bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of the Reactions of NCO Radicals with NO and NH3
Authors: Becker K. H. , Kurtenbach R. , Schmidt F. , Wiesen P.
Published: July 2012

The rate constants for the reaction of NCO (X2Π) radicals with NO and NH3 were measured at 20 Torr total pressure in temperature ranges of 290–1098 K and 295–882 K, respectively, using ClNCO excimer laser photolysis for NCO radical formation in combination with laser‐induced fluorescence detection of NCO. In the temperature range investigated the NCO + NO reaction exhibits a negative temperature dependence which is described by the following three parameter Arrhenius equation:

, with E0 in units of kJ/mol.

For the NCO + NH3 reaction the measurements exhibit a positive temperature dependence over the temperature range investigated with a slight upwards curvature. A modified three parameters Arrhenius fit provides a good description of the experimental data:

, with E0 in units of kJ/mol. In addition, the rate constant of the NCO + NH3 reaction was found to be pressure independent in the range 10–193 Torr at 295 K.
Investigation of sorption and intracrystalline diffusion of benzene and toluene on silicalite‐1
Authors: Cartarius Ralph , Vogel Herbert , Dembowski Jürgen
Published: July 2012

Sorption and diffusion measurements were carried out with a novel, fully automatic gravimetric adsorption apparatus, which makes it possible to measure the adsorption (thermodynamic data) and diffusion (kinetic data) of adsorbates on adsorbents simultaneously in a short time. For that reason this device is best suited for catalyst improvement and development in the industrial laboratory. The well characterized system benzene/silicalite‐1 was first used as a reference system to check the performance and applicability of the new apparatus. A comparison of our experimental results with literature data in the temperature range of 280–353 K shows the expected agreement. We found a striking lack of diffusion data of toluene in silicalite‐1. Consequently our next aim was the examination of the toluene/silicalite‐1 system. The adsorption isotherms and intracrystalline diffusivities of toluene on monocrystals of silicalite‐1 were investigated in the temperature range of 283–333 K. The comparison of the systems benzene, toluene and xylol‐isomers on silicalite‐1 shows the influence of one additional methyl group on the adsorptive and diffusive behaviour. The most remarkable features of the comparison is that the obtained toluene diffusivities are greater than benzene diffusities, as it was already recognized in a comparison of benzene and p‐xylol diffusivities, and that the activation energy of the toluene diffusion shows an abrupt increase at the phase transition concentration.
Sensitivity analysis of complex chemical equilibria in heterogeneous systems
Authors: Fishtik Ilie , Geană Dan
Published: July 2012

Sensitivity analysis of an equilibrium multiple chemical reaction system with several pure condensed phases and one ideal gas phase is considered. It is shown that, in this case, response equilibria also play an important role. The particularity of such systems is that the system's response may be presented as a sum of contributions coming only from those response equilibria defined by gas phase species. The effect of temperature, pressure and initial amounts of species is analyzed for gasification of coal (graphite).
DISQUAC behaviour close to critical points application to methanol + alkane mixtures
Authors: Gonzalez Juan Antonio , De La Fuente Isaias Garcia , Cobos Jose Carlos
Published: July 2012

Interactions present in binary mixtures of methanol + alkanes have been previously characterized in terms of the DISQUAC group contribution model. It was shown that DISQUAC is a reliable tool to represent thermodynamic properties such as molar excess functions: Gibbs energies, GE, enthalpies, HE, or heat capacities at constant pressure, CEP. In this work, we examine the ability of the model to represent liquid‐liquid equilibria, LLE, for the whole series of methanol + n‐alkanes mixtures, as well as for methanol+cyclohexane, + cycloheptane, or + cyclooctane. Up to now, we had only considered LLE of those solutions involving n‐hexane, n‐heptane, or cyclohexane.

Using the interaction parameters previously reported for methanol + n‐alkanes mixtures, which are independent of the non‐polar compound, DISQUAC predicts UCSTs (upper critical solutions temperatures) of the methanol + n‐alkanes mixtures which are lower than the experimental values for those systems containing the longer n‐alkanes. This is in contradiction with the critical exponents theory. The possibility of improving results by modifying only the third interchange coefficients is discussed. So, two groups of these parameters are given depending on n, hereafter the number of carbon atoms in the n‐alkane (n ≤ 7; n ≥ 8). The coordinates of the critical points are then fairly well represented. Nevertheless, the shape of the LLE curves (the experimental ones being much flatter than those calculated) is rather poorly described, mainly for mixtures containing the longer n‐alkanes. The new interaction parameters are tested predicting vapor‐liquid equilibria, VLE, at very high temperatures (up to 473.15 K) and at moderate pressures (up to 40 atm) of methanol + n‐alkanes mixtures. It is noteworthy that DISQUAC correctly predicts the formation of azeotropes for systems with the lower n‐alkanes, and the absence of azeotropes for mixtures with the longer n‐alkanes (from n‐nonane).

Properties of mixtures containing cycloalkanes are more difficult to represent because these compounds do not form an homologous series in terms of the c‐CH2 groups. Nevertheless, it has been shown that the interaction parameters of 1‐alkanols (# methanol)+cyclohexane systems can be applied to calculate HE of mixtures with other cycloalkanes. In the case of LLE of methanol + cycloalkanes mixtures, different first dispersive parameters are needed for each cycloalkane. The quasichemical parameters are, as usually, independent of the n‐alkane. The LLE coexistence curves are better represented than in the case of solutions including n‐alkanes.

