bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Electrical Migration in Electrochemical Cells by the Network Method
Authors: Moya A.A. , Hayas A. , Horno J.
Published: March 2014

Network approach has been used to analyse the electrical properties of a system consisting of three ionic species having different charges in contact with blocking electrodes. A network model for the electrodiffusion process taking place in such a system has been proposed. With this model and the electric circuit simulation program PSPICE, the transient response of the system to a step‐function applied potential difference and the small‐signal ac response of this system subject to a steady external voltage bias have been simulated. Nyquist plots for the electrochemical impedance, and the time evolution of the surface charge density stored in the electrical double layers at the electrode/electrolyte interfaces as well as the electric current density through the system, are given. The ionic concentration, the electric charge density, and the electric potential profiles across the cell were also obtained as a function of time.
Determination of Infinite Dilution Diffusion Coefficients of Polycyclic Aromatic Hydrocarbons in Heptane and in Octane
Authors: Fan Yiqun , Qian Renyuan , Cheng Mingxiao , Shi Meiren , Shi Jun
Published: March 2014

The diffusion coefficients of benzene, naphthalene, anthracene, phenanthrene, and diphenyl at infinite dilution in heptane and in octane in the temperature range 303.2 to 333.2 K were determined by the Taylor dispersion technique. Two empirical estimation methods for diffusion coefficient were tested against our experimental data and a free‐volume‐type expression was used to correlate the diffusion coefficients.
Application of Paramagnetic Relaxation Reagents in Characterization of Fullerene Derivatives
Authors: Kitaygorodskiy Alex , Lawson Glenn E. , Sun Ya‐Ping
Published: March 2014

The 13C spin‐lattice relaxation times of C60/C70 were measured in CS2 solutions containing different concentrations of Cr(acac)3. The coincidence of paramagnetic relaxation times for fullerenes and TMS shows that there is no specific intermolecular interaction between fullerenes and Cr(acac)3. The relaxation times were used to select optimal experimental parameters for accumulation of 13C NMR spectra of fullerenes. It was demonstrated that proper application of Cr(acac)3 overcomes unfavorable relaxation properties of fullerenes and leads to considerable (at least 5‐fold) improvement of signal‐to‐noise ratio in their 13C NMR spectra.
Chaos Control and Tracking of Periodic States in a Forced Thermokinetic Oscillator Model
Authors: Delgado E.J. , Münster A. F. , Schneider F. W.
Published: March 2014

The Sal'nikov thermokinetic oscillator model is investigated in a spherical reactor with a temperature‐dependent surface/volume ratio. If the temperature is driven sinusoidally, period doubling and chaos occurs. A typical chaotic state of the model is analyzed by various methods, like attractor reconstruction, dimensional analysis and computation of Lyapunov exponents. We demonstrate that unstable periodic orbits embedded in the strange attractor are stabilized by a continuous delay time method according to Pyragas. Two simple stabilized orbits are shown and discussed. We also use the continuous method of chaos control for the tracking of unstable orbits through a sequence of period doublings and chaos.
Pressure Dependence of the OH‐Stretch Raman Spectra of Supercooled Water
Authors: Karger N. , Lüdemann H.‐D. , Sceats M.G.
Published: March 2014

Raman spectra of the OH‐stretching region of liquid H2O and 10% H in D2O have been obtained between −50 and + 100°C at pressures up to 240 MPa, extending into the deeply supercooled region. Application of pressure made it possible to study liquid water at temperatures 20 K lower than reported so far.

The low‐frequency shoulder of the H2O‐spectra grows rapidly with falling temperature. The relative intensity of the collective band increases monotonically to the lowest temperatures studied.

Supercooled water shows a number of thermodynamic and transport anomalies, which become apparent from the unusual p‐, T‐dependence of the compressibility and the molecular mobility in the pressure range between 0 and 200 MPa. The Raman spectra, however, do not change significanctly in this pressure region. At the lowest temperatures they are practically independent of pressure.

This finding suggests that the intensity of the collective Raman band originates from short range correlations of the OH‐bond vibrations, that are not identical to the more extended density fluctuations responsible for the well known anomalies of supercooled water.
Firm Binding and Loose Attachment of Ru(II) Complexes to Colloidal Silica in Aqueous Solution. Evidence Based on Biphotonic Ionization and a Kinetic Salt Effect on the Reaction with Hydrated Electrons
Authors: Naik D.B. , Schnabel W.
Published: March 2014

The photoionization of tris‐2,2′‐bipyridyl Ru(II) complexes in dilute aqueous solution (pH = 9.8), yielding hydrated electrons, is enhanced by a factor of about 2.5 by colloidal silica. LiCl reduces the enhancement factor. The photoionization yield decreases with decreasing pH. Moreover, the presence of colloidal silica causes a drastic increase in the lifetime of the hydrated electrons. The results are interpreted in terms of firm binding and loose attachment of Ru(II) complexes to the negatively charged silica particles the extent of which is controlled by the silica concentration at fixed Ru(II) complex concentration. Firm binding causes a reduction in the ionization potential which results in higher photoionization yields. Loose attachment results in a kinetic salt effect on the rate constant of the reactions of hydrated electrons.
Ion Pairing in the Analysis of Voltammetric Data at the ITIES: RbTPB and RbTPBCl in 1,2‐dichloroethane
Authors: Kontturi A. K. , Kontturi K. , Manzanares J. A. , Mafé S. , Murtomäki L.
Published: March 2014

