bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo Simulations of Supported Monolayers of Amphiphilic Molecules
Authors: Stettin H. , Friedemann R. , Mögel H.‐J.
Published: July 2012

MC simulations for a liquid supported monolayer of amphiphilic molecules were carried out within a cubic lattice model using two‐dimensional periodic boundary conditions. The molecules consist of a hydrophilic head and hydrophobic segments. Only excluded volume interactions were taken into account. We varied both the head density and the number of segments. The comparison with attractive interaction including calculations for 15 unit molecules on a cubic lattice provided the same qualitative results in dependence on the head density. The order parameter values in dependence on the head density are greater than the corresponding ones from athermal simulations on a diamond lattice. The difference may arise from the different lattice types. The influence of the chain length on molecular properties as the mean end‐end distance, the mean end‐end projection, the mean height, and the effective layer thickness as well as the order behavior is intensively discussed.
The Debye‐Hückel Theory for Hydrated Ions. V. Enthalpy of Aqueous Solutions of Alkali Halides at 25°C
Authors: Schönert HansjüRgen
Published: July 2012

A recently, presented thermodynamic model which describes the activity and osmotic coefficients of binary and multicomponent aqueous solutions of alkali halides (up to m = 1 mol · kg−1 at 25°C) is applied to the enthalpy of binary solutions. The experimental data can be fitted within their error limits. The model parameters: enthalpy and entropy of transfer of water from the bulk to the hydration sphere of the ions reflect the structure‐breaking/forming properties of the solutions.
Theory of Cyclic Voltammetry for Quasi‐Reversible Electrodeposition Reactions with insoluble Products
Authors: Avaca L. A. , Kaufmann S. , Kontturi K. , Murtomäki L. , Schiffrin D. J.
Published: July 2012

The Matsuda theory of cyclic voltammetry for quasi‐reversible reactions is extended to metal dissolution and electrodeposition. Kinetic data can be conveniently obtained from the measurement of peak potentials and peak currents as a function of sweep rate and switching potentials. As an example, the rate constant for the Zn(s)/Zn++ (aq) couple has been measured to be k0 = 7.5 · 10−7 cm s−1.
A Note on Gravimetric Measurements of Gas‐Adsorption Equilibria
Authors: Staudt R. , Sailer G. , Tomalla M. , Keller J. U.
Published: July 2012

Adsorption equilibria of He, Ar, N2, CH4 on several types of activated carbon (AC) and molecular sieves (MS) have been measured at ambient temperature in the pressure range 0 MPa–15 MPa using a microbalance (Sartorius 4104 S). The resulting experimental data on principle only allow to calculate the difference (m–ρfVas) between the net mass adsorbed m, and the buoyancy related volume Vas of the adsorbent/adsorbate system multiplied by the density of the (fluid) adsorptive ρf. To determine simultaneously m and Vas, the data are fitted to an analytic adsorption isotherm m = m (ρf,T) of generalized Langmuir‐Freundlich type and/or Dubinin‐Radushkeviz type, and to one of four different models for the volume Vas, including the so‐called helium volume, this quantity considered to be constant. – The two times four adsorption isotherms (AI) resulting in this way do not differ much for low pressures (p < 1 MPa), however tend to differ considerably at higher pressures, the helium volume related AI leading to thermodynamic inconsistencies! As a result it can be stated that the buoyancy related apparent volume Vas of a porous adsorbent/adsorbate system strongly depends on the adsorptive used, i.e. on the size of its molecules, and also, to lesser extend, on the amount of mass adsorbed. Consequently, Vas should not simply be identified with the helium volume but instead specified for different adsorptives and pressure ranges used in industrial adsorption processes.
On the Formation of Catanionic Surfactant Precipitate
Authors: Škrtić D. , Babic‐Ivančić V. , Bujan M. , Tušek‐Božić L. J. , Filipović‐Vinceković N.
Published: July 2012

The morphology, structure and composition of catanionic surfactants formed during spontaneous batch precipitation from equimolar mixtures of alkylammonium chlorides and sodium alkyl sulfates, both with alkyl chains containing 10, 12 and 14 carbon atoms, were investigated by elemental, X‐ray and IR analysis. – Size distribution data are used to assess the mechanisms which control the precipitation at different stages of the process. Under experimental conditions employed (low surfactant concentration, high ionic strength) practically pure decylammonium decyl sulfate, dodecylammonium dodecyl sulfate or tetradecylammonium tetradecyl sulfate were formed. Crystalline catanionic surfactant particles exhibited low symmetry and interplanar spacings typical for lamellar structure. Great similarity of IR spectra obtained for the systems with alkyl chains containing 12 or 14 carbon atoms indicates essentially the same type of electrostatic interactions between the headgroups in these systems. – Catanionic surfactant formation could be described by a general equation of the type

dV50 = atb

Determined values of the coefficient a and exponent b varied with the length of alkyl chain and the type of the rate – controlling process (growth, recrystallization and/or dissolution). Microscopic observation showed the coexistence of crystalline and liquid crystalline phase in aged systems.
Radical Analysis in the Pyrolysis of Hydrocarbons by Scavenging with Dimethyl Disulfide
Authors: Guthier K. , Hebgen P. , Loock H. P. , Homann K. H. , Zimmermann G. , Hofmann J.
Published: July 2012

