bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear Quadrupolar Spin Relaxation and Association in Binary Liquid Metallic Alloys
Authors: Elwenspoek M. , Brinkmann R. , Maxim P. , Paulick C. , Quitmann D.
Published: July 2012

We present experimental data for the nuclear quadrupolar spin relaxation rate Rq in liquid InxSb1–x, HgxK1–x and In50Hg50. The results for the concentration and temperature dependence of Rq can be qualitatively interpreted with the framework of association in these systems (quasi ternary solution model). We conclude that the relaxation is mostly due to the decay of associates in HgIn and to rotational diffusion of associates in Hg – K. In In – Sb, the corresponding correlation times seem to be equal so that both relaxation processes may contribute to the relaxation. The analysis of microscopic experiments using the concept of association may prove useful for a better understanding of the nature of the associates.
Free Energy Criteria for Glass Forming Alloys
Authors: Saunders N. , Miodownik A. P.
Published: July 2012

The thermodynamic characterisation of a number of glass forming systems (Au – Si, Pd – Si, Ni – Ti, Ti – Be, Zr – Be and Hf – Be) has been reviewed, and the free energy curves calculated for the glass forming temperature as well as for the temperature of maximum rate of crystallisation, in order to check how far the data which models the equilibrium diagrams provides suitable guidance for metallic glass formation. It is shown that the glass forming range is accurately predicted from the region where the liquid phase is more stable than other competing single phases, thus confirming the importance of the T0 concept. The systems considered offer a variety of behaviour which emphasises the importance of metastable compound formation as well as the inhibition of some equilibrium compounds. The present treatment is compared with other approaches to the problem.
Electron Transfer Reaction Between Ferrocene and Tris (1,10‐Phenanthroline) Cobalt (HI) in Micellar Systems
Authors: Cavasino F. Paolo , Sbriziolo Carmelo , Pelizzetti Ezio
Published: July 2012

The kinetics of the electron transfer reaction between ferrocene and tris (1, 10‐phenanthroline) Cobalt (III) have been studied by the stopped‐flow method at 20.0°C and ionic strength 0.02 mol dm−3 in the presence of anionic (SDS), cationic (CTAB) and non‐ionic (Triton X‐100) micelles. Cationic and non‐ionic micelles inhibit the oxidation reaction according to a model in which the ferrocene is partitioned between the aqueous and micellar pseudo‐phases, the reaction proceeding primarily in the aqueous phase. On the contrary anionic micelles catalyze the reaction which occurs in the micellar phase. The estimated binding constants of ferrocene to the different micelles are quite similar.
A Fluorescence Microscopic Study Concerning the Phase Diagram of Phospholipids
Authors: Lösche M. , Sackmann E. , Möhwald H.
Published: July 2012

The phase diagram of phospholipid monolayers is investigated using fluorescence microscopic and thermodynamic techniques. The images recorded using low light level camera tubes show patterns of inhomogeneities in the condensed as well as in the expanded states. These are ascribed to different dye solubilities and different molecular densities, respectively, in coexisting phases. – For pressures above that corresponding to a sharp break in surface pressure versus area isotherms at least two phases coexist. The monolayer is macroscopically fluid with an almost constant diffusion coefficient throughout the so‐called liquid expanded, liquid condensed and the intermediate phase. For dipalmitoylphosphatidylcholine (DPPC) at molecular areas as small as 55 Å2/molecule a drastic decrease in diffusion by about two orders of magnitude is observed. The gas/liquid transition is observed from a formation of characteristic, symmetrical lipid domains on the water surface.
The Solubility of Electrolytes in Homogeneous Mixtures of Water‐Miscible Organic Solvent (MOS)
Authors: Alfassi Zeev B. , Weiss J.
Published: July 2012

The solubility of several electrolytes in homogeneous mixtures of water‐miscible organic solvent (acetone, methanol, tetrahydrofuran, dioxane and acetonitrile) was found to obey the equation S = Sw exp (‐ λf) where Sw and S are the solubilities in water and the mixture respectively, and f is the volume fraction (or mole fraction) of the organic solvent. This dependence can be explained assuming the additivity of the standard state chemical potential of the electrolyte in the mixture, i.e. μ = f · μ + (1 ‐ f) μ0.
Ultraschalluntersuchungen in flüssigen und plastischen Phasen
Authors: Kreutzenbeck H. J. , Ledwig R. , Würflinger A.
Published: July 2012

Different devices have been developed for ultrasonic measurements at atmospheric and elevated pressures up to 1 kbar. The velocities of sound for liquid toluene, 2,3‐dimethylbutane, cyclohexane, and camphene have been determined. In the case of 2,3‐dimethylbutane also preliminary absorption measurements at elevated pressures have been performed, according to which the activation volume for the hindered internal rotation is negligible. Furthermore some plastic phases have been studied. The velocities of sound (longitudinal mode) of cyclohexane and camphene increase considerably on freezing in contradiction to the findings of others. Additional measurements of the transverse modes allow a rough estimation of the elastic stiffness constants.
Der pKa‐Wert von Redox‐Indikatoren auf Graphitelektroden
Authors: Huck H.
Published: July 2012