The association of rubidium‐tetraphenylborate (RbTPB) and rubidium‐tetrakis(‐chlorophenyl)borate (RbTPBCl) ion pairs in the organic solvent 1,2‐dichloroethane (DCE) have been obtained from condutivity and voltammetric data. Conductivity measurements given KRbJPBCl = 43100 M−1 and yield a lower bound for KRbTPB (KRbTPB > 70000 M−1). The latter association constant is at variance with the previously accepted value. A method for analysing voltammetric data which allows for the determination of the association constants is presented. The positive polarization limit where the transfer of Rb+ takes place is shifted by ca. 200 mV when changing the anion of the organic base electrolyte from TPB− to TPBCl−. If we interpret this shift in terms of the association constant, then KRbTPB = 7.4·107 M−1. The values of KRbTPB and KRbTPCl are discussed in terms of the classical theories by Bjerrum and Fuoss. Finally, we consider if the preferential solvation of p‐chlorophenyl rings of TPBl− could account for the observed difference between the values of the association constants.
UV/VIS‐absorption Spectra of HOBr and CH3OBr; Br(2P3/2) Atom Yields in the Photolysis of HOBr
Authors: Benter Th. , Feldmann Ch R. , Kirchner U. , Schmidt M. , Schmidt S. , Schindler R. N.
Published: March 2014

Gas phase UV/VIS‐absorption spectra are reported for HOBr and CH3OBr in the wavelength range (230 < λ < 400)nm. The quantum yield for Br(2P3/2) atom generation was determined to be ≥0.95 in the laser photolysis of HOBr at λ = 363 nm.
Strukturvorhersage von Kristallen aus binären Edelgasgemischen mit globalen und lokalen Optimierungsmethoden
Authors: Putz H. , Schön J. C. , Jansen M.
Published: March 2014

Using global optimization methods (Simulated Annealing, Quench, Gradient Descent) possible structures of crystals consisting of binary combinations of the four considered noble gases Ne, Ar, Kr and Xe have been investigated. The computer simulations showed that in all instances they should crystallize either in separate phases of the pure noble gases or in a shared close‐packed structure. No other structure types occurred among the optimal configurations. Phase separation was observed in all systems containing Ne and in the system Ar/Xc. Mixing Ar and Kr led to a random distribution of the two species on the sites of a close‐packed structure, i.e. to a solid solution. This corresponds to experimental observations.
Far Precritical Effect in 1,3‐Dimethoxybenzene‐Alkane Mixtures Studied by Nonlinear Dielectric Effect
Authors: Śliwinska‐Bartkowiak M. , Radojewska L.
Published: March 2014

Nonlinear dielectric effect (NDE) was measured in mixtures of 1,3‐dimethoxybenzene with n‐alkanes. The mixtures were found to exhibit an apparent critical point, concealed below the melting point of the mixture and manifesting itself by anomalous NDE behaviour in the vicinity of the critical concentrations in the stable liquid phase.
SERS Study of Acridine Adsorption on Copper Electrode
Authors: Niaura G. , Malinauskas A.
Published: March 2014

It was demonstrated that acridinium cation does not interact directly with copper electrode surface in acid sulfate solution. In the presence of chloride, acridinium cation adsorbed on the electrode as an ion pair with chloride anion. In the whole potential range investigated, from 0 V to a chloride desorption potential at about −0.6 V, acridinium did not undergo any redox‐process. By shifting a potential towards negative values acridinium tends to reorient to a position perpendicular to the electrode plane. The formation of the ion pair stabilized chloride adsorption on the electrode surface.
New Approach to Synthesis of Fractal Materials with a given Fractal Dimension. Synthesis and Some Properties of Amorphous Fractal Films of Copper Sulfide
Authors: Strizhak Peter E.
Published: March 2014

A method of synthesis of fractal films of copper sulfide is proposed. Formation of fractal films is induced by spatial patterns formed in so‐called ‘oxygen’ oscillating chemical reaction – oxidation of ascorbic acid by air oxygen in the presence of hydrogen sulfide ions, methylene blue, and copper(II) coordination compound. The formation of the CuS film in this system is observed due to the slow reaction between copper(II) coordination compound and the hydrogen sulfide ions. A fractal dimension of CuS films correlates with the fractal dimension of chemical patterns. The electrical resistance of the fractal films and the sensitivity of Cu2+‐selective electrodes with the fractal CuS surface to Cu2+ ions were measured. These results are interpreted in terms of fractal dimension.
Differential Thermal Analysis of Long‐Chainn‐Alcohols under High Pressure
Authors: Reuter Jörg , Würflinger Albert
Published: March 2014

Differential thermal analysis (DTA) measurements under pressures up to 250 MPa and temperatures of about 300 to 370 K have been performed on long chainn‐alcohols CnH2n+1OH, including 1‐tetradecanol, 1‐pentadecanol, 1‐hexadecanol, 1‐heptadecanol and 1‐octadecanol. On heating, these alcohols change from a crystalline to a rotator phase a few degrees below their melting points. The rotational state of 1‐tetradecanol can only be reached by cooling from the melt. Thep‐T‐phase diagrams of these alcohols have been established. They demonstrate, that the coexistence region of the rotator phase is increased under pressure. In contrast to the high‐pressure phase behaviour of long chainn‐paraffins the phase transition lines ofn‐alcohols diverge upon increasing pressure and no triple point is observed. This different behaviour is connected with the enlarged enthalpy change at the transitions to the rotator phase that reduces the slope dT/dpof this phase transition line. Dielectric measurements were performed on 1‐pentadecanol which support the orientationally disordered state of the rotator phase.
Adsorption of Gases on Solid Surfaces
Authors: Freund Hans‐Joachim
Published: March 2014

