bluuebunny/crossref_metadata_2025 huggingface dataset:
On Mesoscopic water droplets dispersed in butyl rubber
Authors: Pelster R. , Kops A. , Nimtz G. , Enders A. , Kietzmann H. , Pissis P. , Kyritsis A. , Woermann D.
Published: July 2012

Water dispersed in butyl rubber containing hydrophilic components has been studied with differential scanning calorimetry, dielectric spectroscopy in the frequency range from 5 Hz to 10 GHz, thermally stimulated depolarisation currents, and small angle X‐ray measurements. Hydrophilic components in the rubber matrix act as adsorption sites for water molecules. Two populations of water droplets with radii of the order of magnitude of 2 nm are formed. In the mesoscopic hydrophobic confinement the dielectric relaxation of the liquid water droplets is shifted to higher frequencies compared with bulk water. The relaxation of water in the frozen droplets is slower compared to that of bulk ice. Neither molecular water nor clusters of bulk water are found in the rubber.
Tortuosity Factor in Non‐Homogeneous Membranes
Authors: Maskell W. C.
Published: July 2012

The tortuosity factor, Θ, in an homogeneous gel is substantially greater than that in a matrix composed of nonconducting particles for a given volume fraction of the solid. It is proposed that a non‐homogeneous membrane has a tortuosity which lies between these two extremes and a theoretical framework has been developed to describe such a system. The theory is applied to regenerated cellulose which is a well‐characterised heterogeneous membrane. The assumption made is that the real anionic mobility within the membrane is equal to the anionic mobility in the external solution when a small correction is made for electroconvection. Application of the theory indicates that for regenerated cellulose equilibrated in solutions in the range 0–2 M KOH the fraction of cellulose comprising non‐conducting regions is 32%. This is in good agreement with the value of 36% derived from ion‐exchange measurements.
The WSe2/Tungsten‐Oxide Interface: Structure and Photoluminescence
Authors: Tenne R. , Eherman K. , Mahalu D. , Peisach M. , Kautek W. , Wold A. , Matson R. , Waldeck D. H.
Published: July 2012

A “mixed” surface of WSe2, which contains both the |c and τc facets was produced by mechanical indentation, followed by photoelectrochemical etching, and chemical cleaning. This surface was shown to exhibit low surface recombination velocity, and consequently high solar to electrical conversion efficiency, in the past. Using O18 as a tracer for nuclear activation analysis it is shown that, after the above surface treatment, the surface of the ||c facet is covered with a thin (3–5 monolayers) film of tungsten oxide. The structure of the crystalline oxide phases that comprise the tungsten‐oxide/WSe2 interface are investigated with powder X‐ray diffraction. X‐ray photoelectron spectroscopy is used to study the chemical bonding at the interface. A model is proposed to explain the absence of surface recombination at this interface.

A strong above the bandgap luminescence is observed from ||c facets of “mixed” surfaces, and from crystal edges (||c) which were allowed to “age” fcr a few weeks in the air. The origin of this luminescence was investigated in some detail, and a mechanism, involving partially oxidized ||c surface which possibly leads to quantum confinement of excitons in ||c edges of WSe2, is proposed.
Conductance of Sodium and Tetraethylammonium Iodides in Mixtures of Water with 1‐Propanol and with 2‐Propanol
Authors: Hawlicka Ewa , Grabowski Roman
Published: July 2012

The conductivities of NaI and Et4NI in mixtures of water with 1‐propanol and 2‐propanol at 25°C are reported. The conductivity data were analyzed via the Fuoss‐Hsia equation to find both the equivalent conductance λ0 as well as the association constant KA, simultaneously/Basing on variations of the Walden products the effect of the solvent composition on the ionic solvation has been discussed. In alcohol deficit mixtures, wherein hydrophobic interactions play an important role, the dehydration of Na+ and of Et4N+ ions has been found. For the same compositions the distances between ions forming the ionic pairs also diminish. Et4N+ and I− forming pairs shared one water molecule, whereas Na+ and I− are able to form even contact ionic pairs.
Eine gaskinetische Studie zur Reaktion von HOCl mit F‐, Cl‐ und H‐Atomen bei Raumtemperatur
Authors: Vogt R. , Schindler R. N.
Published: July 2012

The reactions of HOCl with F‐, Cl‐ and H‐atoms were investigated at room temperature in a discharge flow system equipped with an OH‐resonance fluorescence cell and a mass spectrometric detector. All kinetic studies were carried out under pseudo first order conditions with HOCl being the minority component. Branching ratios for individual processes were obtained by following simultaneously the rates of HOCl consumption and product formation. The following rate constants (in units cm3 molecule−1 s−1) were determined

F + HOCl → Products k(1) = (4.9±0.6)·10−11 (1)

→ ClF + OH k(1a) = (1.2±0.4)·10−11 (1a)

CL + HOCl → Products k(2) = (1.4±0.37)·10−12 (2)

→ Cl2 + OH k(2a) = (3.4±1.4)·10−13 (2a)

H + HOCl → Products k(3) = (3.5±0.7)·10−12 (3)

→ HCl + OH k(3a) ≤ (6.7±2.1)·10−13 (3a)

Calibration for [HOCl] using reaction (1) for gas titration is discussed. The data are evaluated to yield ΔHf (298) = ‐79.7 kJ mol−1 for the heat of HOCl formation.
About the Rate of the Reaction of NH(X3Σ−) with O2 over a Large Temperature Range
Authors: Hennig G. , Röhrig M. , Gg. Wagner H.
Published: July 2012