The redox potentials of adsorbed weak aromatic acids (a) and their conjugate bases (b) on graphite electrodes at different pH were measured by means of cyclic voltammetry to obtain the apparent pK'a,ad‐values. In addition the desorption velocities Kd (a) and kd (b) were measured by cyclic voltammetry, from which the pK‐values due to different adsorbabilities of (a) and (b) were calculated. – It is shown that the difference ΔpK'a,ad of the pKa‐values on the surface and in the bulk of the solution is mainly caused by a charge in the adsorbed acid or conjugate base, and in the case of ion pair and chelat complex formation with the counter ions of the buffer also by the local field of the counter ion. Ion pairs were found with the reduced molecules, which have no charge distribution by mesomerie. The electronic structure has only then a notable influence, if the adsorbed molecule has conjugated π‐electrons and if these are easily polarized in the electrical field of the electrode. The dissociation field effect was also taken into consideration.
Das Zünden und Verlöschen einer autothermen Reaktion in einer porösen Partikel in oxidierender Atmosphäre
Authors: Meinköhn D.
Published: July 2012

An investigation of the critical stationary states of an exothermic reaction is presented, by which the phenomena of ignition and extinction are described. The set of critical states is represented in form of a space curve, for which the projection into the parameter plane is discussed. Geometryindependent bounds are derived for the components of the transition point at which criticality disappears.
Periodische und statistische Eigenschaften kohärenter Kurzzeit‐Strukturen in Tankflammen
Authors: Brötz W. , Schönbucher A. , Banhardt V. , Schieß N.
Published: July 2012

Coherent structures of pool flames are visualized by the synchronous holographic interferometry. – There are large coherent structures which have periodical properties and small coherent structures both with periodical and statistical properties. The periodical phenomena can be classified into three types of instabilities. The first type is a low‐frequency instability with frequencies of the order of 12 Hz (for a n‐hexan pool flame, d = 4.6 cm) and depends considerably on the pool diameter. The second and third types have frequencies in the order of 300 Hz and 500 Hz, which depend mainly on the fuel type. – The statistical properties of the small coherent structures indicate that the turbulent exchange coefficients for heat and matter have values six times larger than the exchange coefficients for the momentum. The turbulent Prandtl numbers, Schmidt numbers and Lewis numbers are functions of the distance from the fuel surface. These functions vary between the following limits:
Elementarreaktionen in der Oxidation von Alkenen
Authors: Hoyermann K. , Sievert R.
Published: July 2012

The reactions of OH radicals with the isomers of butene (1‐C4H8, cis‐2‐C4H8, trans‐2‐C4H8, iso‐C4H8) have been studied at low pressure using an isothermal flow reactor (295 – 298 K, p = 0.9 – 10 Torr) and a Laval‐nozzle reactor (p < 0.1 Torr). The hydroxyl radicals have been produced via the reactions H/D + NO2 or F + H2O/D2O, hydroxy butyl radicals via the reactions F + 1‐C4H9OH, 2‐C4H9OH, sec‐C4H9OH, tert‐C4H9OH. Samples were withdrawn continuously by a molecular beam sampling system and were analyzed mass spectrometrically, applying synchronous ion counting and chemical modulation techniques. – The reaction mechanism is found as

The stabilization of the adduct is the main reaction channel at room temperature and around 1 Torr, abstraction reactions are negligeable. – The reaction mechanisms were analyzed in terms of addition/redissociation/stabilization/isomerization/decomposition, using unimolecular rate theory. The results were applied for the prediction of product formation at conditions of technical combustion processes.
Modeling Studies of the Homogeneous Formation of Aromatic Compounds in the Thermal Decomposition of n‐Hexane
Authors: Ebert K. H. , Ederer H. J. , Stabel U.
Published: July 2012

The pyrolysis of n‐hexane – as well as the thermal decomposition of n‐hexane with addition of propene and 1 ‐butene – was studied at 819 K up to very high conversions. A reaction model, consisting of elementary reactions, was developed. With this model the experimental results including the formation of benzene and toluene can be described. Inhibition effects, the rates of formation of various products and the effects of products on the reacting system are discussed.
Calculation of Burning Velocity and Flame Structure in Methanol – Air Mixtures
Authors: Dove J. E. , Warnatz J.
Published: July 2012

An a priori calculation has been made of laminar burning velocities of methanol‐air mixtures over the composition range 8% to 20% CH3OH at 298 K and 1 bar, and for stoichiometric mixtures over the pressure range 0.0625 to 16 bar and over the temperature range 298 to 1200 K. The time dependent conservation equations were solved repeatedly until a time undependent solution was obtained, giving the required flame profiles. The kinetic data set was based on a full survey of high temperature literature data, and comprised 40 elementary reactions with 15 chemical species. The results show generally very good agreement with experimentally measured burning velocities. A kinetic sensitivity analysis shows which elementary reactions are important in determining the flame properties, and enables us to state for which of these reactions it is particularly important to obtain improved rate data.
Temperature Measurements in Flames by Laser Raman Techniques
Authors: Kreutner W. , Stricker W. , Just Th.
Published: July 2012

Laser Raman techniques are assuming an ever increasing role in evaluating temperature data from combustion systems. Non‐intrusive and spatially resolved temperature measurements can be very helpful to improve the understanding of combustion processes. An important possibility of these techniques may be a more detailed check of computer codes for the modelling of flames. In order to test the influence of molecular parameters on the CARS model and the evaluation procedure a comparison of temperature measurements in a premixed propane‐air flame at atmospheric pressure by spontaneous Raman spectroscopy and by CARS (Coherent Anti‐Stokes Raman Scattering) was made.
Laser‐Induced Saturated Fluorescence as a Method for the Determination of Radical Concentrations in Flames
Authors: Kohse‐Höinghaus K. , Perc W. , Just Th.
Published: July 2012

