bluuebunny/crossref_metadata_2025 huggingface dataset:
Adsorption and hydrogenation of CO2 on precipitated iron catalysts: A combined TPD and Mößbauer study
Authors: Gieshoff J. , Buschmann H. W. , Vielstich W.
Published: July 2012

The hydrogenation of CO2 on a precipitated Fe‐catalyst and the formation of oxidic and carbidic iron phases were investigated. The hydrogenation reaction was studied by transient‐ and synthesis‐experiments, changes in the structure of the catalyst were followed by X‐ray‐diffraction and Mößbauer‐spectroscopy. In pure CO2 the iron is converted to magnetite. In CO2‐H2‐mixtures the catalyst is completely converted to cementite. In the initial state of this reaction small amounts of magnetite are formed in the pores of the catalyst. Methane is the main product of the hydrogenation.
Electronic properties of molten Cu‐CuTlTe2 and Ag‐AgTlTe2 systems
Authors: Uemura Osamu , Noguchi Takatoshi , Usuki Takeshi , Kameda Yasuo
Published: July 2012

Measurements of the electrical conductivity, magnetic susceptibility and thermoelectric power in liquid Cu‐CuTlTe2 and Ag‐AgTlTe2 systems have been carried out over wide temperature and composition ranges. These liquid systems exhibit the compound‐forming behavior in the vicinity of stoichiometric compositions, Cu3TlTe2 and Ag3TlTe2, such as the conductivity minimum, diamagnetic maximum and reverse in the sign of the thermoelectric power. Radial distribution analyses of the stoichiometric compositions, Cu3TlTe2 and Ag3TlTe2, by X‐ray and neutron diffractions indicate that the bonding nature of Cu‐Te and Ag‐Te in both alloys is rather covalent, differing from the ionic nature of Tl‐Te in liquid Tl2Te which is well‐known as a typical compound‐forming liquid.
Thermodynamics of liquid oxygen from molecular dynamics simulations
Authors: Lustig R.
Published: July 2012

Oxygen, modelled as a 2‐center Lennard‐Jones fluid, is studied along three isochores‐spanning the liquid region. Eleven different thermodynamic properties are obtained from simulations in the classical molecular dynamics ensemble. It is shown that most of them agree with experimental data within the combined uncertainty of experiment and simulation.
Determination of permeabilities through composite membranes by tracer diffusion experiments with 14C‐labeled Tartrazine®
Authors: Daniel T. , Seidel W.
Published: July 2012

Permeabilities of tartrazine for different composite membranes were obtained by tracer diffusion experiments. 14C‐labeled tartrazine was synthesized from 14C‐aniline hemisulfate and tartaric acid. The composite membranes under investigation consisted of cellulose acetate or polyethersulfone supported by polypropylene membrane backings.
Micellar properties and structure of benzethonium chloride in isotropic aqueous solutions
Authors: Paradies H. Henrich , Thies Michael
Published: July 2012

The micellar structure of the cationic surfactant benzethonium chloride (BZC1) was analysed by small‐angle x‐ray scattering techniques. The shape, size and characteristics of the internal structure of BZC1 was studied by the contrast variation method at 20°C (CMC = 5.35 × 10−4Mol/l) by changing the electron density of the solvent through addition of polyols, e.g. sucrose or glycerol. The obtained scattering data were converted to absolute intensities, and analysed for intermicellar interference effects, by applying the rescaled mean spherical approximation method. The morphological parameters, micellar volume, average electron density, ϱ1, radius of gyration, Rν, second moment of the electron density distribution, “a”, and square average of the electron distribution, (Δϱ12), were determined from scattering data in the range of 0.001<h<0.08 Å−1. The apparent aggregation number (65 ± 10), degree of ionization (α = 0.15) were also determined by static light scattering. The micellar shape of BZCl was computed from Rv, and the maximum dimension of the micelle Dmax = 54.0 Å were obtained from the distance distribution function. The shape of the BZCl micelle is consistent with an oblate ellipsoid of revolution with a = 26.8 Å. The condensation effects of the chloride ions on the BZCl was compared for the “structural” model vs. the “effective model” from static light scattering and x‐ray scattering.

The polydispersity in micellar size was found to be small, 1.55 in the weight‐average molecular weight and 17% in 〈V1〉. These values including (〈Mw,app〉), the one of the radius of gyration of the exclude volume (Rg = 20.3 ± 0.3 Å) are independent of the density of the solvent through addition of polyols.
Deuteron NMR relaxation, phase diagrams, and isotope effects in liquid mixtures of tetrahydrofuran/d2O/salt
Authors: Balevicius Vytautas , Weiden Norbert , Weiss Alarich
Published: July 2012