Radicals formed in the low pressure pyrolysis of hydrocarbons can be quantitatively analyzed by scavenging them with dimethyl disulfide (DMDS) in the condensed phase, the pyrolyses of several hydrocarbons (ethyne, ethene, 1.3‐butadiene, and benzene) have been studied in a flow reactor at 1300 K and 10.7 mbar. Samples of the hot gas mixture leaving the reactor were taken continuously by a quartz probe, the resulting supersonic nozzle beam was frozen together with an excess of DMDS on the inner surface of two hollow hemispheres cooled by liquid nitrogen. While melting the scavenging reaction takes place. The mixture of DMDS, stable pyrolysis products, and methylthio compounds was separated and identified with a GC‐MS‐system. CH*3, C2H*3, C6H*5 radicals and H‐atoms have been detected. The presence of acetone in ethyne pyrolysis has an important influence on the radical concentrations and the product yields.
Activity Coefficients of the Systems: NaBr + Na‐Acetate + H2O and NaBr + Na‐Propionate + H2O at 25°C. Application of Scatchard's, Pitzer's and Lim's Methods
Authors: Hernández‐Luis Felipe , Fernández‐Mérida Luis , González‐Díaz Oscar , Esteso Miguel A. , Khoo Siow‐Kian , Lim Tiong‐Koon
Published: July 2012

Mean activity coefficients for NaBr in NaBr + Na‐Acetate + H2O and NaBr + Na‐Propionate + H2O mixed systems were determined from the emf measurements of galvanic cells without transport. The measurements were carried out at different total ionic strengths I = INaBr + INaR, between 0.1 and 3.5 mol · kg−1 when R = acetate anion, and between 0.1 and 3.0 mol · kg−1 when R = propionate anion. At each total ionic strength, different ratios INaBr/INaR were studied. These experimental mean activity coefficients were comparatively analyzed by using Scatchard's, Pitzer's and Lim's methods, finding that Lim's models lead to better fittings for these mixed systems. From the LH Lim model (that takes into account the Higher Order Limiting Law, HOLL), activity coefficients of traces for both electrolytes in each mixture were determined and qualitatively analyzed. Finally, the Gibbs excess energy of these mixtures was calculated and also qualitatively analyzed against both the size of the non common electrolyte and the composition of the mixed electrolyte.
Transformation of Glassy Palladium‐Zirconium Alloys to Highly Active CO‐Oxidation Catalysts During In Situ Activation Studied by Thermoanalytical Methods and X‐Ray Diffraction
Authors: Baiker A. , Maciejewski M. , Tagliaferri S.
Published: July 2012

Palladium/zirconia catalysts highly active for the oxidation of CO can be prepared by exposing amorphous Pd‐Zr alloys to CO oxidation conditions at 280°C. The bulk chemical and structural changes occuring under these conditions have been studied using thermoanalytical methods (TG, DTA) combined with mass spectrometry and in‐situ powder XRD. Amorphous PdZr2 and PdZr3 alloys exhibit virtually no activity when exposed to CO oxidation conditions, mainly due to their low specific surface area (˜ 0.01 m2/g). The activity develops with time on stream, passes through a maximum and reaches a stable state only after several hours. The maximum in the activity is observed when about 50–70% of the amount of oxygen necessary for complete oxidation of the precursor to PdO and ZrO2 has been consumed. The oxidation of the amorphous Pd‐Zr alloys, which results in a drastic increase of the specific surface area of the samples, starts at significantly lower temperature than the crystallization temperatures of the alloys. The stable catalysts contain poorly crystalline monoclinic and tetragonal ZrO2, metallic palladium and PdO as bulk phases. The concentration of these phases is influenced by a series of simultaneously occurring reactions, including: the oxidation of the alloy constituents by O2 which results in PdO and ZrO2, the oxidation by CO2 resulting in Pd and ZrO2, and the reduction of the PdO formed by CO and by metallic Zr present in the unreacted part of the alloy. The solid state reduction 2 PdO + Zr → Pd + ZrO2 contributes significantly to the reduction of the PdO as long as metallic Zr is abundant in the alloys.
Vibrational Energy Flow from Excited Adsorbates on Ionic Crystal Surfaces Measured by IR Polarization Interferometry and Laser Pulse Spectroscopy
Authors: Heidberg J. , Noseck U. , Suhren M. , Weiss H.
Published: July 2012

Vibrational energy flow in adsorbates on ionic crystal surfaces has been studied in situ by means of IR polarization interferometry, laser‐induced resonant desorption and fluorescence as well as time of flight measurements. Vibrational adsorbate spectra, isotherms and isosteric heats of adsorption were measured. The vibrationally induced desorption of CH3F and CD3F from NaCl(film) and NaCl(100) after resonant excitation of the v3‐CF stretching vibration with a line‐tunable infrared laser is reported in detail. Translational temperatures TMB of the desorbing molecules were derived by fitting Maxwell‐Boltzmann distributions to the time‐of‐flight spectra. TMB of the molecules desorbing from NaCl(film) is much lower (TMB = 30 K at substrate temperatures between 10 K and 78 K) than TMB of molecules desorbing from NaCl(100) (TMB = 125 K), which is ascribed to the different adsorption energies on NaCl(film) and NaCl(100). No preferred desorption of CH3F or CD3F in a 45%:55% mixture at 0.75 of saturation coverage on NaCl(film) after resonant excitation was observed.
Electron Spin‐Resonance (ESR) Studies of Adsorbate Dynamics on Single Crystal Surfaces: Possibilities and Limitations
Authors: Katter U. J. , Schlienz H. , Beckendorf M. , Freund H.‐J.
Published: July 2012

ESR is not one of the standard surface science tools because it is not inherently surface sensitive but rather probes the entire sample. However, ESR can be made into a surface science tool if we use paramagnetic adsorbates on thin nonmagnetic transition metal substrates or transition metal oxide films interacting with paramagnetic or nonmagnetic adsorbates. In contrast to NMR, ESR exhibits a sensitivity which allows one to detect monolayer and submonolayer coverages of spins (>1012 spins). The experiments can be carried out either in ultrahigh vacuum (UHV) or under an ambient gas atmosphere. — ESR provides us with the unique opportunity to study adsorbate dynamics by studying line shape changes as a function of temperature. ESR is also sensitive to molecular orientation so that the orientation distribution of the molecular planes may be derived experimentally. Thus ESR allows us to derive information not easily accessible with other techniques. We describe the set up of a UHV/ESR experiment in which the ESR measurement may be combined with LEED/Auger and TDS experiments. Several types of results are discussed:

ESR of chemisorbed and physisorbed molecules on metal surfaces including angle dependent measurements.

