bluuebunny/crossref_metadata_2025 huggingface dataset:
Reaction Mechanism of the Iron(III)‐Catalyzed Autoxidation of Bisulfite in Aqueous Solution: Steady State Description for Benzene as Radical Scavenger
Authors: Warneck Peter , Ziajka Josef
Published: July 2012

The Fe(III)‐catalyzed oxidation of bisulfite in aqueous solution was studied at pH = 3 in the presence of benzene by monitoring the rise of hydrogen ion activity and phenol product concentration as a function of time, keeping [HS03−/[Fetot]>>l. After a brief initial period, during which product concentrations rose rapidly and Fe(III) was largely converted toward Fe(II), the reaction underwent a period of slower growth characterized by a quasistationary state and nearly constant [Fe(II)]/[Fe(III)] ratio until toward the end of the reaction, when most of the S(IV) was consumed, Fe(II) was reoxidized toward Fe(III). In two sets of experiments either the concentration of benzene or that of [Fe(III)]o was varied in ranges of 0.3–2.2 mmol dm−3 and 8.5–51 μmol dm−3, respectively, while keeping the other parameters constant ([HSO3−]o = 2 mmol dm−3). The data were analyzed by means of a steady state expression developed for the time period of nearly constant [Fe(II)]/[Fe(III)] ratio on the basis of a radical‐driven chain oxidation mechanism presented previously. The data display the behavior predicted by the steady state equation; this allowed the determination of ratios of rate coefficients for reaction pairs: SO4− reacting with HSO3− and benzene, k11/k12 = 0.31±0.04; S05− reacting with Fe2+ and HSO3−, k3/k10 = 54.1±1.7; HSO5− reacting with Fe2+ and HSO3−, k4/k16 = 2.2±0.2; and the branching ratio for the reaction of SO5− with HSO3− leading to (a) SO3− and (b) SO4− radicals, k10b/k10≤0.04. The experimental results largely support the proposed reaction mechanism.
Transport of Mass and Moving Phase Boundaries Observed by Neutron Transmission through Compacted Zeolite NaX
Authors: Stockmeyer Rolf , Strothmann Helmut
Published: July 2012

The density C(x, t) of adsorbates (water, cyclohexane) at moving liquid/gas boundaries in samples of compacted zeolite NaX has been observed by neutron transmission experiments with a resolution dx = 0.2 cm, dt = 30 s, over a distance of 20 cm and during a time of observation up to 400 hours. The front of humidity migrates, driven by capillary forces, from the wet to the dry side of the sample with an initial velocity of about 10−6 ms−1. In terms of a capillary model the absorbate moves with a pseudo‐diffusion‐coefficient in the order of 10−7 m2s−1. The velocity slows down to 10−7 m s−1 if the amount of adsorbate is limited. A slow process of redistribution of the fluid takes place which does not smoothen the profile of the density of mobile molecules at the liquid/gas boundary in the porous solid, as one would expect in the case of diffusive motions of molecules at gradients in a homogeneous phase of an adsorbate. The step of density observed at the moving liquid/gas boundary is formed according to a dispersion/diffusion coefficient D(C) of about 10−9 m2s−1.
Diffusion of the Trimethyl‐Cyclohexadienyl Radical Adsorbed on Silica: Redfield Theory and Results of μSR Experiments
Authors: Schwager Martina , Dilger Herbert , Roduner Emil , Reid Ivan D.
Published: July 2012

The 2,4,6‐trimethyl cyclohexadienyl radical adsorbed on a fully hydroxylated silica surface was investigated using the time‐differential and time‐integrated muon spin resonance techniques near avoided crossings of magnetic energy levels in high longitudinal magnetic fields. Information about surface diffusion is obtained from the relaxation resulting from the partial averaging of the hyperfine anisotropy when the adsorbed species diffuses over the surface of a sphere. A Redfield formalism is developed to analyse the stochastic motion in terms of diffusion coefficients. The results agree with those of a stochastic Liouville approach reported previously. Diffusion of the trimethyl‐substituted radical is described by the same Arrhenius frequency factor but a considerably higher activation energy than that of the unsubstituted analogue.
Nuclear Magnetic Resonance Investigation of Intramolecular Motions in Methylpyranosides
Authors: Latanowicz L. , Reynhardt E. C. , Utrecht R. , Medycki W.
Published: July 2012

Proton spin‐lattice relaxation times T1 and T1 as well as the proton second moment have been measured for polycrystalline methyl α‐D‐glucoside, methyl β‐D‐glucoside and methyl β‐D‐galactoside over a wide temperature range. Analyses of the experimental data have yielded information about intramolecular reorientations in the solid state. C3 reorientations of methyl groups take place in all the samples. Potential energy calculations have shown that the CH2OH group can execute trans‐gauche jumps between two potential minima separated by 120. Analyses of the T1 and second moment data have confirmed the presence of this conformational motion. A weak relaxation mechanism, related to the dynamics of an OH group, has been revealed in methyl β‐D‐galactoside.
Investigation of Double Layer Structure at Platinum in Acid Electrolytes by Modulated IR‐Spectroscopy
Authors: Probst J. , Thull R.
Published: July 2012

The electrochemically modulated infrared spectroscopy (EMIRS) is a highly sensitive in‐situ technique to obtain vibrational spectra of species adsorbed on metal electrodes. The contribution discusses the influence of several experimental parameters as the electrode potential, the frequency and amplitude of the superposed potential modulation and the pH value of the electrolyte on the spectra of water molecules within the Helmholtz Double Layer at a platinum surface. The spectra contain significant information about conformational changes of water molecules, which are coadsorbed by atomic hydrogen on the platinum surface. The comparison of experimental results to those of theoretical calculations with Lagrange formalism indicates that, modulating the potential of a positively charged electrode, a complex molecule structure is varied at the surface.
Charakterisierung von elektrokatalytisch hergestellten Folien und Schichten aus Silizium
Authors: Dürrler Michael , Grüniger Hans Rudolf , Rys Paul , Kiess Helmut , Rehwald Walther
Published: July 2012

Silicon foils, prepared by electrocatalysis, consist of microcrystalline, porous silicon. The size of the crystallites ranges between 15 and 20 nm, whereas the average pore size is about 60 nm. The density of this material is 65% of that of crystalline silicon. It is p‐type and could be made n‐type by neutron activation.