NMR spin‐lattice relaxation timeT1and phase diagrams of deuterosubstituted tetrahydrofurans (THF‐hg, THF‐h4d4, THF‐d8) in D2O and D2O/salt (Salt = MeCl, Me = Na, K, Rb, Cs; CaCl2, AlCl3; MeOH, Me = Na, K) mixtures have been studied close to their lower critical solution points. It has been found that deuteration of THF leads to a shrinkage of the closed‐loop phase diagram THF‐h8‐xdx/D2O. It is an opposite and much stronger effect to the well‐known replacement of H2O by D2O in the system THF‐h8/H2O (D2O). The lower and the upper critical solution points (TC,L,TC,U) shift from 63.7 °C and 143.5 °C in THF‐h8/D2O to 84.5 °C and 128.5 °C in THF‐h4d4/D2O respectively, and they disappear in THF‐d8/D2O mixtures. This phenomena has been studied by precise (±0.01 °C) measurements of dependencies ofT1(2H) of THF and D2O deuterons on temperature. An increase of activation energies (Ea) of reorientational motion of THF‐d8has been found by introduction of ions into the solutions. The theoretical modeling of phase diagrams using renormalization‐group and decorated lattice methods shows that the observed changes ofTC,Lcan not be considered as a pure energetical effect where onlyEachanges due to additional interaction of polar molecules with the electric field of ions. The entropic contribution, viz. the appearance of additional orientations has to be taken into account as well.
Reply to comment on “dielectric relaxation spectroscopy of electrolyte solutions”
Authors: Schütz G. , Stockhausen M.
Published: July 2012

Some remarks are made on the assessment of relaxation times attributable to ionic aggregations.
Molecular dynamics simulation of pattern formation of two‐dimensional model membranes
Authors: Yurtsever Mine , Pamuk H. Önder , Brickmann Jürgen
Published: July 2012

Structural changes in a two‐dimensional model membrane are studied with the aid of the molecular dynamics (MD) technique. The model parameters of the membrane forming molecules are that of a simplified phospholipid head group: each molecule consists of three spheres which represent choline, phosphate and the ester group. The head group molecule is treated as a rigid body. Their translational motion is constrained to two dimensions. The interaction of the molecules is modelled by Lennard‐Jones and Coulomb interactions. Time dependent configurations of a system with 120 molecules (with periodic boundary conditions) are analyzed by visual inspection of trajectory plots and by the study of radial distribution functions and local order parameters. The ensemble of model particles is studied as a function of the interaction parameters and the temperature.

For high temperatures the system shows liquid type behaviour. For moderate and low temperatures the formation of patterns is observed. There are definitely two trends of ordering. For strong dipole‐dipole interaction (relative to the dispersion attraction) of the model particles the individual molecules form ordered chains with decreasing temperature. However, this trend is not monotonous. For T = 400 K the local order parameter has a maximum as a function of temperature which is interpreted as an interference between dipole‐dipole ordering and an ordering principle which is related to the molecular shape.

A different order phenomenon occurs when the dispersive attraction of the molecular force centers is increased while the dipole‐dipole interaction is kept constant. For relatively larger dispersion attraction the dipoles are orientally trapped by this ordering principle leading to the breakdown of dipole order.

Although the present model approach cannot be overinterpreted with respect to real biomembranes, it may be very useful for the systematic studies on the interaction of bulky molecules with membranes and the study of the influence of external parameters (like pressure) on structure building.
Density functional theory: Modelling of surface tensions for molecular fluids
Authors: Winkelmann J. , Brodrecht U. , Kreft I.
Published: July 2012

Both density profiles, surface tension and the corresponding phase equilibria are governed by the same intermolecular forces. Thus an appropriate theoretical model should be able to describe both interfacial and bulk properties by the same interaction potential. The Local Density Approximation to the Density Functional Theory is applied to the modelling of surface tension and saturated liquid densities of nonpolar molecular fluids. To take into account the nonspherical molecular shape a site‐site Lennard‐Jones interaction potential is used. The reference system is described by a hard convex body equation of state whereas the attractive contributions to the free energy were obtained from a mean‐field approximation. For a series of diatomics structures (O2, N2, CO, Cl2, ethane, ethylene) and convex core geometries (n‐alkanes, benzene, CCl4) potential parameters were estimated using surface tensions and liquid densities. The geometrical parameters for the n‐alkanes could be extrapolated up to n‐octane. A functional dependence of the potential parameters on the chain length and geometry of the molecule is discussed.
The determination of Lennard‐Jones potential parameters of fluid hydrogenchloride by RISM calculations over a broad range of densities
Authors: Gutwerk D. , Bausenwein T. , Bertagnolli H.
Published: July 2012

Several interaction potentials of (12‐6) Lennard‐Jones type with added partial point charges were tested for fluid hydrogenchloride. The individual atom pair correlation functions were calculated with the extended RISM theory, and were compared with the weighted superposition of intermolecular atom pair correlation functions that can be determined by a neutron diffraction experiment on fluid deuteriumchloride. Since experimental results are available at the supercritical temperature of 100°C for densities ranging from 0.5 to 1.1 g·cm−3, the RISM‐calculations were performed over that range. By comparing the results of RISM‐calculations at different thermodynamic states with experimental results, we show that one can derive an interaction potential that represents the measured structure of the liquid better than potentials derived from measurements at only one thermodynamic state. Finally a new set of Lennard‐Jones parameters that leads to a fairly good agreement with the experimental results for all densities is deduced. The individual atom pair correlation functions are given and the dependence on density is discussed.
Viscosity of sodium cryolite‐aluminium fluoride‐lithium fluoride melt mixtures
Authors: Fellner P. , Silný A.
Published: July 2012

The viscosity of the molten system Na3AlF6–AlF3 – LiF was investigated using an oscillating cylinder viscometer. The melts contained up to 27.6 mass% AlF3 and 7.0 mass% LiF. The temperature ranges from 840 to 1060°C. The method is absolute and the accuracy of the viscosity data of cryolite‐based melts is better then 3%. A model is presented that reproduces reasonably well the measured data. The model assumes the presence of Na3AlF6, Li3AlF6, and NaAlF4 species in the melt, and the Arrhenius behaviour of the product of viscosity and of molar volume of the melt.
Hydrodynamic studies on benzethonium chloride micelles in dilute aqueous solution
Authors: Paradies Henrich H. , Hinze Ulrike , Thies Michael
Published: July 2012

