bluuebunny/crossref_metadata_2025 huggingface dataset:
The 347.2 nm Laser Photolysis of Tetranitromethane in Polar, Nonpolar, and Micellar Solutions
Authors: Frank A. J. , Grätzel M. , Henglein A.
Published: September 2012

Tetranitromethane in various solvents (water, ethanol, t‐butanol, acetone, n‐hexane, neo‐pentane, carbon tetrachloride, mixtures of n‐hexane and ethanol, sodium lauryl sulfate and dodecyltrimethylammonium chloride micelles) was photolyzed by a pulsed, frequency‐doubled ruby laser (3.57 eV quantum of energy). The products of the photolysis were monitored in the 10−8 to 10−3 s range by recording the optical absorption and electrical conductivity of the solutions. In polar solvents, the anion of nitroform, C(NO2)3−, is formed during the 20 ns laser pulse. The yields of C(NO2)3− are highest in ethanol and lowest in aqueous solutions. In water, ionic dissociation of tetranitromethane is the main photolytic decomposition mode. In the alcohols and acetone a two step mechanism is proposed involving CN bond rupture to form the trinitromethyl radical which subsequently picks up an electron from the solvent to form C(NO2)3− and an electron deficient solvent state. The latter could optically be detected in the case of acetone. In hydrocarbon solutions, aci‐nitroform is produced via H‐atom abstraction by the trinitromethyl radical. In mixtures of n‐hexane and ethanol (0.1 to 5 vol.%), this radical is only able to abstract an electron from clusters of ethanol molecules and not from free, unassociated ethanol. When tetranitromethane is incorporated in the lipoidic core of ionic micelles, the extent of photolytic decomposition is substantially enhanced relative to that in water. In aqueous solutions containing 0.1 to 3 M sodium chloride, the trinitromethyl radical forms a complex with the chloride anion.

Energy considerations involving the formation of electron deficient solvent states are used to explain the observed effects.
Spektroskopische Untersuchungen an Merocyaninen I.) UV‐ und NMR‐Spektren von malodinitril‐substituierten vinylogen Säureamiden
Authors: Scheibe Peter , Schneider Siegfried , Dörr Friedrich , Daltrozzo Ewald
Published: September 2012

Die UV‐ und NMR‐Spektren von malodinitril‐substituierten vinylogen Säureamiden werden anhand von Modellrechnungen in der PPP‐Näherung interpretiert. Durch Einführen von geladenen Pseudozentren läßt sich die Rückwirkung des Lösungsmittelreaktionsfeldes auf die gelösten Moleküle simulieren. Die so berechneten kettenlängenabhängigen Solvatochromie‐Effekte stimmen mit den experimentell gefundenen überein.
Untersuchungen zum thermischen Zerfall von Acetaldehyd und Aceton
Authors: Ernst J. , Spindler K. , Wagner H. Gg.
Published: September 2012

Die thermischen Zerfallsreaktionen von CH3CHO und CH3COCH3 in Argon als Trägergas wurden zwischen 1350 K und 1650 K hinter reflektierten Stoßwellen untersucht. Die Gesamtdichten hinter der reflektierten Stoßwelle lagen zwischen 3 · 10−3 und 9 · 10−6 mol/cm3. Die Zerfallsreaktionen verliefen bei den angewandten Reaktionsbedingungen nach erster Ordnung in CH3CHO bzw. CH3COCH3. Die Extrapolation der Meßwerte zu hohen Drücken für die Reaktionen

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führt zu den Arrheniusausdrücken

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Die Druckabhängigkeit der Geschwindigkeitskonstanten sowie die Zerfallsmechanismen werden diskutiert.
Atomic Transport Properties in Liquid Metals and Alloys
Authors: Nachtrieb Norman H.
Published: September 2012

The atomic transport properties of liquid metals are reviewed, with principal emphasis on self‐diffusion. Experimental methods are surveyed, and published data are compared with the predictions of various models and theories.
Paracrystalline Structure of Molten Lead
Authors: Steffen B. , Hosemann R.
Published: September 2012

It is well known that one can obtain informations of crystalline lattices from powder patterns of polycrystalline solids expanding a three‐dimensional reciprocal lattice. The scattered intensity of molten metals can be analysed in a similar way by a threedimensional convolution polynom, which describes quantitatively the structure including the statistical relations within microdomains. In the case of Pb the micro‐domains can be quantitatively described by a face centered arrangement of bimodal coordination statistics with the same neighbour distance as below the melting point T. The weight of a coordination statistic decreases from 12.0 to 11.7 at T3 indicating the generation of point defects. From the consideration of the shape of the coordination statistics one obtains some information concerning the diffusion of vacancies and an one‐ and two‐dimensional collective motion of atoms.
Critical Remarks on the Ornstein‐Zernike Integral Equation
Authors: Steffen B. , Hosemann R.
Published: September 2012

The Ornstein‐Zernike integral equation is based on the assumption that the structure of an isotropic liquid can be described by spherically symmetric functions. It is shown that the spherical symmetric character of the total correlation function, derived from the observed diffraction pattern, does not exclude non‐spherical symmetric microdomains building up into the structure. In a similar way a spherical Debye‐pattern of a polycrystalline material is understood in terms of the superposition of patterns of randomly distributed microcrystallites. If one introduces a convolution polynomial instead of the crystalline lattice one can synthesize the observed total correlation function. Thus the spherically symmetric “direct correlation function” of the Ornstein‐Zernike‐theory does not have the physical meaning that is given to it nowadays by some authors. However, it does have the character of an annihilation operator, from the mathematical point of view. We conclude that the Percus‐Yevick and hypernetted chain equations, based on the Ornstein‐Zernike‐equation, can therefore give no information about pair‐potentials.
Viscosities of Cesium Vapor to 1620 K and of Liquid Gallium to 1800 K
Authors: Tippelskirch H. V.
Published: September 2012