ESR of molecules on oxide surfaces at submonolayers coverages.

We will touch on possible future experiments involving pulsed ESR techniques to study dynamics in the adsorbate for a wide variety of processes including rotation and diffusion.
Solid/gas‐interactions of Surface‐doped Oxides: C—V, I—V, XPS, UPS, and ELS Studies on Pt/TiO2 and Pd/SnO2 (110)
Authors: Schierbaum K. D. , Wei‐Xing X. , Göpel W.
Published: July 2012

We have investigated Pt and Pd overlayers in the submono‐, mono‐, and multilayer coverage range on TiO2 and SnO2 (110)‐single crystal surfaces. The interaction with O2 was studied at temperatures between 300 and 1070 K in‐situ with current‐ and capacitance‐voltage (I—V and C—V) measurements, X‐ray and ultraviolet photoelectron spectroscopies (XPS and UPS), and electron energy loss spectroscopy (ELS). Under oxidizing conditions, Pt and Pd ions are formed which diffuse into the oxide substrate thereby forming Pd‐acceptor and Pt‐donor type bulk defects. For multilayer coverages of Pt and Pd the electrical conduction across the metal/oxide interface changes drastically from Schottky diode to ohmic behaviour upon oxidation. Under reducing UHV conditions at temperatures T ≥ 700 K we observe the formation of neutral Pd at the SnO2 surface. Total energy calculations of TiO2 with incorporated Pt2(4)+ ions at different lattice positions confirm the experimentally observed fast diffusion of Pt atoms between surface, subsurface, and bulk sites.
In Situ Studies of Adsorption at Liquid/Solid Interfaces and of Intercalation Reactions by γ‐γ‐Correlation Spectroscopy
Authors: Butz T.
Published: July 2012

γ‐γ‐correlation spectroscopy is ideally suited to study adsorption processes in situ at liquid/solid interfaces. This is illustrated by adsorption studies of polymolybdates in solution onto γ‐Al2O3 using 99Mo(β−)99Tc. — Intercalation reactions can be monitored in situ both from the host and the guest point of view. Examples include the lithiation of 2H‐TaS2 and MoS2 using 181Hf(ß−)181Ta and 99Mo(ß−)99Tc, respectively. The intercalation of indium into 2H‐TaS2 was monitored using 111In(EC)111Cd. — First experiments with exfoliated and restacked MoS2 will be described.
In‐situ SHG Studies of Ionic and Molecular Adsorption on Surface Structure of Au(111)‐Electrodes
Authors: Pettinger B. , Mirwald S. , Lipkowski J.
Published: July 2012

We report on the application of Second Harmonic Generation (SHG) to in‐situ studies of the influence of bromide and pyridine adsorption on surface reconstruction of Au(111) electrodes (Au(111)‐(√3 x 23)), and on the potential induced reorientation of adsorbed pyridine molecules. In the latter case a phase transition in the adsorbate layer has been observed which is accompanied by a significant phase shift of the emitted SHG wave, indicating changes of surface electronic levels upon adsorption of pyridine.
SHG Measurements of n‐Si(111)/aqueous Solution Interfaces
Authors: Sorg N. , Krüger J. , Kautek W. , Reif J.
Published: July 2012

A study of photoelectrochemical processes at semiconductor electrodes under short‐pulse laser irradiation shows that in‐situ second harmonic generation (SHG) is feasible in such complex interfacial systems. A Nd:YAG laser (532 nm, 7 ns, 40 mW, soft focus 0.2 cm2) was used for SHG in reflection from n‐Si(111) electrodes in a p‐p polarization configuration. We investigated the azimuthal dependence of the SHG at oxide‐covered and bare n‐Si(111) electrodes with and without Ni deposits. The relatively strong SH signal from an oxide‐covered surface originates at the Si/oxide interface. At the bare electrode, the Si/electrolyte interface gives rise to a much weaker signal. Deposition of moderate amounts of Ni on the oxide reduces the SH signal by shadowing the oxide/silicon interface without changing the azimuthal anisotropy. Complete Ni coverage of bare Si leads to a different SH anisotropy.
In Situ IR external Reflection‐absorption Spectroscopy as a Tool for Investigations of Electrodes in Aqueous Solutions: The Reactions of Lead Electrodes in Sulfuric Acid
Authors: Trettenhahn G. L. J. , Nauer G. E. , Neckel A.
Published: July 2012

The technique of external infrared reflection absorption spectroscopy combined with classical electrochemical techniques was used for the in situ characterization of the oxidation reactions of lead electrodes in sulfuric acid. The generation and consumption of lead sulphate on the lead electrode was measured during galvanostatic and potentiodynamic experiments. The amount of lead sulphate was quantitatively determined by integrating the area of a characteristic absorption band. Furthermore, the break down of the passive lead sulphate layer on the electrode connected with an oxidation of the lead electrode in the course of a cathodic cycle in a potentiodynamic experiment could be demonstrated.
Pulse Measurements for the Investigation of Fast Electronic and Ionic Processes at the Electrode/Electrolyte Interface
Authors: Lohrengel M. M.
Published: July 2012

The electrochemical properties of the interface electrode/electrolyte are often determined by thin surface layers. The formation of barriere type oxides in the range of 5 nm to 25 nm on the valve metals Al, Hf, Nb, Ta, Ti, and Zr is taken as an example. They were investigated by current transients of potentiostatic pulses (PPT) and by instationary impedance spectroscopy. The different processes of