The possibility of modifying the scaling temperature (equal to 298.15 K in DISQUAC) in order to improve LLE results is also briefly examined.

As usually, the experimental HE curves are much flatter than the calculated ones at temperatures close to the critical. Results for methanol+ n‐propane, or + n‐heptane are shown in order to complete information previously given.
Intramolecular vibrational redistribution and unimolecular reaction: Concepts and new results on the femtosecond dynamics and statistics in CHBrClF
Authors: Beil Andreas , Luckhaus David , Quack Martin , Stohner Jürgen
Published: July 2012

We present the conceptual background for intramolecular vibrational (rotational) redistribution (IVR) in polyatomic molecules and its analysis from high resolution spectra. We illustrate some of the basic concepts relating to the use of effective and real molecular hamiltonians for IVR with examples drawn from our previous spectroscopic investigations of the chiral molecule CHFClBr. The importance of the initial state for the dynamics is shown, demonstrating that simple intuitive concepts of survival probabilities for some arbitrary chromophore (“zero order bright”) state are insufficient for a quantitative understanding of IVR. An approximate (C3‐like) symmetry prevents relaxation towards quasi‐equilibrium in highly excited C1‐asymmetrical CHFClBr. The coherent infrared multiphoton excitation of CHFClBr at the CH‐stretching frequency leads to coherent vibrational states with a very wide energy distribution corresponding to short time oscillatory behaviour of the CH‐stretching motion with a period of 11–12 fs. On longer time scales between 50 and 500 fs substantial vibrational motion is found in the CH‐bending coordinates. For modest excitation energies both the initial vibrational angular momentum quantum number (l = 0) and a' symmetry of the wavepacket are well conserved for 1–2 ps. At higher excitations and longer times (2–4 ps) these approximate symmetries are lost. These results are briefly discussed in relation to a general classification of IVR mechanisms and in relation to reactive processes in CHFClBr.
The rovibrational dynamics of hydroxylamine
Authors: Luckhaus D.
Published: July 2012

The combination of overtone spectroscopy and detailed quantum mechanical modelling of rovibrational dynamics provides an unique tool for investigating many aspects of intramolecular dynamics such as dynamical symmetries, coupling hierarchies, and the separation of time scales, which control the intramolecular energy flow at high excitations relevant for unimolecular reactions.

Hydroxylamine NH2OH, which plays an important role in N/O/H chemistry in general, provides an intriguing example for the interplay between high frequency stretch‐bend motions and low frequency torsion/inversion tunneling. This paper discusses the dynamical analysis of its high resolution infrared absorption spectrum up to the visible range on the basis of up to five‐dimensional ab initio models using vibrational DVR grids of several million points.

The torsion‐inversion process is found to follow a consecutive mechanism with very slow (≥ 1 μs) inversion tunneling below the trans‐cis isomerisation barrier (2673 cm−1 at MP2/TZ2P). The metastable cis isomer shows localised zero point and fundamental level eigenfunctions. From the overtone spectrum fast energy redistribution is deduced within the OH and NH2 manifolds, respectively, on time scales below 100 fs. A direct coupling between the two moieties leads to a slow decay of OH stretching excitation within 3 ps. Further significant contributions to the effective homogeneous broadening observed in high OH stretch overtones are predicted from the 1,2‐H shift leading to ammonia oxide NH3O with a barrier around 18200 cm−1 (CASPT2) and a NH3O well depth exceeding 1 eV.

The spectroscopic characterisation of the metastable isomers of hydroxyl amine, cis‐NH2OH and NH3O, by stimulated emission pumping experiments is suggested on the basis of ab initio calculations for electronically excited states.
Predissociating resonances of Cs2 — Theory and experiment
Authors: Lee Sungyul , Kim Bongsoo , Yoshihara Keitaro
Published: July 2012

We present the experimental observation and detailed quantum mechanical analysis of the complex resonances occurring through multiple predissociation pathways. The complex features in the photodissociation spectrum of Cs2 are well reproduced by the close‐coupling calculation including three channels. A very narrow resonance with a linewidth of ˜2×10−7cm−1 is predicted. It is shown that q‐reversal can occur in predissociation with only two channels involved.
Isomerisation of deuterated cyclopropanes — The possibility for stereochemical control
Authors: Bolton Kim , Hase William L. , Doubleday Charles
Published: July 2012

The direct dynamics technique, based on an AM1 semiempirical Hamiltonian modified with specific reaction path parameters, has been employed to study the constant energy and thermal isomerisation of S,S‐trans‐cyclo‐propane‐1,2‐d2 and cyclopropane‐1,2,3‐d3. At a classical energy of 48.25 kcal mol−1 above the conrotatory saddle point, the dynamics is mode specific. This raises the possibility of stereochemical control in this energy regime. The sensitivity of the reaction mechanism to the character of the excited normal mode eigenvector is also apparent under thermal conditions at 695 K. Similar product branching ratios are obtained for the d2 and d3 species at this temperature, when the trajectories are initialised at the conrotatory saddle point.
Photofragment vector correlations as a probe of K‐scrambling in unimolecular dissociation
Authors: North Simon W. , Hall Gregory E.
Published: July 2012

We discuss the relationship between fragment‐rotational polarization and the extent of K‐mixing in an energized molecule undergoing unimolecular dissociation at fixed energy and angular momentum. Accurate measurements of the second Legendre moment of the v · j angular correlation are presented for the CN fragments produced in the photoinitiated dissociation of NCCN at 193 nm. as determined by Doppler spectroscopy using a transient frequency modulation technique. The strength of the correlation significantly exceeds what would be observed if all K states of the dissociating molecule were equally represented.
Models for the analysis of rate data for radical decomposition and multichannel radical‐radical reactions
Authors: Pilling Michael J. , Gang Jun , Robertson Struan H. , Zeng Guang
Published: July 2012