The viscosity of cesium at 1620 K and 40 bar has been determined to 41· 10−6 (Pa· s) by the oscillating cup method. The saturated vapor density at 1580 K could be derived from the viscosity measurements. The viscosity of liquid gallium has been determined from 370 K to 1800 K. The experimental results have been compared with calculations based on the Enskog hard‐sphere transport theory for dense fluids.
Nuclear Quadrupole Relaxation and Viscosity in Liquid Metals
Authors: Schirmacher Walter
Published: September 2012

It is shown that the nuclear quadrupole relaxation rate due to the molecular motions in liquid metals is related to the shear and bulk viscosity and hence to the absorption coefficient of ultrasound. Application of the “extended liquid phonon” model of Ortoleva and Nelkin – which is the third of a series of continued‐fraction‐approximations for the van Hove neutron scattering function – gives a relation to the self diffusion constant. The predictions of the theory concerning the temperature dependence are compared with quadrupole relaxation measurements of Riegel et al. and Kerlin et al. in liquid gallium. Agreement is found only with the data of Riegel et al.
Solutions of Silver and Copper in Their Molten Salt Systems AgClxBr1‐x and CuClxBr1‐x
Authors: Schwind Albert F. , Schuster Erich , Vötsch Reinhard , Weil Konrad G.
Published: September 2012

The solubilities of the metals copper and silver in their molten salt systems AgClxBr1‐x and CuClxBr1‐x, respectively, were measured as functions of x and T. From the experimental data and using sublimation data for the metals from the literature, the enthalpies and entropies for the reaction Me(gas) → Me(dissolved)

were calculated. In both systems, these solvation enthalpies and entropies do not vary monotonically with the composition parameter x of the melt, but show marked extrema at some compositions, indicating discrete structures within the solvation shell of the dissolved species.

Spectroscopic investigations were made on the system Ag/AgCl. The difference spectrum between the pure melt and the metal solution shows a band at 540 nm (540°C), the intensity of which is proportional to the metal concentration. With increasing temperature, the wavelength of maximum absorption is shifted towards higher values.

The influence of the dissolved metal on the electric conductivity of the melts was studied in the silver solutions as a function of T and x. In all cases, this influence was within the experimental error and definitely smaller than should be predicted on the base of a free electron model. Using the concept of electrons trapped in a cavity (spherical box with inifinite potential walls) for interpreting the spectroscopic data. one finds a cavity diameter of 7.1 A at 550°C and a thermal expansivity of the cavity of 8.1 · 10−1 K−1. In accordance with the results on other solvated electron systems, this value is higher than the macroscopic expansivity of the solvents (αv(AgCl) = 1.74 · 10−4 K−1).
Electronic States Densities from Structure and Thermodynamic Data for Liquid Transition Metals
Authors: Young W. H.
Published: September 2012

The entropies of many liquid metals can be written in the form S = Sgas + Spack + Selec where Sgas is the ideal gas expression, Spack arises from the finite sizes of the ions (described by effective hard spheres) and Selec is the valence‐electron contribution 1/3 π2 N(EF) k2/8 T. The shape of the observed structure factor tells us whether the above formalism is applicable in any given case; if it is, we thereby deduce the effective hard sphere diameter and thence Spack. Measured thermodynamic data allow us to obtain S and Sgas and so Selec and thus N(EF) may be inferred in principle.

In practice. for non‐transition metals Selec is typically 1% of S and so it is difficult to extract meaningful results from the experimental data. However for transition metals (for which N(EF) and the melting temperature are both much higher) Selec is typically 20% of S and useful information on N(EF) may be obtained. Such data are presented and related to the additional relevant experimental and theoretical information available to us.
Magnetic Properties of Liquid Metals
Authors: Güntherodt H.‐J.
Published: September 2012

The magnetic susceptibility of liquid metals and their alloys is reviewed and discussed in terms of current theories. For liquid simple metals the susceptibility is interpreted in terms of the free‐electron model. The magnetic properties of transition and rare earth metals can be explained by taking into account the itinerant d‐electrons and the localized f‐electrons, respectively. The present state of the magnetic properties of non‐metallic fluids having metallic constituents is reported. In such systems the magnetic susceptibility gives information on the pseudogap or helps to elucidate the ionic character.
Electron Charge Transfer in Liquid Transition‐Metal and Rare‐Earth Alloys
Authors: Bennemann K. H.
Published: September 2012

The significance of electron (s, d, f) charge transfer in various liquid transition‐metal and rare‐earth alloys is discussed.
Wechselwirkungen zwischen lokalisierten magnetischen Zuständen in flüssigen Cu  Al  Fe‐Legierungen
Authors: Pantasis Anastasios , Wachtel Ernst
Published: September 2012

Es wird über Messungen der magnetischen Suszeptibilität an flüssigen Legierungen des Systems Cu  Al mit Fe‐Zusätzen berichtet. Während auf der Kupferseite auch bei sehr geringen Fe‐Zusätzen (weniger als 1 At.‐ %) ein Curie‐Weiss‐ähnliches Verhalten zu beobachten ist, zeigen die aluminiumreichen Legierungen einen verstärkten Pauli‐Paramagnetismus. Der Übergang von dem “magnetischen” zu dem “nichtmagnetischen” Verhalten verschiebt sich von 42 At.‐ % Al bei 5 At.‐ % Fe zu 58 At.‐ % Al bei 14 At.‐ % Fe. Bei geringen Eisenkonzentrationen läßt sich das magnetische Verhalten der kupferreichen Cu  Al  Fe‐Legierungen mit dem Anderson‐Modell für lokalisierte Momente beschreiben. Bei einer Zunahme der Eisenkonzentration tritt neben der s‐d‐Wechselwirkung zwischen den lokalisierten d‐Elektronen des T‐Metallatoms und den Leitelektronen noch eine Wechselwirkung zwischen den lokalisierten Zuständen auf. Diese Wechselwirkung kann sowohl einen indirekten (RKKY) als auch einen direkten Kopplungs‐Charakter haben. Durch eine Erweiterung des Anderson‐Modelles für den Fall konzentrierter Legierungen lassen sich auch diese Kopplungseffekte weitgehend erfassen und interpretieren.
Thermophysical Properties of Liquid Metals
Authors: Hoch M. , Vernardakis T.
Published: September 2012