Electrical and optical measurements indicate that the charge carrier mobility is limited by the grain boundaries. The grain boundaries give, in addition, rise to strong recombination of charge carriers. The luminescence of the material was investigated in a few experiments, and attempts were made to fabricate solar cells from electrocatalytically produced silicon foils with the pn‐junctions prepared by neutron activation. The luminescence showed a peak at about 570 nm. The open circuit voltages obtained with solar cells were in the range between 120 and 200 mV. Further experiments to increase the intensity of the luminescence and to improve the quality of the cells could not be made within the framework of this project. It is, however, expected that further experimentation leads to a better understanding of the properties of the material and to applications.
Catalysis by Manganese Oxide Monolayers Part 1: Alumina and Magnesia Supports
Authors: Ma J. , Chuah G. K. , Jaenicke S. , Gopalakrishnan R. , Tan K. L.
Published: July 2012

Manganese oxide deposited on alumina and magnesia by different preparation methods has been studied with respect to its surface structure and reactivity. The controlled deposition of mono‐atomic layers is effected by a grafting reaction between surface hydroxyl groups and manganese ethoxide. Repeated grafting allows multiple layers to be built up in a controlled manner. The properties of these catalysts differ from those prepared by conventional wet impregnation techniques and mechanical mixing. Test reactions involving carbon monoxide oxidation and isopropanol decomposition reveal significant differences in the activity and selectivity of the catalysts prepared by grafting, impregnation and mechanical mixing. The manganese oxide grafted to alumina shows bulk‐like properties after a full monolayer is built up. XPS studies show that the grafting reaction leads to continuous films of the manganate covering the entire surface with monolayer thickness, whereas impregnation most likely results in small crystallites which cover only part of the surface. The calcination temperature is an important parameter determining the oxidation state of the manganese and the crystallinity of the oxide. Ammonia and isopropanol temperature‐programmed desorption indicates that the acid/base and redox properties of the catalysts are considerably modified by a strong interaction between the support and the overlayer.
Application of the Transient Grating Method to the Measurement of Transport Properties for High Pressure Fluids
Authors: Kimura Y. , Kanda D. , Terazima M. , Hirota N.
Published: July 2012

We have applied the transient grating method to the measurement of the transport properties for high pressure fluids, such as carbon dioxide and trifluoromethane from the gaseous‐ to the liquid‐density regions for the first time. Using nitrobenzene and methyl red as probe moolecules, we have made the transient grating in a high pressure fluid by a nanosecond‐pulsed laser. By the analysis of the time profile of the transient grating signal in sub‐microsecond to sub‐millisecond range, we have succeeded in measuring the density and the temperature dependences of various transport properties such as the thermal diffusion constant, the sound velocity, the sound absorption, and the mass diffusion constant under the same experimental condition. The thermal diffusion constant of our measurement is identical with 4% error to the value reported in literature, irrespective of probe molecules. We have determined the sound velocity within 0.5% error in a high frequency region around hundreds of MHz. The mass diffusion constant of methyl red is determined within 5% error in trifluoromethane at high densities. We have also demonstrated that the thermal diffusion obeys the critical exponent near the critical point.
Calculation of the Static Dielectric Constant of Multipolar Mixtures by Perturbation Theory. An Application to Supercritical Water‐Benzene Mixtures
Authors: Goldman Saul , Joslin Chris
Published: July 2012

Second‐order perturbation theory for the molecular pair correlation function, together with a y‐expansion of the static dielectric constant (ϵ) is used to predict and interpret ϵ for supercritical benzene‐water mixtures. Our predictions are compared directly with experimental results. We find that this approach, which was previously found successful provided y<3 for neat multipolar fluids, is also successful here in predicting the excess mixture dielectric constant, λϵ. The results are quantitative to semi‐quantitative in accuracy depending slightly on the model chosen and the composition of the mixture. No adjustable parameters were used. We interpret our results in terms of underlying molecular clusters, and make a comparison with the predictions of another (non‐molecular) theory.
Magnetic Relaxation and Anisotropic Molecular Reorientation of Liquid 3‐Acetylpyridine
Authors: Suchański W. , Peplińska B. , Kempka M.
Published: July 2012

The nuclear spin‐lattice relaxation times of 13C and 4N as well as the nuclear Overhauser enhancement factor have been measured as a function of temperature for liquid 3‐acetylpyridine. Principal components of the rotational diffusion tensor have been determined. The results are discussed in terms of relative influence of molecular shape and attractive dipolar forces on anisotropy of the molecular reorientations.
Adsorption of Anionic and Cationic Dyes in Dilute Solutions onto a SnO2 Surface Measured by Total Internal Reflection Fluorescence
Authors: Nakashima Tetsuto , Fujishima Akira
Published: July 2012