Metal surfaces have for a long time been and still are in the focus of experimental and theoretical activities in surface science. One has started to understand in some detail the interaction of gases with respect to structural and dynamical aspects. Non‐metallic substrates on the other hand have only recently received more attention and corresponding studies have been started. In view of the importance of compound surfaces in many fields, including catalysis, this development is not unexpected. We review our efforts in the field of surface science studies of oxide surfaces and emphasize in addition to clean oxide surfaces also metal modified surfaces as a model towards the study of complex systems which are typical for catalysts. In addition to studies of the geometric and electronic structure of compound surfaces we also cover investigations of adsorbate dynamics reporting on newly designed experiments on the basis of magnetic resonance as well as on laser‐induced desorption studies. In the latter investigations we have probed spatially resolved the time‐of‐flight distributions of molecules in individual quantum states as they leave the oxide surface.
Heterogeneous Catalysis at an Atomic Scale
Authors: Sachtler Wolfgang M.H.
Published: March 2014

For the overwhelming majority of processes in modern chemical and petrochemical industry, the presence of an active and selective catalyst is crucial. In the USA the total value of products from catalytic processes has been estimated to be roughly 9·1011 $ per year, corresponding to 17% of the GNP. An arsenal of modern methods enables the physical chemist to characterize active sites and chemisorption complexes; quantum chemical calculations increasingly lead to concrete predictions. The key issue remains, however, to unravel reaction mechanism and to use this knowledge for the design of superior catalysts.

In the present paper some challenging problems are addressed:

How does a “promoter” in a Rh/NaY catalyst direct CO hydrogenation towards synthesis of ethanol and ethyl acetate?

How does NOx decompose over Cu/ZSM 5 catalysts and how is its reduction to N2 enhanced by O2?

How does the isomerization of butane to isobutane avoid primary carbenium ions over some acid catalysts, why are other catalysts with stronger acid sites less active?
Surface Properties and Catalytic Performance of Novel Mesostructured Oxides
Authors: Schüth F.
Published: March 2014

Mesoporous oxides of the M41S family, discovered by scientists of the Mobil Oil Corporation in 1991, are an exciting class of porous materials. Their unique pore system with the extremely sharp pore size distribution, which is adjustable in the range between about 2 and 10 nm at will, and the extremely high surface areas up to 1500 m2/g open very promising prospects with respect to the development of new catalysts. The oxides were initially prepared based on silicon and aluminum, but later other elements could be incorporated. Moreover, totally non siliceous oxides could be synthesized using surfactants, similar to the synthesis of the M41S materials. First examples for the use of these oxides as catalysts have been reported. In addition, also the properties of the materials as supports for noble metals have been investigated recently.
Production and Properties of Nanostructured Metal Oxide Particles
Authors: Becker A. , Benfer S. , Hofmann P. , Jacob K.‐H. , Knözinger E.
Published: March 2014

Two fundamentally different procedures of metal oxide production, which provide nanometer‐sized oxide particles, are described here. Earthalkaline oxides, e.g., are produced by chemical gas phase deposition with MeO molecules (Me = Ca, Mg) and clusters being directly deposited after gas phase reaction between Me atomes and O2 molecules. The procedure also allows the dotation of MgO with a second component such as CaO and vice versa. In order to obtain information on surface properties like reactivity and surface composition, OH groups as probe species are produced on the surface of the resulting particles. The respective chemisorption as well as thermal desorption of OH groups are monitored by FT‐IR spectroscopy. X‐ray powder diffraction provides information on the bulk composition and bulk structure. Cu2O, on the other hand, is produced by deposition of Cu metal from the vapour and subsequent oxidation of the resulting solid particles, which are then characterized by X‐ray powder diffraction and UV/VIS spectroscopy.
Reactivity and Dynamics of Bifunctional Phosphines Immobilized on Oxidic Supports – A Solid‐State NMR Study
Authors: Blümel Janet
Published: March 2014

The successful immobilization of transition metal catalysts on oxidic surfaces via bifunctional phosphines like PPh2(CH2)3Si(OEt)3 is crucially dependent upon the knowledge of the reactions of both their functionalities with the surface. In this study, solid‐state NMR spectroscopy served as a powerful analytical tool. The nature of a P(V) byproduct, generated by the combined action of ethoxysilane groups and silica surface, has been investigated and ways have been shown to avoid it. The study of the reactions of ethoxysilanes with silica surfaces led to the discovery, that addition reactions with surface siloxane groups play a dominant role. Therefore, the surface coverage can be optimized and later “leaching” of the catalyst prevented by using rigorously dried silica. The success of the developed concepts was demonstrated by the selective immobilization of di‐ and tricarbonylnickel complexes. Both types of complexes can be distinguished by their characteristic 31P solid‐state NMR spectra. The dynamics of immobilized phosphines and carbonylnickel complexes in the presence of different solvents has been studied by 31P suspension NMR spectroscopy. Polar, non‐viscous solvents gave the narrowest resonances, corresponding to the greatest mobility of the surface‐bound species.
Two‐Dimensional Imaging of Reactively Desorbing CuF: State‐Selective Angular and Velocity Distributions
Authors: Sugawara K. , Sun W. , Wach Th. , Wanner J.
Published: March 2014