Measurements of the rate of the reaction NH(X3Σ−) + O2 at low and high temperatures show strongly different apparent energies of activation. In order to check the consistency of both sets of measurements the reaction was investigated in the intermediate temperature range. These experiments confirm a strongly curved Arrhenius plot for the rate of this reaction.
On the Stability and on the Formation of Two‐dimensional Condensed Equilibrium Films in an Aprotic and in Aqueous Solution — Part I: The Thermodynamics of Condensed 2‐Thiohydantoin at the Mercury Interface in Nonaqueous Acetonitrile, Tetraethylammoniumperchlorate
Authors: Schrettenbrunner M. , Chaiyasith P. , Baumgärtel H. , Retter U.
Published: July 2012

The behaviour of 2‐thiohydantoin at the interface mercury/nonaqueous acetonitrile, tetraethylammoniumperchlorate has been investigated by measuring the double layer capacitance in the potential range between 1.1 V≤‐E≤0.5 V. It is shown that a condensed adsorbate is established in a specific interval of potential, temperature and concentration of 2‐thiohydantoin. From the experimental data the molecular surface area in the condensed state and the sum of adsorption and intermolecular interaction energy of condensed molecules has been evaluated. The values are comparable to those of aqueous systems.
In‐Situ Electrochemical Actinometry Using An Azo Monolayer Film
Authors: Morigaki K. , Liu Z. F. , Hashimoto K. , Fujishima A.
Published: July 2012

We previously proposed an in‐situ electrochemical actinometric technique. It was established on the photoelectrochemical properties of azobenzene derivatives in the assembled monolayer film where incident photon number can be calculated from the faradaic charge quantity which flows during the light irradiation. Here, we show that the light intensity can be estimated more directly from the saturation current of cathodic reaction in the above azobenzene monolayer system. When the actinometric light is irradiated at a cathodic potential, azo molecules undergo trans to cis isomerization and selective reduction of cis isomer occurs simultaneously. The linearity between light intensity and cathodic current was derived theoretically and examined experimentally. This allows simpler in‐situ measurements of light intensity in photochemical and photoelectrochemical experiments.
Nonlinear Behavior in the Optical Spectra of Solid Fullerene C60
Authors: Diehl M. , Degen J. , Schmidtke H.‐H.
Published: July 2012

Optical emission spectra of solid C60 have been recorded at 1.9 K. Several vibronic transitions are observed. In particular the dependence of the emission spectrum with respect to the excitation intensity has been studied at room temperature and at 12 K under excitation with 514.5 nm and 488.0 nm laser radiation. The emission intensity increases with excitation intensity stronger than linear. At higher excitation powers an additional optical transition centered at 16500 cm−1 becomes dominant. In an absorption experiment in solution (1.4‐10−5 mol/l), the absorbed power of light is also nonlinear with respect to the excitation power.
Sorption and Diffusivity Measurements of Cyclohexane+Benzene and Cyclohexene+Toluene Mixtures in Polyurethane Membranes. Model Calculations of the Pervaporation Process
Authors: Enneking L. , Stephan W. , Heintz A.
Published: July 2012

Data of vapor sorption measurements of the solvents cyclohexane, benzene and toluene in polyurethane (PU) membranes are presented. Vapour sorption isotherms have been obtained from equilibrium data. Kinetic sorption data have been used for determining diffusion coefficients of the solvents in the membrane material. Further measurements of the individual solubilities of liquid cyclohexane+benzene and cyclohexane+toluene mixture components in PU‐membrane material have been carried out using the so‐called swelling density method and a gaschromatographic analytical method. Vapor sorption isotherms as well as solubility data of the liquid mixtures can be described with the UNIQUAC‐model in good agreement with experiments. All results obtained for solubilities and diffusion coefficients are used for predictive calculations of fluxes and separation diagrams in the pervaporation process of cyclohexane+benzene and cyclohexane+toluene mixtures through PU‐membranes. The basis of these model calculations is the solution‐diffusion model. Predicted results of pervaporation agree well with experimental data taken from literature provided diffusion coupling of the components permeating the membrane is taken into account.
Dilute Near‐Critical Solutions of Iodine in Xenon: Determination of V, S and (δp/δx) from Solubility Data
Authors: Fernández Diego P. , Fernández‐Prini Roberto
Published: July 2012

Using recently determined solubility data for solid iodine dissolved in near‐critical xenon, we have calculated the partial molar entropy and volume of the solute. These quantities show a strong density dependence in the vicinity of the solvent critical point. The quantity (δp/δx)V,T' which does not show a strong divergence in the critical region, was also determined from experimental data. Two procedures have been employed to describe the latter quantity and the solubility itself. It is shown that a first order perturbation method may be employed to describe the observed behaviour with a cross intermolecular energy parameter, ε12, which, for low densities becomes dependent on the fluid density, but not on the temperature. The PYLJ integral theory is shown to account very well for the data with the value of ε12 obtained employing the Lorentz‐Berthelot combining rule.
Self‐Diffusion of 18F‐Ions in a PPS‐Cation‐Exchange Membrane
Authors: Daniel T. , Seidel W. , Sattler E. L. , Seibold G.
Published: July 2012

Self‐diffusion of 18F ions in a poly‐phenol‐sulphonate (PPS) membrane was investigated by counting continuously the γ,γ‐coincidence emitted from positron annihilation processes. The apparent coefficient of self‐diffusion was determined for different concentrations.
Vapour‐Liquid Equilibria of Square‐Well Fluids of Variable Width by Barker‐Henderson Perturbation Theory I
Authors: Szalai I. , Liszi J.
Published: July 2012