The paper summarizes the available experimental data for the specific heat, the coefficient of thermal expansion, and the viscosity of lithium, sodium, lead, and mercury both in the solid and liquid state. The data are compared with the concept of clusters in liquids.
Thermodynamische Untersuchungen der Struktur flüssiger binärer Legierungen am System Quecksilber‐Thallium
Authors: Sommer Ferdinand
Published: September 2012

Mit Hilfe der EMK‐Methode konnten die Konzentrationsfluktuationen 〈(Δc)2〉 für flüssige Quecksilber‐Thallium‐Legierungen bei Temperaturen zwischen 25 und 80°C und im Konzentrationsbereich 0 < CT1 < 0,45 direkt bestimmt werden. Die Resultate zeigen eine Hg3 Tl‐Verbindungstendenz. Aus den partiellen Strukturfaktoren aij(0) ergab sich eine bevorzugte Quecksilber‐Thallium‐Nachbarschaft mit einem Maximum bei 26 At.‐% Tl.
The Metal‐Nonmetal Transition in Liquid Semiconductors
Authors: Ten Bosch A. , Morán‐López J. L. , Bennemann K. H.
Published: September 2012

We approach the problem of the metal‐non‐metal transition in simple metal alloys from a chemical point of view and discuss the appearance of a gap in the electronic density of states in terms of covalency and ionicity as suggested by Pauling, Philips and others. In a simple model, we show that for sufficiently large splitting of the two pure component bands, and therefore for large differences in Pauling electronegativity, an energy gap appears in the electronic spectrum, leading to semiconductor behaviour at intermediary concentrations. The alloy electronic density of states is calculated with the truncated continued fraction method and the importance of charge transfer and short‐range order is emphasized.
Metal‐Nonmetal Transition in Metal‐Ammonia Solutions
Authors: Breitschwerdt K. G. , Radscheit H.
Published: September 2012

The properties of metal‐ammonia solutions in the concentration range of the metal‐nonmetal transition between 0.1 and 10 mol percent metal (MPM) are discussed. The high‐frequency electrical properties show a number of characteristic features in this intermediate concentration range, such as additional dielectric relaxations at about 0.1 MPM and 0.7 MPM for LiNH3 and NaNH3, respectively, and a resonance‐like behavior at about 1.0 MPM and 1.5 MPM for LiNH3 and NaNH3, respectively. For both LiNH3 and NaNH3 the real part of the high‐frequency dielectric function changes to large negative values around 2.5 MPM, indicating a transition to metallic behavior at high frequencies. The high‐frequency properties, which are also discussed in terms of electron conductivity, are explained quantitatively as a function of concentration, temperature, and frequency using a model of polaron hopping. The metal‐nonmetal transition is related to structural changes in the solutions which lead to phase separations in LiNH3 and NaNH3 at lower temperatures. The structural properties of the solutions are investigated using sound velocity and ultrasonic attenuation data. Concentration and temperature dependence of the ultrasonic attenuation in LiNH3 and NaNH3 can be described quantitatively in terms of structural fluctuation.
The Membrane/Water Partition Coefficients of Ions: Electrostatic Calculations of Dielectric Heterogeneity
Authors: Anderson J. E. , Pusch W.
Published: September 2012

A continuum electrostatic calculation explores dielectric heterogeneity in membranes and its influence on ion sorption. The spherical shell model of Ullman is used. A transition in predicted sorption behaviour occurs as b, the mean ionic radius, becomes comparable with L, the size of dielectric domains. Since the finite size of molecules establishes a lower limit of L ˜ b, it is likely that no membrane is a strictly homogeneous dielectric from the standpoint of ion sorption. The calculation predicts that changing the dielectric domain size between 5 · 10−8 and 20 · 10−8 cm has a drastic effect on ion sorption. Objections which can arise from the very special nature of Ullman's model are discussed.
Electroluminescence at Semiconductor Electrodes Caused by Hole Injection from Electrolytes
Authors: Pettinger B. , Schöppel H.‐R. , Gerischer H.
Published: September 2012

Light emission from semiconductors has been studied at semiconductor‐electrolyte interfaces, caused by minority carrier injection from the electrolyte at n‐type specimen of SnO2, ZnO, CdS, GaP, and GaAs. Species of very high electron affinity are normally required in order to inject holes into the deep lying valence band of SnO2, ZnO, CdS, and GaP, but such species are not stable in aqueous solution. The short living species SO˙4 and OH˙ were found to have a long enough lifetime to inject holes into these materials when they are generated at the surface by an electrochemical reaction. The luminescence spectra caused by such hole injection have been studied. One can conclude from the spectral distribution of the emitted light that surface states play an important role in this radiative recombination. The quantum efficiency of light emission is in the order of 10−4 or below and depends on the voltage applied. The influence of the energy position of the electronic states of the radicals and of the band edges of the semiconductors on luminescence intensity is analyzed.
Statistisch thermodynamische Berechnungen der Festkörpereigenschaften von Argon
Authors: Hebgen W. , Schäfer Kl. , Schramm B.
Published: September 2012

In der vorliegenden Arbeit wird gezeigt, wie aus dem zwischenmolekularen Paarpotential zweier Molekeln in der Gasphase auf die thermischen, mechanischen und kalorischen Eigenschaften der kondensierten Materie geschlossen werden kann. Die Berechnungen werden für Argon durchgeführt, da dessen zwischenmolekulares Potential kugelsymmetrisch ist und Quanteneffekte bei den Messungen makroskopischer Größen vernachlässigbar sind.
Reorientational Motions in Crystalline (CH3)3NHCl, Studied by Raman Spectroscopy
Authors: Schlaak M. , Couzi M. , Huong P. V.
Published: September 2012