Total internal reflection fluorescence (TIRF) technique was used in measuring the adsoption of anionic and cationic dyes on the interfaces between SnO2 and the dye solutions. The fluorescence intensities of an anionic dye and a cationic dye from their very dilute solutions to an SnO2 surface were measured as functions of time and pH. The site distributions on the SnO2 surface were estimated from the fluorescence intensities. The fluorescence intensity was also measured as a function of the dye concentration. The ratio of the fluorescence attributable to the solution layer to the fluorescence attributable to the adsorbed dyes on the SnO2 surface was determined. The effects of the supporting electrolytes on the measurement results were examined. The specific adsorption of the supporting electrolytes on the interfaces of SnO2 and the dye solutions were studied and directly measured to be in the order of IO3− > Br− > Cl− > I− > ClO4−.
An Optical In‐Situ Study of the Re‐Oxidation Kinetics of Calcia‐Stabilized Zirconia
Authors: He T. , Becker K. D. , Tannhauser D. S.
Published: July 2012

The re‐oxidation kinetics of strongly reduced single crystals of calcia‐stabilized zirconia (black CSZ) have been investigated by an optical in‐situ method at temperatures between 335 and 520°C. The kinetics obey a parabolic rate law. From the analysis of the optical results it follows that the parabolic rate constant, kp, is controlled by the ionic conductivity of the oxygen ions. The temperature dependence of kp can be represented by an Arrhenius‐type equation with an activation energy of 1.05 eV. The nature of the defect center associated with black CSZ is discussed in connection with its oscillator strength.
The Electric Conductivity of Liquid Cesium to High Temperatures
Authors: Keller E. , Franck E. U.
Published: July 2012

An apparatus is used with a thin walled stainless steel cell and a fourpole potentiometric arrangement to perform precise measurements of the electric conductivity s̀ of liquid cesium to high temperatures at equilibrium vapour pressure. Results are given from 200 to 800°C. A five‐parameter equation for use from the melting temperature of 28.4°C to 1200°C is presented. Conductivity values of 17705 and 6435 ohm−1 cm−1 were obtained for 200 and 800°C, respectively. The relative expected error is given in dependence of temperature. A typical value is 0.34%. All data are well within the range of validity of the near‐free‐electron, NFE, model for metallic conductance.
Small Angle Neutron Scattering Experiments with Aqueous Solutions of the Nonionic Surfactant C12E5 with Critical and Noncritical Composition
Authors: Lesemann M. , Belkoura L. , Woermann D.
Published: July 2012

Results of small angle neutron scattering experiments with four solutions of the nonionic surfactant C12E5 in D2O with critical and noncritical compositions in the vicinity of the lower critical point are reported (1.11·10−4 ≤x ≤ 2.042·10−3; x, mole fraction of C12E5; xc = 5.74·10−4, critical mole fraction). They were obtained at temperatures away from the liquid/liquid coexistence curve. The observed angular dependence of scattered neutron intensity is assumed to be caused by micelles formed by surfactant molecules. Two characteristic lengths Ξ1 and Ξ2 are calculated from the scattering profiles. Ξ1 has a value of the order of 10 nm. It is attributed to the extension of noncritical concentration fluctuations. Ξ2 has a value of the order of 1 nm and is attributed to the core of micelles. At constant temperature Ξ1 decreases with increasing surfactant concentration, whereas at constant surfactant concentration it increases with increasing temperature weakly (compared with the divergence of the correlation length of local composition fluctuations approaching Tc). ‐ A combination of light scattering and small angle neutron scattering data obtained with the system C12E5/water gives support to the assumption that in the vicinity of the lower critical point a continuous change will take place from a comparatively weak temperature dependence of the length characterizing the structure of the liquid to a strong temperature dependence of the correlation length of the critical concentration fluctuations.
Aqueous Two‐Phase Systems of Poly(ethylene glycol) and Di‐Potassium Hydrogen Phosphate with and without partitioning Biomolecules – Experimental Results and Modeling of Thermodynamic Properties
Authors: Großmann C. , Tintinger R. , Zhu J. , Maurer G.
Published: July 2012

Experimental results for thermodynamic properties of aqueous two‐phase systems of poly(ethylene glycol) and di‐potassium hydrogen phosphate with and without partitioning biomolecules (glycine, phenylalanine and lysozyme) are reported for temperatures between 277 and 333 K. The results are used to develop a semiempirical group‐contribution expression for the excess Gibbs energy of dilute aqueous solutions containing polymeric as well as ionic solutes. The model is applied to correlate some of the new experimental data, while other experimental results are used to test its ability for predicting the electrical potential difference between the coexisting phases, the partition coefficient of lysozyme and the influence of polymer molecular weight on the phase behaviour of aqueous two‐phase systems – a field where most previously known methods are often inadequate.
Computation of the Diffusion Coefficients in Aqueous Electrolyte Solutions from Onsager‐Fuoss and Pikal Theories
Authors: Lobo V. M. M. , Ribeiro A. C. F. , Andrade S. G. C. S.
Published: July 2012

A comparison of experimental diffusion coefficients in aqueous solutions of electrolytes with those calculated by Onsager‐Fuoss and Pikal theories is presented. The influence of the ion size parameter a, “distance of closest approach” of ions, on the variation of diffusion coefficients with concentration is discussed.
The Excess Molar Gibbs Energy of Nuclidic Liquid Mixtures
Authors: Calado J. C. G. , Deiters U. K. , Lopes J. N. C. , Rebelo L. P. N.
Published: July 2012