‐ charging of the oxide capacity

‐ dielectric relaxation of the oxide

‐ formation of a mobile ionic space charge

‐ high field oxide growth

‐ corrosion

are separated. Contradictory electrochemical investigations of the last 60 years are discussed.
Impedance Characteristics of Platinum Electrodes on Yttria‐Stabilized Zirconia
Authors: van Herles J. , Mcevoy A. J.
Published: July 2012

The impedance response of the cell O2,Pt/(Y2O3)0.06 (ZrO2)0.94/Pt,O2 is measured at temperatures between 600 and 850°C and oxygen partial pressures between 10−3 and 1 atm as well as in low vacuum. The experimental data agree very well with those encountered in Reference [1], where surface diffusion of adsorbed oxygen atoms on the platinum electrode, the activity of which obey a Langmuir relationship, is proposed as the rate‐determining step. Current treatment as well as hydrogen treatment of the cell irreversibly increase the interface impedance. The measurements in vacuum confirm that gas phase diffusion is not rate‐limiting.
Microscopic Aspects of Thin Metal Film Epitaxial Growth on Metallic Substrates
Authors: Günther C. , Günther S. , Kopatzki E. , Hwang R. Q. , Schröder J. , Vrijmoeth J. , Behm R. J.
Published: July 2012

Microscopic processes in epitaxial growth of thin metal films on metal substrates are discussed in the light of recent scanning tunneling microscopy data. Details on the nature and role of different atomic processes, though too fast for direct observation, can be inferred from the characteristic development of the film morphology with increasing coverages and its modification upon varying the deposition rate and temperature. It is shown that for deposition at room temperature or moderately increased temperatures film growth and the resulting film morphology are dominated by kinetic effects, and that film growth proceeds via nucleation and growth of 2D islands. — At room temperature, where adatoms are sufficiently mobile to allow efficient intralayer mass transport, film growth begins by nucleation of supercritical clusters in a supersaturated 2D gas of mobile metal adatoms. These clusters can grow into 2D islands. The correlation between adatom mobility, substrate temperature and deposition rate on the one hand and island density on the other are demonstrated. The shape of the growing islands can vary widely, from dendritic to compact island forms. The different shapes are shown to result from kinetic limitations, specifically from a limited adatom mobility along island edges. — For kinetically controlled film growth in the multilayer regime the film morphology is determined by the amount of interlayer mass transport from higher to lower layer levels. 2D layer growth prevails for practically unhindered interlayer mass transport, while multilayer or 3D growth dominates where mass transport is strongly hindered or even absent. Different processes and kinetic effects determining this interlayer transport are discussed, in particular the effect of modifications in the adatom potential at island or step edges. Only for deposition at or annealing to higher temperatures the film morphologies resemble those expected from the thermodynamically controlled growth modes. In agreement with expectations layer‐by‐layer growth is found for homoepitaxial growth, layer‐plus island growth with one or two layers critical thickness, respectively, for the hetero‐epitaxial growth systems investigated.
On the Reactivity of Alkoxy Radicals. Interaction Between 1‐Phenylethoxy Radical and Ethylbenzene in the Absence of Oxygen
Authors: Danóczy É. , Paál‐Lukács J. , Gál D.
Published: July 2012

The hydrogen abstraction from ethylbenzene by 1‐phenylethoxy radicals generated by the photodecomposition of 1‐phenylethyl tert‐butyl‐peroxide was investigated in acetonitrile as solvent. The rate constant ratios of H‐abstraction to β‐scission were 14 in the case of ethylbenzene, 26 for the peroxide and 0.02 for acetonitrile at 293 K. The activation energy difference of the above two steps was 16.9 ±0.2 kJ mol−1 for ethylbenzene. The quantum yield of the photodecomposition of the peroxide obtained is 0.8. Product accumulation curves received by gas chromatography were simulated using the suggested mechanism with the rate constants compiled both from our experiments and literature data.
Radiationless Transitions in Substituted Benzopyrylium Dyes: Competing Adiabatic Photoreactions Towards Nonradiative Funnels
Authors: Haucke GüNter , Czerney Peter , Steen Dorika , Rettig Wolfgang , Hartmann Horst
Published: July 2012

A wide variety of substituted flavylium salts and bridged derivatives are compared with respect to their fluorescence quantum yields and lifetimes. The dependence of the nonradiative decay rate constant on substitution pattern, on twisting possibility and on solvent polarity could be explained by the formation of non‐fluorescent Twisted Intramolecular Charge Transfer (TICT) states. In some dyes, two different TICT channels compete. Molecules‐in‐molecules (MIM) calculations are used to analyze and predict different TICT formation possibilities.
The Collisional Behaviour of Ground State Atomic Carbon, C(2p2 (3PJ)), with Unsaturated Cyclic Compounds Studied by Time‐Resolved Atomic Resonance Absorption Spectroscopy in the Vacuum Ultra‐Violet
Authors: Haider Nazre , Husain David
Published: July 2012

We present a kinetic investigation of the collisional behaviour of ground state atomic carbon, C(2p2 (3PJ)), with unsaturated cyclic compounds. Atomic carbon was generated by the repetitive pulsed irradiation (λ > ca. 160 nm) of C3O2 in the presence of excess helium buffer gas and the added reactant gases in a slow flow system, kinetically equivalent to a static system. C(23PJ) was then monitored photoelectrically by time‐resolved atomic resonance absorption in the vacuum ultra‐violet (λ = 166 nm, 33PJ←23PJ) with direct computer interfacing for data capture analysis. The following absolute second‐order rate constants for the reactions of C(23PJ) with the following cyclic collision partners are reported (errors 2σ), demonstrating rapid reaction in all cases: magnified image These results constitute the first reported body of absolute rate data for reactions of ground state carbon with these reactants. Whilst a large body of absolute rate data for atomic silicon in its Si(3p2 (3PJ)) ground state has now been determined directly in recent years by time‐resolved atomic resonance absorption spectroscopy in the ultra‐violet itself with a wide range of collision partners, including unsaturated reactants, there are no analogous data for these cyclic reactants. Comparison is made with rate data for C(23PJ) with benzenoid and fluorinated benzenoid collision partners, and the results also discussed in the context of nucleation and soot formation in flames.
Static Light Scattering Experiments with 2‐Butoxyethanol/Water Mixtures of Near Critical Composition in the Vicinity of the Lower Critical Point
Authors: Fusenig St. , Woermann D.
Published: July 2012