During the dry etching reaction of fluorine on copper surfaces, copper monofluoride is the main desorbing product at conditions of low fluorine dosing and surface temperatures above 900 K. Results from a detailed internal product‐state analysis of CuF molecules by laser‐induced fluorescence has been reported recently by Bracker et al., Can. J. Chem.; J.C. Polanyi, Special Issue 72, 643–651 (1994). The present contribution focuses on the state‐selective angular and velocity distributions of the desorbing CuF molecules. The product excitation is based on an actively stabilized ring dye laser in connection with spatially resolved fluorescence imaging by a CCD camera. For all investigated rovibrational product levels the desorbing molecules exhibit a cosn φ distribution with n values between 1.2 and 1.4. The state‐selective velocity distributions of the desorbing CuF molecules are Maxwellian with translational temperatures equal to the surface temperature within the error limits. These results imply that the reaction proceeds indirectly at submonolayer conditions with the following steps: 1/2F2(g)→F(ad) + Cu(s)→CuF(ad)→CuF(g). Furthermore, the associative desorption of CuF from copper surfaces is fully consistent with a non‐activated desorption mechanism.
A PIR, HAS and LEED Study of the Monolayer CH4‐NaCl(001)
Authors: Heidberg J. , Schönekäs O. , Weiss H. , Lange G. , Toennies J.P.
Published: March 2014

The adsorbate CH4‐NaCl(001) at monolayer coverage has been studied by means of helium atom scattering (HAS), electron diffraction (SPA‐LEED) and polarization Fourier‐transform infrared spectroscopy (PIR) in the temperature range between 45 K and 10 K. Above 40 K a splitting of the v4 mode of CH4 into a polarization‐dependent doublet absorption was observed in the FTIR spectra. HAS and SPA‐LEED measurements reveal a (1×1) superstructure with one CH4 molecule per NaCl ion pair. Calculations of the potential energy support these experimental results, yielding a perfect dipod arrangement of the CH4 molecules in the (1×1) structure. Isosteric cooling of the adsorbate results in a two‐dimensional phase transition of order > 1. By means of HAS a p(2×2) superstructure was found at T < 30 K, whereas SPA‐LEED suggests a (2×1) symmetry. Beside of a remarkable sharpening of all IR absorptions two additional features are observed. The phase transition is reversible. Two to three hours after preparation both diffraction methods yield the (1×1) structure even at lowest temperatures. This time behaviour may be indicative of a quantum effect, namely nuclear spin conversion, in the adsorbed methane layer.

Knowledge of the interaction between CH4 and NaCl is necessary to predict the gas migration and therewith the safety aspects for a final repository of nuclear waste in permian salt domes.
Nucleation and Growth of Plasma‐Polymerised Hexamethyldisilazane on Iron‐Substrates
Authors: Grundmeier G. , Stratmann M.
Published: March 2014

Plasma polymer films of hexamethyldisilazane (HMDSN) were deposited on iron substrates by an audio frequency discharge. The investigations focus on the activation of the iron surface by an oxygen plasma, the adsorption of the monomer and the initial states of polymer formation. Surface compositions were examined by means of in‐situ Infrared‐Reflection‐Absorption‐Spectroscopy (IRRAS) and Quartz‐Crystal‐Nanoweighting (QCN). It turned out that during the oxygen plasma treatment an additional layer of iron oxihydroxide is formed. The resulting high density of surface hydroxyls leads to the hydrolysis of the adsorbed silazane. Plasma‐polymerised HMDSN is characterised by a reduced carbon and nitrogen content and the incorporation of siloxane units. In the range of about 4 nanometer the polymer structure changes significantly with the film thickness. With increasing film thickness the concentrations of siloxane and N‐H units decrease. The interface between the oxide and the polymer is characterised by strong polar interactions between surface hydroxyls and the siloxane group and additionally by directed bonds via silanolate units.
Time Resolved Charge Transfer with Hot Electrons at the Silver/Electrolyte Interface
Authors: Diesing D. , Rüße S. , Otto A. , Lohrengel M.M.
Published: March 2014

Tunnel junctions of the type metal/oxide/noble metal are contacted with an electrolyte where the noble metal is the working electrode. Hot electrons passing through the oxide film reach the metal/electrolyte interface and occupy protonic states in the electrolyte. Pulse experiments indicate an adsorbed hydrogen phase at the silver/electrolyte interface.
In‐Situ Photoelectron‐Spectroscopy of Oxygen Electrodes on Stabilised Zirconia
Authors: Zipprich W. , Wiemhöfer H.‐D. , Vohrer U. , Göpel W.
Published: March 2014

Evaporated silver films as an oxygen electrode material were studied in‐situ and ex‐situ by XPS and UPS under UHV conditions. The experimental set‐up consisted of a miniaturised solid state galvanic cell with yttria stabilised zirconia as solid electrolyte and a solid oxide reference electrode. The oxygen activity at the working electrode was changed by controlling the electrode potential versus the reference electrode consisting of a metal/metal oxide system Me/MeO (with Me = Pd or Fe). The electrode surface was investigated by XPS and UPS under cathodic polarisation with low oxygen activity as well as under anodic polarisation with steady‐state oxygen evolution. The measurements have been performed between 720 K and 1100 K.