Apparent micelle molecular weights, intrinsic viscosity, actual frictional coefficients and molal volumes have been determined for benzethonium chloride (BZCl) at 20°C in 0.01 M Tris‐HCl, containing 0.01 M NaCl. The weight average molecular weight of BZC1 was determined to 28 000 ± 1500 by static light scattering, revealing an apparent aggregation number (Napp) of 60–65. Average hydrodynamic dimensions of the BZCl micelle were obtained from measurements of sedimentation velocity, intrinsic viscosity and of the mutual diffusion coefficient above the CMC (8.4 × 10−4mol/l).

By studying the autocorrelation function of light scattering of BZCl solutions above the CMC, the hydrodynamic and thermodynamic perturbations were determined. The dynamics of the micellar BZCl solutions are unperturbated by additions of polyhydric alcohols within the range of 10–40% (w/w). Above the CMC a classical hard‐sphere behavior is derived from the volume fraction dependence of the scattered intensity for BZCl. The diffusivity data are consistent with a micellar hydrodynamic radius, RH of 25.5 Å, with little or no growth of BZCl micelles upon increasing surfactant concentration evident between 0.01 M NaCl and 0.1 M NaCl at pH 7.5 (20°C).

Applying the linear interaction theory we obtained theoretical fits to Dapp vs. BZCl concentrations over a region of low salt concentrations at pH 7.5 (20°C).
An EXAFS investigation of the Lewis acids zirconium tetrachloride and cyclopentadienylzirconium trichloride in tetrahydrofuran solutions
Authors: Bökman F. , Bertagnolli H.
Published: July 2012

The 1:2 Lewis adducts of zirconium tetrachloride (ZrCl4) and cyclopentadienylzirconium trichloride (CpZrCl3) with tetrahydrofuran (THF) have been studied in solutions by means of X‐ray absorption spectroscopy. The organometallic complex CpZrCl3(THF)2 has in THF solution a structure similar to the known crystallographic solid state structure. In solution the average zirconium‐carbon distance is 0.06 Å longer, and the average Zr‐oxygen distance as well as the average Zr‐chlorine distance are 0.05 Å shorter than in the solid state. In the inorganic complex ZrCl4(THF)2 the zirconium‐oxygen distance is short (2.22 Å), and the trans influence difference between chloride and tetrahydrofuran ligands gives two experimentally separable zirconium‐chlorine distances (2.39 Å and 2.49 Å).
Vibrational spectroscopy of purified C76
Authors: Michel R. H. , Schreiber H. , Gierden R. , Hennrich F. , Rockenberger J. , Beck R. D. , Kappes M. M. , Lehner C. , Adelmann P. , Armbruster J. F.
Published: July 2012

C76 was generated by graphite contact arc discharge in helium and purified by high performance liquid chromatography (>98%). We report an infrared and first Raman spectroscopic study of the microcrystalline solid and compare the observed vibrational structure to existing calculations.
Spectral emission during high temperature pyrolysis of fullerene C60 in shock waves
Authors: Von Gersum Sabine , Kruse Thomas , Roth Paul
Published: July 2012

Submicron fullerence C60 particles were dispersed in Ar and heated by shock waves to temperatures between 2370 K and 3500 K. The aerosol particles evaporate under such conditions in a few microseconds to form C60 vapour. From the time‐dependent spectra at specified wavelengths the decomposition rate of C60 was determined. At temperatures above 2600 K spectral lines of C2 appear in the emission spectrum. A comparison between measured and calculated C2 spectra indicates an increasing amount of C2 with increasing temperature.
Changes of the oscillation frequency of a quartz resonator in contact with a binary liquid mixture of critical composition as function of temperature, revisited
Authors: Köhler Th. , Woermann D.
Published: July 2012

New results of measurements of the temperature dependence of changes of the oscillatory frequency Δf(T) of a quartz oscillator in contact with two binary liquid mixtures of critical composition are reported (systems: 2‐butoxyethanol/water; 2,6‐dimethyl pyridine/water, lower critical point). Both systems exhibit an unexpected Δf(T) behaviour approaching the critical temperature. The results lead to the conclusion that even near the critical temperature Δf(T) is determined only by the background viscosity of the systems. The influence of critical contributions to the viscosity can be neglected. It is assumed that this effect is caused by the large shear gradient produced by the quartz oscillator.
Evidence for competing electron and energy transfer for the fluorescence quenching of singlet oxygen sensitizers by molecular oxygen
Authors: Grewer Christof , Wirp Christoph , Neumann Marcus , Brauer Hans‐Dieter
Published: July 2012