The calculation of GmE from VLE measurements has been extended to multicomponent systems including those where chemical reactions can occur. For nuclide mixtures, the methods have to be adapted in order to take into account the similarity of the mixture's components and the pseudo‐multicomponent characteristics of a system with isotopic exchange. Bigeleisen's theory of isotope effects can then be used to calculate self‐exchange equilibrium constants in the liquid phase at low temperatures and the vapour pressure of partially substituted nuclides. The formalism is applied to some relevant cases, namely those of water and ammonia.
Dynamic Light Scattering Experiments with Aqueous Solutions of Polyelectrolytes of Low Charge Density Along the Polymer Chain in the Presence of Salt
Authors: Topp A. , Belkoura L. , Woermann D.
Published: July 2012

Dynamic light scattering experiments are carried out with aqueous solutions of poly(2‐vinylpyridine) quarternized to small extents with ethyl bromide and dissolved in an aqueous solution of KBr (molar mass, Mw = 3.14·105 g mol−1; Mw/Mn = 2.24; degree of quarternization, αe; 0.079 ≤ αe ≤ 0.461; electrolyte concentration, cs = 1·10−2 c+, c+ = 1 mol dm−3). Apparent diffusion coefficients Dapp(αe,c̄p) are calculated from the data (c̄p, polymer concentration (g dm−3)). They are plotted as a function of the reduced composition variable Λ= αecp*/cs (cp*, molar volume concentration of the repeat unit of the polymer backbone). For Λ <<1 one apparent diffusion coefficient is observed. In the range Λ ≈︁1 the value of the apparent diffusion coefficient increases with increasing values of (αecp*) and a slow diffusive mode gradually appears. For Λ >>1 a fast and a slow diffusive process is found. In the literature such a behaviour has been reported for solutions of highly charged polyelectrolytes.
Contribution to the Interpretation of the Multistep Cathodic Reduction of Oxygen at the Pt/Zirconia Base Electrolyte Interface at High Temperature
Authors: Barbi G. B.
Published: July 2012

The multistep cathodic reduction at high temperature of the oxygen molecule at the porous platinum/yttria stabilized zirconia solid electrolyte interface has been critically analyzed. Steady state polarization experiments showed that for very thin and very porous layers and oxygen mixtures containing 1% or more oxygen the rate of the overall process is apparently governed by the electrode/electrolyte interfacial diffusion of neutral and/or single ionized atoms. This process is probably fed by the formation of single ionized oxygen molecules at the electrolyte surface, particularly in the neighbours of the electrode/electrolyte/gas phase triple phase boundary. At lower oxygen partial pressures and/or for thicker and less porous metal layers the control is probably transferred to the interpores molecular diffusion. The adsorption of oxygen onto the metal surface, as a step for feeding the transport of reducible species to the triple phase boundary, looks hardly consistent with the evident increase of the overall reaction rate with temperature. The role of platinum, however, can not be confined as a pure electron supply. In fact, at very negative overvoltages it enters the process of morphological expansion of the triple phase boundary zone and likely affects the activity of the electrolyte in the primary process of oxygen ionosorption.
Study of the Influence of Ionic Strength on the Ionic Product of Water in Saline Media at 25°C Using the Pitzer Equations
Authors: Brandariz Isabel , Fiol Sarah , De Vicente Manuel Sastre
Published: July 2012

We studied the influence of ionic strength on the stoichiometric equilibrium ionization constant of water in KNO3 at 25°C by applying the Pitzer equations to the activity coefficients for the species in equilibrium. Reported values for NaCl and KCl media are also analysed.
Mechanism of Extraction of Trivalent Europium from Perchlorate Medium by a Chloroform Mixture of Thenoyltrifluoroacetone and 18C6
Authors: Shehata F. A. , Daoud J. A. , Aly H. F.
Published: July 2012

The extraction of Eu(III) from perchlorate medium by a chloroform solution of thenoyltrifluoroacetone (HTTA) and 18‐crown‐6 (18C6) was kinetically studied. The effect of the extractants concentration, interfacial surface area as well as other parameters affecting the rate of extraction was separately investigated. The effect of temperature was also studied and the thermodynamic functions were calculated. A mechanism of extraction of Eu(III) was proposed to account for the experimental results.
Electronic Transitions in Metallocenes by Resonance Raman Scattering. II.*) The Low‐Energy Visible Spectrum of Nickelocene
Authors: Sassi Paola , Ceccarani Maria Letizia , Cataliotti Rosario Sergio
Published: July 2012

The resonance Raman spectra of nickelocene, dissolved in benzene and cyclohexane solutions, have been studied in the excitation range 15000–19000 wavenumbers. Excitation profiles and depolarization dispersion curves have been obtained for two totally‐symmetric motions, corresponding to the Ni‐Cp stretching and the ring‐breathing vibrations.

The experimental data have been interpreted in terms of resonating processes of the Franck‐Condon type, and opportune fitting of the experimental excitation profiles and depolarization data has been done, in the framework of this approach, by numerical calculations. The results of our modelling show that the interpretation of the low‐energy electronic absorption spectrum of nickelocene is slightly different from that of the ferrocene molecule, previously studied in our laboratory.
Monte Carlo Simulation of the Rotator Phase of Cyclohexane
Authors: Würflinger A.
Published: July 2012

The reorientational behaviour of cyclohexane molecules in the rotator phase has been investigated with a Monte Carlo simulation on a system of 108 molecules in a cubic box with periodic boundary conditions. Different starting configurations have been tested, including also a special model where the molecules are aligned parallelly to the four cubic threefold axes. This model is characterized by a low potential energy. The discrete molecular orientations of this model are maintained at 195 K, that is, in the immediate neighbourhood to the low‐temperature solid II‐solid I transition. At higher temperatures no preferred orientations can be detected, irrespective of the employed starting set up. Both the molecular three‐fold axes and the angles between them of neighbouring molecules are distributed randomly. Therefore the Frenkel model of a discrete number of preferred orientations is discounted.
A Rate Equation Approach to Nucleation at Solid Surfaces with Application to Diamond Deposition from the Gas Phase
Authors: Tomellini Massimo
Published: July 2012