With XPS, several oxygen species have been detected at the silver surface. Their concentration depends on the applied electrode potential. A species with low XPS binding energy was found whose intensity increased with anodic polarisation. It is attributed to oxygen species at the surface and at subsurface sites. The latter corresponds to oxygen atoms dissolved in the bulk. Under cathodic polarisation, the oxygen species at low binding energy disappeared, but a second oxygen species at higher XPS binding energy grew in intensity with increasing cathodic polarisation. In view of the reducing conditions and the presence of water, this latter oxygen signal is attributed to a steady state concentration of hydroxyl species at the surface. With UPS, the work function of electrons at the silver surface was determined as a function of the applied overpotential. The work function of silver increased by about 1.6 eV in changing from a cathodic polarisation of −1.5 V to an anodic polarisation of +1.5 V. This pronounced change is caused by a concentration decrease of adsorbed OH and a corresponding increase of adsorbed O atoms leading to a higher surface electron affinity. Applying high cathodic as well as anodic polarisation led to the formation of insulated silver particles within open pores of the silver layer on the surface of the zirconia. These particles which are electronically coupled to the Fermi level of the underlying zirconia cause a superposed but slightly shifted second UPS spectrum with the shift depending on the effective overvoltage. The as determined overvoltage at the silver electrode depends linearly on the cell voltage.
Nanostructuring of Electrode Surfaces by Tip‐Induced Metal Deposition
Authors: Ullmann R. , Will T. , Kolb D.M.
Published: March 2014

It is demonstrated how the tip of an STM can be used as a tool for the deposition of small Cu clusters onto flat surfaces at preselected positions. This is done by depositing Cu onto the tip which then acts as a reservoir from which Cu is handed over to the surface during an appropriate tip approach. It is shown how the instrumental parameters can be used to vary the cluster size or, by inducing tip oscillations, to generate cluster trains instead of a single cluster. Cu clusters can also be selectively erased by applying very positive tip potentials. The influence of the substrate on the shape of the tip‐induced Cu clusters is briefly discussed and preliminary results on the electrochemical stability of single clusters of various sizes are presented.
Chemical Sensors for Acid‐Base‐Active Gases: Applications to CO2 and NH3
Authors: Holzinger Michael , Fleig Jürgen , Maier Joachim , Sitte Werner
Published: March 2014

It is shown how acid‐base interactions of complex gases such as CO2, NH3 or H2O with solids can be used to measure the partial pressures of these gases. Two examples developed in our laboratory are presented:

The interactions of acid‐base‐active gases such as NH3 (Lewis base) or BF3 (Lewis acid) with the ionic conductors AgCl or CaF2 cause ionic space charge regions giving rise to a change of the ionic surface conductivity. The response time can be significantly improved by applying a microelectrode impedance method.

The use of a potentiometric arrangement the cell reaction of which is a pure acid‐base reaction, leads to a fast, precise and drift‐free CO2‐sensor. Since the reference electrode is not affected by CO2 itself, the entire cell can be exposed to the CO2 and O2 containing atmosphere without the necessity of sealing the reference electrode. The chemical potential of oxygen even though important for defining the component activities at each electrode cancels in the overall reaction of our cells. The performance of two cells is presented. While the measuring electrode consists of Na2CO3, the reference electrodes discussed are made of Na2Ti6O13/TiO2 or Na2Ti6O13/Na2Ti3O7 two‐phase mixtures, both being stable with respect to a reaction with CO2. The sensors are very fast, response times are of the order of seconds.
Thermodynamics of Fluid Sulfur Hexafluoride from Molecular Dynamics Simulations
Authors: Lustig Rolf
Published: March 2014

An octahedral 6‐center Lennard‐Jones model for sulfur hexafluoride is used in classical molecular dynamics simulations. A variety of thermodynamic properties are computed over a wide range of the fluid state and compared to data obtained from a preliminary fundamental equation developed by de Reuck et al. [IUPAC Thermodynamic Tables Project Centre, London 1991]. Properties which are correlated well by the empirical fundamental equation are also reproduced accurately by the model.
Pulsed Ultraviolet Laser Photolysis of Substituted Phenyl Diazosulphonates at 248 nm
Authors: Nomayo M. , Wokaun A.
Published: March 2014

The photochemical decomposition of aqueous phenyl diazosulphonate solutions by KrF excimer laser pulses at 248 nm is investigated. The present study complements earlier investigations (Franzke et al. 1991, 1992) of the photochemistry of this class of compounds induced by irradiation at 308 nm (XeCl excimer laser), and in the 370–390 nm wavelength range (dye laser pulses). From the comparison, conclusions with regard to the wavelength dependent photolysis pathway are drawn.

Phenyl diazosulphonates carrying methoxy‐ or ester‐type substituents at the aromatic ring are observed to decompose in a two‐step‐reaction in aqueous solution: Photolysis proceeds via the phenyl diazonium ion as an intermediate, to yield the corresponding phenol as a product.

In contrast, the photolysis of 3‐vinyl‐phenyl diazosulphonate in aqueous solution at 248 nm results in a complex reaction involving via more than one intermediate. UV spectra recorded during photolysis show that products characterized by an absorption maximum at 272 nm are formed; these spectra are identical with those of final products from 308 nm photolysis, which are identified as 3‐hydroxyethyl‐phenols. – The photolysis pathway of 4‐hydroxy‐phenyl‐diazosulphonate is found to proceed via the diazoquinone, instead of a diazonium ion.