Vapour‐liquid equilibria of square‐well fluids of variable width (λ = 1.375, 1.5, 1.75 and 2.0) were studied based on the Barker‐Henderson perturbation theory. Orthobaric densities, vapour pressures and heats of vaporization were calculated with local and macroscopic compressibility approximation. Comparison of the results with those of McLure and et al. [J. Chem. Phys. 96, 2296 (1992)] obtained with Monte Carlo simulation on Gibbs ensemble showed good agreement, except for results obtained close to the critical temperatures.
Properties and Design Criteria of Second‐order Nonlinear Optical Materials Based on Side Chain Polyesters with an Aromatic Main Chain
Authors: Servay Th. K. , Winkelhahn H.‐J. , Schulze M. , Boeffel C. , Neher D. , Wegner G. , Kalvoda L.
Published: July 2012

Polymers composed of an aromatic polyester backbone to which NLO‐active chromophores and flexible alkyl side chains are attached have been developed as a class of second order nonlinear optical materials.

Thin films suitable to be used as waveguides could be produced by spin coating technique and were investigated for their NLO‐properties. The polymers were investigated by optical microscopy, DSC, X‐ray diffraction, 2H‐NMR, dielectric relaxation spectroscopy and — for their optical properties — by the method of attenuated total reflection of visible light.

The solid state structure is best described by an arrangement of alternating layers of polyester backbones and flexible side chains with good layer correlation, especially for derivatives with long side chains. The low nonlinear optical response of these derivatives seems to be due to dipole pair formation of the chromophores. Polyesters with short side chains show a similar main chain packing but substantially different optical properties. In addition, they could be macroscopically aligned in strong magnetic fields. Anisotropic samples prepared in this way indicated a restricted orientational freedom of the chromophores in the space available between the backbone layers. Consequently the ratio of the second order susceptibilities χ versus χ deviated significantly from the expected isotropic value of three.
Molecular Weight Dependence of the Rotational Diffusion Constant and the Rotational Viscosity of Nematic Side‐Group Polymers
Authors: Götz S. , Stille W. , Strobl G. , Scheuermann H.
Published: July 2012

A combination of dielectric relaxation spectroscopy and measurements of the rotational viscosity by director reorientation experiments was used to study nematic side‐group polymethacrylates with different molecular weight. The contribution γ of the mesogenic groups to the total rotational viscosity γ is estimated on the base of Marrucci's theory from the rotational diffusion constant Dr obtained by relaxation frequency determinations. γ then is used to separate the contribution Δγ1 of the friction due to rearrangements of anisotropic ordered polymer backbones to γ. The molecular weight dependence of Δγ1 can be described by a power law, as predicted by Brochard's theory. The resulting exponent gives evidence for the presence of nonentangled random coil conformations.
Freely‐Suspended and Transferred Freely‐Suspended Films of Polymeric Liquid Crystals
Authors: Decher G. , Reibel J. , Honig M. , Voigt‐Martin I. G. , Dittrich A. , Ringsdorf H. , Poths H. , Zentel R.
Published: July 2012

Freely‐suspended (FS) liquid‐crystal (LC) films of a polymethylsiloxane homo‐ and a copolymer with different mesogenic side groups have been prepared and investigated. For both substances the preparation of the films succeeded only in the isotropic phase but the higher ordered phases were reached after cooling. The films of the homopolymer have only been obtained with thicknesses estimated to be in the pm‐range and with an unusual “Book‐Shelf” orientation of the smectic layers. In contrast, the films of the copolymer were thinner and showed a homeotropic orientation of the mesogens in the smectic A phase. Interestingly, this material exhibited a different layer spacing in film and bulk, although no differences in the phase transition temperatures could be detected within experimental error. FS‐films of the homopolymer have been transferred to solid supports. Both the FS and the transferred freely‐suspended (TFS) films of this material were particularly stable as compared to films of low molecular weight compounds.
Isothermal Switching of Phases in Lyotropic Liquid Crystalline Surfactant Systems via Photoreactions of Solubilized Molecules
Authors: Wolff Thomas , Klaußner Bernhard , Nees Dieter
Published: July 2012

Light induced phase transitions were found in lyotropic liquid crystalline systems of aqueous cetyltrimethyl‐ammonium bromide (CTAB) and of Aerosol‐OT(AOT)/decane/water: the isothermal transitions isotropic → nematic and isotropic → hexagonal in CTAB systems were triggered by the photocyclization of a solubilized naphthyl vinyl ether, the transition isotropic → inverse‐hexagonal in the ternary AOT system was induced by the trans‐cis photoisomerization of a solubilized stilbazolium salt. The transition time (between starting irradiations and detecting anisotropic phases) was found to increase with the difference between irradiation temperature and transition temperature in the non irradiated case; transition times were shorter by two orders of magnitude in the AOT‐system as compared to CTAB. The position of isotropic/liquid crystalline phase borders produced by partial irradiation of layers of aqueous CTAB were more stable in hexagonal as compared to nematic systems.
Chemistry of Colloidal Silver: Reactions of Lead Atoms and Small Lead Aggregates with Agn
Authors: Henglein Arnim , Holzwarth Arnold , Janata Eberhard
Published: July 2012

