bluuebunny/crossref_metadata_2025 huggingface dataset:
Static light scattering experiments with aqueous solutions of the nonionic tenside C12E5 with critical and non‐critical composition
Authors: Sinn C. , Woermann D.
Published: March 2014

Concentration fluctuations with long range correlations as well as non‐critical background contributions determine the light scattering properties of C12E5/H2O mixtures of critical composition near the lower critical point (critical mass fraction yc = 0.0123; critical temperature Tc = 31.8°C). If the influence of the non‐critical contributions is neglected, an evaluation of the light scattering data in terms of the power laws ξ = ξo · ϵ‐ν and χT = χT,o · ϵ−γ (ξ being the correlation length of local concentration fluctuations and χT the generalized susceptibility; ϵ = (Tc−T)/Tc is the reduced temperature) leads to values of the critical exponents ν and γ which are closer to the mean field values (ν = 0.5; γ = 1) than to the values theoretically expected for binary liquid mixtures from the Landau‐Ginzburg‐Wilson model (ν = 0.63, γ = 1.24). If the background contributions are taken into account empirically by adding temperature independent background terms ξb and χT,b respectively to the simple power laws, the analysis of the light scattering data leads to values of ν ≈︁ 0.65 and γ ≈︁ 1.2, which are close to the values given by the Landau‐Ginzburg‐Wilson model. The background term ξb has a value of about ξb ≈︁ 6 nm and the critical amplitude ξo a value of about ξo ≈︁ 1.2 nm. This value for ξo is one order of magnitude larger than that found for simple binary liquid mixtures (O(ξo) ≈︁ 0.1 nm). — In mixtures of non‐critical composition (−0.79 < (y−yc)/yc < 0.63) the scattered intensity shows an angular dependence which is also a function of temperature corresponding to correlation lengths 20 nm < ξ < 206 nm for 0.5 K < (TP−T) < 7.0 K. They are assumed to reflect contributions of micelles which also contribute to the scattering of the mixture of critical composition away from the critical temperature.
Impedance measurements of amorphous AgIx · (Ag3PO4)1−x over a wide composition range
Authors: Gross S. , Freyland W.
Published: March 2014

Using a rapid quenching technique amorphous samples of AgIx(Ag3PO4)1−x have been obtained over a wide composition range up to x = 0.85. Above this composition the cooling rate of > 106 K s−1 was not sufficient to prevent partial crystallinity. All samples have been characterized both by X‐ray diffraction and impedance spectroscopy for temperatures near room temperature. From impedance measurements the dc‐conductivity σ has been determined which for amorphous materials varies from 7.6 · 10−5 ω−1 cm−1 (x = 0.5) to 4.4 · 10−2 ω−1 cm−1 (x = 0.85) at 298 K. A plot of log σ versus x yields a straight line which at x = 1 hits the value of the pure fast ionic conductor α‐AgI extrapolated to 298 K.
Bifurcations — a possibility to generalize the thermodynamic description of phase diagrams of two‐component fluids
Authors: Boshkov L. Z.
Published: March 2014

A new thermodynamic formalism has been developed for the analysis of the phase behaviour of two‐component fluids. Azeotropy and critical pressure maxima or minima in binary fluids have been interpreted as bifurcations of two‐phase equilibria and critical points, respectively. The analogous approach has been applied to some boundary states: hypercritical and isolated critical points, critical pressure step‐points. The thermodynamic conditions of these states have been derived for the first time by a uniform way.
Temperature dependence of interfacial tension of 2‐butoxyethanol/water mixtures near the lower critical point
Authors: Kreuser H. , Knecht B. , Woermann D.
Published: March 2014

The pendant drop method and the capillary rise method are used to measure the interfacial tension σ of 2‐butoxyethanol (2‐C4E1)/water mixtures near the lower critical point (critical composition, mass fraction of 2‐C4E1, yc = 0.2945; critical temperature Tc(visual) = 49.41°C) as function of temperature (0.6 K ≤ (T  Tc) ≤ 18.0 K). It is found that at temperatures 0.6 K ≤ (T  Tc) ≤ 7.0 K the temperature dependence of σ is represented by a power law of the form σ = σ0ϵμ (≤ = (T  Tc(visual))/Tc) with μ = (1.26 ± 0.02) and σ0 = (8.8 ± 0.2) mN m−1. The value of μ is consistent with the theoretically expected universal value of μ = 1.26. The amplitude ratio Rσ,ζ+ = σ0(ξ0ζ+)2/kBTc calculated from the system specific values of the critical amplitude σ0 and the critical amplitude ξ0 of the correlation length of local concentration fluctuations (ξ0ζ+ = (0.44 ± 0.04) nm) leads to a value of Rσ,ξ+ = (0.383 ± 0.070). It is close to the median value of Rσ,ξ+ calculated for several one‐ and two‐component fluids from experimental data taken from the literature (Moldover, Phys. Rev. A 31, 1022 (1985); median value Rσ,ξ+ = 0.386). – The ratio of [νT/R̄(∂T/∂z)] (νT, thermophoretic velocity (Marangoni convection); (∂T/∂z, temperature gradient) for droplets of radius R̄ of a 2‐C4E1) rich phase suspended in its coexisting H2O rich phase is calculated from the data.