As a consequence of the high energy of 248 nm photons, the mentioned substituted phenols are not the final products of the photochemical reaction. These molecules are further decomposed by absorbing 248 nm photons; the quantum efficiency of these secondary photochemical reactions is lower by one to two orders of magnitude, as compared to the primary photolysis of the parent compounds.
Femtosecond Time‐Resolved Measurement of Electron Relaxation at Metal Surfaces
Authors: Aeschlimann M. , Pawlik S. , Bauer M.
Published: March 2014

Time resolved two‐photon photoemission, based on the equal pulse correlation technique, is used to measure the energy relaxation of the photoexcited electrons in various polycrystalline metal samples. While for Ag the inelastic lifetime of excited electrons is, within our time resolution, in agreement with the Fermi‐liquid theory, the result obtained for Au is very different. Scanning tunneling microscopy studies reveal that the enhanced inelastic lifetime of gold is not caused by surface effects. The measured inelastic relaxation time for transition metals with unoccupied d‐orbitals is shorter as compared to the noble metals, indicating that the inelastic decay depends on the number of unoccupied d‐orbitals below the probed energy state.
On the Kinetics of the Anodic Oxidation of GaP
Authors: Heckner K.‐H. , Majoros G. , Kraft A. , Landsberg R.
Published: March 2014

The formation of anodic oxides on n‐GaP were studied by means of neutron activation analysis measuring the 32P activity in the film and in the solution. The oxide film formation under potentiostatic conditions and the competing oxide dissolution during film formation and under currentless conditions were investigated. The best description of the oxide growth is a combination of the parabolic growth law for film formation and of a zeroth order process for the simultaneous film dissolution. The rate constant for film formation linearily depends on the square of the applied voltage. The dissolution rate also increases with increasing the applied voltage. The dissolution rate of oxide films decreases under currentless conditions compared with dissolution during growth.
Temperature Programmed Surface Reaction Studies of the Methanol to Gasoline (MTG) Conversion over ZSM‐5
Authors: Jayamurthy M. , Vasudevan S.
Published: March 2014

The methanol to gasoline conversion over ZSM‐5 has been studied by the Temperature Programmed Surface Reaction (TPSR) technique. The technique is able to delineate the two steps in the process: the dehydration of methanol to dimethyl ether and the subsequent conversion of dimethyl ether to hydrocarbons. The activation barriers associated with each step was evaluated from the TPSR profiles and are 108 kJ/mol and 195 kJ/mol respectively. The methanol desorption profile shows considerable change with the amount of methanol molecules adsorbed per Brönsted site of the zeolite. The energy associated with the desorption process, (CH3OH)nH+ –ZSM‐5→(CH3OH)n–1H+ –ZSM‐5 + CH3OH, shows a spectrum of values depending on n. The spectrum is not continuous and has a gap for n = 1. The trend is similar to that for the corresponding gas‐phase reaction, (CH3OH)nH+ →(CH3OH)n–1H+ +CH3OH. The present investigation highlights the importance of the protonated methanol cluster, (CH3OH)nH+ –ZSM‐5, in the primary step of the MTG process, the formation of dimethyl ether. The reaction is compared with the corresponding gas phase ion‐molecule reaction of CH3OH2+.
Size Distribution and Characterization of Si Nanometer‐Size Particles Obtained by CO2 and Nd: YAG Laser Irradiation of SiH4
Authors: Cáceres Jorge O. , Nájera Juan J. , Lane Silvia , Ferrero Juan C.
Published: March 2014

Silicon ultrafine particles have been obtained from SiH4 by laser irradiation under different experimental conditions. The powders produced are amorphous except for those obtained at 350°C which are a mixture of amorphous and crystalline particles. Sizes are in the range 2–54 nm and mean diameters between 5.3 and 8.1 nm. The particle sizes fit a narrow, log‐normal distribution function (LNDF). No significant variation in size is observed with increase of pressure or temperature within the studied interval.
An Approach to the Intrinsic Kinetics of the Zirconium Oxide Carbochlorination
Authors: Bohé Ana E. , Pasquevich Daniel M.
Published: March 2014

A procedure to overcome the experimental difficulties found in the study of the intrinsic kinetics of zirconia carbochlorination was analyzed. The effect of experimental variables on the carbochlorination kinetics was studied by means of thermogravimetry. The effect of temperature on the extent of two reaction stages was observed: the first reaction stage dominates the reaction at high temperatures and low reaction‐degrees. The second one was of first order with respect to the chlorine partial pressure at 1223 K.
Decrease in the Oxidation Potential of the Tris‐2,2′‐bipyridyl Ruthenium(II) Complex Upon Electrostatic Binding to Colloidal Silica as Evidenced on the Basis of the Reaction with the Azidyl Radical
Authors: Naik Devidas B. , Schnabel Wolfram
Published: March 2014

The azidyl radical which is otherwise unreactive towards the Ru(bpy)32+ complex reacts with this complex in aqueous solution provided negatively charged colloidal silica particles are present. The increase in reactivity is explained in terms of ion binding, i.e. Ru(bpy)32+ complexes becoming rather firmly attached to the negatively charged particles. The attachment causes a decrease in the redox potential of the system Ru(bpy)33+/Ru(bpy)32+ from E0 = 1.27 V vs. NHE (in the absence of colloidal silica) to E0 = 1.17 V vs. NHE (in the presence of colloidal silica). This value was obtained on the basis of E0 = 1.35 V vs. NHE for the system N3/N3−.
Kinetic and Mechanistic Studies of the Reactions of CF3O Radicals with NO and NO2
Authors: Fockenberg Chr. , Somnitz H. , Bednarek G. , Zellner R.
Published: March 2014