The laser‐induced saturated fluorescence method was further developed with the aim of increasing the accuracy of radical concentration measurements in flames. Absolute number densities for CH and OH in a low‐pressure acetylene/oxygen flame were obtained from saturation curves based on a two‐level rate equation model, whose validity was checked for the experimental conditions. From these saturation curves, approximate oscillator strengths could be deduced, which could serve as a cross‐check for the evaluated number densities. Temperatures were determined from rotational spectra of the excited molecules. – For CH as well as for OH, the concentrations obtained with different excitation methods agree well with each other. They were compared with kinetic model calculations. For the extension of the saturated fluorescence method to higher pressures, a multi‐level model is being developed.
Analyse des Verbrennungsablaufes im Ottomotor
Authors: Müller H.
Published: July 2012

The analysis of the combustion process in spark ignition engines is important because their operation accounts for about 20% of the total oil consumption. A gain in efficiency will be beneficial for both energy consumption and exhaust emissions. Combustion in an engine differs in several points from ideal combustion process. Detailed information is given in the paper by considering three consecutive parts of combustion: the inflammation period, the main burning period, the afterburning period. In spark ignition engines practically only the inflammation period depends on the equivalence ratio. Quantitative details of the combustion process and of flame spread is obtained by pressure measurements, ionisation gaps and local radiation measurements.
Investigation of the Formation of High Molecular Hydrocarbons and Soot in Premixed Hydrocarbon‐Oxygen Flames
Authors: Bockhorn H. , Fetting F. , Wenz H. W.
Published: July 2012

Measurements of concentrations of high molecular hydrocarbons in laminar flat low pressure flames with various hydrocarbons under sooting conditions are reported. The results show that for all fuels investigated in that region of the flames where the bulk of soot is formed besides the main combustion products some characteristic groups of species are to be found. Within these groups of species only few fuel specific characteristics are stated. The main fuel specific influence lies in the relative concentration for the species. A reaction scheme for the qualitative explanation of the results found is discussed.
Charged Particles in Sooting Flames II. Determination of the Fraction of Charged Soot
Authors: Homann K. H. , Wolf H.
Published: July 2012

A new technique has been developed allowing the determination of the relative amounts of charged and neutral soot in fuel‐rich premixed low‐pressure flames. Results on C2H2 and C6H6 flames are reported and used, together with charged particle number densities, to calculate soot mass fractions and particle sizes. The occurrence of charged soot particles is discussed within the adopted mechanism of soot formation.
Rußbildung in verschiedenen Brennstoff‐Luft‐Flammen
Authors: Baumgärtner L. , Jander H. , Wagner H. Gg.
Published: July 2012

The mass growth of soot and coagulation of soot particles were measured for different fuels in mixture with air on a flat flame burner. Neither the coagulation rate constant kcoag nor the rate constant for the mass growth of soot kf show a pronounced dependence of the type of fuel used. The total amount of soot formed increases strongly with increasing fuel content of the mixture for all fuels investigated; it decreases with increasing temperature within the used temperature range.
Die gezielte Oxidation der Kohle: Synthesegas durch Kohlevergasung
Authors: Cornils B.
Published: July 2012

In the medium and long term a reconnection between coal – as a source of carbon – and chemistry – as a consumer of carbon – will prove to be necessary. Syngas will be the most effective means of establishing this link, and coal gasification processes will be required which produce the syngas by partial oxidation. – This contribution reviews the existing coal gasification plants of the “first generation” and reports on the status of the “second generation” processes under development.
An ESCA Study on the Electrochemical Double Layer of Emersed Electrodes
Authors: Kolb P. M. , Rath D. L. , Wille R. , Hansen W. N.
Published: July 2012

Gold electrodes were emersed from the electrolyte during potential control and subsequently transferred into a UHV chamber for their surfaces to be analysed by ESCA as a function of emersion potential and electrolyte composition. The ESCA measurements confirm the view that electrodes can be removed from the electrochemical cell with the electrochemical double layer unchanged and the bulk electrolyte otherwise absent. The potential power of ex‐situ studies, such as ESCA, on emersed electrodes is demonstrated by determining surface excesses and adsorption isotherms for a number of weakly and strongly adsorbing ions, as well as for metal deposits. Observations of chemical shifts for double‐layer constituents are reported and briefly discussed.
Small Angle Neutron Scattering Studies on Viscoelastic Detergents
Authors: Hoffmann H. , Kalus J. , Thurn H. , Ibel K.
Published: July 2012

Small angle neutron scattering experiments (SANS) on solutions of cetylpyridiniumsalicylate (CPS) in D2O over a large concentration range show a characteristic scattering maximum due to mutual interactions between the rodlike micelles. From the scattering rates structure factors S(Q), pair correlation functions g(r) and corresponding mean potentials W(r) are derived. Furthermore it is shown, that the length L of the scatterers decreases in a concentration range from 20 mM to 160 mM CPS. To study the influence of interaction on the rods, increasing amount of salt (NaCl and NaSal) was added to a 5 mM solution of CPS. As one would expect, the scattering maximum decreases, while the length of the micelles increases. It is shown, that the rods remain rather stiff when small amounts of salt are added. In the case of 32 mM NaCl it was also possible to fit the data with a persistence length model showing that the rods may become flexible when large amounts of salt are added. A persistence length of 8000 – 12000 Å was evaluated for these conditions.
Low Temperature Photoreactivity of Diacetylene – Phenazine Complex Crystals
Authors: Bubeck C. , Xuan T. H. Nguyen , Sixl H. , Tieke B. , Bloor D.
Published: July 2012