Measurements of the concentration and temperature dependence of the correlation length ζ of local concentration fluctuations in seven 2‐butoxyethanol (C4E1)/water mixtures of different non‐critical but near‐critical compositions are carried out in the vicinity of the lower critical point of the system in the composition range ‐0.016≤(y‐yc)≤0.075; (yc = 0.2947; y, mass fraction of C4E1; yc, critical composition). The data are analysed in two ways: (a) On the basis of the concept of the pseudo‐spinodal temperature Tps. The temperature dependence of ζ and the quantity χ*T which is proportional to the generalized susceptibility χT can be described by power laws of the form ζ = ζ'0lps−v' (ζ'0, amplitude; v', exponent) and χ amplitude; χ, exponent) with lps = (Tpc ‐ TP/Tps); (TP, temperature of phase separation). Tps is obtained as one of the parameters of a three parameter fit (ζ'0, v', Tps; χ*'T, 0, γ' Tps) of the corresponding power laws to experimental ζ−[T‐TP (vis)] and χ*T‐[T‐TP (vis)] data sets. Tps is larger than the visually determined temperature of phase separation TP (vis). As expected, the temperature difference (Tps‐TP (vis))<0 has its largest value for the mixture with the largest value |y‐yc| and its smallest value for the mixture with the smallest value |y‐yc|. The values of ζ'0 v′, and y' are independent of concentration (ζ0 = (0.46±0.04) nm; v′ = (0.61±0.01); y' = (1.20±0.09)). They are only slightly different from the corresponding values of the 2‐C4E1/H2O mixture of critical composition (ζ0 = (0.44±0.04) nm, v = (0.63±0.03); y = (1.22±0.02); universal value for binary liquid mixtures, Landau‐Ginsburg‐Wilson model, v = 0.630; y = 1.241). (b) On the basis of a scaled equation of state (linear model). This model describes qualitatively the temperature dependence of ζ of the mixtures of non‐critical composition.
Spectroelectrochemical Investigations of Nanocrystalline ZnO Films
Authors: Hoyer P. , Eichberger R. , Weller H.
Published: July 2012

Transparent nanocrystalline ZnO films were prepared from colloidal ZnO solutions containing particles of different sizes. The colloidal solution as well as the films exhibit size quantization effects. The absorption and stationary and time resolved fluorescence of the films as well as the photocurrent strongly depend on the applied potential. The electrochemical and spectroscopic investigations allow direct measurement of the quantum mechanical confinement energy for electrons in the nanocrystalline particles of the films. The optical properties and the charge carrier transport through the films are explained by a model involving electronic levels of the individual particles.
Osmotic Properties of a Cation Exchange Membrane: Reflection Coefficients of a Solute Larger than 1 in a System with Aqueous Mixed Electrolyte Solutions
Authors: Yaroshchuk A. E. , Röttger H. , Woermann D.
Published: July 2012

The reflection coefficient of HCl of a cation exchange membrane separating two homogeneous aqueous solutions containing HCl and NaCl [c' (HCl) = 5 × 10−3c+,c” (HCl) = 2 × 10−2c+;c' (NaCl) =c” (NaCl) =c(NaCl): 0≤c(NaCl)≤0.5c+;c+= 1 mol dm−3] exhibits a characteristic dependence on the concentration of NaCl. In the absence of NaCl the reflection coefficient σ(HCl) has a value close to 1. With increasing values of the concentration of NaCl the value of the reflection coefficient σ(HCl) increases and reaches a maximum value of about σ(HCl) ≈︁ 2.5 at [c(NaCl)/〈c(HCl)〉] ≈︁ 5.0. Above this value the reflection coefficient σ(HCl) decreases reaching values of σ(HCl) ≈︁ 1 at values of [c(NaCl)/〈c(HCl)〉] ≈︁ 45. This concentration dependence of σ(HCl) is in qualitative agreement with recent theoretical predictions and independent calculations based on the model of the membrane with narrow pores.
Molecular Orbital Calculations of Diketo‐dipyridyl‐pyrrolopyrrole, Diketo and Dithioketo‐diphenyl‐pyrrolopyrrole on Protonation and Deprotonation
Authors: Mizuguchi Jin
Published: July 2012

PPP, CNDO/S and INDO/S calculations have been carried out on the title compounds (abbreviated to DPPP, DPP and DTPP, respectively; industrially important pigments) in order to study spectroscopically the diketopyrrolopyrrole chromophore on protonation and deprotonation. Protonation which takes place at the pyridyl nitrogen (DPPP only) and deprotonation (in all three molecules) which occurs at the NH group induce large spectral shifts in solution towards longer wavelengths (protonation: 35 nm (ca. 1236 cm−1); deprotonation: 77–150 nm (ca. 1820–4380 cm−1)). Geometry optimization by the AM1 method showed that the pyridyl rings in DPPP and the phenyl rings in DPP and DTPP are twisted, in the same direction, out of the plane of the planar heterocyclic system by 15–21°. The deviation is asymmetrically reduced due to mono‐deprotonation: the ring on the deprotonated side is less twisted than the other. Di‐deprotonation makes the molecule completely planar. On mono‐protonation of DPPP, the protonated pyridyl ring becomes less twisted while the unprotonated remains almost unchanged. In contrast, on di‐protonation, the two pyridyl rings become even more twisted than in the initial state. The electronic spectra calculated on the basis of the optimized structures reproduce well qualitatively the trends of the optical absorption, but generally underestimate the experimental values.
Magnetic Relaxation Under Fast Internal Rotation in Liquid
Authors: Suchański W.
Published: July 2012