Values of [νT/R̄(∂T/∂z)] refering conditions along the liquid/liquid coexistence curve are given.
A new approach to the determination of fluid phase Equilibria: Concentration measurements by Raman spectroscopy
Authors: Kaiser T. , Voßmerbäumer C. , Schweiger G.
Published: March 2014

We present a new in‐situ method for the measurement of fluid phase equilibria, which offers many advantages in contrast to conventional sample techniques. To the author's knowledge, this is the first time that the vapor‐liquid‐equilibrium of a binary system is determined by measuring the concentrations in the gaseous as well as in the liquid phase by Raman spectroscopy. The isothermal data for the system cyclohexane‐toluene are compared to literature data at a temperature of T = 50°C and correlated by van Laar's equation. In addition some new data for the system mentioned above are given at temperatures of T = 60°C and T = 70°C.
Dielectric relaxation of aqueous electrolyte solutions. I. Solvent relaxation of 1:2, 2:1, and 2:2 electrolyte solutions
Authors: Barthel J. , Hetzenauer H. , Buchner R.
Published: March 2014

Complex permittivity measurements on aqueous solutions of CdCl2, CuCl2, MgSO4, CdSO4, Na2SO4, Cd(ClO4)2, and MgCl2in the frequency range from 0.9 to 90 GHz are reported. The data analysis reveals the superposition of 2 Debye dispersion steps for the solvent thus supporting multi‐step relaxation mechanisms discussed for water in the literature. An additional low frequency process is found for CdCl2, CuCl2, MgSO4, CdSO4, and Na2SO4solutions due to solute relaxation, but not for Cd(ClO4)2and MgCl2solutions. – The decrease of the static solvent permittivity at increasing electrolyte concentrations is interpreted in terms of irrotational bonding and kinetic depolarization and is used to determine effective solvation numbers. The dependence of the main (low frequency) relaxation time of water on electrolyte concentration is explained with the help of the reorientation and residence times of water in the hydration spheres of ions and in the bulk. The high frequency relaxation time is approximately concentration independent, whereas the dispersion amplitude of the process increases with electrolyte concentration.
Enhanced catalytic activity of metal salts of metal phthalocyanine tetracarboxylic acids in the autoxidation of thiophenol in hexane
Authors: Kusuda Kousuke , Kanda Taiji , Tanisaka Keizo
Published: March 2014

Catalytic activities of metal (Fe3+, Co2+, Ni2+ and Cu2+ salts of metal (FeCl2+, Co2+, Ni2+ and Cu2+)) phthalocyanine tetracarboxylic acids dispersed on a carrier in the autoxidation of thiophenol have been investigated. Absorptions of O2 in the presence of the catalysts were measured. P values (percentages of the absorbed O2 after 30 min. per theoretical volume) and T values (absorbed O2 mol s−1 (cat. mol)−1/substrate mol l−1) at the original point were adopted to evaluate the catalytic activities. Fe3+ salt of cobalt phthalocyanine tetracarboxylic acid showed the highest activity. The mechanism of the activity was investigated electrochemically by using carbon paste electrodes containing the catalyst.
The crystal and molecular structure of 3‐aminophthalhydrazide (Luminol)
Authors: Paradies Henrich H.
Published: March 2014

The crystal structure of 2‐aminophthalhydrazide (luminol) has been determined by X‐ray diffraction analysis. The space group determined was P&1macr; (No. 2) with cell constants of a = 12.714 Å, b = 14.132 Å. c = 7.1027 (Å), α = 101.24°, β = 94.84° and γ = 116.60° with six molecules per unit cell of formula molecular weight 177.16. The three luminol molecules form a hydrogen bonded trimeric unit. There is one intramolecular hydrogen bond per luminol molecule involving the NH2 group and the adjacent carbonyl group. All other hydrogen bonds are intermolecular. – Luminol crystallizes as amide‐hydroxyimunol tautomer. The protonated carbonyl group acts as hydrogen bond donor to a neightbouring unprotonated carbonyl group.
Generation of SnO by photoproduction and ‐mobilization of oxygen atoms in krypton matrices doped with N2O and Sn
Authors: Schriever U. , Hebert T. , Kolb D. M.
Published: March 2014

SnO molecules are photochemically formed by irradiation of a Sn: N2O mixture in solid krypton. A KrxO complex which is produced by VUV photolysis of N2O at 8.8 eV has been identified from a new absorption band at 6.9 eV. The mobilization of oxygen in Sn:N2O:Kr matrices, photoinduced by excitation of the KrxO species, was studied by trapping the oxygen at Sn atoms and by using the SnO generation as a monitor. Photolysis studies in Sn:N2O:Kr matrices as well as in Sn:Kr/N2O:Kr sandwich structures revealed an extraordinary high mobility of oxygen. A qualitative model of the mobilization scheme is discussed.
Investigations of the reaction between CH2(X̃3B1) and O2 in the temperature range 233 K ≤ T ≤ 433 K
Authors: Bley U. , Temps F. , Wagner H. Gg. , Wolf M.
Published: March 2014

The reaction between CH2(X̃T3B1) radicals (3CH2) and O2

3CH2+O2→products,

has been studied in a discharge flow reactor with Laser Magnetic Resonance (LMR) detection of 3CH2 and OH radicals and Electron Spin Resonance detection of O and H atoms. From the measured concentration‐versus‐time profiles of [3CH2] in the absence and presence of a large excess of O2 the overall rate coefficient of the reaction was found to be

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In the temperature range 233 K ≤ T ≤ 433 K. A limit for the contribution of H atom forming reaction channels of <20% was determined. The results are discussed in relation to available literature data on the formation of stable products. Main reaction channels leading directly to production of CO + H2O and H2 + CO2 are concluded to be of importance.
Investigation of the 3CH2 + O2 reaction in shock waves
Authors: Dombrowsky Ch. , Wagner H. Gg.
Published: March 2014