Two models are described for use in the analysis of experimental rate data for dissociation and association reactions. The first is a method for calculating partition functions and densities of states for molecules and radicals with asymmetric internal rotors. Its application to calculation of the heat capacity of butane and to analysis of pressure‐dependent rate data for the dissociation of 2‐C4H9 are described. The second technique is the use of the master equation to analyse rate data for multichannel radical‐radical reactions. It is applied to the CH3 + OH reaction.
The gas phase reactions of benzyl radicals with O, O3, and NO3: Rate, mechanism, and unimolecular decomposition of the chemically activated benzoxy radical
Authors: Hoyermann K. , Seeba J. , Olzmann M. , Viskolcz B.
Published: July 2012

The reactions of the benzyl radical with O, O3, and NO3 are investigated in a discharge flow‐reactor with mass spectrometric detection. For the rate coefficients of the latter two reactions, we obtain values of 2.8·1013 and 1.93·1012 cm3 mol−1s−1, respectively (T≈300 K, P ≈ 2 mbar). The main products for all three reactions are C6H6 and C6H5CHO with relative yields of 0.60/0.40 (M. Bartels, J. Edelbüttel‐Einhaus, and K. Hoyermann, 22nd Int. Symp. on Combustion, p. 1041, The Combustion Institute. Pittsburgh 1988), 0.37/0.66, and 0.23/0.77, respectively. These branching fractions are interpreted in terms of the unimolecular decomposition of an intermediarily formed benzoxy radical, using statistical rate theory. The molecular data needed are calculated by quantum chemical methods. The verification of the experimental branching fractions requires the assumption of a direct reaction channel leading from C6H5CH2O to C6H6. The nature of this channel is still uncertain.
Complex‐forming bimolecular reactions of metastable NH(a1Δ) with H2O(X̃1A1) and H2O2(X̃1A)
Authors: Hack W. , Jordan R.
Published: July 2012

The elementary reactions:

equation image

and

equation image

were studied in a quasistatic laser photolysis cell at a pressure of 20 mbar in the temperature range 295 ≤ T/K ≤ 523 and at room temperature respectively. NH(a1Δ, v) was produced by excimer laser photolysis of HN3(X̃) and detected by laser‐induced fluorescence (LIF). A variable delay time between photolysis and detection pulse brought about the time resolution. The NH(a) depletion yielded the following rate constants:

k1(T = (3.5±0.8)1013(T/295 K)−(1.5±0.2)cm3/mols

k2(v = 0) = (7.5±1.4)1013cm3/mols

k2(v = 1) = (7.1±0.9)1013cm3/mols

The reaction products of reaction (1) are NH2(X̃) + OH(X). For reaction (2) NH2(X̃) radicals were detected (24%); the quenching channel was found to be unimportant kq < 7.5 · 1011 cm3/mol s. The reaction mechanism is discussed. The reaction NH(a) + H2O(X̃) is compared to the reaction NH(X) + H2O(X̃).
Dynamics of charge‐transfer state formation in supercritical fluid solvent
Authors: Kajimoto O. , Sekiguchi K. , Nayuki T. , Kobayashi T.
Published: July 2012

The rate of the intramolecular charge‐transfer state formation has been determined for 4‐(N, N‐dimethylamino)‐benzonitrile (DMABN) in supercritical CF3H by means of a time‐correlated single‐photon counting technique. The rate constant increases rapidly with increasing CF3H density, indicating the importance of the polar environment offered by the CF3H molecules which are clustering around a DMABN molecule. With increasing clustering number, the activation barrier is lowered and hence the rate increases exponentially. The observation is semiquantitatively interpreted on the basis of a molecular dynamics simulation of clustering in supercritical solutions.
Description of solvent effect on the visible absorption spectrum of fluorenone radical anion
Authors: Wagner‐Czauderna E. , Lipka R. , Kalinowski M.K.
Published: July 2012

The solvatochromic shift of the most intensive band of fluorenone radical anion (FN*‐) in the visible region has been examined in 10 polar formally aprotic media. It has been found that this shift depends on the solvent acceptor number (AN) and static dielectric constant (D) according to planar regression:

It is suggested that the ground state of FN*‐ is relatively stabilized in a solvent with a high acceptor number and the dipole moment of the solute increases during an excitation.
Coherent interference patterns of optical second‐harmonic waves from substrate‐free ultrathin poly(methyl methacrylate) films asymmetrically incorporating amphiphilic dyes
Authors: Yamada Sunao , Shimada Yoshihisa , Kawazu Mitsuhiro , Matsuo Taku
Published: July 2012

An ultrathin poly(methyl methacrylate) film, as prepared by a casting‐on‐water method, emitted optical second harmonic (SH) light in association with asymmetric alignment of an amphiphilic dye. Coherent interference due to SH waves from a pair of films in parallel afforded a periodic pattern with the film, and the pattern was 180° phase‐shifted on flipping either one of the films. These observations were ascribed to asymmetric orientation of the dye in the film and negligibly small thickness of the film in comparison with the coherence length. Overall orientation of dyes in the film could be estimated from the experiments.
Partitioning of some combination di‐ and tripeptides in aqueous two‐phase systems of poly(ethylene glycol) and Di‐potassium hydrogen phosphate at 293 K: Experimental results and predictions
Authors: Tintinger Ralf , Zhu Jiandung , Großmann Christoph , Maurer Gerd
Published: July 2012

