vary distinctly in the short‐range distance of the particles and exhibit relatively large departures from the composition of the mixture for the wider neighborhood of the particles.
Collision‐Induced Spectra of Simple Liquids
Authors: Arning H.‐J. , Tibulski K. , Dorfmüller Th. 
Published: July 2012

AbstractThe far infrared spectra (20–200 cm−1) of nine liquids (CH4, C2H4, C2H6, C3H8, C6H12, CCl4, C2Cl4, CH2C12, CHC13) have been measured and the corresponding induced dipole autocorrelation functions have been calculated. Using the Kubo‐Mori‐Zwanzig formalism we calculated the characteristic relaxation times of the correlation functions and of the first and second order memory functions. A comparison of these relaxation times with the free rotator reorientation times leads to the conclusion that the spectra reflect both rotational and translational components. The higher order memory functions appear to be less sensitive to the details of molecular dynamics of the liquid. The relaxation between the dynamics of the two polar molecules CH2Cl2 and CHCl3 and that of the non polar molecules is shortly discussed.
Catalytic Oxidation of Carbon Monoxide over Ag0.35V2O5
Authors: Van Berg J. Den , Brans‐Brabant J. H. L. M. , van Dillen A. J. , Flach J. C. , Geus J. W. 
Published: July 2012

AbstractThe oxidation of CO over the silver‐vanadium bronze ß‐Ag0.35V2O5 was studied between 150 and 550 °C in a continuous flow reactor. Results show that the catalytic activity of Ag0.35V2O5 is strongly influenced by its pretreatment; partial surface reduction leads to a high oxidation activity. Evaluation of the kinetic parameters leads to the conclusion that at temperatures above 450°C the activity of Ag0.35V2O5 can be described with a defect V2O5‐like structure.—Furthermore, carbon is deposited on the catalyst near 375 °C in excess oxygen atmosphere due to disproportionation of CO which leads to a low activity. A model is proposed for the reoxidation of carbon by adsorbed water to CO and H2 near 200 °C. This reaction results in an enhancement of the low‐temperature oxidation activity of the bronze.
Untersuchungen zur Reaktion OH + HO2 → H2O + O2 mit Hilfe eines Laser‐Magnetischen Resonanz‐Spektrometers
Authors: Temps F. , Gg. Wagner H. 
Published: July 2012

AbstractThe reaction OH + HO2 → H2O + O2 (1) was studied at room temperature in several isothermal discharge‐flow reactors. OH‐ and HO2‐radicals and O‐atoms were monitored with an optically pumped lmr‐spectrometer. The radicals were produced by the reaction F + H2O → OH + HF and OH + HO2 H2O, F + H2O2 → HO2 + HF or H + O2 + M → HO2 + M, respectively. The influence of side reactions due to the presence of H2O2 or the possible presence of O‐ or H‐atoms with small concentrations was investigated and eliminated or taken into account by using suitable reaction conditions. The rate constant at room temperature was found to be k1 (296 K) = (4.0 ± 1.4) · 1013 cm3/mol s.In the range 2 mbar ≤ p ≤ 14 mbar k1 is invariant with pressure.
Transport Properties of Liquids, III. Viscosity of Athermal Liquid Mixtures
Authors: Vogel Herbert , Weiss Alarich 
Published: July 2012

AbstractThe mass density ρ and the dynamic viscosity ρ of eleven binary liquid mixtures were measured as a function of concentration and temperature, in order to study the influence of the entropy of mixing on the viscosity of athermal liquid mixtures.—ζ was determined via an Ubbelohde micro‐viscosimeter and ρ via a vibrating densimeter.—The species of the mixtures differ to a large extent in size and in mass only (Si‐, Sn‐, and Ti‐Tetraalkyl and Tetraalkoxy compounds).—With the Grunberg‐Nissan equation the experimental data can be described in good approximation. As a measure for the non‐ideal behaviour of the mixtures, the Grunberg‐Nissan Parameter ρ is correlated with the difference of the molecular diameter of the components, and with the entropy of mixing.
The First Excited Singlet State of Trans‐Thioindigo
Authors: Karstens T. 
Published: July 2012

AbstractThe first excited singlet state S1 of trans‐thioindigo has been investigated mainly by fluorescence emission, excitation and lifetime measurements in various solvents over a wide temperature range. The experimental results are interpreted in terms of a dual luminescence model, which arises from the flexibility of the thioindigo central bond in the excited singlet state. It is shown that the population density of planar and twisted configurations depends on temperature, viscosity and solvent properties as well as on the excitation wavelength.—As only planar trans‐molecules have been shown to undergo efficient intersystem crossing to the trans triplet and subsequent decay to the cis ground state (trans‐cis isomerization), it is quite important to understand the influence of the above parameters on population of twisted transoid configurations.
Dissociative Attachment and Ion Pair Formation in CF4, CHF3, CH2F2, and CH3F under Low Energy (0 – 20 eV) Electron Impact
Authors: Scheunemann H.‐U. , Heni M. , Illenberger E. , Baumgärtel H. 
Published: July 2012