The 13C nuclear spin‐lattice relaxation times for ring and methyl carbons in liquid 3,5‐lutydyne (3,5‐dimethylpyridine, 3,5‐DMP) have been measured as a function of temperature. The results have been analyzed in terms of two relaxation mechanisms: intramolecular dipole‐dipole coupling and spin‐rotation interaction. In order to separate these contributions, also the nuclear Overhauser enhancement factors have been studied. The results have been analyzed in terms of the theory of extended diffusion (ED) model for internal motion of methyl groups with a low barrier to internal rotation.
Thermodynamics of Hydrogen Dissolved in Pd‐Tb and Pd‐Dy Alloys
Authors: Chen F. L. , Sakamoto Y. , Flanagan F. B.
Published: July 2012

The thermodynamic parameters for absorption of hydrogen by Pd‐Tb alloys with up to 8.0 at.% Tb and Pd‐Dy alloys with up to 6.0 at.%. Dy have been determined from measurements of the pressure‐composition isotherms at temperatures between 273 K and 473 K and hydrogen pressures up to 100 Torr. The results are compared with those of previously determined palladium‐rare earth (RE = Sc, Y, Ce, Gd, Yb) alloys. The relative partial molar enthalpy of solution of hydrogen, ≈︁, at infinite dilution, and the standard enthalpy change, ΔH, for β‐hydride formation for both Pd‐Tb and Pd‐Dy alloys become more exothermic with increasing Tb and Dy contents. The relative chemical potential, Δμ, of dissolved hydrogen at infinite dilution at a given temperature in Pd‐RE alloys decreases with a decrease of apparent H—H attractive interaction energy with several exceptions. With the exception of Pd‐Ce alloys and some high solute metal content alloys, the stabilities of dissolved hydrogen at infinite dilution andβ‐hydride phase for a series of Pd‐RE‐hydrogen systems are mainly governed by the lattice expansion of palladium by the substituent RE atoms which reduces the elastic strain energies necessary for hydrogen occupation of the octahedral interstices.
ARAS Measurements on the Thermal Decomposition of Silane
Authors: Mick H. J. , Smirnov V. N. , Roth P.
Published: July 2012

In the present investigation the thermal dissociation of silane was measured behind reflected shock waves using the Atomic Resonance Absorption Spectroscopy (ARAS) for detecting Si, H, and O atoms. The experiments were performed at temperatures 1250 K ≤ T ≤ 2115 K and pressures between 0.7 and 1.5 bar. Initial mixtures of 0.15 to 5 ppm SiH4 diluted in Ar and 5 ppm SiH4 with 500 ppm O2 diluted in Ar were studied. The H atom measurements show formation rates, which are much less than the respective rates for Si atom formation. This indicates that the H atoms were formed by secondary reactions and are not primary dissociation products of silane or silylene. A reaction mechanism suitable to describe all measured H atom concentration profiles is given in this paper.

Si atoms also measured during the silane thermal decomposition were found to be useful to understand the kinetics of this process. From the Si concentration profiles together with computer simulations rate coefficients for the reactions

SiH4 + M ⇋ SiH2 + H2 + M (1)

SiH2 + M ⇋ Si2 + H2 + M (2)

were derived, which can be summarized by the following Arrhenis expressions:

k1 = 9.9×1015exp(−24000 K/T) cm3mol−1 s−1

k2 = 9.1×1013exp(−15100 K/T) cm3mol−1 s−1.

In the case of the SiH4/O2/Ar mixtures no detectable Si atom concentrations were found, while the observed O atom formation rates were identical to that of Si atoms in mixtures without O2 under comparable reaction conditions. This means that Si originating from the thermal decomposition of silane is directly converted into O by reaction with O2, i.e. O is in this system a measure of Si.
Diffusion Processes of Interacting Brownian Particles in Blockcopolymer‐Microemulsion Transient Networks
Authors: Stieber F. , Hofmeier U. , Eicke H.‐F. , Fleischer G.
Published: July 2012

Quasielastic light‐scattering and pulsed field gradient NMR were used to investigate the effects of a triblock copolymer and a α‐ω telechelic ionomer on the interaction potential and transient network formation of nanodroplets in w/o microemulsions. The NMR self diffusion measurements yield a crossover from restricted polymer diffusion to free self diffusion. The relation between the copolymer self diffusion and the dynamic properties of the transient network are explained in the framework of reversibly cross linked polymer chains. Quasi‐elastic light‐scattering, only sensitive to the correlations between the waterdroplets, yields three diffusive processes, which are due to fast collective diffusion and slowly decaying correlations, controlled by the specific interactions of the hydrophilic and hydrophobic blocks with the water and oil phases.
On the Stability and on the Formation of Two‐dimensional Condensed Equilibrium Films in an Aprotic and in Aqueous Solution – Part II: The Dynamics of 2D Absorbate Centers Formation of 2‐Thiohydantoin in the Adsorption of 2‐Thiohydantoin at the Interface Mercury / Nonaqueous Acetonitrile / Tetraethylammoniumperchlorate
Authors: Schrettenbrunner M. , Chaiyasith P. , Baumgärtel H. , Retter U.
Published: July 2012

The kinetics of the two‐dimensional condensation of 2‐thiohydantoin deposited at the interface mercury/non‐aqueous acetonitrile/tetraethylammoniumperchlorate has been analysed for different electrode potentials by the time dependent differential capacitance. The condensation of deposited 2‐thiohydantoin for various temperatures, concentrations and electrode potentials is explained by a dynamic equilibrium of adsorbate clusters. This dynamic equilibrium involves a compensation of center growth at the periphery and of desorption of condensed molecules lying inside the center. The islands have a constant size which depend on the potential of the electrode. A corresponding formula of the coverage‐time dependence has been derived.