The reactions of lead atoms with 70 Å colloidal silver particles in aqueous solution are investigated. The lead atoms are generated by a short pulse of high energy radiation. The formation of a lead mantle around the silver particles is recognized by the changes in the shape of the surface plasmon absorption band of the silver particles. At low intensities (low lead atom concentration of 5·10−8 M) almost all the lead atoms generated reach the silver particles before they form larger aggregates by coalescence reactions in the bulk of the solution. The specific rate of the reaction of lead atoms with silver particles is about 5 times smaller than expected from a diffusion controlled rate. The plasmon absorption band is blue‐shifted when the lead atoms react with the silver particles. It is concluded from the details of this shift that the first Pb atoms reaching the silver particles transfer an electron to them, and that the atoms, which arrive later, are just deposited. Time resolved measurements show that small aggregates of lead, which are formed at higher intensities, can still contribute to mantle formation around the silver particles. Lead particles with agglomeration numbers larger than 10 to 20 do no longer contribute to lead deposition; they form colloidal lead.
Information of the Nature of the Transition State of the Addition of Pyrazole to an α,β‐unsaturated Fischer Carbene Complex from a Combined Solvent, Temperature and Pressure Dependence Study
Authors: Pipoh Rolf , Martinez Pablo , Eldik Rudi Van
Published: July 2012

The temperature and pressure dependence of the addition of pyrazole to the carbene complex (CO)5WC[(OC2H5)(C2C6H5)] in a series of solvent mixtures (acetonitrile/toluene) were studied, and the corresponding activation parameters are reported. The solvent dependence data enables the estimation of the radius and dipole moment of the transition state, following different theoretical treatments. The results are in good agreement and demonstrate that the transition state is significantly more polar than the reactant state, and leads to the formation of a zwitter‐ionic intermediate.
Semi‐Empirical Calculations on the Optical Absorption of Methylviologen and p‐Cyanophenylviologen in Different Oxidation States
Authors: Mizuguchi Jin , Karfunkel Heinrich
Published: July 2012

Viologen compounds are known as materials suitable for electrochromic displays based on the electrochemical color change. INDO /S, PM3 and MNDOC calculations have been carried out on methylviologen and p ‐cyanophenylviologen in order to interpret the spectral changes in the visible region upon electrochemical reduction. The viologens investigated are colorless in the dication state, but they exhibit an intense optical absorption band in the visible region due to the formation of monocation radicals upon reduction. Molecular geometries are optimized by the AM1 and PM3 methods for the initial dication state, monocation radical state and fully‐reduced neutral state. Bipyridyl rings in both methylviologen and p ‐cyanophenylviologen are considerably twisted by about 40–50° in the initial state, but these become almost planar in the first‐reduced state and completely planar in the second‐reduced stat e. Optical absorptions are calculated on the basis of the optimized geometry. The results show a satisfactory agreement with experimental values, although the calculated longest‐wavelength absorption in the visible region is overestimated towards longer wavelength s. The planarity of the bipyridyl rings as well as the resulting delocalization of the unpaired electron of the free monocation radical is found to be important to cause the appearance of the optical absorption band in the visible region.
Treatment of Ionic Transport Processes in Electrolytic Conductivity by the Dynamic Frictional Formalism of Nonequilibrium Thermodynamics
Authors: Vink Hans
Published: July 2012

Ionic transport in electrolytic conductivity has been considered in terms of the dynamic frictional formalism of nonequilibrium thermodynamics. The treatment includes multicomponent electrolyte mixtures and solutions containing polyelectrolytes and colloids. It is shown that the dissipation function for the process can be split into two terms characterising interionic friction and ion‐solvent friction, respectively. The corresponding friction coefficients are well‐defined and experimentally determinable. They have been evaluated for a number of binary electrolytes from electrolytic conductivity data found in the literature. For 1:1 electrolytes the reduced interionic friction coefficients vary slightly and in a regular fashion with concentration. For higher valency type electrolytes deviations from this behaviour occur, which in general can be explained by ionic association.
Formation of Nanometer‐Size Silicon Particles in a Laser Induced Plasma in SiH4
Authors: Fojtik A. , Giersig M. , Henglein A.
Published: July 2012

Crystalline silicon particles of cubic structure are formed in the plasma which is initiated in an argon‐silane mixture by a focussed 694 nm Ruby laser flash. Part of the particles can be dissolved as colloid in organic solvents. The solubilization is increased by small amounts of 1,3‐propane‐dithiol. The raw material has a broad size distribution. Centrifugation and filtration methods are applied to obtain samples with narrow size distribution. Small silicon particles have structured absorption spectra. The particles luminesce after etching with HF under air. The larger particles have a red luminescence (peaking at 720 nm) and the smaller particles emit a blue luminesce. The luminescence effects are explained by size quantization of the electronic energy levels in the particles.
Flow Characterization in Particle‐Loaden Coal Burner Systems
Authors: Schnell Uwe
Published: July 2012

In pulverized coal combustion, one of the most important parameters for pollutant formation in the near‐burner zone is the flow and mixing process of fuel and oxygen. To study the near‐field aerodynamics of pulverized coal burners, non‐intrusive optical measurements with Laser Doppler Velocimetry (LDV) were performed. In order to provide a better understanding of the mixing process of the small coal particles with the surrounding combustion air, the unavoidable formation of ropes and the dispersion of the particles was first investigated in an idealized two‐phase flow with glass beads under isothermal conditions.

