bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Molecular Dynamics Study of the Liquid Mixture CHCl3/CCl4 on the Basis of Lennard‐Jones Type Potentials
Authors: Hoheisel C. , Deiters U. 
Published: September 2012

AbstractThe liquid mixture CHCl3/CCl4 is investigated by molecular dynamics calculations based on (18–6) Lennard‐Jones type potentials. Self‐diffusion coefficients are in good agreement with experiment over the whole concentration range, and the thermodynamic results are satisfactory compared with calculated values obtained by a semiempirical method due to Redlich and Kwong.—The pair‐distribution functions show the usual behaviour typical of “Lennard‐Jones liquids”.
Direct Rate Measurements for OH + OH → H2O + O in the Range 1200–1800 K
Authors: Ernst J. , Wagner H. Gg. , Zellner R. 
Published: September 2012

AbstractRate constants for the disproportionation reaction (1) OH + OH → H2O + O in the range T = 1200 ‐ 1800 K have been measured by a direct technique using shock heating of HNO3/Ar mixtures as a source of a strongly non‐equilibrated OH concentration and time resolved UV resonance absorption as its monitor. The result. k1 = 3.4 1013 exp(−21 kJ mol−1/RT) cm3/mol·s does not correlate with the accepted absolute data at room temperature and implies that the Arrhenius plot for this reaction is strongly curved. It is shown that presently available data in the range 300–2000 K can be represented best by a k = ATm expression. Whereas an empirical interpolation based on the weighted absolute values of all rate constants yields k1 = 1.5 109(T/K)1.14 cm3/mol·s, the result of a transition state theory calculation implies a slightly stronger temperature dependence (k1TST = 6.6. 108 (T/K)1.23 cm3/mol·s) with apparent Arrhenius activation energies of zero around room temperature and ∼20 kJ mol−1 in the 1000–2000 K range
Reaktionen von Molekülen in definierten Schwingungszuständen (V), Schwingungsangeregte mehratomige Moleküle im Elektronengrundzustand: CH3F(2v3, v1, v4) + D(2S), O(3P)*)
Authors: Kneba M. , Wolfrum J. 
Published: September 2012

AbstractDer Einfluß einer selektiven Schwingungsanregung auf das Reaktionsverhalten mehratomiger Moleküle in der Gasphase wurde für die Reaktionen von CH3F(v) mit H‐, D‐ und O‐Atomen mit Hilfe der Methode der laserinduzierten Fluoreszenz in einem Strömungsreaktor untersucht. Nach Anregung der C‐F‐Streckschwingung (v3) in CH3F bei niedrigen Drücken (10 m Torr) mit der P(20)‐Linie bei 9,55 μm eines gepulsten CO2‐Lasers (Laserleistung 105—106 W/cm2) konnte anhand der Fluoreszenz der C—H‐Streckschwingung (v1 v4) bei 3, 3 μm gezeigt werden, daß eine direkte Beobachtung der modenspezifischen Infrarotfluoreszenz nach Mehrphotonenabsorption im Bereich der Stoßzeiten der Moleküle möglich ist. Die Besetzung höherer Schwingungszustände erfolgt dabei um etwa zwei Größenordnungen rascher als durch Schwingungsenergieübertragung.—Durch zeitaufgelöste Beobachtung der Atom‐Konzentration nach der Laseranregung war eine Unterscheidung zwischen reaktiven und energieübertragenden Prozessen möglich. Bei Zusatz von H‐ und D‐Atomen wurde kein beschleunigter Verbrauch von CH3F in den Schwingungszuständen 2 v3, v1 v4 gefunden. Für die Geschwindigkeitskonstante der Reaktionmagnified imageerhält man als obere Grenzemagnified imageBei O‐Atomen wird eine effektive Schwingungsdesaktivierung beobachtet.magnified image
Investigation of a Homogeneous Solid‐State Polymerization by Brillouin‐Scattering
Authors: Leyrer Reinhold J. , Wegner Gerhard , Wettling Wolfram 
Published: September 2012