The reaction of 3CH2 with O2 was investigated in incident shock waves for pressures near 1 bar and temperatures from 1000 to about 1800 K. 3CH2 source was diazomethane. The concentration time curves of CO and CO2 were obtained from infrared emission, the OH profiles by laser absorption measurements. Data for O and H atom formation in this reaction were reported recently. – The measurements show that about a quarter of the reaction proceeds by forming radicals directly. Three quarters of the reaction form stable products only. Main reaction product is CO with a CO to CO2 ratio near 4:1. Direct formation of OH does not exceed a few percent. A reaction channel distribution is given. – Rate constants for the total reaction 3CH2 + O2 obtained by computer simulation of the product profiles in the temperature range mentioned are below the data extrapolated from measurements performed by Vinckier et al. and Bley et al. in the temperature range around room temperature. A rate expression fitting the measured date over the whole temperature range is reported.
Electronics of Colloidal Nanometer Particles
Authors: Henglein Arnim
Published: March 2014

Small colloidal particles *) and clusters *) of semiconductors and metals exhibit unusual properties and may be considered as a new physico‐chemical dimension between the molecules and the bulk materials. The surface to volume ratio is extremely large; small‐particle research therefore constitutes a combination of solid state and surface science. The electronic properties of the particles (light absorption, colour, fluorescence, catalytic and photocatalytic activity, electrochemistry etc.) depend on particle size. Chemical surface modification affects these properties and allows one to prepare new nano‐structures in solution, in layers, and in the crystalline state. No attempt is made in the present article to review the whole field, but to describe this new branch of colloid chemistry by focussing on a few selected topics.
Internal Solid State Reaction: Formation of Perovskite in NiO‐Matrix
Authors: Schmalzried H. , Frick T.
Published: March 2014

Isothermal internal reactions of the type A + B = AB taking place in a crystal matrix C are studied experimentally. The matrix crystal C is NiO, A = CaO, B = TiO2 (NiTiO3) and the reaction product AB is the perovskite CaTiO3. Both the morphology of the reaction product and the kinetics of its formation have been investigated and are discussed in the light of a previous theoretical study. In addition, chemical diffusivities of Ca‐ and Ti‐ions in the NiO‐matrix are determined.
Thermal Diffusion in Crystalline Binary Compounds with Narrow Range of Homogeneity – I. A New Experiment for the Determination of the Heat of Transport
Authors: Janek J.
Published: March 2014

The formal analysis of the coupling between diffusional matter and heat transport shows that diffusional matter fluxes are driven by both temperature and composition gradients, and that matter fluxes are always connected with heat fluxes. An important concept in the description of this coupling is the introduction of so‐called heats of transport. The heats of transport, being combinations of phenomenological transport coefficients, denote the relation between individual matter fluxes and related heat fluxes for isothermal systems. For the case of mixed ionic/electronic conducting binary compounds with narrow ranges of homogeneity, A1+δXV, a new experiment for the determination of the reduced heat of transport of metal A is proposed and discussed with respect to a possible realization. The experiment is based on the direct measurement of the flux of the metal component in a temperature gradient, under special boundary conditions for the composition of the sample, and gives direct access to the (reduced) heat of transport, Q*A. Alternative ways for the determination of the heat of transport are summarized and compared with the proposed experiment.
Mixed Carbon Dioxide‐Krypton Solids: A New Diluted Quadrupole System
Authors: Langel W. , Fleger H.‐W. , Knözinger E. , Schuller W.
Published: March 2014

Mixtures of carbon dioxide and krypton gases were codeposited from the gas phase. The resulting solids were studied by X‐ray powder diffraction and IR absorption. Molecular dynamics simulation was applied to the system.

Under equilibrium conditions phase separation occurs. If diffusion is suppressed, solids with extremely short coherence lengths were found in the concentration range of 30–70 mol% Kr. The simulation allows to reproduce this disorder. It is due to internal distortions rather than to grain size effects. The addition of krypton reduces the quadrupole‐quadrupole interaction. This leads to orientational and to centre‐of‐gravity disorder. The properties of CO2: Kr are discussed in comparison with the well known quadrupole glass N2: Ar. For the molecular dynamics simulation a flexible model of the CO2 was adopted. This allowed to reproduce the influence of the local environment on the band shape of the bending mode v2.
Viscosity of the System KF–KBF4–K2TiF6
Authors: Silný A. , Danêk V. , Nguyen D.K.
Published: March 2014

The viscosity of the melts of the system KF–KBF4–K2TiF6 has been measured by means of the computerised torsional pendulum method.

The viscosity of KF is higher than that of KBF4 at the same temperature, most probably due to the substantial overheating of KBF4. In the ternary system the viscosity increases with the increasing content of K2TiF6.

Additivity of the logarithms of viscosity was adopted as the ideal behaviour of the mixture. Negative deviations from such additive behaviour were found in the binary system KF–KBF4 probably due to the breaks of the B‐F‐B bridges caused by the excess of F− ions. Positive deviations from the ideal behaviour were found in the binaries KF–K2TiF6 and KBF4–K2TiF6 due to the formation of larger TiF3−7 anions caused by the reaction

Statistically significant ternary interaction confirmed that the above chemical reactions take place also in the ternary system.
Electrochemical Characterisation of Oxide Layers on Single Grains of a Polycrystalline Ti‐Sample
Authors: Kudelka S. , Michaelis A. , Schultze J.W.
Published: March 2014

Electronic properties of passive films (d≤20 nm) on single grains of polycrystalline Titanium were investigated by micro‐ellipsometry and electrochemical methods using photoresist microelectrodes with defined areas. A number of experimental improvements are reported here: i) The minimisation of the electrochemical active area down to 3×10−6 cm2, ii) the determination of the crystallographic orientation of single grains by anisotropy microellipsometry, as well as iii) the determination of local film thicknesses under potentiostatic control by in‐situ micro‐ellipsometry. iv) The capacity C of the microelectrodes was measured applying a new droplet technique. Anodisation of Ti single grains up to the same potential U yields different oxide thicknesses, anodic charges, donor densities and oxygen evolution. Thin passive layers need less anodic charge qOx for the oxide formation and have a higher donor density Nd. The great extent of oxygen evolution at these grains can be explained by an increased tunnel probability for the transition to the conduction band. The properties vary with the substrate orientation in a systematic manner, indicating a change of the properties at the (0111) orientation.
Determination of Rate Constants and Product Branching Ratios for the Reactions of CH3O2 and CH3O with Cl Atoms at Room Temperature
Authors: Jungkamp T. P. W. , Kukui A. , Schindler R. N.
Published: March 2014

Reactions of CH3O2 and of CH3O radicals with Cl atoms have been investigated at 300 K using a discharge flow system with LIF and mass‐spectrometric detection.