Aqueous two‐phase systems are effective extraction systems for separating peptides and enzymes from aqueous phases. Such extraction processes are based on the finding that peptides and enzymes show different preferences for the coexisting phases. Methods to calculate and predict the liquid‐liquid phase equilibrium in those systems can only be developed when an extensive experimentally determined data base is available. The present contribution contributes to that goal by presenting experimental data for the partitioning of small amounts (micrograms solute per kilogram of solution) of low molecular‐weight combination peptides of glycine, 1‐glutamic acid, 1‐phenylalanine, and 1‐lysine in aqueous two‐phase systems of di‐potassium hydrogen phosphate and poly(ethylene glycol) of molecular mass of about 6000 and 35000 at about 293 K. A group‐contribution model for the excess Gibbs energy is used to predict liquid‐liquid phase equilibrium. A preliminary set of binary interaction parameters was taken from the literature. These model parameters were determined using experimental results for the partitioning of single amino acids and some of their peptides in the same aqueous two‐phase system. No experimental results for the partitioning of combination peptides had been used for parameter estimation, i.e. those peptides were products of condensation reactions of molecules of a single amino acid. Therefore, partition coefficients calculated for combination peptides are predictions. For some peptides predicted and measured partition coefficients agree within experimental uncertainty. In a few cases predicted partition coefficients deviate from experimental results by a factor of about two. However, the model always correctly predicts which phase (polymer‐rich or salt‐rich) is preferred by the peptide.
On the production of different carbon forms by electric arc graphite evaporation
Authors: Belz T. , Find J. , Herein D. , Pfänder N. , Rühle T. , Werner H. , Wohlers M. , Schlögl R.
Published: July 2012

We report results gained in the operation of a fullerene‐generating graphite evaporator in an attempt to evaluate its suitability for a rationally designed production of different new forms of carbon. The effects of varying experimental conditions on the composition of the products as well as on observable properties of the carbon arc have been examined. The primarily produced fullerene blacks and electrode deposits were characterized by powder X‐ray diffraction, transmission electron microscopy and oxidation experiments monitored by TGA/DTA. Yield and composition of the soluble fullerenes were determined gravimetrically and by HPLC, respectively. Furthermore, the arc plasma was investigated by UV/VIS emission spectroscopy under varied conditions to detect possible correlations of the fullerene yield with properties of the hot plasma.
Constitution and thermodynamics of Cu‐Y alloys
Authors: Abend U. , Schaller H.J.
Published: July 2012

The thermodynamic properties of Cu‐Y alloys were determined between 973 and 1073 K by emf measurements on galvanic cells using CaF2 single crystals as solid electrolytes. Results yield a complete set of thermodynamic functions for the intermetallic phases (Cu), Cu6Y, Cu4Y, Cu7Y2, Cu2Y, and CuY, as well as information on the phase relations. The system is characterized by moderate negative deviations from ideality. A comparison with analogous systems indicates the influence of the electronic structure of the components on thermodynamic functions. The phase relations of the Cu‐Y system were additionally investigated by DTA and X‐ray diffraction.

The present results as well as literature data on the thermodynamics and phase diagram of the Cu‐Y system were used as a basis for a thermodynamic optimization of the system using a computer program based on the least squares method. Optimized and experimental data turned out to be in good agreement.
The kinetics of structural changes in anionic adlayers on stepped Au(111)s electrodes from sulfuric acid solutions
Authors: Dretschkow T. H. , Wandlowski T. H.
Published: July 2012

The kinetics of structural changes in anionic adlayers on stepped Au(111)s electrodes has been investigated in sulfuric acid solutions by potential step experiments. The experimental transients obtained with “quasi‐ideal” (miscut <0.5°) surfaces could be modelled with the exponential law of nucleation in combination with 2D surface diffusion‐controlled growth which is preceded by an adsorption process. The semi‐quantitative analysis was restricted to i vs. t‐traces, which revealed significantly different time constants of these two processes. The current transients with higher miscut angle showed (i) a systematic increase of the nucleation rate with increasing step density and (ii) a decrease of the macroscopically detectable charge density associated with the nucleation and growth process. The latter could be parameterized within a first approximation employing the general Avrami‐ansatz in combination with an adsorption process. In‐situ STM experiments showed that increasing step density of the substrate surface is accompanied with decreasing domain size of the ordered (√3 X √7) (hydrogen) sulfate adlayer patches. Respective correlations with the kinetic data obtained will be discussed.
Applied laser spectroscopy in technical combustion systems
Authors: Dreizler Andreas , Sick Volker , Wolfrum Jürgen
Published: July 2012

Several laser‐based diagnostic techniques for nonintrusive measurements of species concentrations and temperatures were developed during recent years and have become valuable tools to study technical combustion processes. Data gained from such experiments are the basis for a comparison with detailed mathematical modelling of chemical processes in laminar and turbulent flows including heat and species transport. Examples for the application of laser‐induced fluorescence (LIF), laser‐induced thermal grating spectroscopy (LITGS), Rayleigh scattering (RS), differential absorption (DIAL) and emission in the infrared in ignition processes, internal combustion engines, municipal waste incinerators, and pressurized fluidized bed reactors are described.
Electric conductivity of supercritical cesium‐cesium hydride mixtures at high temperatures and pressures
Authors: Keller E. , Franck E. U.
Published: July 2012

Above a critical temperature of 665° liquid cesium and nonmetallic ionic liquid cesium hydride are completely miscible. This has been demonstrated previously with high pressure phase equilibrium measurements. An equilibrium hydrogen pressure belongs to each temperature and mixture composition and is used to prepare a desired sample composition. An autoclave for high pressure hydrogen is described into which electric conductance cells can be placed. With the cylindrical cell A the sample resistance is measured parallel to the thin stainless steel walls. With cell B, the resistance is determined between two tantalum electrodes separated by alumina.