Furthermore, non‐intrusive measurements of velocity and turbulence intensities in the complex flow situation of radiating pulverized coal flames have been performed using a two component LDV system with a 15 W Argon‐ion laser, operating in backscatter mode. It has been used for flow characterization in a semi‐industrial pulverized coal combustion facility with a maximal thermal load of 500 kW. LDV is an indispensable research instrument to study the interdependencies between fluid flow, combustion reactions and pollutant formation processes in reactive flows. Additionally, results of numerical simulation obtained with a pulverized coal combustion code are validated with the LDV measurements and the experimentally observed phenomena are further explained. The influence of the flow pattern in the near‐burner region on pollutant emission will be discussed.
In Situ Measurements of Concentration and Temperatures. Laser Raman Diagnostics for Propulsion Systems Development
Authors: Eckbreth Alan C , Anderson Torger J. , Shirley John A.
Published: July 2012

Raman‐based laser diagnostics for combustion temperature and major species measurements in propulsion development test facilities are discussed. Focus is primarily directed toward multi‐color, coherent anti‐Stokes Raman spectroscopy (CARS) techniques for simultaneous multiple species capability and ultraviolet spontaneous Raman scattering vis‐a‐vis its utility for hydrocarbon‐fueled combustor testing. Field instruments employed for feasibility demonstrations and measurement programs are described.
Surface Analysis by Laser Ionization
Authors: Schröder H. , Wagner M. , Kaesdorf S. , Kompa K. L.
Published: July 2012

A new reflecting time of flight mass spectrometer is described which allows to display absolute saturation of laser ionization. For each specific chargeq/mthe new TOF instrument creates two ion bunches containing the ions originating respectively inside and outside a sharply‐limited acceptance volume of the spectrometer. Thus quantification of laser ionization is possible. This method has been applied to non‐resonant KrF excimer laser post‐ionization of sputtered metal atoms. It may be developed into a very sensitive tool for quantitative surface analysis.
On‐Line Diagnostics for Industrial Laser Surface Treatments
Authors: Bergmann H. W.
Published: July 2012

The paper presents some recent developments in sensor technology for on‐line diagnostics and control of laser materials processing. The results focus on three topics e.g.

—pyrometric temperature measurements and on‐line output power control of cw‐lasers

— quality control using differential reflectometry

— short time detection techniques for process monitoring of laser beam interaction with materials during short (50 ns) and intense (MW/cm2 to GW/cm2) laser pulses.
Investigations on a Spark‐Ignited Engine Using Two‐Dimensional Laser‐Induced Fluorescence
Authors: Bäuerle B. , Hoffmann F. , Behrendt F. , Warnatz J.
Published: July 2012

The method of laser‐induced fluorescence (LIF) was applied to a modified industrial two‐stroke engine with a single cylinder and spark ignition. Together, the disc‐shaped combustion chamber and the low clearance height of the piston ensure mainly two‐dimensional flame propagation. Formaldehyde is used as a natural tracer species for detecting and studying exothermic centres (so‐called “hot spots”) in the end gas. The latter contain a larger amount of formaldehyde than the enclosing end gas due to the slightly higher temperatures. To obtain two‐dimensional excitation of the formaldehyde a laser light sheet enters from sideways through a ring‐shaped quartz window. The fluorescence is detected via a full‐size top window by means of an ultrashort‐exposure ICCD‐camera, and the frames are stored in a PC. Here, frames are presented which show 2D‐LIF of formaldehyde in non‐knocking as well as in knocking cycles.
An ab initio investigation of structure and energetics of clusters KnCln and LinFn
Authors: Ochsenfeld Christian , Ahlrichs Reinhart
Published: July 2012

Results of a systematic study of clusters KnCln and LinFn up to n = 32 are reported within self‐consistent‐field (SCF), second‐order Møller‐Plesset perturbation theory (MP2), and the single‐ and double‐excitation coupled cluster method with a perturbational estimate of triple excitations CCSD(T). Stationary geometries are characterized as local minima by SCF force field calculations up to K9Cl9 and Li8F8, respectively.

The clusters KnCln show great similarities with previously studied NanCln. The energetically most stable isomers of even the smaller potassium chloride clusters show a clear preference for geometries which are fragments of the solid state lattice. This effect is enhanced by electron correlation.

Lithium fluoride clusters, LinFn, show a different behaviour: hexagonal structures (stacked six‐rings) are prefered to lattice fragments (cubic) on the SCF level at least up to Li18F18. This preference is only slightly reduced by electron correlation.

The present results for KnCln and LinFn allow for an estimate of lattice energies by extrapolation n → ∞, which is in good agreement with, experiment. The structure constants found for K32Cl32 approach that of the solid. This is different for Li32F32: clusters of LiF show a slower convergence towards bulk properties on increasing cluster size.
Oxidative decarboxylation of cyclohexane monocarboxylic acid as a degenerate branching chain reaction. I. kinetics
Authors: Nemes I. , Héberger K. , Keszler Á. , Vasvári G. , Gál D. , Cotarca Livius , Delogu Pietro
Published: July 2012

Kinetics of product accumulation during the oxidative decarboxylation of cyclohexane monocarboxylic acid has been followed by GCMS, inhibitor and chemiluminescence methods. Results indicate that in the degenerate branching chain process selective (peroxy) radicals abstract predominantly tertiary hydrogen atoms from the substrate while non‐selective (e.g. hydroxyl, alkoxy) radicals attack also secondary hydrogen atoms. The rate constant of the chain propagation was found to be kp = 7.5×106exp(‐57.6kJmol−1/RT) 1mol−1 s−1. Furthermore it has been established, that the oxidative decarboxylation proceeds via two parallel pathways: one resulting in cyclohexanone, while the other avoiding the formation of the latter.
Substituent effects on the intramolecular electron exchange reaction in 5‐substituted 1,3‐dinitrobenzene radical anions
Authors: Telo João P. , Shohoji M. Cândida B. L.
Published: July 2012