Rate constants k1 = (1.15±0.3)·10−10 and k2 = (1.00±0.2)·10−10, in units cm3 molecule−1 s−1 have been obtained observing pseudo‐first‐order decays of CH3O2 and CH3O radicals, respectively. The branching ratio k1a/k1 = 0.51 ±0.09 has been found from the determination of OCl yields. Formation of the Criegee intermediate CH2O2 in reaction (1b) was inferred from CO2 generation. A lower limit of 0.8±0.5 was derived for the CO2 yield from unimolecular CH2O2 decomposition.

Possible reaction pathways for steps (1a) and (1b) are suggested on the basis of ab initio model calculations. The calculations include the estimation of structures and energies of intermediate CH3O2Cl collision complexes and the decomposition of CH3OOCl to yield products.
Composition Dependence of the Liquid/Air Interfacial Tension of 2‐Butoxyethanol/Water Mixtures at Temperatures below the Lower Critical Temperature
Authors: Knecht B. , Woermann D.
Published: March 2014

Measurements of the liquid/air interfacial tension σα,βγ (α, vapour phase; (βγ), homogeneous liquid phase) of 2‐butoxyethanol (abbreviated C4E1)/water mixtures carried out as function of temperature (15°C≤T≤50°C) and composition (O≤x≤1; x, mole fraction of 2‐butoxyethanol) reveal the existence of extrema in the σα,βγ versus x curves measured at constant temperature. The location of the minimum on the composition axis xmin approaches the critical composition xc when temperature approaches the critical temperature Tc. For composition xc<x<xr (xr, mole fraction of C4E1 in the C4E1/water in the mixture forming the right boundary of the closed loop coexistence curve) the interfacial adsorption ΓC4E1(w) of C4E1 relative to water w calculated from the σα,βγ versus x isotherms has a negative value indicating the existence of a water‐rich layer at the α,βγ interface in this range of compositions. The extent of the depletion of C4E1 from this region increases if xc is approached from values x>xc. This could reflect the existence of a wetting transition from partial wetting of the α,γ interface by water‐rich phase γ to complete wetting of this interface by phase γ at a temperature very close to Tc. The existence of such a transition was presumed in the literature.
Dynamics of Molecular Hydrogen Interactions with Silicon Surfaces
Authors: Hasselbrink Eckart
Published: March 2014

Molecular hydrogen exhibits an exceedingly low dissociative sticking coefficient on the (100) and (111) faces of silicon. This finding would suggest that the molecule experiences a large barrier (> 100 kJ/mol) when it attempts to adsorb. However the assumption of such a large barrier is in conflict with the known desorption activation energy and the estimated bond strength of hydrogen atoms to silicon surface atoms. In recent experiments it has been observed that the desorbing molecules do not carry away a large extend of excess energy as translational energy nor in their internal degrees of freedrom. This apparent contradiction can be resolved if one considers that the dangling bonds on the silicon surface are localized and that hydrogen adsorption induces significant alterations of the surface structure. Hence, hydrogen adsorption is expected to be activated in degrees of freedrom localized in the surface. This proposition has been substantiated by the observation of an increasing adsorption probability with increasing sample temperature. Recent total energy calculations lend theoretical confirmation to this model.
Analysis of the Hydrogen Formation at GaAs Electrodes by Impedance Spectroscopy Investigations
Authors: Uhlendorf I. , Reineke‐Koch R. , Memming R.
Published: March 2014

The kinetics of the hydrogen formation from protons as well as from water has been studied over a large potential range by measuring the interfacial current and the impedance spectrum in dependence of the electrode potential simultaneously. According to a quantitative analysis of the experimental data a semilogarithmic plot of the current j versus the potential across the space charge region ϕsc yielded a straight line of an ideal slope of 60 mV/decade. In addition it was found that the j‐ϕsc behavior at n‐GaAs electrodes can be described by the thermionic emission model, i.e., the electron transfer rate is controlled by the electron transport across the space charge region. From this result it has been concluded that the reduction of protons is an extremely fast process. The mechanism and the consequences of this surprising result are discussed in detail.
High Pressure Electrolyte Conductivity of the Homogeneous, Fluid Water‐Sodium Hydroxide System to 400°C and 3000 bar
Authors: Eberz A. , Franck E.U.
Published: March 2014

Above the melting temperature of 319°C the ionic fluid sodium hydroxide is completely miscible with dense water. The electrolyte conductivity of such a fluid “water‐salt”‐system has been studied from dilute aqueous solution to the ionic melt. Apparatus and procedure are described to perform conductance measurements from 25 to 400°C and from 100 to 3000 bar with eight NaOH‐mole fractions from 0.024 to 0.93 and with the pure NaOH‐melt. At 400°C and 2000 bar the specific conductance rises slightly from 2.09 ohm−1cm−1for the pure melt to 2.58 ohm−1at 64.0 mol% NaOH and reaches a maximum of 4.28 ohm−1cm−1at 30 mol%. Density measurements permitted the determination of molar NaOH conductivity isotherms at nearly constant molar concentration of 50 mol · dm−3. At 350°C and 400°C the isotherms ascend continuously from molten hydroxide to dilute aqueous solutions. A function is presented which describes the conductance over the whole composition range with a quadratic combination of the two limiting conductances, with a Debye‐Hückel addition and with two realistic adjustable parameters for viscosity and interionic approach.
Ligand‐Substitution Reaction of Cobalt(III) Complexes of [CoCl(N)5]2+‐type with Carbonate: Activation of Kinetic Processes by Steric Chelate Effect
Authors: Masuda Chié , Jitsukawa Koichiro , Masuda Hideki , Einaga Hisahiko
Published: March 2014