The IR and Raman vibrational spectra of crystalline (CH3)3NH+X− (X = Cl, Br, I) are recorded. A complete assignment of the measured frequencies to the internal vibrational modes of the (CH3)3NH+ cation in the three compounds is obtained. Above the phase transition of (CH3)3NH+ Cl− (at 308 K) a reorientational motion of the cation around its threefold axis is deduced from the Raman spectrum. This motion is studied by a line shape analysis of the degenerate νCN(E) vibration. A rotational diffusion constant D∥ = (0.38 ± 0.05) · 1012 sec−1 is deduced in agreement with quasielastic neutron scattering results.
Differential Thermal Analysis (DTA) under High Pressure VI: Phase Transitions of Some Liquid Crystals up to 3 kbar
Authors: Spratte W. , Schneider G. M.
Published: September 2012

With a high pressure DTA apparatus previously described the phase transition temperatures solid/nematic (melting temperatures) and nematic/liquid isotropic (clearing temperatures) of the liquid crystals MBBA, EBBA, PBBA, PEBAB, PAA, and PAP were measured as a function of pressure up to 3 kbar and in the temperature range 273 K to 550 K. For PBBA the pressure dependence of the transition temperature smectic/nematic was additionally determined.

For all compounds rising pressure causes an increase of the transition temperatures as well as an extension of the nematic range (especially for PAA and PEBAB). According to the thermal pretreatment two different melting curves were found for MBBA, EBBA and PEBAB separating the nematic liquid from a stable and a metastable solid phase respectively. The melting curves diverge slightly for MBBA and EBBA: for PEBAB, however, an intersection point can be extrapolated at about 2600 bar and 450 K.

From the peak areas at atmospheric pressure the transition enthalpies ΔHand from these the transition entropies ΔSwere determined. Using these values and the slopes of the experimentalT(p)transition curves the volume changes ΔVaccompanying the transitions solid/nematic, smectic/nematic and nematic/liquid isotropic respectively were calculated from the Clausius‐Clapeyron equation. The ΔH, ΔSand ΔVvalues thus obtained are discussed and compared with the literature data available.
Photo‐Induced Oxydation of Carbonate Ions by Duroquinone, a Pathway of Oxygen Evolution from Water by Visible Light
Authors: Scheerer R. , Grätzel M.
Published: September 2012

The oxydation of carbonate, CO32‐, by triplet state duroquinone (DQT) was studied in aqueous micellar solutions of dodecyltrimethyl‐ammoniumchloride (DTAC) using laser photolysis technique. The primary step involves transfer of an electron from CO32‐ located in the micellar Stern layer to DQT residing in the interior of the micelle. This proceeds at an extremely rapid rate the reaction being completed within the 15 ns duration of the laser pulse. CO3− anion radicals formed in this redox process subsequently reduce duroquinone according to

with a rate constant of 2 ‐ 109 M−1 s−1 pulse radiolysis results substantiate the occurance of such an electron transfer process. The decomposition of CO3 leads to formation of oxygen and carbonate.
Molecular Dynamics Calculations for Liquid Neon and Methane
Authors: Hoheisel Claus
Published: September 2012

Molecular dynamics calculations with 256 and 864 particles were performed for liquid methane, neon and for comparison also argon. Empirically determined Lennard‐Jones (12–6) potentials, theoretical Kim‐Gordon potentials and for neon the ‘best’ experimental pair‐potential were used as effective pair‐potentials.

The known experimentally measured self‐diffusion coefficients and pair‐distribution functions were reproduced satisfactorily by the molecular dynamics calculations on methane between 95 and 170 K, on neon between 25 and 45 K and for argon in the region of 95 and 130 K. The Kim‐Gordon potential leads to the best agreement with experiment.

Compressibility factors were only preliminarily calculated for high densities, they do not agree with the experimental data.
Rate Measurements for the Reactions H + NO2 → OH + NO and H + NOCl → HCl + NO by Lyman‐α Fluorescence
Authors: Wagner H. Gg. , Welzbacher U. , Zellner R.
Published: September 2012

Rate constants for the reactions of hydrogen atoms with NO2 (k2) and NOCl (k2) have been determined in a discharge flow system using the detection of H atoms by Lyman‐α resonance fluorescence. From temperature dependent measurements in the range T = 240 – 460 K the Arrhenius expressions (in units of cm3/mol · s)

k1 = (4.3 ± 1.8) 1014 exp(–4.2 ± 0.7 kJ mol−1/RT) and k2 = (4.6 ± 1.2) 1013 exp(–3.8 ± 0.6 kJ mor−1/RT) could be obtained.
Temporal and Spatial Structures in Chemical Instabilities
Authors: Ross John
Published: September 2012

We discuss the formation of temporal and spatial structures in chemical systems far from equilibrium by means of the occurrence of instabilities. Multiple stationary states, hysteresis and oscillations of chemical species are cases of temporal structures and some simple models and experiments serve as examples. Chemical reactions and diffusion combine to yield macroscopic spatial structures such as periodic precipitation phenomena (Liesegang rings), chemical waves, and cooperative effects in fields of localized instabilities. We conclude with the close analogies between certain instability phenomena and the kinetic phase transitions.
Information, Memory and Statistical Theories of Elementary Chemical Reactions
Authors: Quack M. , Troe J.
Published: September 2012

The dissipation of information in collisions involving strongly bound intermediates is considered. A quantitative measure for the memory μ in such collisions is introduced. It is shown that the memory is important even for strong coupling situations where statistical theories may be valid. The relationship between various statistical theories for product state distributions, like phase space theory and the statistical adiabatic channel model, and the “prior distributions” in the information theoretic approach is discussed. The microcanonical equilibrium distribution is found to be theoretically unsatisfactory as a reference distribution. We propose replacing it by another distribution without memory and without dynamical constraints apart from angular momentum conservation. The concepts are illustrated with several simple model calculations for atom‐diatomic molecule collisions. The question of linear surprisal plots is discussed briefly.
Phänotypische Information von Nukleinsäuren: Die Initiationssignale für die RNA‐Replikation durch die Qβ‐Replikase
Authors: Küppers Bernd
Published: September 2012

An Viren lassen sich besonders gut die grundlegenden molekulargenetischen Prozesse wie Replikation, Transkription und Translation einschließlich deren Regulation untersuchen. Verhältnismäßig einfach aufgebaut sind die RNA‐haltigen Viren des Bakterienstammes Escherichia coli.