Nine new radical anions of 1,3‐dinitrobenzenes with various substituents on position 5 (2, 3, 5–7, 9–11 and 13) were prepared by electrochemical reduction in acetonitrile and studied by EPR at temperatures between 240 K and 320 K. Another eight known radicals of the same type were reexamined in the same conditions in order to complete the set of data. Their EPR spectra showed alternating linebroadening effects due to intramolecular electron exchange induced by asymmetric solvation of the two nitro groups. Rate constants at 293 K range from 1.4×109s−1 (3,5‐dinitrophenolate) to 1.2×1010s−1 (3,5‐dinitrobenzonitrile). Good Hammett correlations between the rate constants of intramolecular electron exchange and the parameter σm of the substituent on position 5 were obtained. The reaction is accelerated by electron withdrawing groups. ρ values range from 0.95 at 240 K to 0.74 at 320 K. Activation parameters were estimated by using the Rips and Jortner equation for the rate constant of a uniform adiabatic reaction. ΔG* was found to increase with the electron donating ability of the substituent, mainly due to an increase of the interaction between the reactants and the solvent. The pre‐exponential factor A is constant within the experimental error, as predicted by theory.
High‐pressure differential thermal analysis of lamellar to lamellar and lamellar to non‐lamellar lipid phase transitions
Authors: Landwehr A. , Winter R.
Published: July 2012

Hydrated phospholipids, which provide model systems for lipid membranes, display a variety of polymorphic phases, depending on their molecular structure and environmental conditions. In this study, high hydrostatic pressure has been used as a physical parameter to study the thermodynamic properties and phase behaviour of phospholipid systems, and because high pressure is a characteristic feature of certain natural membrane environments. We built a new high‐pressure differential thermal analysis (DTA) apparatus, which allowed us to study the calorimetric properties and the temperature and pressure dependent phase behaviour of lipid systems up to temperatures of 360 K and pressures of 250 MPa. In particular, we focussed on the effect of pressure on lamellar to lamellar and on lamellar to non‐lamellar phase transitions of phospholipid systems, differing in lipid chain saturation and headgroup structure. The possible biophysical implications of this study are discussed.
Zero length column chromatography to characterise microporous sorbents by means of kinetic data
Authors: Micke A. , Bülow M. , Kočiřik M.
Published: July 2012

Alternative methods for simulation of ZLC chromatography behaviour are presented. The phenomena of accumulation in the fluid phase, non‐linearity of the adsorption isotherm and inlet concentration disturbance are analysed. Models for pure diffusion and barrier limited sorption kinetics for the ZLC chromatography are compared. In addition the asymptotic behaviour of the model solutions for small times is examined.
Conformational order of amphiphilic chain molecules in lyotropic liquid‐crystalline phases
Authors: Schnepp Werner , Schmidt Claudia
Published: July 2012

The nonionic surfactant hexa(ethyleneglycol) n‐dodecyl methylether in aqueous liquid‐crystalline phases is studied by deuterium NMR Spectroscopy. From the quadrupole splittings of the surfactant, which is deuterated either in the hydrophobic alkyl chain or in the hydrophilic oxyethylene chain, order profiles of both the alkyl and oxyethylene moiety are obtained. Characteristic features of the order profiles are related to the conformations of the surfactant molecules. The observed temperature dependence of the quadrupole splittings is explained by changes of the conformational equilibrium.
Comparison between IR‐emission spectra of CaO ‐ Al2O3‐melts (1873 K) and IR‐absorption spectra (293 K)
Authors: Mausbach Klaus , Nowack Norbert , Schlegelmilch Franz
Published: July 2012

The IR‐emission of CaO ‐ Al2O3‐melts (1873 K) is caused by IR‐active molecular vibrations of AlO‐ and AlO‐complexes. In the CaO ‐ Al2O3‐melts the equilibrium AlO + O2‐ ⟺ AlO dominates. At lower temperatures (1000°C) the formation of condensed AlO‐complexes was observed (solid phases).
Two‐dimensional phase transitions in electrochemically formed adlayers on gold
Authors: Hölzle M. H. , Kolb D. M.
Published: July 2012

Two‐dimensional phase transitions occurring during electrodeposition of the first Cu monolayer onto Au(111) at underpotentials or during adsorption of coumarin from solution at Au(111) and the reconstructed Au(100)‐ (hex) electrodes have been studied by cyclic voltammetry and potential step experiments. Rising current transients were observed for both systems, indicating the presence of nucleation‐and‐growth phenomena during monolayer formation. However, phase transitions in the adlayers were observed only for the densely packed gold surfaces, and not for the more open surfaces of Au(100)‐(1×1) or Au(110). A comparison between experiment and classical model transients revealed that surface imperfections may have to be taken into account when working with solid electrodes, rather than with mercury for which these models have been derived.
Prewetting of helium on weak binding substrates
Authors: Taborek P. , Rutledge J. E.
Published: July 2012