Kinetics and mechanisms of coordination by ligand‐substitution of HCO3− for Cl− on the cobalt(III) complexes of [CoCl(N)5]2+‐type having different (N)5 backbone chelate ring structures to form those of [Co(CO3)(N)5]+‐type have been investigated in a weakly alkaline aqueous 0.10 mol dm−3 sodium perchlorate solution at ambient temperatures, in order to elucidate any possibility for the fixation of atmospheric CO2 on the coordination sphere of the transition metal center in the form of CO2−3. The HCO3− in the aqueous solution easily and substitutionally coordinates to the cobalt(III) complexes in place of coordinated chloro ligand via two consecutive rate‐determining steps, the faster one with two parallel pathways of aquation and hydroxide‐anation and the slower one with a pathway of carbonate‐anation. Of these reaction pathways, the hydroxide‐anation was explained by a dissociative interchange mechanism via conjugate base (IdCB), whereas the carbonate‐anation was explained by a nucleophilic attack of coordinated oxygen atom on the central cobalt(III) atom to the carbon atom of HCO3− while maintaining the Co – O bond throughout the step by taking the result of an EHMO calculation into consideration. The (N)5 backbone chelate ring structure served to enhance the rate of coordination of HCO3− on the cobalt(III) center as well as that of preceding aquation and hydroxide‐anation steps chiefly by its entropy effect. The pentadentate tetren backbone structure was recommended for the rapid fixation of CO2 in the form of CO2−3 on the cobalt(III) complexes of [CoCl(N)5]2+‐type.
Excess Enthalpy HE of Binary Mixtures Containing Alkanes, Ethanol and Ethyl‐Tert. Butyl Ether (ETBE)
Authors: Mier W. , Oswald G. , Tusel‐Langer E. , Lichtenthaler R.N.
Published: March 2014

The excess enthalpies of all possible binary mixtures of n‐heptane, isooctane (2,2,4‐trimethylpentane), ETBE (ethyl‐tert. butyl ether) and ethanol have been measured at 298.15 K and 313.15 K and atmospheric pressure using a quasi‐isothermal flow calorimeter. The experimental excess enthalpies HE and published excess heat capacities CEP and excess volumes VE are used to test the applicability of the ERAS (Extended Real Associated Solution)‐model.
Influence of Charge Density and Concentration on the Dynamics of Aqueous Polyelectrolyte Solutions
Authors: Walkenhorst R. , Dorfmüller Th. , Eimer W.
Published: March 2014

We have investigated the dynamics of protonated poly(2‐vinylpyridine) (Mw = 135000) in aqueous solution by dynamic light scattering over a wide concentration range (0.5 ≤ cpe ≤ 100 g/l). The charge density on the polymer chain (degree of protonation α) was varied from 0.26 to 0.62 by hydrochloric acid. The reduced composition variable Λ = αcmpe/ with cmpe and cs the molar concentrations of the polymer repeat unit and salt, respectively, was constant for a given charge density.

We always observed two well separated relaxation processes (a fast and a slow mode). At low charge density the diffusion coefficient of the fast mode reveals an increase‐maximum‐decrease pattern with concentration while the diffusion coefficient of the slow mode decreases with increasing concentration. The relaxation times of both modes as well as the ratio of their amplitudes were found to depend strongly on the degree of protonation of the polymer chains. Temperature‐dependent measurements at low polymer concentration (cpe = 2g/l) exhibit that both modes follow the Stokes‐Einstein prediction, except that we observed a significant non‐zero intercept for the fast mode. A possible influence of hydrophobic effects on the dynamics of protonated poly(2‐vinylpyridine) in aqueous solution is discussed.
HF Vapor
Authors: Suhm Martin A.
Published: March 2014

IR absorption spectroscopy of HF clusters in synchronized pulsed supersonic jet expansions and at thermal equilibrium is combined with a 1 +2 + 3 body decomposition scheme of the potential energy surfaces, different quantum chemical approaches and multidimensional vibrational quantum Monte Carlo calculations to characterize all major constituents (HF)n (n = 1–8) of the strongly associated HF vapor phase in terms of their structure, spectra, energetics, dynamics and abundance. From this data base, a microscopic quantum statistical model of HF vapor up to moderate pressures is constructed. Comparison to existing bulk thermodynamic data confirms that the model provides a globally correct and detailed microscopic description of this unique association phenomenon together with its explanation.
Fundamentals of Sorption Kinetics of Gas Mixtures in Porous Media under High Pressure Conditions
Authors: Micke André , Bülow Martin
Published: March 2014

Based on the Volterra integral technique, a universal method to calculate the sorption uptake curves of multi‐component gas mixtures in porous solids under variable high pressure conditions with non‐ideal behavior of the gas phase has been proposed. It takes into account a non‐linearly behaving concentration dependence at the surface of the porous medium. The applicability of the introduced method presupposes an isothermic gas phase and a constant diffusivity matrix. For the description of the non‐ideal gas phase behavior, equations of state were utilized.
UV Absorption Cross Sections of Acetyl Peroxynitrate and Trifluoroacetyl Peroxynitrate at 298 K
Authors: Libuda H.G. , Zabel F.
Published: March 2014