The process of desorption during the condensation process may be explained by the influence of noncondensed molecules which come from the bulk solution and attack the surface of the electrode and the islands permanently. This assumption has been proofed analytically.

The influence of water on the phase transition of 2‐thiohydantoin in acetonitrile has been proofed by some experiments. The experimental results have been compared with those of nonaqueous solution.

The kinetics of the desorption process of a stabilised film of 2‐thiohydantoin has been investigated. The desorption process is explained by a dynamic equilibrium of adsorption and desorption of holes. It has been found that the existence of holes may be explained by the influence of single deposited molecules of the solution.
Fast Flow Kinetic Studies of the Reaction CH2OH + HCl ⇋ CH3OH + Cl. The Heat of Formation of Hydroxymethyl
Authors: Dóbé S. , Otting M. , Temps F. , Wagner H. Gg. , Ziemer H.
Published: July 2012

The kinetics of the chlorination equilibrium of methanol, CH2OH + HCl ⇋ CH3OH + Cl (1, – 1), have been studied using the fast flow technique with Laser Magnetic Resonance and Electron Paramagnetic Resonance detection. The rate constants of the forward and reverse reactions were found to be k1 = (2.3±0.9) ·1011 exp [‐(20.9±2.9) kJ·mol−1/RT] cm3/mol·s in the temperature range 500 K≤T≤812 K and k‐1 = (3.7±0.4)±1013 cm3/mol·s at room temperature. These kinetic results were utilized in third law and second law procedures to obtain the value of the heat of formation of the hydroxymethyl radical. The entropy of CH2OH, S0f,298(CH2OH) = (254±4) J/mol·K, and the activation energy of reaction (‐1), E‐1 = (0±4) kJ/mol, which are required for the calculations, were selected by critical assessment of the available literature data. The average of the third law and second law determinations provided SfH0298(CH2OH) = ‐(9±6) kJ/mol. This value is higher by 17 kJ/mol than the heat of formation value in common use and implies a stronger C – H bond energy in methanol, D298(H–CH2OH) = 410 kJ/mol. These new thermochemical quantities are in excellent agreement with the very recent recommendations of Seetula and Gutman [J. Phys. Chem. 96, 5401 (1992)] and have important implications for modeling studies of complex chemical systems such as the combustion of methanol.
Migration of Air Bubbles in Silicone Oil under the Action of Buoyancy and Thermocapillarity
Authors: Morick F. , Woermann D.
Published: July 2012

The buoyancy driven migration of air bubbles in dimethyl‐polysiloxane and phenylmethyl‐polysiloxane under isothermal conditions is studied. The radius of the migrating bubbles increases or decreases with time The changes of the radii are attributed to an exchange of gas between the bubbles and polysiloxane. The direction of the gas transport depends of the state of saturation of the liquid with air. The velocity of migrating air bubbles as function of time in dimethyl‐polysiloxane can be described by the Rybczynski‐Hadamard relation using the instantaneous values of the velocity of migration and the instantaneous value of the radius of the bubbles. The analysis of corresponding the data obtained with air bubbles migrating in phenylmethyl‐polysiloxane reveal that in that liquid the velocity of migration is described by the Stokes relation using the instantaneous values of the velocity and the radius of the bubbles. The bubbles behave like “hard spheres with a time dependent radius”. The different behavior of air bubbles in the two types of polysiloxane is attributed to structural differences between macromolecules forming them. The observed thermocapillary motion of air bubbles in dimethyl‐polysiloxane in the presence of buoyancy forces is described by the theory of Young, Goldstein, Block (J. Fluid. Mech. 6, 350 (1959)). No thermocapillary motion of air bubbles is found in phenylmethyl‐polysiloxane. This is expected from the behaviour of air bubbles in phenylmethyl‐polysiloxane under isothermal conditions.
ARAS Measurements on the S(1D) Formation in Shock Heated COS/Ar mixtures
Authors: Woiki D. , Roth P.
Published: July 2012

The formation of electronically excited S(1D) atoms was studied during the thermal decomposition of carbonyl sulfide behind reflected shock waves by using atomic resonance absorption spectroscopy (ARAS). The experiments were performed in highly diluted mixtures of Ar with relative concentrations of COS between 8 to 100 ppm in the temperature range 2130 K≤T≤3020 K at pressures of about 1.2 bar. The measured rate of the linear S(1D) increases divided by the initial reactants was found to obey the Arrhenius law: magnified image.

Assuming a fast thermalisation between the (3P) and (1D) states of S atoms this result is in agreement with previous measurements of the S(3P) formation during the thermal decomposition of COS reported recently [1].
Morphology Dependent Resonances in Raman Spectra of Optically Levitated Microparticles: Determination of Radius and Evaporation Rate of Single Glycerol/Water Droplets by means of Internal Mode Assignment
Authors: Schaschek K. , Popp J. , Kiefer W.
Published: July 2012

An experimental setup for studies of morphology dependent resonances (MDRs) in Raman spectra of optically levitated microdroplets is described. This instrumentation is used for the study of MDRs in the Raman spectra of glycerol/water (3:1) droplets. Furthermore we show how the MDRs observed in the Raman spectra and their change with time can be used to determine the radius and the index of refraction of single optically levitated droplets with very high accuracy. We further show how the results of this study can be used to calculate the efficiency factor of the radiation pressure and compare it with the experimental monitored laser power.
Effect of the Kinks Blockage by Adsorbed Hydrogen on the Kinetics of Iron Electrode
Authors: Plonski I. H.
Published: July 2012