Conductances have been measured along seven isotherms from 550 to 800°. To cover mole fractions x (CsH) from 0.01 to 0.98, hydrogen pressures up to 1000 bar had to be applied. In the cesium‐rich, “metallic”, region conductances between 3000 and 9000 Ω−1 cm−1 were observed with negative temperature derivatives. In the cesium hydride‐rich, “ionic”, region conductances between 20 and 100 Ω−1 cm−1 were found with positive temperature coefficients. For the metallic region the conductance is discussed with the Mott “nearly free electron” (NFE) model in comparison with cesium‐gold and cesium‐halide systems. The NFE region extends down to 1300 Ω−1 cm−1 for the hydride systems. The metallic‐nonmetallic transition region extends from 1300 to 250 Ω−1 cm−1. At the critical consolution point (665°, x(CsH) = 0.68, p(H2) = 157 bar) the conductivity is 830 Ω−1 cm−1.
Formation of carbynoid structures by chemical dehydrohalogenation of poly(vinylidene chloride). A 13C solid‐state NMR study
Authors: Evsyukov S. E. , Paasch S. , Thomas B. , Heimann R. B.
Published: July 2012

The products of the interaction of poly(vinylidene chloride) (PVDC) powder with a mixture of alcoholic KOH solution and tetrahydrofuran were studied by solid‐state 13C NMR spectroscopy. The reaction was found to be a complex process involving dehydrochlorination as a target reaction and some side reactions, viz., nucleophilic substitution, cross‐linking, and secondary transformations of intermediate and final products. The endproducts are “carbynoid‐type” polymeric materials containing short carbyne fragments along with various defect links such as alkoxy‐ and hydroxy groups, carbonyl species, as well as cross‐links. The reasons for the concurrent formation of both polyyne and cumulene structures, and the nature of side reactions are discussed.
Metal‐metal interactions in improved Pt‐Co‐Cr catalysts used in phosphoric acid fuel cells
Authors: Tröger Larc , Freund Andreas , Albers Peter , Seibold Klaus , Prescher Günter
Published: July 2012

Metal‐metal interactions were studied on high performance Pt‐Co‐Cr catalysts used in commercial phosphoric acid fuel cell power plants by means of X‐ray absorption fine‐structure spectroscopy (XAFS), X‐ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry. In addition, samples were characterized by transmission electron microscopy and X‐ray diffraction. The XAFS measurements of the alloy catalyst revealed different kinds of interactions between the metal atoms as well as between the metal and carbon atoms. A Pt‐Pt distance considerably shorter than in Pt metal indicated a complete alloying of that metal. There was no evidence for local atomic arrangements including all three metals. On the other hand, the Co XAFS data suggest a tetragonal‐ordered structure of PtCo in HgMn arrangement. Missing Cr‐Cr interactions are likely to be a consequence of a highly disordered Pt‐Cr alloy partially depleted from Cr. Upon annealing a surface segregation and preferential oxidation of Cr was observed by XPS measurements and supported by the SIMS results. The segregational tendency of Cr and the favorable reduction behavior of Co promotes the formation of a tetragonal PtCo structure while cooling down to ambient temperature.
Ab initio study of structural properties of stage‐1 alkali graphite intercalation compounds
Authors: Hartwigsen C. , Witschel W. , Spohr E.
Published: July 2012

First‐principles electronic structure calculations are carried out for the stage‐1 alkali graphite intercalation compounds LiC6 and XC8 (X = Li, Na, K, Rb and Cs). Lattice constants and atomic positions are determined by total energy minimization. It is demonstrated that the experimentally observed AA stacking order of the graphite host is partly a consequence of the electronic charge transfer from the alkali atoms to the graphite host.
Change of the resonance frequency of a quartz crystal microbalance in contact with an aqueous dispersion of solid particles
Authors: Bell J. , Köhler T. , Woermann D.
Published: July 2012

The change of resonance frequency of shear oscillations of an AT‐cut quartz crystal with a resonance frequency f0 of f0 = 5 MHz operated with one face in contact with air and the other in contact with an aqueous suspension of non‐porous solid particles is studied. The experiments are carried out as function of the concentration of the colloidal particles at constant temperature. The aqueous suspensions are prepared with three kinds of particles of different size (radius r ≈︁ 500, 200, 5 nm). It is found that the resonance frequency is independent of the concentration of the colloidal particles with r ≈︁ 500 and 200 nm. It has approximately the value of the resonance frequency of the fluid medium in the absence of the colloidal particles. For the colloidal particles with r ≈︁ 5 nm a small change of the resonance frequency with the concentration of the colloidal particles is observed. An attempt is made to rationalize this finding. The observation could be of importance to practical applications of the quartz crystal microbalance as a sensor in fluids.
A differential anomalous X‐ray scattering study of the formation of lead zirconate titanate via sol‐gel process
Authors: Beudert R. , Bertagnolli H. , Gutwerk D. , Kolb U. , Weigelt J.
Published: July 2012