Dic RNA‐Phagen besitzen eine bemerkenswerte Eigenschaft. Sie induzieren in der Wirtszelle jeweils eine RNA‐abhängige RNA‐Polymerase (Replikase), die spezifisch hinsichtlich der Replikation ihrer homologen RNA ist. Das RNA‐Replikationssystem des Bakteriophagen Qβ kann man isolieren und in vitro untersuchen.

Mit Hilfe von synthetischen Nukleinsäuren läßt sich zeigen: Jedes Oligo‐ bzw. Polynukleotid, das eine 3′‐terminale CCC‐Sequenz und darüber hinaus eine zweite CCC‐Sequenz in eine definierte räumliche Anordnung zur Qβ‐Replikase bringen kann, dient als aktive Matrize für die Synthese einer komplementären Nukleinsäure.

Durch entsprechende chemische Modifikationen kann man nunmehr Qβ‐inaktive Nukleinsäuren in Qβ‐aktive RNA‐Matrizen umwandeln. Damit besitzt man ein Verfahren für eine allgemeine RNA‐abhängige RNA‐Synthese.
Technische Informations‐Speicher
Authors: Kaufmann Hans
Published: September 2012

Die wichtigsten Eigenschaften der Speicher für die Daten‐Verarbeitung sind Speicher‐Kapazität und Zugriffszeit; ihre Kenngrößen überdecken Bereiche von mehr als 10 Zehner‐Potenzen. Diese Speicher, die in sehr verschiedenen Technologien realisiert werden, kann man in grober Unterscheidung erfassen als Schnell‐Speicher (Zugriffszeit unter 1 Mikrosekunde, Kapazitäten bis zu wenigen Megabyte und Kosten von mehr als 1 Pf./bit) und als Massen‐Speicher (Zugriffszeiten über 1 Millisekunde, Kapazitäten über 30 Megabyte und Kosten von weniger als 1/100 Pf./bit). Die Schnell‐Speicher werden heute vollständig in Halbleiter‐Technologie verwirklicht: Stand und Zukunft werden dargestellt: dabei hat man zu erwarten, daß die Speicher‐Dichte auch weiterhin sehr erheblich ansteigen wird: Hand in Hand damit gehen die Bemühungen um die Herabsetzung des Leistungsbedarfs. Die Massen‐Speicher sind noch immer Magnetschicht‐Speicher; hier wird über den Stand berichtet und eine Darstellung der anderen technologischen Möglichkeiten gegeben.
Energiebedarf der molekularen Informationsübertragung
Authors: De Maeyer Leo C. M.
Published: September 2012

Technische Kommunikationssysteme verwenden in der Regel zeitlich diskontinuierliche oder modulierte Energieflüsse als informationsübertragende Signale. Für den Kommunikationsprozeß stellt sich die Frage, unter welchen Bedingungen ein maximaler Informationsfluß bei vorgegebenen Eigenschaften des Signalflusses bzw. des gesamten, einen Detektor erreichenden Energieflusses erreicht werden kann. Die optimale Ausnutzung eines vorhandenen Übertragungskanals ist eine Kernfrage der technischen Nachrichtenübertragung: sie führt zum Problem der Nachrichtenkodierung.

Die chemische Spezifizität molekularer Wechselwirkungen und die Verkettung chemischer Umwandlungsprozesse im biologischen Be‐reich besitzen den Charakter eines molekularen Kommunikationssystems. Für die theoretische Untersuchung solcher Systeme stellt sich zunächst die Aufgabe, einfache Modelle zu definieren und die evtl. vorhandene Analogie mit den bereits eingehend untersuchten informations theoretischen Konzepten der Nachrichtentechnik zu analysieren.

Die Frage nach dem grundsätzlichen Energiebedarf informationsübertragender Wechselwirkungen wird in der klassischen Informations‐theorie nicht gestellt. Sie hat jedoch für ein molekulares Kommunikationssystem eine besondere Bedeutung: hier steht das Problem des optimalen Ühertragungskanals für einen Informationsfluß vorgegebener Kodierung im Vordergrund. Es wird gezeigt, unter welchen Bedingungen der bei einem informationsübertragenden Prozeß entstehende Informationsgewinn mit prinzipiell dissipativem Energieaustausch verknüpft ist.
Model Orientation Dependent Pair Distribution Functions Describing the Association of Simple Carboxylic Acids and of Ethanol in Aqueous Solution
Authors: Hertz H. G. , Tutsch R.
Published: September 2012

Nuclear magnetic relaxation rates of the CH proton of formic acid and of the methyl and methylen protons of acetic, propionic, and butyric acid and of ethanol are reported. All these substances are dissolved in water (D2O) and the organic molecules are such that the hydrogen nuclei whose relaxation is not studied are deuterons. The corresponding deuteron relaxation rates (in H2O) have also been measured and the results are converted to yield the proton intramolecular relaxation rates and the intermolecular relaxation rates. Lastly, intermolecular proton relaxation rates which are caused by the interaction with protons in other groups have been measured. All these data are given as a function of the acid mole fraction x2. From these experimental results first coordination numbers of the acids with respect to the acid and closest distances of approach between the various hydrocarbon groups have been derived. Model molecular pair distribution functions have been constructed which show that propionic acid and butyric acid molecules undergo a change in the relative pair configuration as more and more water is added such that a side by side configuration of the hydrocarbon rests is produced. In the ethanol water mixture the structural change is the reverse one and here no hydrophobic association is observable.
An Investigation of the Structure of Acetic Acid and the Mixture Acetic Acid/CCI4 by the Nuclear Magnetic Relaxation Method
Authors: Berg V. , Hertz H. G. , Tutsch R.
Published: September 2012