The low temperature photoreactivity of diacetylene‐phenazine complex crystals has been studied by ESR‐ and optical spectroscopy. The optical excitation of phenazine at 4.2 K creates a stable, triplet diradical. It is caused by an electron‐transfer reaction from the diacetylene to the phenazine and a protonation of the phenazine. The diradical can be bleached optically at 4.2 K and thermally at temperatures above 90 K. The diacetylene units polymerize in the dark, as soon as the preirradiated crystals are warmed up to temperatures above 200 K. The solid‐state photochemistry of phenazine at low temperatures and its relation to the sensitized photopolymerization are discussed.
Thermodynamics of Polydimethylsiloxane Solutions. I. Calorimetric Results of the Enthalpy of Dilution with Seven Organic Solvents
Authors: Neff B. , Heintz A. , Lichtenthaler R. N.
Published: July 2012

A titration calorimetric method is described which has been used for the determination of heats of dilution of seven Polydimethylsiloxane (PDMS)/solvent systems with different molecular weight of the PDMS samples at 25°C and 40°C. From the data obtained the χH‐parameter due to Flory's theory has been calculated. A systematic increase of χH with concentration of PDMS and a decrease with increasing molecular weight of PDMS has been observed.
p‐V‐T and Bubble‐point Measurements in the System HBr – H2O and its Critical Behaviour
Authors: Rau Hans , Friedrichs Hans Adolf , Mathia Wolfgang
Published: July 2012

p‐V‐T measurements on HBr/H2O mixtures up to 820 K and 1500 bar in the complete range between pure H2O and pure HBr are reported. The bubble‐point line has been determined by visual observation up to about 690 K and 500 bar. – For the vapour phase an equation of state (Dieterici‐type) with mixing rules is applied. The experimental data including literature values are analyzed by integration of the Gibbs‐Duhem equation. – The system HBr/H2O is azeotropic even at elevated pressures. The azeotropic line intersects the high temperature branch of the critical curve at about xHBr = 0.045, 684 K and 335 bar. The low temperature branch of the critical curve is nearly identical to the critical point of HBr.
Diffusion Coefficients and Thermal Diffusion Factors for the Systems H2–N2, D2–N2, H2–O2 and D2–O2
Authors: Trengove R. D. , Robjohns H. L. , Dunlop P. J.
Published: July 2012

Diffusion coefficients and thermal diffusion factors are reported for the systems H2–N2, D2–N2, H2–O2 and D2–O2. Using approximate spherical potential functions for the like and unlike interactions, the experimental results are compared with corresponding values predicted by the Chapman‐Enskog theory.
The Nitroprusside Ion as a Nitrosating Reagent. Kinetic Studies on the Nitrosation of Morpholine
Authors: Casado J. , Quintela M. A. López , Mosquera M. , Rodr Prieto M. F. Íguez , Tato J. Vázquez
Published: July 2012

This article reports a kinetic study of the nitrosation of morpholine (MOR) by the nitroprusside ion, [Fe(CN)5NO]2−, to form N‐nitrosomorpholine, a substance of proven carcinogenicity. The reaction is of order one with respect to the nitroprusside ion and order two with respect to morpholine. The influence of the pH and the ionic strength of the medium on the rate of reaction has been studied in detail. A reaction mechanism is proposed whose first step is a fast reaction between the amine and the coordinated nitrosyl group to form a complex which reaches equilibrium with the reagents and then reacts with another molecule of amine to produce the corresponding nitrosamine and the complex [Fe(CN)5MOR]3−. The acidity constant of morpholine has been determined kinetically.
The Reaction Mechanism of the Nitrosation of Ureas
Authors: Casado J. , Castro A. , Mosquera M. , Rodr Prieto M. F. Íguez , Tato J. Vázquez
Published: July 2012

The nitrosation of methylurea has been studied under catalysis by acetate and mono‐, di‐ and trichloroacetate buffers. The following general equation for the rate of reaction as a function of the total concentrations of the reagents has been deduced:

where K1 is the acidity constant of nitrous acid and K2 that of carboxylic acid. The catalysis observed has been found to be due to the organic anions, and Brønsted relation is obeyed with β = 0.24. – The experimental results have been interpreted in terms of a reaction mechanism which features the rapid formation of a intermediate, MeNH(NO)CONH2, when the methylurea is nitrosated. The rate controlling step is the transfer of a proton from this intermediate to the solvent or to a basic catalyst (the nitrite ion or the organic anion). That it is this step that controls the overall rate of reaction is supported by the isotopic effect (kH/kD = 3.5) observed on carrying out kinetic measurements in D2O.
Differential Electrochemical Mass Spectroscopy (DEMS) — a New Method for the Study of Electrode Processes
Authors: Wolter O. , Heitbaum J.
Published: July 2012

A new technique is presented which allows the gaseous and volatile products of electrochemical reactions to be measured quantitatively and with high sensitivity. The equipment consists of the electrochemical cell, the membrane inlet system and the mass spectrometer. Products being formed at the porous working electrode are sucked through the porous membrane into the ion source of the mass spectrometer. The mass intensity detected is proportional to the corresponding faradaic current. A rate of formation of 5 · 10−11 mol s−1 can well be measured. The rise time of the mass intensity is short enough to allow it to be quantitatively correlated to the faradaic current even at variing electrode potential. This is utilized in mass spectroscopic cyclic voltammetry. The feasibility of the method is described.
Scanning Calorimetry as an Analytical Tool to Characterize DNAs
Authors: Klump Horst , Herzog Klaus
Published: July 2012