A differential anomalous X‐ray scattering (DAS) investigation on gels, produced by hydrolysis of a mixture of lead(II)acetate and zirconium‐ and titanium‐n‐propoxides, and calcinated at the temperatures 200, 300, and 450 °, is presented. Anomalous X‐ray scattering was applied to get more precise information on the structural changes of the gel during calcination. Two different scattering experiments for each sample were performed with synchroton radiation of the energy below the L3 edge of lead, namely at 11500 and 13025 eV. The data were corrected for absorption, fluorescence radiation and multiple scattering. The Compton and atomic scattering were subtracted after normalization to absolute units with values for the anomalous dispersion corrections, determined by an absorption experiment. The Fourier transform of the total and differential scattering intensities yields the total and differential atom pair correlation functions (TAPCF, DACPF), which provide information on the local structure of lead and its changes during the calcination process. The analysis of the TAPCF's and DAPCF's indicates a structure, similar to that existing in the pyrochlore or perovskite phase of lead zirconate titanate (PZT), even at low temperatures. By comparison of the corresponding atom pair correlation functions (APCF's) it can be deduced that the near range as well as the long range order in the local environment of lead nearly remains unaltered during the calcination process.
State of copper species during N2O decomposition over Cu‐ZSM‐5
Authors: Bossmann Stefan H. , Ottaviani M. Francesca , Turek Thomas
Published: July 2012

The state of copper species in Cu‐ZSM‐5 during isothermal oscillations in nitrous oxide decomposition was monitored by CW‐ESR. A change in the copper oxidation state could not be observed. The prevailing species in the state of low activity is Cu2+ (O6) · NO while in the more active state Cu2+ (O6) · O2 could be identified as intermediate. A simple set of reactions involving these species was proposed, which is able to explain the occurrence of oscillations and is in agreement with the experimental observations.
Rh(III)/Rh(I)‐Catalyzed homogeneous oxidation of hypophosphite by water
Authors: Jusys Z. , Lenkaitiene J. , Genutiene I. , Jurevičius A.
Published: July 2012

Homogeneous hydrolytic oxidation of hypophosphite in HCl solutions catalyzed by Rh(III)/Rh(I) has been studied by cyclic voltammetry and on‐line mass spectrometry. The effect of H/D substitution in both hypophosphite and water on the kinetics of the process has been studied. A deuterium tracer evidenced hydrogen to evolve entirely from water in the course of Rh(III)/Rh(I)‐catalyzed homogeneous oxidation of hypophosphite. No kinetic H/D isotope effect (kH/kD) has been found for H/D substitution in hypophosphite. kH/kD = 1.4 ± 0.1 has been found for H/D substitution in water. Possible transformations in both structure and composition of Rh(III) and Rh(I) complexes occurring during homogeneous catalytic hypophosphite oxidation by water are discussed.
Application of spin trapping in the study of the electrochemical and photochemical synthesis of phenylated C60 derivatives with iodonium salts
Authors: Fedurco Milan , Rapta Peter , Kurán Pavel , Dunsch Lothar
Published: July 2012

A spin trap technique was used to investigate the fullerene phenylation both electrochemically and photochemically using the reactions of iodonium salts. Phenyl radicals, produced in the cathodic reduction as well as during the photolysis of iodonium salts, were trapped by nitroso‐tert‐butane (BuNO) and nitrosodurene (ND) spin traps. However, no phenyl radicals could be detected by ESR during the irradiation of diphenyliodonium iodide, or during its electrochemical reduction, in the presence of C60. This indicates that prior trapping of phenyl radicals to d̊BuNO and ND spin trap agents, their trapping by fullerenes occurred. The radical mechanism of electrochemical and photochemical phenylation of C60 using iodonium salts are discussed and these two phenylation techniques are compared.
Effect of adsorbed S‐benzylisothiouronium cation on hydrogen evolution reaction at mild steel electrode
Authors: Pillai K. Chandrasekara
Published: July 2012

S‐benzylisothiouronium (SBTU) chloride and S‐methylisothiouronium (SMTU) sulphate retard the hydrogen evolution reaction (HER) on mild steel in HCl solutions, and increase the cathodic Tafel slope (‐bc) of HER to different extent depending on their concentration. The cause for the occurrence of high ‐bc values, and the dependence on additive concentration (cA), of the two parameters ‐bc and the electrochemical reaction order with respect to additive concentration (zA), have been explained in terms of a mechanism based on blocking of the electrode surface by the additive and its dependence on cA and the electrode potential. According to this treatment ‐bc of HER is a function of the interaction parameter rA‐A of the adsorbate and y, the parameter which measures the change of free energy of adsorption of the adsorbate with potential. Basing on the two sets of values for rA‐A and y by SBTU at lower and higher concentrations, effects by SBTU on zSBTU and ‐bc have been suggested as a result of different orientations the molecule adopts at two concentration regions, y and rA‐A have been interpreted in terms of adsorbate‐electric field and adsorbate‐solvent interactions at the interphase. The general applicability of the equation for calculating surface coverage (θHA) from polarisation measurements has been discussed.
Time‐resolved laser‐induced thermal grating experiments induced by short pulse CO2‐laser radiation
Authors: Latzel H. , Dreier T. , Giorgi M. , Fantoni R.
Published: July 2012