AbstractResonance dissociative electron attachment and ion pair formation following electron impact have been studied in the energy range from 0 – 20 eV. The translational excess energies of the negative ion fragments have been determined using a time‐of‐flight technique in combination with mass analysis in a quadrupole mass filter. Compared with other halogenated methanes, the resonances in CHF3, CH2F2, and CH3F leading to negative fragments appear at considerable higher energies. The experimental results indicate that those resonances are associated with multiple fragmentation reactions.
The Independent Molecular Interaction Sites Model II. The Structure of the Reference Fluid for Homonuclear Hard Dumbbell Systems
Authors: Naumann Karl‐Heinz 
Published: July 2012

AbstractThe structural properties of the Independent‐Molecular‐Interaction‐Sites (IMIS) reference fluid for homonuclear hard dumbbell systems are investigated in the Percus‐Yevick and in the Hypernetted‐Chain approximation, respectively. The interaction‐site pair distribution functions obtained from the IMIS model are compared with the “exact” results from a Monte‐Carlo study and with predictions from the RISM theory. The calculations presented in this publication are suggesting, that the IMIS model represents a close approximation to the site‐site pair correlations of the real system.
An Equation for the Ideal‐Gas Heat Capacity of Molecular Oxygen for Temperatures from 30 K to 3000 K
Authors: Wagner Wolfgang , Ewers Johannes , Schmidt Robert 
Published: July 2012

AbstractA semi‐empirical equation has been established to calculate very accurately the ideal‐gas heat capacity cp0 of molecular oxygen in the temperature range from 30 K to 3000 K. The new equation contains special terms derived from statistical‐thermodynamic considerations in order to represent that part of cp0 resulting from the vibration energy of the molecule and the energy of electronic excitation. The cp0‐values calculated with the new equation have been compared with values directly calculated by evaluation of the partition functions for fixed temperatures listed in known tabulations. Because of the “physical” background of the equation extrapolations beyond 3000 K are possible. Corresponding expressions for the ideal‐gas enthalpy and entropy of oxygen are also given.
Some Properties of Small Gas Molecules Determined by Refractive Index Measurements
Authors: Kerl K. 
Published: July 2012

AbstractThe dispersion of the refractive index of the gases He, Ne, Ar, H2, N2, O2, CH4, and C(CH3)4 at low densities is determined in the visible wave length range 400 nm ≦ λ ≦ 700 nm by means of scanning‐wavelength interferometry. The measurements are fitted by one‐term Kramers‐Heisenberg dispersion relations and used to calculate some macroscopic and molecular properties like mean polarizabilities, effective eigenenergies and oscillator strengths, oscillator strength sums, Verdet and related constants, Rayleigh scattering cross sections and dispersion force constants. The theoretical background as well as the significance of the different relations between refractive index and these properties is presented and discussed briefly.
Vibrational Spectroscopic and Dielectric Studies of Nitromethane in Liquid Mixtures
Authors: Knözinger Erich , Kollhoff Helmut , Wittenbeck Rüdiger 
Published: July 2012

AbstractIR spectroscopic data obtained for binary and ternary liquid mixtures show that nitromethane may act as proton donor for weak hydrogen bonds with appropriate acceptor groups. At low concentrations of nitromethane in CCl4 an equilibrium between monomer molecules and predominantly antiparallel (⇌) dimers may be inferred from IR spectroscopic and static dielectric studies. The IR and Raman spectroscopic data provide conclusive evidence for the preservation of a predominantly antiparallel correlation at high nitromethane concentrations and even in pure liquid nitromethane.
Theoretische und experimentelle Untersuchungen über die Stromverteilung in elektrochemischen Zellen mit Gasverzehrelektroden
Authors: Führer Oliver 
Published: July 2012

AbstractThis paper deals with charge dislocation problems occuring during overcharge in sealed nickel‐cadmium‐accumulators. In the case of catalyst particle forming gas consumption electrodes, the model “point electrode over flat electrode” was used for the determination of the current distribution. It was solved for linear polarized electrodes. The solution integral is analyzed numerically. A test apparatus for experimental testing was designed and built. This enlarged model enables a measurement of the current distribution. The theoretically predicted results are confirmed experimentally. Additionally the current distribution in the model “point electrode between two ideal unpolarized electrodes” is calculated.
aci‐nitromethane —generated and characterized by neutralization reionization mass spectrometry
Authors: Egsgaard Helge , Carlsen Lars , Florêncio Helena , Drewello Thomas , Schwarz Helmut 
Published: July 2012