The investigation of the native DNA structure of various sources with the help of X‐ray diffraction techniques of fibres reveals a striking similarity of the structural dimensions of all DNAs. Contrary to these results sequence analysis of the nucleotide bases demonstrates the uniqueness of the vast majority of domains even within the DNA of a single species. In this paper we will demonstrate that there is a possibility to characterize the different DNAs by the help of differential adiabatic scanning calorimetry. The heat capacity as a function of temperature is unique for each DNA and can serve to identify the particular DNA and can help to group the eucariotic, procariotic and the viral DNAs. This will be shown for eleven different DNAs.
Die Temperaturabhängigkeit der optischen Konstanten des Chlorbenzols im infraroten Spektralbereich
Authors: Köser Heinz J. K.
Published: July 2012

The optical constants of chlorobenzene between 1500 and 600 cm−1 have been determined with the help of ATR spectroscopy in the temperature range between — 30 and + 80°C. — The observed decrease of the integral intensity with temperature can be explained by the change of density and lokal field. The increase of the band half‐width is a result of faster molecular motion. Form and intensity of the band near 900 cm−1 are temperature insensitive. — The temperature dependence of the refractive index in regions with negligible absorption has to be explained by the combined influence of density and change of lokal field with density. Even after taking due account of this effect the real and imaginary parts of the molecular polarizability remain temperature dependent within the band region.
Rate Constants for the Reactions of OH Radicals with Aromatics: Benzene, Phenol, Aniline, and 1,2,4‐Trichlorobenzene
Authors: Rinke Monika , Zetzsch Cornelius
Published: July 2012

Reactions of OH radicals with aromatics were investigated in the presence of He at pressures ranging from 5 to 800 mbar using pulsed vacuum uv photolysis of H2O for the production of OH and time resolved resonance fluorescence for the detection of OH. At room temperature (296 K) in the presence of 133 mbar He the rate constants, k, were observed to be in the high pressure limit. The rate constants, (k ± Δk)/10−12 cm3 s−1, were determined to be: (1.0 ± 0.2) for benzene; (120 ± 24) for aniline; (28 ± 6) for phenol, (0.50 ± 0.10) for 1,2,4‐trichlorobenzene. — For the temperature dependence of the rate constant for 1,2,4‐trichlorobenzene the Arrhenius expression (k ± 3σ) = (2.3 ± 1) · 10−12 exp [ — (430 ± 125) K/T] cm3 s−1 is obtained from measurements at 273 to 368 K. — The rate constants at room temperature can be correlated with the ionization potential, I, of the aromatics, yielding the equation: logk/cm3s−1 = 0.74–1.36 · I/eV. This equation is seen to represent the rate data on 18 aromatics to within a precision of a factor of two; with some precautions it might be used to predict rate constants for further substituted benzene aromatics. Outliers in such a diagram are benzaldehyde and the cresols (being more reactive than predicted), and diphenyl and chlorinated aromatics (being less reactive).
Spectral Properties and Kinetics of Cationic Transients Generated in Electron Pulse Irradiated C7‐ to C16‐Alkanes
Authors: Mehnert R. , Brede O. , Naumann W.
Published: July 2012

After electron pulse irradiation of n‐heptane, 3‐methylheptane, n‐decane, n‐dodecane, n‐tetradecane, and n‐hexadecane containing CCl4 as electron scavenger, transient optical absorption bands were observed with peak wavelengths between 550 and 880 nm. The bands are assigned to the corresponding alkane radical cations. For n‐heptane radical cations a maximum extinction coefficient of 8.8 · 103 dm3 mol−1 cm−1 is estimated. Alkene radical cations were also identified in neat alkane solutions. They seem to be generated by fragmentation of vibronically excited alkane radical cations and exhibit strong optical absorption bands (π‐π*‐transitions) around 280 nm. — The kinetics of the electron transfer from n‐hexadecane as solute to cationic transients present in n‐heptane after irradiation was experimentally studied and compared with calculations using the phenomenological model of ion pair recombination presented by Infelta and Rzad [1]. From two alternative reaction mechanisms applied, differing mainly in that one assumes short‐lived mobile holes, it is concluded that positive mobile holes should also exist in n‐heptane at times <10−9 s. Then they should be transformed into massive n‐heptane radical cations. — Electron transfer efficiencies were determined in n‐heptane for 11 solutes such as alkanes, alkenes and aromatics. These efficiencies are related to rate constants of the electron transfer from the solutes to mobile positive holes. The observed dependence of the rate constants on the free energy ΔG of the electron transfer reaction is explained in terms of changes in the Franck‐Condon vibrational overlap factors.
On the Mechanism of Reversible Unimolecular Reactions and the Canonical (“High Pressure”) Limit of the Rate Coefficient at Low Pressures*)
Authors: Quack Martin
Published: July 2012

Jost's [1] treatment of generalized first order kinetics is used for a new discussion of the mechanism of reversible unimolecular reactions. A detailed analysis of time dependent average microscopic rate coefficients and level populations is presented using exact solutions for a realistic model of an isomerization reaction. It is shown that unimolecular fall‐off for the macroscopic relaxation is not mainly due to a reduced population of reactive levels as suggested by the irreversible Lindemann mechanism, but rather due to a fast reverse reaction even at early times. It is furthermore shown that the average microscopic rate coefficients can be measured directly, in principle. At equilibrium they are equal to the canonical (“high pressure”) limit of the rate coefficient even for arbitrarily low pressures. Practical experimental schemes are suggested for thus obtaining high pressure limiting rate coefficients without extrapolation procedures.
A Generalized van der Waals Equation of State III. Calculation of Excess Thermodynamic Quantities from Density Measurements
Authors: Kohler F. , Svejda P.
Published: July 2012