Using a high pressure carbon dioxide laser with pulse lengths of 80 ns laser‐induced thermal grating spectroscopy (LITGS) experiments have been carried out in gas mixtures consisting of an absorbing species (ethylene) and buffer gases (nitrogen/helium) at various temperatures and pressures. The grating structure is written into the medium by absorption and subsequent collisional relaxation of CO2‐laser radiation. Transport properties in these mixtures such as thermal conductivity and the speed of sound have been determined from the time‐resolved signal generated by Bragg scattering of a continuous wave HeNe‐laser beam off the grating structure. Accurate numerical values for transport coefficients are obtained from fitting analytical expressions to the measured oscillating signal traces and are compared with literature values.
Electrochemical scanning tunnelling microscopy (EC‐STM) study of silver electrodeposition from a room temperature molten salt
Authors: Endres Frank , Freyland Werner , Gilbert Bernard
Published: July 2012

Preliminary results by in situ EC‐STM on the electrodeposition of silver on highly oriented pyrolytic graphite (HOPG) from a room temperature molten salt are presented. The molten salt was composed of 55 mol‐% AlCl3 and 45 mol‐% 1‐methyl‐3‐butyl‐imidazolium chloride — this mixture is liquid at ambient temperature — and contained AgCl in a concentration of 0.025 mol/l. The results show for the first time that HOPG can be imaged at this interface with atomic resolution and that the silver deposition/dissolution process can be viewed in situ.
An X‐ray diffraction study on the kinetics of the cation redistribution in the spinel NiAl2O4
Authors: Röttger R. , Schmalzried H. , Günter M.
Published: July 2012

A study of the relaxation kinetics in the partially inverse NiAl2O4 spinel after temperature jumps T1 T2 is reported. The change of the lattice parameter was measured by high temperature X‐ray diffraction at T2 (695–760°C) using NiAl2O4 powder samples equilibrated with NiO in air. For the temperature range of T1 under study (1100–1450°C), the kinetics can be well described by an equation which is formally equivalent to a third‐order rate law. Changes of the diffraction line widths occur during the relaxation which are due to elastic stresses, strongly dependent on the initial temperature T1. Comparison with recent results from optical spectroscopy indicates that the process observed by lattice parameter measurements is not the homogeneous exchange reaction between the two cation sublattices. The nature of the various relaxation phenomena occurring on different time scales is discussed taking concentration inhomogeneities of structure elements and elastic stress fields on different length scales into account.
Effect of barium and cesium promoters on copper/zirconia methanol synthesis catalysts: An FTIR investigation
Authors: Weigel J. , Wokaun A. , Horbaschek K. , Baiker A.
Published: July 2012

Hydrogenation reactions occurring on the surface of a copper/zirconia (Cu: Zr = 50: 50 at.%) catalyst, as well as on Cs and Ba promoted (1 at.%) Cu/Zr samples, have been investigated by means of in situ diffuse reflectance FTIR spectroscopy. Both carbon monoxide and carbon dioxide hydrogenation reactions are monitored with the aim of acquiring information on the methanol synthesis mechanism, and on the role of the promoter components.

The promoter metals are found to enhance the surface concentrations of both methoxy and surface‐bound formaldehyde species, as compared to the unpromoted catalyst. On the surface of the promoted samples, the stretching frequency of singly surface‐bound CO is red shifted by 10cm−1, demonstrating that the C‐O bond is weakened. This behavior is interpreted in terms of an interaction between the promoter ion and the 1π orbital of the adsorbed CO species.
A comparison of metal/vacuum and metal/electrolyte interfaces : The Au(100)/(dimethylsulfoxide) and (dimethylsulfoxide + acetonitrile) systems
Authors: Roelfs B. , Schröter C. , Solomun T.
Published: July 2012

Metal/vacuum and metal/electrolyte Au(100)/dimethylsulfoxide (DMSO) and Au(100)/(DMSO+acetonitrile) interfaces were studied by means of thermal desorption (TDS), photoelectron spectroscopy (XPS), work function change (Δø), differential capacitance and interfacial infrared spectroscopy (SNIFTIRS) measurements. The adsorptive properties of DMSO in gas phase experiments are scrutinized for their relevance to the electrochemical systems. At monolayer coverages DMSO desorbs from Au(100) from two states that are situated at relatively high temperatures of 240 and 275 K. The adsorbed molecule, however, shows no chemical shifts in its core levels, indicating that the chemical contribution to the surface bond is small. Only extra‐atomic relaxation of the O(1s) and S(2p) electron holes were observed in the XPS spectra. This is rationalized by a bonding model that involves a bidentate DMSO interaction with the surface through the electron lone‐pairs on the O and S atoms. The adsorption geometry agrees also with the behavior of the work function (ΔøDMSO = −770mV). Despite the large dipole moment of DMSO, the differential capacitance of the Au/DMSO interface is found to be rather low. It is argued that this is due to the molecule‐surface interaction that is sufficiently strong to hinder a reorientation of DMSO in the interfacial field. The adsorptive properties of DMSO and acetonitrile under competitive conditions provide a further support for this. Since DMSO bonds to Au(100) significantly stronger than acetonitrile (Tdes = 172 K), DMSO displaces acetonitrile from the surface in UHV, as well as under electrochemical conditions. In the latter case this results in a large decrease in the differential capacitance.
Molecular level interface designs using self‐assembling technique for stabilizing Langmuir‐Blodgett films
Authors: Liu Zhong‐Fan , Zhao Chun‐Xia , Zhang Jin , Tang Ming , Zhu Tao , Cai Sheng‐Min
Published: July 2012