Intermolecular proton magnetic relaxation rates of the methyl and hydroxyl group of acetic acid involving the magnetic interaction among the various groups are reported. The data are given as a function of the mole fraction in the mixture acetic acid/CCI4. From these experimental results model atomic pair distribution functions and model molecular pair distribution functions are derived. It is shown that in the pure acid OH and CH3 never approach closely towards one another. At mole fractions x2 ≤ 0.3 the classical dimer can be observed which, however, appears in a more or less folded form.
Fluid Mixtures at High Pressure. Phase Separation and Critical Phenomena in Binary Mixtures of a Polar Component with Supercritical Carbon Dioxide, Ethane, and Ethene up to 1000 Bar.
Authors: Alwani Ziad , Schneider Gerhard M.
Published: September 2012

In order to study the polarity effect on the critical phase behaviour of fluid binary systems the critical temperatures of binary mixtures of carbon dioxide, ethane, ethene, hexane, or 1‐hexene with a second component of very different polarity such as methanol, 2‐hexanol, 2‐octanol, 2,5‐hexanediol, nitromethane, N,N‐dimethylformamide, or N‐methylacetamide were determined as a function of pressure up to 1000 bar. The critical p(T) curves obtained exhibit a whole pattern of different transition types between liquid‐gas, liquid‐liquid, and gas‐gas equilibria; they are compared with data for other systems taken from the literature.

The results verify a previous hypothesis that there are continuous transitions between liquid‐gas, liquid‐liquid, and gas‐gas critical phenomena in fluid binary mixtures at high pressures. The measurements are of interest for fluid extraction and supercritical fluid chromatography (SFC).
Fluid Mixtures at High Pressures. Computer Calculations of the Phase Equilibria and the Critical Phenomena in Fluid Binary Mixtures from the Redlich‐Kwong Equation of State
Authors: Deiters U. , Schneider G. M.
Published: September 2012

Using the Redlich‐Kwong equation of state (RK‐equation) thermodynamic relations are derived from which the phase equilibria and the critical phenomena in fluid binary systems can be calculated at high pressures.

From these relations p‐T diagrams and p‐x diagrams are calculated for binary mixtures with components differing considerably in structure, molecular size and/or polarity (80K to 500 K; up to 3 kbar); quadratic mixing rules are assumed for the two parameters of the RK‐equation. All kinds of phase equilibria and critical phenomena hitherto known can be represented in reasonably good agreement with experimental data.
The Molecular Structure of Allenes and Ketenes VII [1] 13CH Nuclear Spin‐Spin Couplings in Monosubstituted Allenes
Authors: Runge W. , Kosbahn W.
Published: September 2012

From high‐resolution 13C‐NMR spectra direct and long‐range (up to four‐bond) carbon‐proton coupling constants of allenes have been obtained. Relative signs of the coupling constants have been determined relating them to the (absolute) signs of couplings in selected model compounds.

The substituent effects on the coupling constants are discussed in terms of empirical correlations with other molecular properties of allenes or usual substituent increments, and on the basis of the independent‐electron MO treatment of the Fermi contact term using CNDO/S wave functions.

Spin density information via π‐type conjugation plays an important role for many kinds of carbon‐proton couplings in allenes.
Eine unbekannte Magnetfeldabhängigkeit des Faradayeffekts
Authors: v. Löwis Michael
Published: September 2012

Im Faradayspektrum von Benzol, Anthracen und Naphthalin wurde ein Anteil entdeckt, dessen Vorzeichen unabhängig von der Magnetfeldrichtung ist (parallel oder antiparallel zum Lichtstrahl). Dieser Anteil hängt ebenfalls linear von der Magnetfeldstärke ab. Er läßt sich experimentell vom feldrichtungsabhängigen Effekt abtrennen. In der Theorie des Faradayeffekts existiert ein Term, auf den der feldrichtungsunabhängige Effekt zurückgeführt werden kann.
Study of Mica Membranes with Known Pore Geometry Measurements of Electrical Conductivity
Authors: Klump B. , Woermann D.
Published: September 2012

The track‐etch technique is used to prepare mica membranes with known pore structure. The electrochemical properties of the pore wall in contact with aqueous KCl solutions are studied by measuring the electrical conductivity of the pore fluid. The experimental results are discussed in terms of the model of the membrane with narrow pores. The experiments indicate that the charge of the pore wall is a net charge formed by positive and negative charges. The negative charges are present in small surplus (about 10%). The total charge density corresponds to 1 elementary charge per 104 A2 of pore wall.
The Reactivity of Electronically Excited Species
Authors: Husain D.
Published: September 2012

A general review of electronically excited species is centred on a discussion of the collisional behaviour of specific states arising from the overall ground state configurations for the atoms:
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Experimental rate data for the excited atomic species are surveyed with an emphasis on direct monitoring of the optically metastable states, principally by time‐resolved attenuation of atomic resonance radiation following pulsed initiation. The overall structure employed in the discussion is to consider the symmetry of the potential surfaces involved in the collision, mainly for encounters of the type A + BC and also A + BCD, using Cs symmetry for the collision complex in both cases. Light atom‐molecule collisions are described in terms of the weak spin orbit coupling approximation and heavy atom‐molecule collisions, using (J, Ω) coupling via the method of extended groups. The (J, Ω) coupling procedure permits discussion of individual spin orbit atomic states and the collisional quenching data for these are considered in some detail, including isotope effects and theories of long range interaction which are concerned with near resonance E r̊ V transfer processes. Product states are also generally considered, especially for heavy atom‐molecule collisions that might lead to population inversions for electronically excited molecular diatomic molecules of interest to laser systems operating in the visible region of the spectrum. Some brief consideration of the atmospheric chemistry of species such as O(21D2), N(22D1) and N(22P1), atomic transition lasers for Br(42P1/2) and I(52P1/2), and stratospheric pollution by fluorinated hydrocarbons is also given.
Stepwise Two‐Photon Excitation of Tetracene; Fluorescence from Upper Excited Singlet States
Authors: Nickel Bernhard , Roden Gabriele
Published: September 2012

By stepwise two‐photon excitation S0 + hv r̊ S1 and S1 + hv r̊ Sp upper excited singlet states Sp of tetracene are populated. A fluorescence Sn r̊ S0 (n > 1) was observed. The states Sn seem to be the same electronic states (but not necessarily the same vibronic states) as in the one‐photon absorption spectrum Sn I̊ S0.