An equation of state reported previously is further developed for the calculation of thermodynamic excess functions in mixtures. The only mixture quantity used is the excess volume. With this quantity, one of the two mixing rules is determined. For the second rule, a plausible, but essentially empirical prescription is applied. Numerical calculations are carried out for the system benzene + cyclohexane.
Temperature Dependence of Number and Size of Triton‐X‐100 Micelles in Aqueous Solution
Authors: Rau Hermann , Greiner Gerhard , Hämmerle Hugo
Published: July 2012

Stationary and dynamic fluorescence experiments with pyrene as a probe molecule indicate higher aggregation numbers in Triton‐X‐100 micelles at higher temperatures well below the cloud point. The structure of the micelles is changed considerably as (in spite of higher aggregation) the hydrophobic compartment available to the probe molecules becomes smaller. The increase of aggregation is combined with a decrease of the number of micelles, i. e. micelles are dissolved or merge with others.
Mass Spectrometric Study of the Vaporization of Cesium Iodide and Thermochemistry of (CsI)2(g) and (CsI)3(g)
Authors: Viswanathan R. , Hilpert K.
Published: July 2012

Knudsen cell mass spectrometric investigations of the vapour over CsI(s) between 604 and 833 K show the existence of CsI(g), (CsI)2(g), and (CsI)3(g). The enthalpies of sublimation to monomer and to dimer as well as the enthalpy of dimerization are determined with both, the second and third law method, at 298 K as 191.2 ± 2.0, 233.3 ± 4.6 and –149.2 ± 4.4 kJ mol−1, respectively. The values obtained with the second law method at 768 K for the enthalpy of sublimation to trimer and for the enthalpy of trimerization are 256.9 ± 8.3 and –289.9 ± 8.6 kJ mol−1, respectively. Equations for the partial pressures of (CsI)i(g) (i = 1, 2, 3) are given for the temperature range of measurements. The appearance potentials 14.5 ± 0.2(I+), 7.5 ± 0.2(CsI+), 7.2 ± 0.2(CsI+), 12.0 ± 0.2(Cs2I+), 7.2 ± 0.2(Cs2I+), 6.3 ± 0.2(Cs2I2I+), and 7.0 ± 0.2 V (Cs3I2I+) are obtained for the ions given in parentheses which are detected upon vaporizing CsI(s). The obtained findings are compared with data reported in the literature.
On the Fe2+ –Mg2+‐Interdiffusion in Olivine (II)
Authors: Nakamura A. , Schmalzried H.
Published: July 2012

Interdiffusion experiments have been performed in the quasibinary system Fe2SiO4–Mg2SiO4. Interdiffusion coefficients D̄ have been evaluated for polycrystalline (FexMg1‐x)2SiO4 between 1050°C < T < 1280°C and compositions x ranging from 0.9 to 0.1. It was found that D̄, at given T and po2, increases almost exponentially with composition x in (FexMg1‐x)2SiO4, in accordance with other oxide solid solutions. For x > 0.3, a po21/5‐dependence is found. For smaller x‐values, D̄ is rather proportional to po21/5.5. It is also found that the oxygen pressure dependence of D̄, and of the vacancy concentration in the sublattice of the divalent cations, is the same. This means that indeed a vacancy mechanism is operative in the interdiffusion process. The strong composition dependence of D̄ is almost entirely due to the strong composition dependence of the vacancy concentration. Various other olivine solid solution systems (where Me2+ = Ni2+, Co2+, Mn2+) can be shown to behave similar to the iron‐olivine. It is also found that DFe > DMg. The meaning of D̄ is discussed in terms of the selfdiffusion coefficients DFe and DMg.
Ellipsometry During the Growth of Electrochemically‐Formed Mercury Nuclei
Authors: Greef R.
Published: July 2012

Mercury can be deposited electrochemically from mercurous nitrate solutions onto glassy carbon in conditions which allow the number density and radius of the growing nuclei to be estimated. This system can be taken as a model for a surface of controlled roughness. In this paper the ellipsometric response of the system is described, and a simple graded‐film model is presented that accounts for the salient features of the results.
Photochemistry of Colloidal Metal Sulfides 6. Kinetics of Interfacial Reactions at ZnS‐Particles
Authors: Henglein A. , Gutiérrez M. , Fischer Ch.‐H.
Published: July 2012

ZnS sols containing alcohol or formate as reactants for positive holes and nitrous oxide or carbon dioxide as reactants for electrons were illuminated and the yields of the various products determined. Alcohols are oxidized via a one‐hole mechanism, the product being an 1‐hydroxyalkyl radical which undergoes reaction in the bulk solution. Carbon dioxide is exclusively reduced to formic acid via a two‐electron mechanism. Formate is mainly (77%) oxidized to CO2 in a two‐hole process and less frequently via one‐electron transfer, i.e. formation of intermediate CO2− which reacts with other radicals in the bulk solution. A possible role of intermediate zinc atoms in the two‐electron reductions is discussed. In the presence of two reactants for one kind of charge carrier, the yields of the products can often be described by conventional competition kinetics. A scavenger for electrons influences the yield of the reaction of the scavenger for positive holes and vice versa. This influence is described for various pairs of scavengers (such as strong h+ and weak e− scavenger; strong h+ and strong e− scavenger etc.).
Mobility and Self‐Diffusion Coefficient of Higher Valent Co‐Ions in Ion Exchange Membranes
Authors: Chakravarti A. K. , Schlögl R.
Published: July 2012