Self‐assembled monolayers (SAMs) of HS‐(CH2)2‐X with X being ‐COOH, ‐OH, ‐NH2, and ‐CH2SO3Na were fabricated on Au surfaces for deposition of C8H17‐C6H4‐N=N‐C6H4O‐(CH2)3‐COOH(ABD) LB films. Thus‐created SAM/LB interfaces were studied by the grazing‐angle incident reflection absorption FTIR technique. For ‐NH2 group, the interface was proved to be dominated by ‐NH3+‐ OOC‐ ionic bonding structure. When X was ‐COOH, an eight‐membered face‐to‐face hydrogen bond was observed at the SAM/LB interface. With the ‐OH terminated interface, two types of hydrogen bond were created: one is the face‐to‐face hydrogen bond and the other one is the side‐by‐side hydrogen bond. In the case of Au/‐CH2SO3Na/HOOC‐ interface, two terminal groups seem to exchange their cations, forming a ‐CH2SO3H/NaOOC‐structure. The stability of these monolayer assemblies was investigated using Atomic Force Microscopy (AFM). It is found that all these films showed a greatly improved structural stability and the destructive three‐dimensional rearrangement of ABD molecules has been effectively prohibited. The sequence of film stability was ‐NH2>‐COOH>‐OH>‐CH2SO3Na, with the first two interfaces exhibiting even nice stability in aqueous solution, strong enough for tolerating the interfacial electron transfer studies.
Micellar solutions of octyl monoglucoside in the presence of butanol: A small angle and light scattering study
Authors: Möller A. , Lang P. , Findenegg G. H. , Keiderling U.
Published: July 2012

Aqueous solutions of β‐D‐octyl‐monoglucoside (β‐C8G1) with different amounts of 1‐butanol have been studied using static and dynamic light scattering and small angle X‐ray and neutron scattering. Analysis of the small angle scattering data reveals that in the absence of butanol the size and shape of the β‐C8G1 micelles is nearly independent of the surfactant concentration in the experimental range (up to 10 wt‐%). The micelles can be represented by a core‐shell model of a prolate ellipsoid of revolution with a ratio of the minor to major semi‐axis of 3:1. Although the micelles do not change in size, their apparent molar mass and the apparent hydrodynamic radius exhibit a pronounced concentration dependence in this range, which indicates attractive intermicellar interactions. Addition of butanol to the solution causes the micelles to grow with respect to the longer axis (the minor semi‐axis), whereas the cross‐sectional radius (the major semi‐axis) remains constant. Near the solubility limit S of butanol in the micellar solution the scattering particles become apparently larger. Here, the core‐shell model of a prolate ellipsoid of revolution fails to fit the experimental results.
Activity coefficients and solubilities of the system (Ag/Cs)NO3‐H2O from vapour pressure measurements
Authors: Geerlings Jürgen , Richter Joachim , Rørmark Lisbeth , Øye Harald A.
Published: July 2012

Vapour pressures of water over (Ag/Cs)NO3‐H2O (0, 40, 60, and 100% AgNO3) are reported at three temperatures: 152,179, and 218 °C. The water activities derived from these data are fitted with equations for multicomponent electrolyte solutions developed by Van Laar and Pitzer (three models: Van Laar model, Pitzer‐Van Laar model, Pitzer‐Simonson model). With these models the mean activity coefficients of the salts and the solubilities of the pure salt components (AgNO3 or CsNO3) in the ternary mixture are calculated. The advantages of the Pitzer‐Simonson model are underlined.
Thermodynamic study of the NaCl + MgCl2 + H2O mixed system by emf measurements at different temperatures
Authors: Hernández‐Luis Felipe , Fernández‐Mérida Luis , Esteso Miguel A. , Galleguillos‐Castro Héctor R.
Published: July 2012

Mean activity coefficients of NaCl in NaCl + MgCl2 + H2O mixed system were determined from the emf measurements of galvanic cells without transport and at 15, 25, 35 and 45 °C. The measurements were carried out at total ionic strengths of 0.1, 0.3, 0.5, 1, 2, 3, 4 and 6 mol·kg−1 and at ionic strength fractions for MgCl2 between 0 and 0.8 mol·kg−1. These activity coefficient values were analysed by using the Harned rule and the treatments of Scatchard‐Rush‐Johnson and Pitzer. From these, it can be deduced that binary ionic interactions are only significant in this mixed system and hence triple ionic interactions are negligible (except for the mixture of 6 mol·kg−1 for which these high‐order interactions probably cannot be considered irrelevant). Moreover, a decrease in the ion‐ion interaction (and therefore an increase in the ion‐solvent interaction) takes place by the simultaneous presence of Na* and Mg2+ ions in the mixture, specially when the ionic strength increases, probably as a consequence of the larger hydration of the Mg2+ ions. Finally, the excess properties of the mixtures were determined and qualitatively analysed against the composition of the mixed system.
Kinetics of the photochemical reaction of C2F5I and C4F9I with C2F4
Authors: Linyang Zhang , Xiaoyu Zhang , Weihua Yang , Xudong Lou , Fuß W.
Published: July 2012

Although the formal insertion of C2F4 into the CI bond of iodides is a chain reaction, we found quantum yields clearly below 1. We show that this is due to an inhibition reaction: the very rapid reaction of the radicals with molecular iodine, which accumulates during the reaction in amounts equal to the radical dimers. The corresponding kinetic model quantitatively describes the quantum yields and product distributions, if we assume for the rate constants kn for the addition of the F(C2F4)n radicals to C2F4 (in 107 cm3 mol−1 s−1 at 373 and 303 K, respectively): k1 = 19 and 3.6. k2 = 8.0 and 1.9, k3 = 1.6 (303 K).