The particle size distribution function and the total number of stable clusters formed at solid surfaces during the initial stage of the CVD process, have been modeled. This is done on the basis of a kinetic scheme for nucleation in which the elementary steps are the attachment and the detachment of monomers to and from the clusters. The model is solved in terms of the eigenvalues of the associated kinetic matrix. It is shown that the microscopic growth law of the nucleus directly stems from the kinetics through the rate constants for monomer addition to the nucleus. A relationship between the particle size distribution function and the nucleation kinetics is derived that is used to process experimental data on the size distribution of diamond crystallites at the Si substrate. The overall activation energy for nucleation is obtained from the Arrhenius plot of the eigenvalues extracted from the experimental kinetics. The rate equation approach shows that the observed induction period of the nucleation kinetics can indeed be related to the dimension of the nuclei.
A Shock Tube Study of the Thermal Decomposition of Si2H6 Based on Si and SiH2 Measurements
Authors: Mick H.‐J. , Markus M. W. , Roth P. , Smirnov V. N.
Published: July 2012

In the present investigation the thermal dissociation of disilane (Si2H6) mixed with different additives was measured behind reflected shock waves. Atomic Resonance Absorption Spectroscopy (ARAS) was applied for detecting Si atoms and Ring Dye Laser Absorption Spectroscopy (RDLAS) for detecting SiH2 radicals. Three different series of experiments were performed.

In the first group of experiments mixtures of 0.1 to 0.25 ppm Si2H6 diluted in Ar were shock heated to temperatures 2000 K≤T≤3135 K and pressures between 0.8 and 1.4 bar. From the Si‐measurements silane and silylene were found to be the main primary products during disilane decomposition. The SiH2 absorption measurements were carried out at temperatures 1070 K ≤T≤ 1381 K and pressures between 0.35 and 1.3 bar. In these experiments the SiH2 formation was found to be mainly caused by the dissociation reaction Si2H6⇌ SiH4+SiH2 (R1). The rate coefficient k1 was determined by fitting SiH2 profiles calculated based on a simplified reaction mechanism to measured profiles with k1 to be a variable parameter. The value obtained was interpreted based on RRKM calculations. For bath gas concentrations of 3.1 × 10−6≤[M]≤ 4.6 × 10−6 mol cm−3 the rate coefficient k1 can be summarized by the Arrhenius expression k1 = 5.2×1010 exp(‐16850 K/T) s−1. For longer reaction times the SiH2 radicals were consumed due to the reaction SiH2+SiH2 ⇌Si2H2 (R4). The rate coefficient k4 was determined to be k4 = 6.5×1014 cm3 mol−1 s−1 (70%).

The second group of experiments was carried out in mixtures with molecular hydrogen as an additive. SiH2measurements were performed in the temperature range 1082 K≤T≤1417 K at pressures 0.24 bar ≤p≤ 1.23 bar by using initial mixtures of 15 to 30 ppm Si2H6 and 5 to 50% H2 diluted in Ar. The aim of this part was to increase the influence of the recombination reaction SiH2 + H2→ SiH4 (R‐2) and to measure the dissociation barrier for the silane decomposition via the equilibrium constant. The data evaluation results in a mean value of E0,2 = 244.1 kJ/mol which is in good agreement to previous investigations.

In the last part of this study the influence of silane used as an additive during Si2H6 decomposition was investigated. Initial mixtures of 30 ppm Si2H6 and 300 to 1000 ppm SiH4 diluted in Ar were used under conditions 1060 K ≤ T ≤ 1198 K at pressures between 0.36 and 1.3 bar. From SiH2 concentration measurements an estimation for the rate coefficient of the disproportionation reaction SiH2+SiH4 →H3SiSiH+H2 (R5), k5 = 1.3 × 1013 cm3 mol−1 s−1, was found.
The Microwave Spectrum of the Isothiazole‐Argon van der Waals Complex
Authors: Kretschmer U.
Published: July 2012

Using molecular beam Fourier transform microwave spectroscopy I measured and assigned the rotational spectra of the 32S‐ and 34S‐isothiazole‐argon complexes. The rotational constants are A = 3479.53543(15) MHz, B = 1225.68820(9) MHz, and C = 1154.69246(11) MHz for 32S‐isothiazole‐argon and A = 3428.10063(23) MHz, B = 1216.56872 (19) MHz, and C = 1140.87783(24) MHz for the 34S‐isotopomer. The 14N quadrupole coupling constants χaa = 1.3824(17) MHz, χbb = 0.9126(17) MHz, χcc = ‐2.2951(17) MHz, and χbc = 2.804(35) MHz could be extracted from the analysis of the spectra. For the 34S‐isotopomer I derived χaa = 1.3907(17) MHz, χbb = 0.9242(20), χcc = ‐2.3148(20) MHz, and χbc = 2.829(55) MHz. The spectroscopic constants were used to propose a structure of the isothiazole‐argon van der Waals complex. The argon atom is located 3.55 Å above the ring plane.
Anisotropic Structures in Aqueous Solutions of Aggregated Pseudoisocyanine Dyes
Authors: Stegemeyer H. , Stöckel F.
Published: July 2012