AbstractNeutral gaseous aci‐nitromethane has been generated and characterized by neutralization/reionization mass spectrometry (NRMS). Decomposition and isomerization patterns have been established based on studies of the corresponding nitromethane and methyl nitrite isomers in combination with appropriate deuterium labelling experiments. A comparison of the isomeric CH2NO(OH), CH3NO2 and CH3ONO neutrals as well as radical cations is presented.
Amplification of intrinsic fluctuations along the center manifold
Authors: Fernández Ariel 
Published: July 2012

AbstractWe consider a dissipative system sustaining a center manifold beyond a hard‐mode instability. The evolution towards the far‐from‐equilibrium organization is shown to be caused by the correlation of subsystems with a common coarse‐grained phase space. Critical induction periods are calculated for the onset of macroscopic organization.
Enthalpies of mixing of KCl‐AlCl3 melts
Authors: Hatem G. , Østvold T. 
Published: July 2012

AbstractPartial enthalpies of mixing of solid KCl in the liquid mixture KCl‐AlCl3 were determined calorimetrically at 543 K in the concentration region 0.48 < XAlCl3 < 0.75. ΔH̄KCl(1) is negative and shows as expected a pronounced variation at XKCl = 0.5. Calculated integral enthalpies for the subsystems KCl‐KAlCl4, AlCl3‐KAlCl4 show regular enthalpies of mixing with the values — 3.1 kJ mol−1 and — 7.3 kJ mol−1, respectively, for XKAlCl4 = 0.5.
A structural phase transition in RNA
Authors: Fernández Ariel 
Published: July 2012

AbstractWe analyze a soliton‐induced structural phase transition in double‐stranded RNA. A novel feature emerges which is absent in the extensively studied DNA situation: A tautomeric rearrangement induced by the kink on the ribose residue is coupled directly to the cleavage of the hydrogen bond in the base pair. This feature appears to be a consequence of a potential catalytic rǒle of RNA in proton transfer events. Thus, a topological soliton is effective in energy transfer.
Photoionization Mass Spectrometry and Valence Photoelectron‐Photoion Coincidence Spectroscopy of Isolated Clusters in a Molecular Beam
Authors: Rademann Klaus 
Published: July 2012

AbstractA new and versatile photoelectron‐photoion coincidence spectrometer has been developed and advanced to facilitate for the first time the investigation of the valence electronic structure of isolated metal atom clusters up to a mass range of approximately 40000 amu. The neutral cluster distribution, which is synthesized in a doubly skimmed seeded supersonic molecular beam, is probed 130 mm down‐stream by the pulsed and monochromatized output of a newly developed sub‐nanosecond vacuum‐UV/UV‐flashlamp in the photon energy range between 3 and 11.8 eV. Single photoelectrons are energy analyzed and time‐correlated detected either in a field‐free or in a magnetic type time‐of‐flight spectrometer. The corresponding cluster cations are mass analyzed and counted in coincidence in a modified Wiley‐McLaren time‐of‐flight mass spectrometer. The data acquisition electronics is capable of recording and storing simultaneously photoion‐photoelectron coincidence spectra of all those neutral clusters that have sufficient intensity in the molecular beam. First photoelectron spectroscopic results for mass selected mercury clusters up to Hg78 are used to discuss the performance of this new technique. — A photoionization mass spectrometry study of sodium cluster beams has revealed shell closings at the sizes being predicted by the cluster shell model. For the case of large mercury clusters a gradual transition from van der Waals type bonding to metallic cohesion occurs in the size range between 20 and 70 atoms. The occurrence of this transition, which has been observed by energy resolved mass spectrometry, is strongly confirmed by photoelectron‐photoion coincidence spectroscopy. Moreover, the photoelectron spectra clearly indicate that the evolution of the valence band structure toward the metallic state is almost fully accomplished for clusters larger than Hg70. The gradually size dependent transition is found to be induced by the rapid increase of the averaged number of nearest neighbours. Hence, the transition can be explained semi‐quantitatively in the framework of the tight‐binding approximation.
Dielectric Relaxation Rate and Static Dielectric Permittivity of Water and Aqueous Solutions at High Pressures
Authors: Pottel R. , Asselborn E. , Eck R. , Tresp V. 
Published: July 2012

AbstractMeasurements of the complex dielectric permittivity of water and various concentrated aqueous electrolyte and non‐electrolyte solutions were performed at several frequencies between 5.3 and 18 GHz in dependence of hydrostatic pressure up to 200 MPa at temperatures 5 and 25°C. The dielectric relaxation rate and static permittivity as derived from the experimental spectra show characteristic variations with rising pressure. These are discussed with respect to pressure‐induced changes in molecular motion and spatial arrangement.