Recent theoretical and experimental work has shown that alkali metal surfaces have extremely weak potentials for physical adsorption, which leads to very unusual thermodynamic properties of adsorbed films. We have used a microbalance adsorption isotherm technique to investigate the phase diagram of He films on cesium. This experimental system has provided the first example of a surface which is not wet by superfluid helium, and the first experimental observation of the prewetting line. Near the wetting temperature Tw ≈ 2 K, we have observed large hysteresis effects associated with the nucleation of the thin phase. At higher temperatures, the prewetting line terminates at a prewetting critical point T ≈ 2.5 K. This system is particularly well suited to surface phase transition studies, since the interaction parameters can be tuned continuously by varying the thickness of the cesium substrate, or by doping the film with 3He.
Spinodal decomposition in thin polymer films
Authors: Krausch Georg , Dai Chi‐An , Kramer Edward J. , Bates Frank S.
Published: July 2012

We have studied the influence of the boundary surfaces on spinodal decomposition in thin films of a critical polymer mixture. The wetting layer formed during spinodal decomposition is found to grow as t1/3 and the corresponding composition vs. depth profiles exhibit dynamic scaling behavior. For sufficiently thin films, the effects of the two boundary surfaces interfere and the overall domain structure is found to be strongly thickness dependent.
Universal order‐parameter profiles for critical adsorption and the extraordinary transition: A comparison of ϵ expansion and Monte Carlo results
Authors: Smock M. , Diehl H. W. , Landau D. P.
Published: July 2012

The universal, scaled order parameter profiles P± (z/ξ) for critical adsorption of a fluid or fluid mixture onto a wall or interface, and for the extraordinary transition of the semi‐infinite Ising model, are discussed theoretically, where z is the distance from the interface, ξ(T) is the bulk correlation length, and the subscript + (‐) refers to the approach from above (below) Tc. Recent results to first order in the ϵ = 4–d expansion are extrapolated to d = 3 space dimensions and compared with new Monte Carlo results. In order to obtain meaningful extrapolations it is crucial that both the exponential decay at large ζ as well as the known algebraic behavior P±(ζ)∼ζ−β/v small ζ be correctly reproduced. To this end a recently developed novel RG scheme involving a z dependent amplitude renormalization is used. Reasonable agreement of our extrapolations with the Monte Carlo results and some experimental results is obtained.
Primary products of the elementary reactions of CH2CO with F, Cl, and OH in the gas phase
Authors: Grußdorf J. , Nolte J. , Temps F. , Wagner H. Gg.
Published: July 2012

The absolute yields of the primary products of the reactions of CH2OH with F and Cl atoms and OH radicals were measured in the gas phase at room temperature using a discharge flow apparatus connected to a Far Infrared Laser Magnetic Resonance (FIR‐LMR) spectrometer. Quantitative determinations of the reaction pathways were carried out by employing reference reactions with known product yields. The measurements yielded the branching ratios for the following channels

magnified image

Thus, the main reaction channels were found to be addition of the F, Cl, or OH, respectively, to the CH2 moiety followed by elimination of CO.
Electronic transitions of salicylaldehydeethylenediimine and its Cu(II) complexes
Authors: Hoshi Toshihiko , Inomaki Yoshihiro , Wada Mikiko , Yamada Yasunori , Okubo Jun , Kobayashi Michio , Inoue† Hiroyasu
Published: July 2012

Electronic absorption spectra of Salicylaldehydeethylenediimine (salen) and its Cu(II) complexes have been measured in various media at various temperatures. It is found that salen takes an enol‐imine‐type structure in cyclohexane and exists as an equilibrium mixture of enol‐imine and keto‐amine type species in alcoholic media. The polarization spectrum of salen‐Cu(II) measured in the stretched PVA film shows that 282, ∼ 290, ∼ 250, and 230.4 nm bands are polarized along the longer‐molecular‐axis, and 354, 273.0, 242.4 and ∼ 220 nm bands along the shorter‐molecular‐axis. The 242.4 and ∼ 250 nm bands can be assigned to intramolecular charge transfer (CT) transitions between the metal ion and ligand and between the two π‐electronic systems of the ligand, respectively. The complex of salen‐Cu(II) forms a dimer in EPA (ether: isopentane: ethanol = 5:5:2 in volume) at low temperatures. The first two bands of the monomer at 380 and 362 nm are blue‐shifted by the dimer formation, and appear at 370 and 351 nm, respectively, and the 278 nm monomer band splits into two bands at 275 and 267 nm. These spectral changes on the dimer formation are well reproduced by an extended PPP calculation.
Near‐infrared spectroscopic investigations on phase behaviour and hydrogen‐bonding of polar substances in supercritical chlorotrifluoromethane. Part I — phase behaviour
Authors: Ochel Henning , Schneider Gerhard M.
Published: July 2012

The phase behaviour of fluid mixtures of polar substances in supercritical chlorotrifluoromethane CClF3 was investigated at pressures up to 100 MPa and temperatures from 323 K to 398 K. The measurements were performed by high pressure near‐infrared spectroscopy using the analytical method. An optical high pressure cell equipped with sapphire windows and fibre optics was used. The total substance concentration was obtained from the first overtone region of C‐H stretching vibration (1600–1800nm), as well as from the second overtone region (1150–1300 nm) and its combination with other vibrational molecular modes (2100–2350 nm). Solubilities of dodecanoic acid, hexadecanoic acid, their corresponding methyl esters, δ‐valerolactam and δ‐caprolactam in the supercritical gas are presented. The influence of molecular properties on the phase behaviour is discussed.
Polymer bridging forces between a colloidal sphere and a flat plate
Authors: Biggs Simon
Published: July 2012