The UV absorption cross sections of acetyl peroxynitrate (PAN) and trifluoroacetyl peroxynitrate (FPAN) were determined at 298 K in the wavelength ranges 220–325 nm and 230–305 nm, respectively. Both peroxynitrates were prepared from nitric acid and the corresponding peroxy acids in n‐tridecane solution. The UV spectra were measured in a large cell (v = 420 dm3) equipped with White mirror systems for the simultaneous detection of gas phase species by long‐path UV and IR absorption. Impurities in the samples were quantified by their IR and/or UV absorption, and the UV spectra were corrected for contributions from these impurities using appropriate reference spectra. Concentrations of acetyl peroxynitrate and trifluoroacetyl peroxynitrate were derived from their IR absorptions by application of Beer's law. IR absorption coefficients were determined based on pressure measurements of the pure compound (for PAN) or on the stoichiometric CO2 yield in the thermal decomposition of the peroxynitrate in the presence of NO and O2 (for FPAN). The resulting UV absorption cross sections of PAN are larger than literature values, leading to photolysis rate constants on the Earth's surface which are higher by a factor of 4 than previous values (Senum et al., 1984). The absorption cross sections of FPAN were measured for the first time and result in photolysis rate constants which are slightly higher than those of PAN, suggesting that CF3C(O)O2NO2 and, by analogy, other haloacetyl peroxynitrates have too short a lifetime in the upper troposphere to be of importance for the transport of halogens into the stratosphere.
Proton NMR Studies on the Structure of Water at Interfaces of Aqueous Micelles. Part 4: Effects of Cationic and Zwitterionic Headgroups
Authors: El Seoud Omar A. , Blaskó Andrei , Bunton Clifford A.
Published: March 2014

Fractionation factors, φM, of interfacial water at surfaces of cationic and zwitterionic surfactants were determined from the dependence of the 1H chemical shift of water on the isotopic composition of the solvent (H2O plus D2O). Values of φM are greater than unity, showing that interfacial water is more structured than bulk water, whose fractionation factor = 1, by definition. The structuring increases with increasing bulk of the headgroup, but is unaffected by the length of the cationic surfactant hydrophobic tail. The effect of zwitterionic sulfobetaine surfactants on the structure of their water of hydration is less than that of cationic surfactants that have otherwise similar headgroups. Values of φM for cationic micelles are: cetyldimethylphenylammonium chloride, 1.08; cetylpyridinium chloride, 1.06; and dodecyltrimethylammonium bromide, 1.06. Values of φM for sulfobetaine micelles are: 3‐N‐tetradecyl‐N,N‐di‐n‐butylammonio‐1‐propane sulfonate, 1.07, and 3‐N‐tetradecyl‐N,N‐diethylammonio‐1‐propane sulfonate, 1.03.
Anorganische und organische “Modell”‐Oberflächen für chemische Sensoren
Authors: Schierbaum Klaus‐Dieter
Published: March 2014

A brief introduction is given on charge transfer reactions and inclusion reactions for oxide‐based and supramolecular compound‐based chemical sensors, respectively. TiO2 serves as inorganic “model” d0 oxide in the present study. By employing different surface spectroscopies and scanning tunneling microscopy, the formation and the role of intrinsic defects and Pt dopants at the thermodynamic most stable (110) surface is characterized with implications for the design of Schottky diode sensors and heterogeneous catalysts.

Organic supramolecular compounds like calix[4]arene and resorcin[4]arendialkylsulfide form molecular recognition structures at surfaces which act as specific interaction sites for small organic molecules. Adsorption/desorption properties have been studied using quartz microbalance oscillators, thermal desorption spectroscopy and theoretical force field calculations.
Structural Aspects of Tetramethylthiourea Adsorption on Au(111) Electrodes Investigated by In Situ Scanning Tunnelling Microscopy
Authors: Bunge E. , Nichols R.J. , Baumgärtel H. , Meyer H.
Published: March 2014

We have examined tetramethylthiourea (TMTU) adsorption on Au(111) with capacitance measurements and in situ scanning tunnelling microscopy (STM). Capacitance measurements of the TMTU‐containing solution indicate that the organic molecule is adsorbed over a wide potential range. High resolution STM images at +20 mV are totally different to those in the absence of TMTU and point to an ordered structure of the organic adsorbate. Three distinctive bright spots are seen in the STM images. A model has been developed with the molecules lying near to horizontal on the surface, forming a (3×3) adlayer.
Dynamik der Wechselwirkung von Molekülen mit Oberflächen
Authors: Ertl Gerhard
Published: March 2014

A multitude of methods from surface physics in combination with molecular beam and laser spectroscopic techniques provides detailed insight into the various aspects of the dynamics of interactions between molecules and surfaces, reaching from macroscopic kinetics over phenomena of spatiotemporal self‐organisation to the microscopic elementary process. The present state of our knowledge is illustrated by means of selected examples, concerning mainly single crystal surfaces of metals.
Multi‐Nuclear Solid‐State NMR Study of the Local Structure of SiOHAl Groups and their Interaction with Probe‐Molecules in Dehydrated Faujasite, Mordenite and Zeolite ZSM‐5
Authors: Hunger M. , Horvath T.
Published: March 2014