Donnan concentration, self‐diffusion coefficient, and mobility of SO4− ‐ co‐ion in phenolsulphonic acid membrane have been determined using 0.0005 to 0.5 M MgSO4 as external electrolyte solutions. At lower external electrolyte concentrations (<0.25 M) the experimentally determined Donnan concentrations are higher than the corresponding theoretically calculated values; the discrepancy is larger at lower concentrations. Both the true self‐diffusion coefficient and the mobility decrease (although not appreciably) with increase in external solution concentration, but they increase with increasing temperature at a particular concentration (viz., 0.05 M).
Level Structure and Dynamics of Clusters
Authors: Jortner Joshua
Published: July 2012

Some features of the structure, the dynamics of nuclear motion, the nature of electronic states, excited‐state energetics and relaxation phenomena in “isolated” nonmetallic clusters are reviewed, with an emphasis on the interrelationship between the characteristics of molecular and condensed phase systems.
Penning, Photo and Electron Impact Ionization of Argon Clusters
Authors: Birkhofer H. P. , Haberland H. , Winterer M. , Worsnop D. R.
Published: July 2012

Mass spectra of argon clusters from a supersonic expansion measured by electron impact or photo ionization are similar to those obtained by Penning ionization. Associative ionization of clusters is not observed. This allows a determination of the condensed fraction in the beam. The mean cluster size is compared to data of other authors and heavy fragmentation of the clusters upon ionization is found. The ionized atom in a cluster will react very rapidly to a dimer ion, whose large binding energy of about 1 eV will lead to cluster fragmentation. A time table of events happening in a rare gas cluster after ionization is conjectured.
Multiphoton Ionization of Ammonia Clusters with a Tunable Laser
Authors: Echt O. , Morgan S. , Dao P. D. , Stanley R. J. , A. W. Castleman
Published: July 2012

Clusters of ammonia, formed by adiabatic expansion, were subjected to analysis in a time‐of‐flight mass spectrometer following multiphoton ionization. All cluster ions had the composition (NH3)n · H+ (with n ranging up to approximately 65) and none corresponding to (NH3)n·+ were detected with the exception of n = 1. An unusually stable species (NH4+)(NH3)4 was produced under all expansion and ionizing conditions investigated; it is attributed to an especially stable ion structure. Well resolved rotational structure for the β and c̄ states of a cold monomer beam were obtained and rotational assignments are presented for the c̄' band. A search for resonances in the ammonia clusters failed to reveal any well resolved structure, although isotope shifts in the monomer spectra were found through use of deuterium substitution.
Supersonic Metal Clusters
Authors: Morse Michael D. , Smalley R. E.
Published: July 2012

Recent developments in laser and molecular beam technology have now made it possible to produce supersonic beams of metal clusters of virtually any metal in the periodic table. The availability of these clusters for study in the gas phase provides an opportunity to investigate in detail the physics and chemistry of economically important and scientifically interesting metal cluster species. Initially, studies have involved the investigation of the metal‐metal bond in transition metal dimers, including Cr2, Mo2, V2, and Ni2 through resonant twophoton ionization spectroscopy. These studies have demonstrated the importance of 3d (and 4d) electrons in the metal‐metal bond in Cr2, Mo2, and V2. A comparison of V2 and Cr2 illustrates the importance of the 3d contraction with increasing nuclear change, and this is found to be of central concern in Ni2, where no 3d contribution to the chemical bond is found. Finally, Cu3 is investigated, providing the first gas‐phase spectrum of a triatomic transition metal cluster. Electronically, Cu3 is analogous to Na3 and other alkali trimers, so it is not surprising that the observed spectrum is best explained as arising from a Jahn‐Teller distorted 2E' state (in D3h symmetry), as has been calculated for Li3. The observed transition in Cu3 is assigned to be 2E”←2E', with both upper and lower states undergoing Jahn‐Teller distortions.
Electronic Structure and Properties of Small Al and Ge Clusters
Authors: Pacchioni Gianfranco , Koutecký Jaroslav
Published: July 2012

Stabilities, geometries and electronic structures of Aln (n = 3–5) and Gem (m = 3–6) clusters have been determined by means of pseudopotential MRD CI calculations. Most stable Al clusters are characterized by high spin multiplicities and can be considered as deformed sections of the Al fcc crystal lattice. On the contrary, most favoured Ge clusters have singlet ground states and geometrical structures which cannot be identified as parts of the diamond‐like Ge crystal lattice. – The differences in the properties of Al and Ge clusters can be rationalized on the basis of their respective electronic structures.
Differential Scattering Analysis of Cluster Beams
Authors: Buck U. , Meyer H.
Published: July 2012

The formation of Arn and (NH3)n clusters in a supersonic expansion and the fragmentation by electron impact ionization are measured by analyzing the kinematically different behaviour in a scattering experiment with a light He atom. Appreciable fragmentation of dimers and trimers is found.
Interaction of Accelerated Cluster Ions of Hydrogen with Gas Targets
Authors: Henkes P. R. W. , Pfeiffer U.
Published: July 2012