The rate constant of fluorescence quenching by molecular oxygen k was measured for a series of singlet oxygen (1O2)‐sensitizers in toluene and adopts values between 3.5·1010 and 0.4·1010M−1 s−1. log(k) shows a correlation with the free energy of electron transfer ΔGel as calculated according to Rehm and Weller. k decreases with increasing ΔGel in the endergonic region. The efficiency ϕ for 1O2‐formation accompanying the S1‐state quenching by energy transfer of the S1‐state of the sensitizer is substantially >0 only in the cases, where the S1‐T1‐energy gap exceeds the excitation energy of 1O2(1Δg), 94 kJ/mol, where electron transfer is energetically unfavourable and the T2‐state of the sensitizer is lying above the S1‐state. Furthermore the temperature dependence of k was measured in toluene for two sensitizers. The quenching process for dicyanoanthracene (DCA) is activationless in the high temperature region which could be explained either by activationless energy transfer, or by exciplex formation.
Co‐adsorption of mono‐ and multivalent ions on silica and alumina
Authors: Kosmulski Marek
Published: July 2012

Adsorption of calcium and europium from 0.001‐1 M solutions of different 1:1 electrolytes on silica and alumina was studied as a function of pH, surface charge density σ0, ionic strength and temperature. Adsorption of multivalent cations on a negatively charged surface is competitive with respect to monovalent cations, i.e., the increase of the ionic strength leads to a decrease of multivalent ions adsorption. In contrast, adsorption of multivalent cations on a positively charged surface is insensitive to the concentration of monovalent cations or even increases with the ionic strength.
Isochoric heat capacity and liquid‐gas coexistence curve of carbon dioxide in the region of the immediate vicinity of the critical point
Authors: Abdulagatov I. M. , Polikhronidi N. G. , Batyrova R. G.
Published: July 2012

The paper contains the results of new experimental measurements of the isochoric heat capacity and the liquid‐gas coexistence curve of carbon dioxide in the one‐phase region near the critical point. The measurements were performed in a high temperature adiabatic calorimeter used earlier for the determination of the isochoric heat capacity of several liquids and liquid mixtures near the critical points [1, 2].

The experiments have been performed at seven isochores, namely: 461.2, 464.5, 467.5, 470.1, 477.7, 499.0, and 509.8 kg·m−3 in the neighbourhood of the critical point and the coexistence curve. The measurements were made with samples of constant mass contained in a calorimeter vessel of nearly constant volume. Uncertainties of the heat‐capacity measurements are estimated to be less than 2 percent far from Tc and 3 percent in the immediate vicinity of the critical point. The uncertainty in temperature was less than ±10 mK.
Solubility of carbon dioxide in aqueous solutions of ammonium chloride at temperatures from 313 K to 433 K and pressures up to 10 MPa
Authors: Rumpf B. , Nicolaisen H. , Maurer G.
Published: July 2012

The solubility of carbon dioxide in aqueous solutions of ammonium chloride was measured in the temperature range from 313 K to 433 K, up to 6 m salt solutions and total pressures up to 10 MPa. Pitzer's [1] model was used to correlate and predict the new data. Results are reported and compared to literature data and correlations.
The RNA world. Empirical explorations of sequence space: Host‐guest chemistry in the RNA world
Authors: Ellington Andrew D.
Published: July 2012

Using data from a number of recent in vitro selection experiments, general conclusions have been drawn about the shapes of landscapes that map nucleic acid sequences to functions (in particular, the ability to bind a ligand). It appears that local optima on these landscapes are dispersed; that is, that there are a variety of sequences that can bind to a given ligand. In addition, though, there are usually one or two apparently global optima. A comparison of aptamer shapes suggests that nucleic acids can easily form simple pockets by using short helical segments. These results have implications for the origin and evolution of metabolism: short nucleic acids may be much better suited to ligand‐binding than short peptides or other biopolymers.
Principles and origins of coding systems. Does information acquire meaning naturally?
Authors: Wills Peter R.
Published: July 2012

Natural selection among replicative entities allows for the accumulation of information during biological evolution, but it does not account for the orderly development of selected biochemical processes which now constitute a restricted mapping from genotype to phenotype. The self‐organisation of biochemical processes is described in terms of a set of simple rate equations, which are solved for the special case of systems for which functions are mapped onto structures in a random fashion. When catalytic action is dependent on symbol recognition, so that biochemical synthesis is instructed by information, coding self‐organisation can take place, but loss of information beyond a certain threshold results in catastrophic loss of function. It is argued that a partnership between Darwinian selection and functional self‐organisation is fundamental to biological evolution.
Pattern formation by transcriptional cascades in the Drosophila embryo
Authors: Rivera‐Pomar Rolando , Hoch Michael , Sauer Frank , Brönner Günter , Wimmer Ernst A. , La Rosée Anna , Jäckle Herbert
Published: July 2012

Genetic and molecular analyses have combined to yield insights into functional cascades of transcription factors necessary to establish the molecular blueprint of the Drosophila body pattern in response to positional information already present in the egg. This maternal information is based on a small set of asymmetrically distributed maternal transcription factors that act as graded morphogens along the anterior‐posterior and the dorsal‐ventral axes of the embryo. Recent progress in the field provides first insight into the molecular mechanisms by which long‐range positional information in the egg causes a series of localized zygotic transcription factor gradients to position development fate along the axes of the blastoderm embryo.
Lattice polymer automata
Authors: Rasmussen Steen , Smith Joshua R.
Published: July 2012

We present a new style of molecular dynamics and self‐assembly simulation, the Lattice Polymer Automaton [LPA]. In the LPA all interactions, including electromagnetic forces, are decomposed and communicated via propagating particles, “photons”. The monomer‐monomer bond forces, the molecular excluded volume forces, the longer range intermolecular forces, and the polymer‐solvent interactions may all be modeled with propagating particles.