Structural variations of Si–O–Al bridges in dehydrated zeolites have been studied by 29Si CP/MAS NMR and 27Al NMR spectroscopy. After deammoniation of zeolites Y (nSi/nAl = 2.6 and 8.0), mordenite (nSi/nAl = 8.0) and ZSM‐5 (nSi/nAl = 22.0) 29Si NMR high‐field shifts of Si(1 Al) signals of maximum 0.8 ppm and of about 2.7 ppm and 4.0 ppm, respectively, were observed. This is explained by a protonation‐induced increase in the mean Si–O–T bond angles of SiOHAl groups. Simultaneously, an increase in the aluminium quadrupole coupling constant from about 5.0 MHz to about 16.0 MHz was determined indicating a strong protonation‐induced shear strain of framework AlO4 tetrahedra. On the other hand, the proton transfer from Si–O–Al bridges to basic probe‐molecules causes a decrease in the aluminium quadrupole coupling constant which corresponds to a higher AlO4 symmetry. The high symmetry of AlO4 tetrahedra in zeolite HZSM‐5 loaded with one methanol molecule per SiOHAl group, the mobility of the hydroxyl protons existing in this sample and their chemical shift value observed at the temperature of T = 295 K by 27Al, 2H and 1H NMR, respectively, indicate a rapid exchange of hydroxyl protons between bridging OH groups, hydrogen‐bonded methanol molecules and methoxonium ions. At the temperature of T = 85 K methanol molecules are fixed at the zeolite framework by hydrogen bonds.
Structure and Reactivity of Small Metallic and Bimetallic Clusters Hosted in Molecular Sieves
Authors: Shpiro Efim S. , Jaeger Nils I. , Schulz‐Ekloff Günter
Published: March 2014

The relationship between the electronic structure of small metallic (Pt, Ir, Rh) and alloyed (Pt‐Cr, Pt‐Cu) particles and their chemical reactivity has been established using zeolite matrix and a set of physical techniques, such as XPS, XAES, HRTEM, electron microdiffraction, FTIR of CO and catalytic model reactions.
Adsorption of Water Vapor on the MgO(100) Single Crystal Surface
Authors: Heidberg Joachim , Redlich Britta , Wetter Dirk
Published: March 2014

The adsorption of H2O on the MgO(100) surface prepared by cleaving a single crystal in situ under ultrahigh vacuum has been studied. For the first time Low Energy Electron Diffraction (LEED) has revealed an ordering of the H2O monolayer with a c(4×2) translational symmetry at 150 K, highly sensitive Polarization Fourier Transform Infrared Spectroscopy (PIR) has shown a strong, very broad polarized absorption from ∼3050–3500 cm−1 in the spectral range of the symmetric and antisymmetric H2O stretching vibration v1 and v3. The peak absorption is less than 0.1%, the integrated absorption 0.07 cm−1 and 0.11 cm−1 for p‐ and s‐polarization, respectively, indicating that the molecular plane is nearly parallel to the surface. This broad polarized band is assigned to the ordered, nearly planar H2O monolayer with all OH groups participating in strong O–H ⃛O bonds between nearest neighbor H2O molecules. In the ordered monolayer no dangling OH groups have been found. Additionally a sharp, p‐polarized absorption at 3680 cm−1 has been observed, attributed to dangling OH bonds of the adsorbate on steps. At temperatures above 190 K three sharp, polarized absorptions at 3672, 3626 and 3513 cm−1 with integrated absorptions in the range from 4·10−4 to 5·10−3cm−1 and their disappearance above 240 K have been detected. They are ascribed to isolated H2O molecules on steps (3672 cm−1) and terraces, respectively. For D2O on MgO(100) all corresponding absorptions have been measured.
Dynamics of the Cyclohexadienyl Radical Adsorbed in Porous Silica and NaZSM‐5
Authors: Roduner Emil , Schwager Martina , Tregenna‐Piggott Philip , Dilger Herbert , Shelley Mee , Reid Ivan D.
Published: March 2014

Avoided level crossing muon spin resonance spectra are reported for the muon substituted cyclohexadienyl radical which is formed on irradiation of benzene adsorbed on porous silica and in NaZSM‐5. The shapes of the resonances are discussed in terms of the reorientation dynamics of the adsorbed radical and of freezing of the pore‐confined benzene.
Quantum Theory of Photodesorption of Neutrals from Metals: Ab Initio Calculations and Active Control
Authors: Saalfrank Peter , Klamroth Tillmann
Published: March 2014

In continuation of previous work, two aspects of the ultraviolet laser‐induced desorption of NO from Pt (111) and ammonia from Cu(111) are investigated using different, quantum mechanical tools. First, for NO/Pt(111) it is shown with the help of simple, ab initio electronic structure cluster calculations, that previously introduced phenomenological two‐ and multiple‐state models are consistent with the more refined quantum chemical picture. Within this picture, the finite lifetime of a resonance state (“quenching”) is microscopically a consequence of the non‐adiabatic coupling of the resonance state to the metal electronic excitations. Further, both for NO/Pt(111) and ammonia/Cu(111) the possibility to actively control the desorption yields is investigated. For this purpose, time‐dependent wave packet propagations based on the nuclear Schrödinger equation are used. The proposed control mechanisms are (i) thermal and (ii) optical preparation of vibrational states of the adsorbate/substrate complex. The latter strategy, which is also supported by IR transition probabilities, is found to be much more efficient.
Rotational Alignment of D2 Desorbing from Pd(100)
Authors: Wetzig D. , Dopheide R. , David R. , Zacharias H.
Published: March 2014

The rotational alignment of D2 molecules desorbing from a Pd(100) single crystal surface is measured by laser‐induced fluorescence via the \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm B}^{\rm 1} \Sigma _{\rm u}^ + \leftarrow {\rm X}^{\rm 1} \Sigma _{\rm g}^ + $\end{document} Lyman bands around λ = 106 nm and 110 nm. Different rotational states in the vibrational ground state υ″ = 0 are probed. For low rotational states, J″ = 2, an isotropic distribution of the J vector is found. For higher rotational states J″ ≥ 3 a preference of the desorbing molecules for helicoptering over cartwheeling motion is observed, in agreement with recent theoretical predictions.
Atomic‐Scale Imaging of Catalytic Surface Reactions
Authors: Block J.H. , Drachsel W. , Ernst N. , Sieben B. , Gorodetskii V.
Published: March 2014