Durch stufenweise Zweiphotonenanregung S0 + hv r̊ S1 und S1 + hv r̊ Sp/ werden höhere angeregte Singulettzustände Sp von Tetracen besetzt. Eine Fluoreszenz Sn r̊ S0 (n > 1) wurde beobachtet. Die Zustände Sn scheinen dieselben elektronischen Zustände (aber nicht unbedingt dieselben vibronischen Zustände) wie im Einphotonenabsorptionsspektrum Sn I̊ S0 zu sein.
The Primary Process in the Photolysis of CH3CCl3
Authors: Yuan T. S. , Wijnen M. J. J.
Published: September 2012

The photolysis of CH3CCl3 has been investigated in the presence of I2 at room temperature. The results indicate that the reaction products CH3CCl2I and CH2CCl2 originate from two different excited states
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CH3CCl3* is produced mainly at λ > 2200 Å, CH3CCl3** predominantly at λ < 2200 Å. The results are compared with primary processes observed in the photolysis of chlorinated ethylenes and other chlorinated ethanes.
Kinetic Study of the Anodic Reaction at the Electrodic Interface α‐AgI(s)/I2(g), C
Authors: Bazan J. C. , Dayen E. A.
Published: September 2012

The anodic evolution of Iodine from solid α‐AgI was studied in the solid‐state cell Ag/AgI/I2(g), Graphite at different I2‐pressures and temperatures. A single pulse galvanostatic technique was used. The kinetic parameters obtained allowed the postulation of a fast discharge‐slow recombination (at low coverage) reaction mechanism. A dependence of the exchange current density upon the iodine partial pressure was found and interpreted on the basis of the postulated mechanism. A sort of “anode effect” was found.
Studies of Water‐Salt Systems at Elevated Temperatures and Pressures
Authors: Valyashko V. M.
Published: September 2012

Several basic types of phase diagrams for binary and ternary water‐salt systems may be elucidated from experimental investigations of phase equilibria to elevated temperatures (up to 550 °C) and pressures (up to 2.5 kbar). The temperature dependence of some physico‐chemical quantities as the concentrations of solutions in monovariant equilibria, molar volumes, electrical conductivities and spectroscopic properties are carefully analysed. The results indicate a clearly different behaviour between dilute and concentrated hydrothermal solutions. The salt concentrations where the transition between water like and melt like characteristics in 1:1, 1:2, 2:2 electrolyte solutions occurs are determined and the correlation of these concentrations with the molecular characteristics of electrolytes are established.
On the Kinetics of the Formation of Ionic Micelles II. Analysis of the Time Constants
Authors: Chan S.‐K. , Herrmann U. , Ostner W. , Kahlweit M.
Published: September 2012

In relaxation experiments on aqueous solutions of surfactants one observes two processes. Following the pioneer work of Aniansson and Wall, the fast process is attributed to the change of the mean aggregation number of the micelles, while the slower one is attributed to the change of the total number of micelles. In this paper, the analysis of the fast relaxation process is first clarified. Second, the slower of the two relaxation processes is reexamined. It is suggested that their assumption of negligible flux in the abundant region leads to unphysical behavior of the micelle distribution. An alternative treatment is given which leads to a different result. The concentration dependence of the time constant is then derived for ionic systems in which the role of the counter ions has to be considered. This new result for the slow relaxation process together with the original result for the fast relaxation process are compared with experiments on the ionic systems H2O — NaTS and H2O — TTABr. Since results for nonionic systems form a limiting case of the more general results, comparison with experiments on the nonionic Triton‐X‐100 is also made. Satisfactory agreements are obtained for both types of systems
Defects and Cation Diffusion in Magnetite (II)
Authors: Dieckmann R. , Schmalzried H.
Published: September 2012

A critical evaluation of diffusion data and measurements of the nonstoichiometry as a function of the oxygen potential in magnetite allows the following conclusions to be drawn: At high oxygen potential, magnetite exists with a cation deficit (cation vacancies); at low oxygen potential, magnetite exists with a cation excess (interstitial cations). Assuming the point defects to form an ideal solution with the crystal, the point defect thermodynamics describes the known data on diffusion and nonstoichiometry in magnetite quantitatively. The mobility of interstitial iron cations in magnetite (at T = 1200°C) is approximately 15 times faster than the cation vacancy mobility.
Spektroskopisch bestimmte Temperaturprofile bei der Pyrolyse von Methan im Stickstoff‐Plasmastrahl
Authors: Winkelmann G. , Lachmann J. , Spangenberg H.‐J.
Published: September 2012