On increasing concentration in highly diluted aqueous solutions of pseudoisocyanine dyes an intensive absorption band of extremely small half‐width (Scheibe band) occurs which is attributed to the formation of dye aggregates (Scheibe or J‐aggregates). By polarizing microscopy it is shown that aqueous solutions of pseudoisocyanine diethylchloride at low temperatures and at concentrationsc>0.2 wt% become birefringent and exhibit a Schlieren texture characteristic for nematic liquid crystals. Above a certain clearing temperatureTcthe solution becomes optically isotropic during a discontinuous phase transition as shown by DSC. The Scheibe band vanishes at temperatures some degrees aboveTc. The phase behaviour is displayed in terms of aT‐c diagram. The aggregation numbers have been determined spectroscopically to about 40 to 50 only slightly increasing belowTc. Obviously, the Scheibe aggregates exhibit a long‐range orientational order even at high dilution typically for a nematic lyotropic liquid crystal. The phase diagram indicates that on increasing temperatures the orientational long‐range order vanishes first before the Scheibe aggregates will be thermically decomposed.
Monolayer Model Simulations of Mixtures of Amphiphilic Molecules
Authors: Stettin H. , Mögel H. ‐J. , Care C. M.
Published: July 2012

Athermal Monte Carlo simulations for a mixed monolayer built up from flexible molecules with different chain lengths have been carried out within a cubic lattice model. Only excluded volume interactions are taken into account. The number of chain segments per molecule, the head density, and the mole fraction of each component are varied. It is the aim of the work to investigate the orientational order in such mixtures. The calculated correlation lengths and snapshots did not show any evidence for demixing. In order to understand the effect of mixing on ordering some additional properties of the system have been investigated. Results demonstrating the influence of the mole fraction and chain length on the orientational order parameter, the end‐end distance, the end‐end projection, and the density profiles are presented. These quantities exhibit deviations from an ideal mixing rule. The deviations get stronger with increasing relative chain length difference. The shorter chains do not align in the local environment of long chains.
Chemical Reactions in Supercritical Water ‐ 1. Pyrolysis of tert.‐Butylbenzene
Authors: Kruse Andrea , Ebert K. H.
Published: July 2012

Supercritical water is a powerful solvent and a favourable reaction medium for oxidation of organic material. The role of supercritical water in these processes is not fully understood. The influence of supercritical water on the pyrolysis of tert.‐butylbenzene as a model compound was investigated. Experiments were carried out in a flow reactor at pressures between 5 and 25 MPa, at temperatures between 505 and 540°C and residence times between 15 and 55 s. Water, nitrogen, and water‐nitrogen mixtures, respectively, were used as reaction media; no significant differences in the product formation rates and distributions were detected. In an experiment with D2O, instead of H2O, it was proved, that deuterium is incorporated in all the product substances in various amounts. Interpretating the results with a reaction model based on a radical mechanism it was made probable that H‐D exchange reactions occur with radical intermediates.
Tailoring Surface Electronic Properties to Promote Chemical Reactivity
Authors: Bertel E. , Sandl P. , Rendulic K. D. , Beutl M.
Published: July 2012

One of the foremost objectives in the search for improved catalysts is the promotion of molecule dissociation, which in many catalytic reactions is the rate limiting step. It is shown that modification of electronic surface states by surface dopants allows to control the dissociation barrier. The relation of this new type of promotion mechanism to the effect of surfactants in metal epitaxy opens a new perspective in the search for both, promoters and surfactants.
Observation of Fluorescence Background Suppression in Raman Scattering on Single Microparticles
Authors: Kaiser T. , Esen C. , Moritz H. , Borchers M. , Schweiger G.
Published: July 2012

Raman scattering experiments were performed on single optically levitated microparticles. In comparison with bulk experiments an dramatic enhancement of the Raman scattering relative to the fluorescence scattering was observed. Two real‐world samples, a monomer for use in laser stereolithography and an engine lubricant, were investigated. Furthermore Dioctylphthalat (DOP), doped with fluorescent dye Coumarin 6, was studied by Raman spectroscopy in a droplet chain, on an optically levitated particle and in a cuvette. The combination of Raman spectroscopy and optical levitation could be a new offspring for analytical applications of Raman spectroscopy. Liquid and solid microparticles with a few nanograms in mass can be investigated by this technique with excellent signal‐to‐noise ratio.
Nonionic Microemulsions
Authors: Schubert K.‐V. , Kaler E. W.
Published: July 2012

We review and summarize the features of nonionic microemulsion phase behavior. Particular emphasis is given to the behavior of mixtures of oil, water or other polar materials with nonionic surfactants from the family of n‐alkyl polyglycol ethers, usually denoted as CiEj. The patterns of phase behavior are reviewed and the roles of various additives such as electrolytes and alcohols are discussed.
The Effect of Temperature on the Adsorption of Non‐Ionic Surfactants and Non‐Ionic Surfactant Mixtures at the Air‐Water Interface
Authors: Penfold J. , Staples E. , Thompson L. , Tucker I. , Thomas R. K. , Lu J. R.
Published: July 2012

Neutron reflectivity has been used to study the effect of temperature on the adsorption of non‐ionic surfactants and non‐ionic surfactant mixtures at the air‐water interface. For a range of polyoxyethylene non‐ionic surfactants the adsorption is invariant with temperature in the range 25 to 50 c; however some subtle changes in the structure of the adsorbed layer are observed.

For the non‐ionic mixture of monododecyltriethylene glycol, C12EO3, and monododecyloctaethylene glycol, C12EO18, measurements over a wide concentration range, from below to above the cmc (10−5 to 10−2 M), provide a direct qualitative confirmation of the abrupt change in surface composition at the cmc due to the onset on mixed micelle formation predicted recently by Nikas, Puvvada, and Blankschtein, Langmuir, 8 (1992) 2680.