The reactions of CF3O radicals with (1) NO and (2) NO2 were studied using two different experimental techniques. A laser photolysis/LIF detection method was applied for measuring the rate constants as a function of temperature (T = 222–302 K) and total pressure (ptot = 7–107 mbar). Whereas the reaction with (1) NO was found to be independent of temperature and pressure with k1 = (4.5±1.2)×10−11 cm3 s−1, the reaction with (2) NO2 was found to be dependent on both of these variables. The temperature dependence of k2 in the high pressure limit can be given by the expression k2,∝ (T) = (8±5)×10−13 exp ((863±194) K/T) cm3 s−1. The product distributions of the two reactions were determined in separate experiments using steady‐state photolysis combined with FTIR spectroscopy. For reaction (1) only CF2O was found as a reaction product with a yield of 0.93±0.10, independent of temperature. For reaction (2) several products (CF3ONO2, CF2O, FNO2) were identified, the overall yield, however, is dominated (≥90%) by the recombination product CF3ONO2. A theoretical analysis of the detailed mechanisms of both reactions was made by performing ab initio energy and geometry predictions in combination with RRKM calculations. Both reactions were found to proceed via an initial addition mechanism involving the CF3ONOx (x = 1, 2) intermediate and a four‐center transition state. A direct abstraction of an F atom by NO or NO2 can be excluded.
Far Infrared Laser Magnetic Resonance Detection of CF3, CHF2, and CH2F
Authors: Nolte J. , Wagner H. Gg. , Temps F. , Sears T.J.
Published: March 2014

Far infrared laser magnetic resonance (FIR‐LMR) spectra of CF3, CHF2, and CH2F radicals were observed in the 300–800 μm wavelength region in the reactions of F atoms with a series of different hydrocarbon and partially fluorinated hydrocarbon molecules. To identify the carriers of the observed resonance patterns and to exclude or identify contamination of the spectra by additional resonances from other paramagnetic species, numerous chemical tests were developed and performed. With optimized sources and the chemical tests in hand, many spectra could be unambiguously attributed to CF3, CHF2, and CH2F, respectively. The present study reports the first gas phase detection of CHF2 radicals in their ground electronic state.
High‐Pressure Picosecond Time‐Resolved Fluorescence Studies on the Excited Intramolecular Charge‐Transfer Kinetics of 4‐(9‐Anthrylmethyl)‐N,N‐Dimethylaniline in Alcohol
Authors: Hara Kimihiko , Bulgarevich Dmitry S. , Kajimoto Okitsugu
Published: March 2014

Picosecond time‐resolved fluorescence spectroscopy has been used to examine the dynamic solvent effect on the excited intramolecular charge‐transfer (ICT)‐state formation in 4‐(9‐anthrylmethyl)‐N,N‐dimethylaniline (AMDMA) in linear alcohol solvents as a function of pressure. The non‐exponential population decay of the local excited (LE)‐state emission is analyzed by fitting to a double exponential function. As solvent viscosity increases, the rate of the ICT‐state formation of AMDMA becomes noticeably faster than the solvent relaxation time, which is gauged by the longitudinal relaxation time of the solvent (τL). The pressure effect on the ICT reaction of AMDMA in the excited state can be accounted for in terms of the pressure‐tuning effect of the solvent viscosity.

In addition, the time‐dependent Stokes shift (TDSS) of the ICT emission is measured at high pressures.
Phase Diagrams with Asymptotic Transition Lines
Authors: Dunkel H. , Bärner K. , Zavadskii E.A.
Published: March 2014

While linear and curved phase transition lines in P(T) or H(T) diagrams can be described by adding linear and quadratic terms in a joint expansion of the Landau coefficients a, b in terms of P–Pt and T–Tt where (Pt, Tt) is a critical point, a new class of phase diagram is obtained by allowing for bilinear, ϵ(P–Pt)(T–Tt), and higher product terms. In this contribution we relate these new expansion terms to some hitherto unexplained experimental P–T and H–T phase diagrams.
The Molecular Structure of Sodium Octanoate Micelles Studied by Molecular Dynamics Computer Experiments
Authors: Kuhn Hubert , Rehage Heinz
Published: March 2014

In this article we discuss the results of molecular dynamics simulations which were performed to get more information on the physical properties of sodium octanoate micelles. The calculations were based on the AMBER forcefield and we succeeded in simulating the dynamic features of the micelle for a period of 300 ps. The aggregate was surrounded by 870 water molecules and the simulation was performed in the isothermic‐isobaric constant NPT ensemble at a temperature of 300 K and a pressure of 105 Pa. From the results, thus obtained, it was possible to obtain some typical properties of the micelle. It turns out that the average radius of the micelle coincides pretty well with experimental results of small angle neutron scattering experiments. It was also possible to determine the actual conformations of monomers outside and inside the micelle. These data are in general agreement with nuclear magnetic resonance studies and with raman scattering experiments. On close inspection it was found that the micelle attains a slightly ellipsoidal shape.
Solvation and Counterion‐Distribution of Sodium Octanoate Micelles Studied by Molecular Dynamics Simulations
Authors: Kuhn H. , Rehage H.
Published: March 2014

In this publication we have studied molecular details of the solvent layer and the counterion distribution around sodium octanoate micelles. The results were obtained from computer experiments using molecular dynamics simulations. From the model it was possible to calculate the radial distribution functions, which give informations on the average distance between water molecules and the polar surfactant head groups. We observed different types of solvent layers. From these experiments it was also possible to calculate the number of hydrogen bonds between surrounding water molecules and the polar surfactant head groups. These results coincide well with experimental data and with other types of computer experiments. In analogy to water molecules it was also possible to get informations on the distribution of sodium counterions around the charged micelle. These results are in general agreement with experimental and theoretical data and they can be used to calculate Coulomb interactions and the net surface charge of the micellar aggregates.
Electron‐Energy‐Loss Spectroscopy of Spin‐Forbidden Transitions with Vibronic Resolution: The Lowest Triplet State of Fluorobenzenes
Authors: Swiderek P. , Schürfeld S. , Winterling H.
Published: March 2014