Bei der Methanpyrolyse in einem laminaren Stickstoff‐Plasmastrahl (p ≈ 1 atm) wurden anhand der Rotationsfeinstruktur der (0–0)‐ und (1–1)‐Bande des C2‐Moleküls die Verteilungen der Rotations‐ und Schwingungstemperaturen und der relativen C2‐Konzentration im Plasmastrahl bestimmt. Die so erhaltenen Ergebnisse werden mit Messungen der Quenchkonzentrationen der entstehenden Hauptkomponenten (HCN, C2H2) und der Enthalpie des Plasmas verglichen. Es ergaben sich Differenzen der Rotations‐ und Schwingungstemperaturen bis 600 K axial und bis zu 1000 K radial bei einer Rotationstemperatur von 4000 — 5000 K. Diese Abweichungen treten vor allem in Gebieten auf, wo verstärkt Radikalbildungs‐ bzw. Rekombinationsprozesse ablaufen.
Untersuchungen des stationären Zustandes der Thermodiffusion in Thermoketten mit Nitratschmelzen
Authors: Richter J. , Prüser U.
Published: September 2012

Es wird eine neue Meßapparatur beschrieben, mit der der stationäre Zustand der Thermodiffusion in Salzschmelzen untersucht werden kann. Mit dieser Zelle gelingt es zum ersten Mal, zuverlässige Endwerte der Thermokraft der betrachteten Thermoketten zu bestimmen. Untersucht werden die Systeme LiNO3 + AgNO3 und NaNO3 + AgNO3 im Temperaturbereich von 220°C bis 340°C in Abhängigkeit von der Zusammensetzung. Der Zeitverlauf der EMK der Thermokette bis zum Erreichen des stationären Zustandes der Thermodiffusion wird diskutiert, und die Überführungsentropien der Silberionen in beiden Salzschmelzen werden als Funktion der Zusammensetzung berechnet.
ESR‐ und mößbauerspektroskopische, röntgenographische und magnetische Untersuchungen zur Bildung von hochdispersen Eisenoxiden auf Faujasit
Authors: Wiedenmann A. , Schmidt F. , Gunsser W.
Published: September 2012

Die hochdispersen Eisenoxide wurden durch Fe(II)‐Ionenaustausch, Hydroxidfällung, Oxidation und anschließendes Glühen von Zeolithen des Faujasit‐Typs unter Erhaltung der Struktur dargestellt. Aus Untersuchungen der magnetischen Suszeptibilität, der Magnetisierung, der Mößbauer‐ sowie der ESR‐Spektren wird auf die unter verschiedenen Glühbedingungen auftretende Verteilung der Eisen(III)‐Oxidteilchen geschlossen. Neben Eisen(III)‐Ionen der Ausgangssubstanz und kollektivparamagnetischen Teilchen entsteht ‐ außerhalb der Hohlräume ‐ durch Glühen bei 600°C vorwiegend γ‐Fe2O3 bei 900°C dagegen überwiegend α‐Fe2O3.
Pulse Radiolysis and Electron Spin Resonance Studies on the Formation of Phenoxyl Radicals by Reaction of OH Radicals with Methoxylated Phenols and Hydroxybenzoic Acids
Authors: O'Neill P. , Steenken S.
Published: September 2012

OH radicals react with methoxylated phenols and methoxylated hydroxybenzoic acids by addition to the aromatic ring to yield hydroxycyclohexadienyl radicals (OH adducts) (k = (1—2) · 1010 M−1 s−1). With respect to the sites of attachment, OH shows a preference for ring positions activated by the electron donating OH or OCH3 groups. Only those hydroxycyclohexadienyl radicals which are produced by addition of OH to ring positions not occupied by methoxyl groups yield phenoxyl type radicals. Formation of phenoxyl radicals is enhanced in the presence of acid or base. Acid catalysis of phenoxyl formation is suggested to proceed via cationic intermediates similar to those proposed for formation of radical cations. In alkaline solution, OH− is eliminated from deprotonated hydroxycyclohexadienyl radicals to yield phenoxyl radicals (k > 106 s−1).—The phenoxyl radicals undergo reaction with a) each other (2k ∼ 1 · 109 M−1 s−1), b) OH adducts (k ∼ 1.3 · 109 M−1 s−1), and c) H adducts (k ∼ 4 · 109 M−1 s−1). The absorption maxima of the isomeric methoxyphenoxyl radicals are blue‐shifted relative to those of radical cations from structurally analogous di‐ and trimethoxybenzenes.
Evaluation of Measurements on Thermocells Containing Molten Salt Mixtures
Authors: Haase R. , Prüser U. , Richter J.
Published: September 2012

We derive the general relations for the thermoelectric power of a thermocell consisting of a two‐component ionic melt with three ion constituents and of two similar electrodes reversible to one ion constituent. We also establish the interrelation between the thermoelectric power and the Soret coefficient. The transport quantities relevant to thermal diffusion and related phenomena in the melt are the transported entropies of two ion constituents and a certain linear combination of the heats of transport of the same constituents. It is shown how these quantities can be derived from experimental data.—In particular, we discuss the molten salt mixtures LiNO3 + AgNO3 and NaNO3 + AgNO3. Since, besides the thermoelectric powers of thermocells containing these systems, all the composition‐dependent quantities necessary for the evaluation (transport numbers and activity coefficients) have been determined in this laboratory, we can consistently compute the two transported entropies, the difference between the two heats of transport, and the Soret coefficient from our measurements. The experimental data relate to various compositions in the temperature range between 220°C and 340°C.
CdS/S Anode System in an Electrochemical Solar Cell
Authors: Minoura H. , Tsuiki M. , Oki T.
Published: September 2012

Polarization characteristics of the sintered CdS electrode under illumination in S2‐1+x (sulfide or polysulfide) ion‐containing electrolyte are reported. Differential capacity of the CdS/electrolyte interface and performance of the photocell, CdS/electrolyte/Pt, were also measured. S2‐1+x ion in the electrolyte shifts remarkably the flatband potential of CdS electrode toward the cathodic direction and makes this electrode photoelectrochemically stable. The possibility of an efficient electrochemical photocell with CdS electrode using S2‐1+x ion‐containing electrolyte has been demonstrated. S2‐ and SO2‐3 ion in the electrolyte for electrochemical photocell can dissolve the elemental sulfur produced by the photoanodic reaction on CdS electrode to form S2‐1+x and S2O2‐3 ion respectively.