Recent experimental work is reviewed showing that a field ion microscope (FIM) can also serve as an in situ catalytic flow reactor. A platinum field emitter (model catalyst, grain diameter > 200 Å) exposes different small single‐crystal planes with well‐defined crystallographic orientations. The molecules reacting on the catalyst surface are also used as the FIM imaging gas. Due to preferential O2 field ionization on O(ad) layers, different surface sites (O(ad) and CO(ad)) can be discriminated in situ and in real time during the ongoing catalytic CO oxidation. The H2 oxidation on a Pt field emitter is distinguished by a preferential imaging of catalytically active sites with the product molecule H2O (desorbed mainly as H3O+). Isothermal, non‐linear dynamic processes of CO‐ and H2 oxidation reactions on Pt are investigated, involving the formation of face‐specific adsorption islands, mobility of reaction/diffusion fronts and the creation of chemical waves. The electric fields in the FIM (≈ 1.5 V/Å) appear to have a minor influence.
The Growth of Cobalt on a Rhenium (0001)‐Surface at 300 K
Authors: Parschau M. , Christmann K.
Published: March 2014

We report on combined LEED and scanning tunneling microscopy (STM) results of the initial growth of thin cobalt films on a Re(0001) surface at 300 K, whereby the coverage range 0 < ΘCo < 2 monolayers was investigated. At ΘCo ≈ 0.1 homogeneous nucleation of Co on the flat terraces of the Re(0001) surface and heterogeneous nucleation at defect (step) sites can be distinguished: Individual Co nuclei grow to dendritic islands with “arms” extending preferentially in the \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{\bar 12\bar 10} \right],\left[{2\bar 1\bar 10} \right] $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm \bar 1\bar 120}} \right] $\end{document} directions. At medium and high coverages kinetic limitations in the diffusivity of the impinging Co atoms provide additional growth in the second layer, while the first Co layer still remains incomplete: coalescence of individual first‐layer islands only occurs close to the monolayer coverage. Accordingly, we observe an incomplete layer‐by‐layer or ‘pseudo‐Frank‐van‐der‐Merwe’ growth for Co on the Re(0001) surface at room temperature.
The Growth and Properties of Pd and Pt on Al2O3/NiAl(110)
Authors: Bäumer M. , Libuda J. , Sandell A. , Freund H.‐J. , Graw G. , Bertrams Th. , Neddermeyer H.
Published: March 2014

Small metal particles have strongly size‐dependent properties, which – in the case of supported particles – are also influenced by the particle substrate interaction. We have investigated such effects for Pd deposited on a thin alumina film grown on NiAl(110) by probing the adsorption behaviour of CO. Structure and size of the metal islands were varied by employing different substrate temperatures during evaporation. We found that at 90 K small, disordered aggregates are formed, whereas deposition at 300 K results in larger crystallites with (111) facets. The CO thermal desorption spectra show a size‐dependent behaviour which can be attributed to a higher degree of CO coordination with decreasing particle size. The results are compared with the corresponding behaviour of Pt. In contrast to Pd, Pt leads to a strong interaction with the substrate at 300 K. This gives rise to a desorption feature of CO in a temperature range which is typical for transition metal oxides.
In Situ Controlled Promotion of Catalyst Surfaces Via Solid Electrolytes: The NEMCA Effect
Authors: Vayenas Constantinos G. , Yentekakis Ioannis V. , Bebelis Symeon I. , Neophytides Stylianos G.
Published: March 2014

The catalytic activity and selectivity of metal films interfaced with solid electrolytes can be varied in situ in a dramatic and reversible manner by applying currents or voltages (typically ± 1–2 V) between the catalyst film and a counter electrode also deposited on the solid electrolyte. Catalytic rates can thus be varied by up to a factor of 200. The induced steady‐state change in catalytic rate is up to five orders of magnitude larger than the steady‐state rate of electrochemical supply of ionic species from the solid electrolyte onto the catalyst surface. This novel effect termed Non‐Faradaic Electrochemical modification of catalytic activity (NEMCA) has been studied for over 40 catalytic reactions on Pt, Rh, Pd, Ag, Ni and IrO2 catalysts using a variety of solid electrolytes (O2−, F−, Na+, H+ conductors) and also, more recently, in aqueous alkaline solutions. Besides potential technological applications, this new effect allows for a systematic study of the role of promoters in heterogeneous catalysis. In this paper the main features of in situ controlled promotion are reviewed and the origin of the effect is discussed on the basis of recent XPS, TPD and cyclic voltammetric investigations.
Surface Characterisation and Modification by the Scanning Electrochemical Microscope (SECM)
Authors: Borgwarth K. , Ricken C , Ebling D.G. , Heinze J.
Published: March 2014

Methods of surface analysis and micromodification using the scanning electrochemical microscope (SECM) are described. An ultramicroelectrode (UME) is scanned in a liquid electrolyte a few microns above a sample's surface. The principles of SECM are explained. Local surface conductivity and reactivity can be imaged in the feedback and collector/generator mode. The same set‐up allows micromodification processes as well. The degree of doping of polyaniline deposited on a PETG film was increased locally. The generated structure formed an inter‐digital array consisting of doped and undoped polyaniline. Its local conductivity was successfully analysed in a second step. To fabricate a polymer microstructure the monomer 2,5‐bis(1‐methyl‐pyrrol‐2yl)‐thiophene was deposited by evaporation on an ITO substrate. Polymerisation was induced by the tip via an oxidation reaction. The remaining monomer was easily removed by organic solvents. A new method for the microdeposition of silver on a gold substrate is described. Silver cations were complexated in an aqueous solution of ammonia. Protons locally generated by the tip shifted the complexation equilibrium to create free silver cations. When the sample is held on an adequate potential they were deposited on the gold surface.