The LPA approach differs significantly from both of the standard approaches, Monte Carlo lattice methods and Molecular Dynamics simulations. On the one hand, the LPA provides more realism than Monte Carlo methods, because it produces a time series of configurations of a single molecule, rather than a set of causally unrelated samples from a distribution of configurations. The LPA can therefore be used directly to study dynamical properties; one can in fact watch polymers move in real time. On the other hand, the LPA is fully discrete, and therefore much simpler than traditional Molecular Dynamics models, which are continuous and operate on much shorter time scales. Due to this simplicity it is possible to simulate longer real time periods, which should enable the study of molecular self‐organization on workstations; supercomputers are not needed.
Emergence of regular superstructures in macromolecules
Authors: Botti S. A. , De Santis P. , Fuá M.
Published: July 2012

A general method is described in which the harmonic analysis of perturbations is applied to the study of superstructures of macromolecular chains. The theoretical approach employed has been to apply harmonic perturbations on the conformational parameters in macromolecular helices of various periodicities and to study the overall variation in structure and its dependency on the periodicity of the perturbation. The results clearly show that when these perturbations do not contain harmonics close to the fundamental periodicities of the polymer chain, the consequent structural effects remain localized and are not productive at a superstructural level. Furthermore, the features of these superstructures are dependent only on the amplitude of the fundamental periodicity component of the perturbation and are generated by topologically equivalent transformations. These findings enable us to devise a model to study and identify transconformational pathways leading to global variations in the structure of the macromolecular chain.
Diffusion of C in TiC
Authors: Albertsen Knuth , Schaller Hans‐Jürgen
Published: July 2012

Diffusion of carbon in titanium carbide was investigated over the entire phase field between 1179 and 2413 K using suitably designed diffusion couples.

Concentration‐depth profiles of carbon were taken by SNMS and EMPA. The diffusion coefficients of carbon obtained by the two analytical techniques in different temperature ranges agree remarkably well. Above 1468 K, they exhibit a strong concentration dependence and can be expressed by

The thermodynamic factor obtained from a thermodynamic analysis of the TiC system was used to describe the concentration dependence. Tracer diffusion coefficients calculated from the chemical diffusion coefficients with the help of the thermodynamic factor are in accordance with literature data. Below 1468 K concentration‐independent diffusion coefficients were obtained which yielded a lower energy of activation:

This behavior is attributed to the preponderance of grain boundary diffusion over volume diffusion at low temperatures in the samples at hand.
An electrochemical study of the passive film formed on Ni–Cr (80/20) coating
Authors: Metikoš‐Huković M. , Omanović S. , Babić R. , Milošev I.
Published: July 2012

The passive state of Ni–Cr (80/20) coatings prepared by a plasma beam sputter deposition process was studied using cyclic voltammetry and impedance spectroscopy techniques. The highly protective quality of the film formed in acetate buffer, pH = 5.7, is probably based on chromic species. The nickel content in the film was very low and influenced only the electronic properties of the film.

The appearance of a distinct transition in the capacitance potential characteristic may be correlated with the presence of higher valent chromium species. Cyclic voltammetry demonstrated that Cr(VI) was incorporated into the outer part of the oxide film, or was tenaciously adsorbed on the electrode surface. Its formation and reduction were reversible.
Photochromic reaction of peroxopolytungstic acid thin films
Authors: Itoh Kiminori , Yamagishi Kazunori , Nagasono Mitsuru , Murabayashi Masayuki
Published: July 2012

Spin‐coated Thin films of peroxopolytungstic acid (PTA) showed pronounced photocoloration under UV irradiation only when the films contained a reducing reagent having OH groups. Decoloration occurred when the colored films were exposed to oxidizing reagents. The origin of the photocoloration is likely a reaction between excited triplet state of PTA and OH groups of the reducing reagents. Accumulation of reducing power in the films, and competition between the photocoloration and known photohardening process were discussed; an application of these characteristics was also shown.
Pulse radiolysis of benzyl chloride and ‐bromide; The UV‐visible absorption spectrum of the benzyl cation
Authors: Fujisaki Noboru , Comte Pascal , Gäumann Tino
Published: July 2012

Pulse radiolysis study of liquid benzyl chloride has been carried out at room temperature. In order to identify transient species that absorb in the UV‐vis region, various scavengers were used including oxygen, ethanol, pyrrole, biphenyl, and mesitylene (1,3,5‐trimethylbenzene). The spectrum of the benzyl cation was obtained by subtracting the transient spectrum for the 0.6 M solutions of ethanol in O2‐saturated benzyl chloride from that for O2‐saturated benzyl chloride. The difference spectrum obtained has a strong absorption band at 303±2 nm and a weak broad band near 500 nm. The analyses of end products formed in the γ radiolysis of benzyl chloride were done in the presence and absence of scavengers. The formation of benzyl ethyl ether with a G value of 0.9 from a 0.6 M solution of ethanol in O2‐saturated benzyl chloride was taken as evidence that added ethanol reacts with benzyl cations to give benzyl ethyl ether. Some pulse radiolysis experiments were performed with benzyl bromide. Transient spectra observed in benzyl bromide are similar to those observed in benzyl chloride. It is, however, inferred from the product analysis that the radiolytic mechanisms of benzyl bromide appreciably differ from those of benzyl chloride.
Quantitative interpretation of the red edge excitation (REE) effect of 9,9′‐bianthryl in polyisobutene by band shape analysis of the temperature‐dependent optical fluorescence spectra
Authors: Elich Karsten , Wortmann Rüdiger , Petzke Frank , Liptay Wolfgang
Published: July 2012