Hydrogen cluster ions of 800 keV were passed through an H2O gas target. The production and destruction of charged fragments was followed as a function of the target thickness. The comparison of the experimental results with those of a model calculation shows that the dominant process for fragment production is most probably the evaporation of H2 molecules.
Mass Spectrometric Study of Sodium Clusters under Equilibrium Conditions with a Knudsen Cell
Authors: Hilpert K.
Published: July 2012

The vaporization of Na(l) was studied under equilibrium conditions by the high‐temperature mass spectrometric method with a Knudsen cell. The atomization enthalpies of Na2(g) and Na3(g) were determined as 71.8 ± 4.0 and 103 ± 12 kJ mol−1 respectively. Knudsen cells developed for the study of alkali metals are described.
The Preparation of Metal Clusters and Molecules by Means of the Gas Aggregation Technique
Authors: Schulze W. , Frank F. , Charlé K.‐P. , Tesche B.
Published: July 2012

The gas aggregation technique has been brought up to the point, where metal clusters can be produced continuously in the size range from 105 atoms per cluster down to molecules. The knowledge of the parameters controlling the cluster growth allows the shift of the mean cluster size within the above given size range with reasonably narrow size distributions of the Gauss‐type. The cluster size down to 10 Å in diameter is measured by electron microscopy; the existence of smaller particles can be monitored by optical spectroscopy. – The cluster source can be stabilized for hours. Thus a sufficient amount of clusters can be accumulated and stabilized in matrices, allowing, e.g. EXAFS and IR measurements.
Cluster Ion Formation in Free Jet Expansion Processes at Low Temperatures
Authors: Beuhler R. J. , Friedman L.
Published: July 2012

An experimental high voltage post‐acceleration facility for the detection of high molecular weight cluster ions is described. A summary of results obtained with this facility in studies of high molecular weight water and argon cluster ions is presented. Results on studies of hydrogen cluster ion formation in the expansion of pure weakly ionized hydrogen gas are also presented. Attempts to limit cluster ion formation in hydrogen to quasi equilibrium conditions inside the ion source with source apertures as small as 0.00125 cm were inconclusive. These studies indicated that approximately 25–33 cluster‐ion hydrogen molecule collisions could serve to stabilize the growing cluster ions.
Mass Spectra of Negatively Charged Water and Ammonia Clusters
Authors: Haberland Hellmut , Schindler Hans‐Gerg , Worsnop Douglas R.
Published: July 2012

Slow electrons are mixed into a heavily clustered supersonic expansion of water and ammonia. The resulting negatively charged cluster ions are mass analyzed. Mass spectra for (H2O)n−, (D2O)n−, and (NH3)n− are presented. The smallest cluster ions observed contain 11, 12, and 36 water, heavy water and ammonia molecules per clusters, respectively.
Mass Spectral and Electric Deflection Study of Acetic Acid Clusters and Sulfur Trioxide/Water Clusters
Authors: Keesee R. G. , Sievert R. , Castleman A. W.
Published: July 2012

A beam of the clusters of interest was produced and analyzed with respect to polar nature via passage through an electric quadrupole focusing field. Subsequently, the beam was ionized using electron impact and the resulting distribution of ions determined with a quadrupole mass spectrometer. Acetic acid clusters containing up to twelve molecules were produced. The polarity and ionizing fragmentation of the clusters were investigated by the effect of stagnation conditions and electrostatic focusing on the intensity of the detected fragment ions. Both the dimer and tetramer were found to be nonpolar while the trimer was polar. Evidence that some larger clusters have polar structures was also found. For the SO3/H2O experiment, beside protonated water clusters, a less abundant series of ions of the form SO3(H2O)nH+ was observed. Focusing experiments indicated that any SO3 · H2O adduct which is formed becomes rapidly isomerized to sulfuric acid. The precursor neutral to the ions HSO3+ and H2SO4+ were strongly focused, but the neutral clusters giving rise to the larger cluster ions were defocused.
Spectroscopy of Neutral and Charged Metal Clusters
Authors: Delacrétaz G. , Fayet P. , Wöste L.
Published: July 2012

The technique of supersonic molecular beams is used to investigate alkali clusters by means of resonant Two‐Photon‐Ionization (TPI). Under specific stagnation conditions the clusters are sufficiently cooled to exhibit well resolved vibrational structures. The interpretation of highly excited Rydberg states permits a determination of the molecular constants of the related cluster ions. All excitation and ionization processes, however, exhibit strong fragmentation channels. With growing particle size, therefore, a proper assignment of the observed spectra to the original unfragmented particle becomes more and more difficult. For this reason an experiment was established, which allows the spectroscopic investigation of single size particles.
Electronic Structure of Small Metal Particles: Self‐Consistent Spherical Jellium Background Model
Authors: Ekardt W.
Published: July 2012

Ground state properties of small metal particles are investigated with the use of the local density approximation applied to the spherical jellium background model. Large quantum size effects are obtained for the work function, in strict analogy to those obtained for thin metal films. The convergence of the various physical properties to their value of a semi‐infinite half‐space is investigated. The static polarizability of small metal particles is obtained and compared both to the classical result and to the Thomas‐Fermi approximation. The importance of self‐consistency is discussed.
Metal Halide Clusters
Authors: Martin T. P.
Published: July 2012

The mass spectra of clusters of NaCl, CsI and CuBr are very similar, whether the clusters are formed by quenching the vapor in He gas or by bombarding a solid surface with high energy ions. This fact is quite surprising when one remembers that these materials condense into three distinct crystal structures; rock salt, CsCl‐type and zinc blende, respectively. We present evidence that all of these materials seem to prefer the rock salt structure in their early stages of growth.