Low‐energy electron‐energy‐loss spectra in the range of the lowest triplet state are presented for solid benzene, fluorobenzene, and p‐difluorobenzene deposited at a temperature of 30 K. Vibronic structure within the triplet bands of fluorobenzene and p‐difluorobenzene is observed for the first time. The spectrum of fluorobenzene closely resembles that of benzene, whereas p‐difluorobenzene shows characteristic differences. The spectra of all three molecules are dominated by pure progressions of the totally symmetric ring‐breathing vibrational modev1. In addition, less intense transitions to vibronic levels relating to the e2gmodes in benzene are observed and their assignment is given. The occurrence of e2gmodes in all three spectra underlines that the vibronic coupling pathways between the lowest and the second triplet state are similar in benzene and its derivatives. In p‐difluorobenzene a splitting of the extremely low frequency mode that relates to thev8(e2g) vibration in benzene is observed. This is in agreement with theoretical predictions of an asymmetric shape of the lowest triplet potential energy surface along a symmetry coordinate relating tov8in substituted benzenes.
Electronic Structure of Polymerized C60 Phases
Authors: Schulte Joachim , Böhm Michael C. , Schedel‐Niedrig Thomas , Schlögl Robert
Published: March 2014

The band structure and solid state electronic properties of three polymerized C60 phases are investigated by a crystal orbital (CO) approach based on an intermediate neglect of differential overlap (INDO) Hamiltonian. We have considered a one‐dimensional (1D) body‐centered orthorhombic phase as well as two 2D phases crystallizing in a body‐centered tetragonal and a rhombohedral lattice. The CO results derived for the polymerized C60 systems are correlated with electronic structure data of the isotropic body‐centered cubic van der Waals crystal. We analyze the energy bands ϵi(k), the associated electronic density of states (DOS) profiles as well as the atomic net charges and so‐called Wiberg bond indices which measure the strength of covalent bonds. The formation of intermolecular CC σ bonds leads to an enhanced alternation between formal double and single bonds on the soccerball. The dimensionality of the four C60 fullendes considered is discussed on the basis of the different quantities evaluated by the CO formalism. The theoretical results are supplemented by C 1s near‐edge X‐ray absorption fine structure (NEXAFS) spectra of polymerized and non‐polymerized C60 films before and after oxygen contamination.
Special Features of the Preliminary γ‐Irradiation Influence on Photoluminescence of Multi‐Component Silicate Glasses
Authors: Kasymdzhanov M.A. , Kasimova S.S. , Kurbanov S.S. , Khabibullaev P.K.
Published: March 2014

In multi‐component silicate glasses, under the UV‐excitation, time‐resolved luminescence spectra were observed. These spectra occupied the region of 350–700 nm. The dynamics of changes in radiation induced absorption and spectral‐kinetic characteristics of luminescence of γ‐irradiation glasses at the expiry of prolonged time were studied. It is assumed that the luminescence in these glasses is caused by quasi‐molecular compelxe centers which include the elements of base substance and impurity atom. These centers can appear in the glass both in the process of its melting and under the action of ionizing radiation. It is shown that, the centers of different origin are characterized by different spectral‐kinetic properties of their photoluminescence.
Ab Initio Modelling of Defects in Non‐Metallic Systems
Authors: Jones R.
Published: March 2014

The simplicity of density functional methods and the increasing availability of computer‐processing power have enabled ab initio modelling techniques to be applied to very large systems. Our own code, AIMPRO, enables the relaxation of clusters as large as 800 atoms while still maintaining full self‐consistency and a realistic basis. Moreover, the use of pseudopotentials means that applications to Ge clusters are no more time consuming than those built of C. An important thrust of our work has been the computation of accurate vibrational modes of defects and this has caught the attention of several prominent experimental groups with the consequence that joint studies of rather complicated defects have been successfully made. We outline the procedures used and discuss applications that have been made to a wide variety of non‐metallic systems such as vacancy defects in diamond, interstitial centres in silicon and carbon‐related defects in III–V materials.
Modelling Point Defects Diffusion and Interaction in Silicon: The Tight‐Binding Molecular Dynamics Approach
Authors: Colombo L. , Bongiorno A.
Published: March 2014

In this work we discuss the application of tight‐binding molecular dynamics to the study of migration of intrinsic point defects in c‐Si. In particular, we investigate self‐diffusion and formation of vacancy clusters. Furthermore, by means of Hartree‐Fock calculations, we present a quantitative picture for the chemical bond in silicon when point defects are present.
The Heat of Transport of Solute Atoms in Solid Argon
Authors: Jones Clive , Grout P.J. , Lidiard A.B.
Published: March 2014

Molecular dynamics simulations of the solute migration by a vacancy have been made for a Lennard‐Jones model of solid argon. The results have been used to analyse the heat of transport, Q*, for solutes with masses corresponding to those of the noble gases. The theory shows that there are three contributions to Q*, coming from the fluxes of the kinetic energy, potential energy and a virial of the forces. Trends in the kinetic and potential terms are found with increasing mass of the solute atoms which it seems would be shown by solute atoms more generally. The molecular dynamics calculation is in the centre of mass frame and we give the necessary transformations to the required lattice frame.