Theoretical relationships for the kinetics of iron corrosion in acid media were derived taking into account the preferential adsorption of the intermediate atomic and molecular hydrogen on the kinks, assumed as main dissolution sites. Anodic initial and steady state Tafel slopes of 59 and 25 … 45 mV, respectively, anodic reaction order with respect to OH− between 1 and 2, inductive transients, as well as open circuit values dEcor/dpH = ‐59 …‐47 mV and d log icor/dpH = 0.0…‐1.0 were found, in agreement with the experimental data reported in the literature.
Raman‐Spectroscopic Evidence for Four‐Fold Coordinated Titanium in Silicalite I
Authors: Pilz W. , Peuker Ch. , Tuan V. A. , Fricke R. , Kosslick H.
Published: July 2012

Raman spectroscopic investigations reveal the synthesis of Ti‐Silicalite I with four‐fold coordinated titanium. A new Raman band at 960 cm−1 assigned to tetrahedrally coordinated titanium in the SiO2 matrix is found. Non‐framework TiO2 species containing octahedrally coordinated titanium could be also distinguished.
Dielectric Relaxation Spectroscopy of Electrolyte Solutions: LiClO4 in Tetraethyleneglycol Dimethylether
Authors: Schütz G. , Stockhausen M.
Published: July 2012

The frequency dependent complex permittivity of LiClO4 solutions in tetraethyleneglycol dimethylether (tetraglyme) with concentrations up to 1.5 mol/1 is measured at 20 °C over a broad frequency range (5 MHz to 72 GHz). Apart from the conductivity contribution, there are two distinguishable absorption regions. The relaxation at higher frequencies is due to the solvent. The lower frequency feature is due to ionic processes. It comprises two spectral components, which both are unlikely to be caused by rotational tumbling motion of well‐defined ionic species (e.g. ion pairs) but rather seem to involve some other processes such as confined translational modes of ionic motion.
Determination of Potential Functions for Unlike Interactions from Transport Properties of Dilute Gases
Authors: Harris K. R. , Dunlop Peter J.
Published: July 2012

Calculations are reported to illustrate that whenever possible it is preferable to utilise binary diffusion coefficients to determine potential functions rather than the cross‐term viscosity coefficients extracted from viscosities of binary systems.
Catalytic Oxidation of Sulfurous Acid by Molecular Oxygen. Investigations on the Electrochemical Estimation of the Catalytic Activity
Authors: Timpe O. , Schlögl R.
Published: July 2012

The catalytic oxidation of sulfurous acid S(IV) to sulfuric acid S(VI) can be monitored by measuring the increasing conductivity of the solution while the reaction proceeds. The turnover‐frequency and thereby the activity of the catalyst sample examined is calculated from the conductivity derivative by multiplying it with a factor (f); this factor is based on the difference between the molar conductivities of the reaction product S(VI) and the educt S(IV). The factor was found to depend on both the temperature and slightly on the starting concentration [SIV]0. An empirical interpolation formula for calculation of the factor was derived from the calibration experiments. The molar conductivities (λ) of S(IV) and S(VI) were determined at 6 different temperatures from 228 to 313 K in the concentration range from 0.1 to 2.0 mM. To illustrate the method some applications are presented. These include measurements with Fe‐graphite and NH3 treated carbon black samples as catalysts. For the latter the catalytic activity is discussed in relation to XPS surface characterisation and elemental chemical analysis. The exemplary experimental runs prove the method's plausibility but indicate that such reactions are very complex in their kinetics: when estimating catalytic activities reaction parameters like especially the temperature and the S(IV)‐concentration should be adjusted carefully, to warrant reproducible results.
On the Kinetics of Hydrogen Bonded Association of Pyri(mi)dines with Hexanolactam in Cyclohexane
Authors: Hopmann Rudolf F. W.
Published: July 2012

The kinetics of the formation of bivalently hydrogen bonded complexes of hexanolactam with 2‐amino‐pyri(mi)dines in cyclohexane is diffusion controlled with association rate constants of 3.2·1010 (2‐aminopyrimidine, 2AP), 1.65·1010 (2‐amino‐pyridine, APA) and 0.9·1010 M−1·s−1 (2‐amino‐6‐methyl‐pyridine, AMP), respectively. In reference to APA, 2AP is faster, because there is a second nuclear nitrogen atom in α‐position to the amino group capable of accepting a hydrogen bond, whereas the association kinetics of AMP is slower, because the methyl group in α‐position to the ring nitrogen exerts an steric effect. The evaluation of the kinetic amplitudes supports simplexation over duplexation.
Continuous Coupling of Chaotic and Periodic States of Chemical Oscillators With and Without Time Delay
Authors: Zeyer K.‐P. , Holz R. , Schneider F. W.
Published: July 2012

We present continuous coupling experiments and calculations of two mutually flow‐rate‐coupled Belousov‐Zhabotinsky (BZ) oscillators. The Ce4+‐concentration of one BZ‐reactor controls the flow rate into the other BZ‐reactor and vice versa. Flow‐rate control is proportional to the difference between the (time delayed) Ce4+‐and an average Ce4+‐concentration. When both period one (P1) BZ oscillators are weakly coupled, the P1 oscillations are retained in both oscillators whose periods increase with increasing coupling strength. At high coupling strengths statistically aperiodic oscillations are produced. The introduction of time delayed coupling does not reduce the noise in the strongly coupled system. We distinguish between statistical aperiodicity due to experimental noise and deterministic chaos due to the system's nonlinear dynamics. At constant coupling strength a rising delay time produces a “sawtooth” like behaviour of the P1 periods. Mutual flow‐rate‐coupling of two chaotic states without time delay retains chaos in both reactors at low coupling strengths. When the coupling strength increases the Hausdorff dimension passes through a maximum (≈︁ 2.5). At very high coupling strengths, a transition from chaos to periodic states takes place.