bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractWe 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractMicroscopic 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

AbstractThe 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

AbstractA 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

AbstractWe 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

AbstractMeasurements 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

AbstractTransparent 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

AbstractThe 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

AbstractPPP, 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

AbstractThe 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

AbstractThe 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

AbstractIn 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 reactionsSiH4 + 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−1k2 = 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

AbstractQuasielastic 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

AbstractThe 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

AbstractThe 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.