Optical fluorescence spectra of 9,9′‐bianthryl (BA) in polyisobutene (PIB) were measured as a function of the excitation wavelength at various temperatures between 210 and 293 K. Irradiation at the red edge of the absorption spectra selectively excites distinct conformers with respect to the torsional angle. This leads to a strong dependence of the vibronic band shape of the fluorescence spectra on the excitation wavelength. The marked temperature dependence of the band shape may be attributed to the viscosity‐dependent deceleration of the torsional relaxation of BA in the highly viscous polymer which prevents the excited state ensemble from reaching thermal equilibrium. The predominant broadening mechanism affecting the band shape is given by a combination of the S1 torsional distribution and the torsional angle‐dependent transition frequency. These effects are interpreted quantitatively within a torsional relaxation model based on the description of the torsional dynamics according to a Smoluchowski equation which is adapted to the steady state case. The band shape analysis of the fluorescence spectra enables the determination of the effective S1 torsional potential as well as the friction coefficient related to the internal torsional motion of BA in the polymer matrix. A value of ΔV = 325 cm−1 is deduced for the local barrier of the S1 double minimum potential at ϕ = 90° while the minimum torsional angle is found to be ϕmin = 61°. Additionally, model calculations on time‐resolved fluorescence spectra of BA in apolar solvents are carried out as a function of excitation wavelength and temperature showing the importance of conformational relaxation for the interpretation of transient spectra of flexible molecules.
On the significance of molecular surfaces and thermodynamic interactions for the excess viscosities of liquid mixtures
Authors: Mertsch Rüdiger , Wolf B. A.
Published: July 2012

The viscosities η of homogeneous binary mixtures of liquids are usually approximated as In η = ϕ1 In η1 + ϕ2 In η2 where ϕi and ηi are the volume fractions and the viscosities, resp., of the i‐th pure substance; the behavior of real systems is then discussed in terms of Δ In η, the deviations from the above reference behavior. Here a semi‐empirical approach is presented according to which volume fractions are replaced by the surface fractions Ωi to create a more realistic reference state, and the thermodynamic interaction parameter g is taken into account. The new equation reads (expressing it for practical purposes still in the terms of ϕi)

γ is a geometric factor, measuring the difference between Ωi and ϕi, and δ  In (η2/η1). The comparison of calculations according to the above equation with experimental data demonstrates that the first term is decisive in the majority of cases and only with systems of large interaction does the second become important. For all nine systems under investigation quantitative agreement between experiment and theory can be achieved using a theoretical value for either γ or g, and adjusting the other within physically reasonable limits. Possible explanations for the necessity to fit one of the parameters are given.
Effective self‐diffusion coefficients of 14C‐urea in a polyphenolsulfonic acid cation exchange membrane in the presence of different counterions
Authors: Daniel T. , Seidel W.
Published: July 2012

Effective self‐diffusion coefficients of the polar non‐electrolyte urea were obtained from tracer experiments with 14C‐urea. For a membrane loaded with Na+ the tracer‐diffusion coefficient was investigated as a function of the total urea concentration. Also tracer‐diffusion was observed for membranes loaded with different counterions at constant urea concentration in solution.
Density functional theory: Prediction of ellipsometric parameters and structural behaviour of pure fluid vapour‐liquid interfaces
Authors: Winkelmann J.
Published: July 2012

Both structural properties, like density profiles, interfacial behaviour and the corresponding phase equilibria are governed by the same intermolecular forces. The prediction of ellipsometric parameters requires a profile of the optical dielectric constant across the vapour‐liquid interface. This profile is provided by the Density Functional Theory (DFT). We apply the Local Density Approximation (LDA) to the DFT to a molecular system with a cut‐and‐shifted Lennard‐Jones potential. The potential parameters were determined by modelling surface tensions and saturated liquid densities of a pure fluid. The calculated density profile is then transformed into a profile of the refractive index across the interface. Using Crook's multilayer algorithm we predict the ellipsometric parameters Ψ, Δ and the ellipticity e as a function of the angle of incidence of a laser light beam over a range of temperatures. Predicted values for argon, cyclohexane and water are compared with experimental results.
Generation of ionic species by photolysis of polysilylenes in dilute solution
Authors: Eckhardt A. , Nešpůrek S. , Schnabel W.
Published: July 2012

From flash photolysis studies (at λinc = 266 and 347 nm) involving the electrical conductivity and the optical absorption detection method it is inferred that poly(methylphenyl silylene), PMPSi, and poly(biphenylmethyl silylene), PBMSi, form ionic species in a monophotonic process in dilute tetrahydrofuran and dichloromethane solution at 295 K (ϕ(ion) ≈ 4×10−2, PBMSI and 1×10−2, PMPSi, in THF at λinc = 266 nm). The ionic species possess optical absorption bands between 350 and 500 nm with a maximum at about 380 nm. Both the photocurrent and the optical density at 380 nm decay with identical rates by a second order process (k2 ≈ 3 × 1011 dm3 mol−1 s−1, PBMSi in THF at 295 K).
Thermodynamics and separation of mixtures
Authors: Prausnitz J. M.
Published: July 2012