The forces of interaction between a single colloid particle and a flat plate in a dilute solution of a high molecular weight polymer have been measured. Under conditions of low polymer surface coverage the observed forces of interaction are explained by bridging of the polymer between the sphere and the plate.
Magnetic relaxation and molecular motions in liquid 3,5‐dimethylpyridine
Authors: Suchański W. , Kempka M. , Peplińska B. , Pająk Z.
Published: July 2012

The nuclear spin‐lattice relaxation times of 14N have been measured as a function of temperature for liquid 3,5‐dimethylpyridine. These results together with the values of the 13C spin‐lattice relaxation times and the factor of nuclear Overhauser enhancement for the ring C2,6 and C4 carbons presented previously [15], have been analyzed in terms of relative influence of molecular shape and attractive dipolar forces on anisotropy of the molecular reorientations. Principal components of the rotational diffusion tensor have been determined.
Molecular dynamics study of the dielectric constant of water under high pressure and temperature conditions
Authors: Wasserman Evgeny , Wood Bernard , Brodholt John
Published: July 2012

The static dielectric constant of a water model (extended simple point charges, SPC/E) was evaluated by molecular dynamics simulations in the (N, V, E) ensemble for temperatures ranging from T = 324 K to 1278 K and densities from 0.257 g/cm3 to 1.1108 g/cm3. The dielectric constants calculated from fluctuations of the total dipole moment of the simulation box in the absence of an external field, and those obtained from the polarization response to an applied field were demonstrated to be consistent. Simulations within the pressure‐temperature range (up to 500 MPa and 823 K) of available experimental data yield dielectric constant in very good agreement with experiment. It appears therefore that the SPC/E potential model can be used for the simulation of the dielectric properties of supercritical water and of aqueous solutions under supercritical conditions.
Precise viscosity measurements of binary liquid mixtures of acetonitrile‐water and 1,3‐dimethyl‐2‐imidazolidinone‐water
Authors: Wode H. , Seidel W.
Published: July 2012

Viscosities of binary aqueous mixtures of Acetonitrile (AN) and 1,3‐Dimethyl‐2‐imidazolidinone (Dimethylethyleneurea, DMEU) have been measured at atmospheric pressure and temperatures of 20, 25, 30, 35 and 40°C over the entire concentration region by means of Ubbelohde capillary viscometers, type 0c. For a set of 6 viscometers kinetic energy correction functions (Hagenbach‐Couette correction) have been experimentally determined for each viscometer using tridistilled water and commercially available liquids. Further corrections accounted for buoyancy and surface tension. Viscosity measurements were carried out with at least three, usually 5 to 6 viscometers, giving viscosities with an estimated uncertainty of 0.3%. Hydrodynamic volumes were determined from relative viscosity vs. concentration curves by means of the viscosity‐B‐coefficient and compared to van der Waals volumes calculated using increments for functional groups from the literature. Our data indicate the formation of associated species of DMEU and water.
Free radicals of isatoic anhydride and its derivatives as studied by in situ electrochemical‐ESR‐technique
Authors: Petr A. , Dunsch L. , Neudeck A. , Oesterreich Nadja , Mann M. , Domschke G.
Published: July 2012

The electrochemical reduction of isatoic anhydride and its derivatives was studied by simultaneous electrochemical and ESR‐measurements. For the first time 9 new radicals were characterized by its formal redox potentials, hyperfine coupling constants, g‐factors and lifetimes. The advantage of measuring the kinetic data in stagnant and renewed electrolyte combined with accumulation of the ESR‐spectra is demonstrated in the case of shortlived radicals. It is shown that the electrochemical reduction of isatoic structures follows a self protonation mechanism.
Electrolytic conductivity of mixed electrolyte solutions
Authors: Vink Hans
Published: July 2012

Electrolytic conductivity of mixed electrolyte solutions has been studied theoretically and experimentally on the basis of recent phenomenological theories of conductivity. For 1:1 electrolytes a generalised mixture rule is deduced, applicable to mixtures of any number of ionic species. For mixtures of dissimilar electrolytes the simple mixture rule does not apply. However, for mixtures of 1:1 electrolytes with electrolytes of other charge type (2:2, 2:1 electrolytes), when the 1:1 electrolyte is present in marginal quantities, a modified additivity rule is established. In this case the 1:1 electrolyte can be used to probe the properties of the dominant electrolyte in the solution.
capillary wave study of linear and branched polysiloxanes at the air/water interface
Authors: Runge F. E. , Yu H. , Woermann D.
Published: July 2012

The surface properties of two commercially available polysiloxanes, AK 1000 and AV 1000, have been examined at the air/water (A/W) interface in terms of the surface quasi‐elastic light scattering technique (SLS) in conjunction with surface pressure‐area (II–A) isotherm studies. Both are found to form stable, insoluble and promptly equilibrating monolayers at A/W. Being a mixture of linear poly(dimethylsiloxanes) (PDMS), AK 1000 is shown to follow the well established surface properties of PDMS. On the other hand, AV 1000, a mixture of linear and phenylsiloxane‐branched PDMS, referred to as PPMS, shows a different isotherm. The profiles of the surface dynamic viscoelastic parameters deduced from SLS, i.e., the surface dilational elasticity, ϵd, and the corresponding viscosity, K, relative to the surface mass density, γ, are rather different. The magnitudes of ϵd and K for both monolayers are comparable, while small but distinct differences are observed. In particular, in the high surface mass density region, the dynamic surface viscosity of PPMS films is about twice that of PDMS, but all values are still in the regime of very small viscosities (K< 5×10−8 kg/s). These findings are discussed in the context of the differences found in thermocapillary experiments between the two polymers.