For the same non‐ionic mixtures and at concentrations below and above the cmc (at concentrations of 1.25 × 10−5 and 5 × 10−4 M) a change in surface composition with increasing temperature is observed. The surface becomes more rich in the least surface active component, the C12EO8. In the same temperature range the total adsorption from the mixture at the interface decreases slightly.
II. Theoretical Modeling: An Introduction
Authors: Widom B.
Published: July 2012

The major classes of models that have been applied and analyzed in the theoretical discussion of microemulsions are described. These include both continuum and lattice models, and models based on phenomenological free‐energy densities as well as those based on microscopic Hamiltonians. Some of the issues addressed by such models are the progression of microemulsion phase equilibria, the interfacial tensions, the wetting or non‐wetting of the interfaces, and the small‐angle X‐ray or neutron scattering from microemulsions. The ways in which the models address these issues are described and some characteristic results are quoted. Most of these matters are taken up later with more technical detail by other authors; the present paper is intended only to provide an overview.
Ginzburg‐Landau Theories of Ternary Amphiphilic Systems
Authors: Gompper G.
Published: July 2012

Ginzburg‐Landau models of ternary amphiphilic systems have been studied intensively over the last few years. A wide range of phenomena of amphiphile systems has been investigated with these models, such as the internal structure and the dynamical behavior of microemulsions, phase transitions between microemulsions, oil‐rich, water‐rich and lamellar phases, interfaces between coexisting phases and their wetting properties, and systems in confined geometry. The paper reviews some recent results of the Ginzburg‐Landau approach concerning these phenomena.
Length Scale for Configurational Entropy in Microemulsions
Authors: Reiss Howard , Kegel Willem K. , Groenewold Jan
Published: July 2012

In this paper we study the length scale that must be used in evaluating the mixing entropy in a microemulsion. The central idea involves the choice of a length scale in configuration space that is consistent with the physical definition of entropy in phase space. We show that this scale may be sensitive to the model employed in the description of a microemulsion, but that in most cases it is of the order of the cube root of the average molecular volume in the system. We also show that other much larger length scales used by workers in the field can be partially reconciled with the fundamental scale through a consideration of the constraints to which the microemulsion is subject. We have attempted to perform the analysis in as rigorous a manner as possible. Many interesting features appear and the importance of using the correct length scale as well as methods (some of which are extensions of current theory) for incorporating it into theories of microemulsions are discussed.
On the Physical Contribution to the Extend Real Associated Solution Model
Authors: Hofman T. , Casanova C.
Published: July 2012

The mixing rules and the expressions of the physical contributions to the excess functions of mixing given by the ERAS model are critically re‐examined. As a result, new and more rigorous equations are derived. Calculations performed on the typical systems confirm meaningful differences between the old and new formulation at low concentrations of the associated substance.
The Reactions of 1CH2(ã1A1) with C2HxF4‐x(x = 0, 2, 3, 4) and 1, 1‐C2HF2CI
Authors: Carstensen H.‐H. , Rehbein C. , Gg. Wagner H.
Published: July 2012

The rate constants of the reactions of 1CH2 with C2H4, CH2 = CF2, CHF = CHF, CF2 = CHF, C2F4, and CF2 = CHCl were investigated with a laser photolysis/laser induced fluorescence apparatus at room temperature under quasistationary conditions. 1CH2 was produced via photolysis of ketene. The obtained rate constants show a regular dependence on the amount of fluorine substitution: an increasing fluorine part leads to a decrease of the overall rate constant. This also holds for CF2 = CHCl, which shows nearly the same reactivity towards 1CH2 as CF2 = CHF does. Some of the investigated reactions were measured for both 1CH2(v = 0) and 1CH2(v = 1). The obtained rate constants are very similar.

In the reactions of 1CH2 with CH2 = CF2, CF2 = CHF and C2F4 the radical 1CF2 could be detected as a reaction product. In the 1CH2 reactions with CHF = CHF and CF2 = CHF the radical 1CHF could be observed.

These results underline the importance of the addition channel for this kind of reactions.
Dynamics and Molecular Order of the Liquid‐Crystalline Complexes of 5‐Octadecyloxyisophthalic Acid and Cyclic Oligo‐Amines, Investigated by 2H n. m. r. Spectroscopy
Authors: van Genderen Marcel H. P. , Pfaadt Marcus , Macho Volker , Valiyaveettil Suresh , Spiess Hans W.
Published: July 2012

Complexes of 5‐octadecyloxyisophthalic acid with piperazine, 1,4,7‐triazacyclononane and 1,4,7,10‐hexaazacyclooctadecane were selectively deuterated in various positions, and investigated with variable‐temperature solidstate 2H n. m. r. spectroscopy. All systems form stable, enantiotropic liquid‐crystalline phases at high temperature, and the dynamics in these phases can be described by a single motional model. This model involves fast rotation around the director coupled with a rapid phenyl flip. Macroscopically oriented liquid‐crystalline phases with the director parallel to the magnetic field are found on cooling in a magnetic field of 7 T for the piperazine complexes, but only partial macroscopic order was achieved for the complexes with 1,4,7,10‐hexaazacyclooctadecane and 1,4,7‐triazacyclononane under these conditions, and also for the former in a magnetic field of 11 T. In contrast to the pure acid C18ISA, the stability of the phases is determined by the hydrogen/ionic bonds between the acid and the bases, and not by the alkyl‐alkyl interactions.
Catalysis by Manganese Oxide Monolayers Part 2: Zirconia Support
Authors: Ma J. , Chuah G. K. , Jaenicke S. , Gopalakrishnan R. , Tan K. L.
Published: July 2012