The classical foundation of chemical thermodynamics was essentially completed by J. W. Gibbs when he defined the chemical potential in 1875. However, this formulation gives only the point of departure for applying thermodynamics to a quantitative description of phase equilibria; these equilibria are required for design of separation operations that depend on transfer of molecules from one phase to another. To apply thermodynamics to real problems, we need meta‐thermodynamic information as supplied by molecular physics and physical chemistry. This need was recognized at the end of the 19th century by numerous outstanding scientists (e.g. Max Planck) who made efforts to establish practical theories for calculating chemical potentials; similar efforts continue today. To illustrate the applicability of thermodynamics, three examples are presented here: removal of hydrogen sulfide from gasified coal; precipitation of proteins from aqueous solution; separation of small and large solutes using a temperature‐sensitive hydrogel which exhibits a first‐order phase transition. Attention is given to the increasing role of molecular simulation that can provide not only quantitative thermodynamic “data” but, in addition, a qualitative “picture” of complex phenomena. Such pictures provide the first step for development of quantitative models.
On the stability and on the formation of two‐dimensional condensed equilibrium adsorbate films in an aprotic and in aqueous solution. Part III: Inversion from irreversible to reversible phase transition of adsorbed 2‐thiohydantoin at the interface mercury/water, sodiumfluoride due to coadsorbed polyethylenglycol
Authors: Schrettenbrunner M. B. , Chaiyasith P. , Baumgärtel H. , Retter U.
Published: July 2012

The following is an investigation on the influence of polyethylenglycol on the two‐dimensional phase transition of 2‐thiohydantoin. The two‐dimensional phase at the interface mercury/aqueous electrolyte has been characterised by measuring the potential as well as the time dependence of the differential capacitance.

In the absence of polyethylenglycol, the irreversible phase transition is indicated by a discontinuous change of the capacitance with the potential. The condensed film is formed by two‐dimensional nucleation according to an exponential law and a constant growth rate.

However in the presence of polyethylenglycol, the reversible phase transition is connected with a continuous change of the capacitance‐potential dependence. At the state of equilibrium different capacities have been observed. Different equilibrium states also can well be described theoretically as two‐dimensional instantaneous nucleation and growth of 2‐thiohydantoin, too. But in the case of reversible phase transitions of adsorbates a polyethylenglycol induced desorption being proportional to the area of 2‐thiohydantoin centres has to be considered.
Enthalpies and entropies of complexation of silver(I) and diaza‐18‐crown ethers in polar solvents
Authors: Burchard T. , Firman P. , Schneider H. , Cox B. G.
Published: July 2012

The enthalpies of complexation of Ag+ with diaza‐18‐crown ethers containing various combinations of donor atoms have been determined in polar organic solvents using calorimetric and potentiometric techniques. Enthalpies of complexation are also reported for two silver ion cryptates. The results are combined with previously determined free energies of complexation to obtain the corresponding entropies. In dipolar aprotic solvents, the enthalpies of transfer of the complexes are very similar to those of the free ligands, so that changes in enthalpies of complexation are dominated by the enthalpies of solvation of the silver cation. The thermodynamics of ligation, i.e., of complex formation between the gaseous silver ion and the diaza‐crown and cryptand ligands in solution, are calculated and, for the free energies, partitioned into contributions from each of the donor atoms (N, O, and S). Among the aprotic solvents, contributions of oxygen and sulphur atoms in the ligand bridges to the stabilities of diaza‐crown and cryptand complexes are additive and independent of solvent. In methanol, hydrogen bonding between methanol molecules and the free ligands reduces the magnitudes of both the free energies and enthalpies of formation of the silver complexes.
Approximate determination of rovibrational densities of states ρ(E,J) and numbers of states W(E,J)
Authors: Olzmann M. , Troe J.
Published: July 2012

Compact approximate equations for rovibrational densities of states ρ(E,J) for harmonic oscillator‐rigid rotor molecular systems are derived. Linear molecules, spherical tops, prolate and oblate symmetric tops are considered. Vibrational densities of states are represented by the Whitten‐Rabinovitch approximation which then is convoluted with the contribution from the K‐rotor (for a symmetric top). Likewise, numbers of states W(E,J) are approximated for prolate symmetric top molecules. The derived expressions allow for quick calculations of specific rate constants k(E,J) of unimolecular reactions.
Brownian reorientation in a smectic phase with quadrupolar ordering
Authors: Schiller P.
Published: July 2012

The reorientation of molecules in smectic liquid crystalline phases around their long axes is accompanied with a dielectric dispersion in the high frequency region. This spinning motion is influenced by the anisotropy in the layers of smectic phases with tilted molecules and can be regarded as a Brownian process in a periodic potential. The solution of the corresponding Smoluchovsky equation allows to determine the two‐time correlation function for the transversal dipole moment and the dielectric susceptibility. It is found that a quadrupolar potential causes a pronounced deviation from the semicircle in a Cole‐Cole diagram, whereas the deviations are much smaller when a dipolar ordering is considered.
Kinetics and mechanisms of the reactions of O(1D)‐Atoms with CF3Br and CF2BrCF2Br in the gas phase and in solid argon matrices
Authors: Lorenzen‐Schmidt Heike , Weller Rolf , Schrems Otto
Published: July 2012

The rate coefficients and mechanisms for the reactions of O(1D) atoms with CF3Br (halon 1301) and CF2BrCF2Br (halon 2402) have been investigated in the gas phase at room temperature. The experiments have been carried out in a static photochemical reactor. Photolysis of ozone at 253.7 nm provided O(1D) atoms. The competitive reaction O(1D)+N2O has been chosen as internal standard to determine the rate coefficients. The course of the reactions was followed by FTIR spectroscopy. The measured data correspond to rate coefficients of (4.0±0.4)×10−11 cm3 s−1 for the reaction O(1D) + CF3Br and (8.8±1.2)×10−11 cm3 s−1 for the reaction O(1D) + CF2BrCF2Br.

For further mechanistic studies, the reaction O(1D) + CF3Br has been investigated in solid Ar‐matrices at T = 14 K. Codeposition of O3/CF3Br/Ar mixtures and irradiation at 250 nm yielded F2CO as dominant reaction product. Experiments with 18O3 indicate that CF3OBr was formed during the course of the reaction. Our observations can be interpreted with the formation of an excited CF3OBr molecule which can be stabilized in the matrix cage or decompose rapidly to the final product F2CO. No further intermediates could be detected in the matrix experiments.
Electrochemical and Simultaneous Spectroscopic Study of Reduction Mechanism and Electronic Conduction During Electrodeposition of Tantalum in Molten Alkali Chlorides
Authors: Bachtler M. , Freyland W. , Voyiatzis G. A. , Papatheodorou G. N.
Published: July 2012

We have studied the reduction mechanism and electronic conduction during electrodeposition of tantalum in various TaCl5‐alkali chloride melts at temperatures up to 1100 K. This has been performed by simultaneous measurements of impedance and Raman spectra together with cyclic voltammograms. A detailed analysis of electrochemical and spectroscopic results yields the following predominant reduction steps during electrodeposition in pure alkali chloride melts: Ta(V)‐Ta(IV)‐Ta(0). The equilibrium potentials of the corresponding redox reactions are separated by 40 mV which is clearly resolved in impedance measurements. In LiCl/KCl‐eutectic melts a three step mechanism is found with Ta(III) being the intermediate species. In evaluating the impedance data we found indications for electronic contributions which are most prominent with added oxide impurities to the molten electrolyte. Direct evidence for an appreciable electronic conductivity has been obtained by electrochemical polarization measurements. These are reported here the first time for fused KCl‐TaCl5/Ta at 1050 K, where electronic conductivities up to 0.5ω −1cm−1 have been measured, i.e. of same order of magnitude as ionic conductivities.
A Multi‐Functional Electro‐Optical Molecular Device. The Photoelectrochemical Behavior of Spirobenzopyrans in Dimethylformamide
Authors: Zhi Jin Fang , Baba Ryo , Hashimoto Kazuhito , Fujishima Akira
Published: July 2012

The photoelectrochemical investigation of l,3,3‐trimethylspiro(2H‐l‐benzopyran‐2,2′‐indoline) (SP‐O) and l,3,3‐trimethyl‐6‐nitrospiro(2H‐l‐benzopyran‐2,2′‐indoline) (SP‐1) has been performed in a dimethylformamide (DMF) solution at room temperature and at a low temperature (‐42°C). Nitro‐substituted SP‐1 is electroactive in the experimental potential range of ‐1.8V to +0.8 V (vs. Ag/Ag, while no nitro‐substituted parent spirobenzopyran SP‐0 is lacking in electroactivity. In the case of SP‐1, nearly identical electrochemical behavior was found for the closed‐ring (SP) and open‐ring (MC) isomer at room temperature or at ‐42°C, suggesting that the ring form, i.e. open or closed, has no influence on the redox reaction of SP‐1. Moreover, reversible color changes were observed in the DMF solution of SP‐1 depending on reduction and oxidation potentials, namely, a change to yellow in the reduction and to deep violet in the oxidation. Both voltammetric and spectroelectrochemical evidences suggest the production of a nitrobenzopyran radical anion of closed‐ring (yellow) in a reduction and an open‐ring isomer MC (deep violet) in an oxidation either from SP and from MC of SP‐1 in the DMF solution. This behavior leads to the discovery of a novel photochromism and electrochromism “three state” conjugated system which may potentially be applicable to the construction of multi‐functional electro‐optical molecular devices.
On the Nature of the Nonanoic Acid Monolayer Adsorbed at the Hg/Aqueous Solution Interface: Influence of Conformational Freedom in Bulk Aqueous Solution
Authors: Bordi S. , Carlå M. , Passamonti P. , Fontanesi C. , Pelloni P.
Published: July 2012

The adsorption of the nonanoic acid at the electrified Hg/aqueous solution interface is studied by means of capacity and surface tension measurements. Comparison of the experimental rmax value with the calculated more favoured solvated conformation suggests that the acid is adsorbed in a partially coiled conformation. The adsorption free energy here determined, together with previously reported values found in the literature concerning other saturated acids and alcohols, is compared with reactivity and calculated molecular descriptors. The collected evidence suggests that the hydrophobic nature of the acid is responsible for the adsorption, while the electric field/molecule interaction, occurring at the electrified interface, governs the desorption. Lastly, some experimental (capacitive transients, effect of the temperature on the tensammetric curves) and theoretical findings are discussed which indicate that the adsorbed acid monolayer should be regarded as a usual, in the field of adsorption at electrodes, disordered network. Thus excluding the occurrence of a two‐dimensional phase transition involving the formation of a 2D solid‐like film.