The catalytic and structural properties of two different preparations of manganese oxide supported on high surface area zirconia are compared. The catalyst were prepared by grafting from an alkoxide precursor and by conventional aqueous wet impregnation technique. Reaction of manganese ethoxide with the hydroxyl groups at the surface of the zirconia support is highly specific and allows manganese oxide to be deposited layer by layer. The zirconia used in this study has a mesoporous structure; pores with diameters ≦ 5.8 nm were found to be inaccessible to the manganese ethoxide precursor. Hence, only about half of the total surface area is available for the reaction with ethoxide. A quantitative evaluation of the XPS intensities for manganese and zirconia shows that about 2.5 layers of manganate are deposited after five grafting steps. Activity tests made on these catalysts confirm the monolayer buildup. The specific activity of the isolated manganese ions which result from the first grafting step is very low; the specific activity increases by an order of magnitude once the first monolayer is completed, and shows a further increase in the second and third layers. In contrast, impregnation with manganese acetate results in small manganate crystallites, which most likely form inside the pores. The specific activity of these catalysts and their selectivity towards acetone in isopropanol decomposition are very similar to that of bulk manganese dioxide whereas the grafted samples show a high selectivity towards propene.
Optical Detection of Electron Transport in Thin Films of Prussian Blue
Authors: Ochs S. , Grabner E. W. , Mohler E.
Published: July 2012

Potassium‐iron(III)‐hexacyanoferrate(II) (Prussian blue) is deposited electrochemically as a thin film (thickness: 300 nm) on a Pt‐disk substrate electrode. The relative change in optical reflectivity of this electrode is detected time‐resolved upon galvanostatic reduction of Prussian blue to Everitt's salt and subsequent reoxidation. Considering different transport properties of electrons and cations within the film, the experimental result is fitted by numerical modelling. The specific diffusion coefficient for electrons is deduced as 5·10−11 cm2/s.
Transport of Photogenerated Charge Carriers Through Crystalline GaP Networks Investigated by Intensity Modulated Photocurrent Spectroscopy
Authors: Vanmaekelbergh D. , Iranzo Marín F. , van De Lagemaat J.
Published: July 2012

The transport of photogenerated electrons through porous n‐GaP electrodes has been investigated with Intensity Modulated Photocurrent Spectroscopy. Porous layers with a thickness of between 1 and 200 μm were formed on GaP substrates by anodic etching of crystalline n‐GaP electrodes. They consist of a network of crystalline GaP interpenetrated with the electrolyte. It is shown that the transit time of photogenerated electrons through the depleted porous network is larger than the RC response time. Hence, IMPS performed in the frequency window below (RC)−1 directly probes the transient photocurrent flow in the depleted porous network. The relatively long transit times observed with IMPS are attributed to strongly meandering paths of the photogenerated electrons through the crystalline network, probably determined by the potential distribution in the depleted network.
Metal Ion Induced Conformational Changes of Double‐Stranded Polynucleotides: Poly (dG‐m5dC) and Poly (dA‐dT)
Authors: Middendorf S. M. , Diebler H.
Published: July 2012

Like poly(dG‐dC), also double‐stranded poly(dG‐m5dC) can adopt a left‐handed Z‐conformation. The concentrations of Ni2+ or Mg2+ which are required in order to induce the structural transition are much lower than in the case of the unmethylated polynucleotide. At ionic strength I = 0.001 M, one Ni2+ ion bound per 20 mononucleotide units is sufficient to trigger the conformational change. The kinetics of the binding of Ni2+ to the polynucleotide are characterized by a reaction effect with a time constant of 7–9 milliseconds (stopped‐flow and T‐jump), indicating innersphere binding. The kinetic data are consistent with a 3‐step mechanism which includes two inner‐sphere substitution processes, presumably involving a phosphate 0 atom and a guanine N7 atom. The slow kinetics of the BZ transition was monitored up to 1 hour. The reaction curves can be fitted excellently by 3 exponentials, the two shorter time constants being dependent on the Ni2+ concentration. A simple mechanism which is consistent with the experimental data is proposed and discussed.

Also with poly(dA‐dT)·poly(dA‐dT) a drastic change in conformation after the addition of Ni2+ can be observed, presumably reflecting again a B→Z transition. Here, however, high concentrations of Ni2+ (0.075–0.55 M) and of NaCl (0.1–5 M) are required in order to start the transition. The rate of the conformational change is much faster than with poly(dG‐m5dC), the time constant was evaluated to be 0.9–1.9 seconds for 0.5–0.7 M of Ni2+ in 0.1 M NaCl solution.
Translational Diffusion of a Transient Charge‐Separated Species in Carbon Dioxide and Trifluoromethane Studied by the Transient Grating Method
Authors: Kanda D. , Kimura Y. , Terazima M. , Hirota N.
Published: July 2012

By means of the transient grating method, we have measured the translational diffusion constant of a transient charge‐separated species created by the photo‐isomerization of 1′,3′,3′‐trimethyl‐6‐nitrospiro[2H‐1‐benzopyran‐2,2′‐indoline] in carbon dioxide and trifluoromethane from ρr = 0.8 to 2.0, where ρr is the reduced density by the critical density of the solvent. It has been revealed that the effect of the charge‐separation on the diffusion constant is small in these fluids due to the large molecular size of the transient molecule. The viscosity dependence of the diffusion constant is well simulated by an empirical equation which also works well for benzene and naphthalene.