AbstractMatrix‐elements of the elasticity modulus of a single crystal of 2.4‐hexadiine‐1.6‐diol‐bis(p‐toluene sulfonate) (PTS) and of the corresponding polymer single crystals were determined by Brillouin scattering. The solid‐state polymerization was achieved by annealing at 60°C and the variation of three selected elastic constants with conversion was determined. – The elastic constant in chain direction increases from 0.97·104 N·mm−2 to 4.38·104 N · mm−1 going from the monomer to the polymer. The magnitude of this constant changes smoothly with conversion. The dependence on conversion can be described by a model in which infinitely long linear macromolecules all extended along b but randomly distributed are embedded in the matrix of the residual monomer. – At low conversion there is some deviation from the predicted elastic behaviour due to the finite length of the macromolecules formed at the onset of the reaction.
The Influence of Cationic Micelles on the Dismutation of Br2− ‐Radical Anions in Aqueous Solution (A Pulse Radiolysis Study)
Authors: Proske Th. , Henglein A. 
Published: September 2012

AbstractThe retarding effect of the tenside hexadecyl trimethyl ammonium bromide on the dismutation of Br2− radicals was investigated. Br2− radicals adsorbed singly at different micelles do not directly react with each other. The detachment of Br2− is required. A residence time of 1.5 ± 10−5s of Br2− on the micelles was derived from the kinetic data. Below the critical micelle concentration the tenside does not retard the reaction.
Reactivity, Electronic Structure and Geometry of Nonpolar Zincoxide Surfaces
Authors: Göpel W. 
Published: September 2012

AbstractZnO(1010)/O2 was chosen as a model system to study characteristic interaction mechanisms of reactive gases with surfaces of compound semiconductors. Reactions between 120 and 1000 K depend on thermodynamically controlled surface structures. – Reconstruction and point defects characterize the geometric and electronic structure of clean surfaces. – Reversible physisorption data car be determined at 120 ≤ T ≤ 250 K (coverages θ < 10−10 for P < 10−4 Pa) characterized by adsorption isotherms and isosteric heats of adsorption. – Chemisorption of O2 is found in the range of 300 to 650 K (θ<2.5 · 10−4) on crystals with negligible amount of point defeats at the surface. The energy of chemisorption and reaction rates can be described quantitatively by electron transfer models. – From crystal sublimation measurements at T > 700 K desorption rates for zinc and oxygen are derived. The latter depend strongly on the concentration of point defects (most probably oxygen vacancies) at the surface, which can be determined quantitatively as a function of pressure and temperature and may be removed during reactions at lower temperatures (T < 700 K). Under these conditions a strong influence of oxygen vacancies on sticking coefficients and rates of electron transfer during oxygen exposure is found. – Investigations with various independent techniques (such as AES, LEED, EPR, thermal desorption spectroscopy, isotopic exchange as well as changes in the surface conductivity and work function) are shown to be necessary for a unique interpretation of experimental results. This enables the separation of chemisorption processes and reactions with point defects during oxygen interaction which is of importance to understand the elementary steps during oxidation catalysis on ZnO.
Thermodynamic Properties of Palladium‐Indium Alloys
Authors: Schaller H.‐J. , Brodowsky H. 
Published: September 2012

AbstractThe thermodynamic properties of Pd – In alloys with 2 to 70 at.% In have been determined in the temperature range 800 to 1000°C from e.m.f. measurements on galvanic cells with an oxygen‐conducting solid electrolyte. Heats of mixing calculated from the activities are in excellent agreement with calorimetric data. The relative partial excess free energy of indium assumes unusually large negative values, up to −175 kJ/mol for palladium‐rich alloys. Two effects are discussed to account for the non‐ideal properties: The rise of the Fermi energy as the valence electrons of indium enter the 4d and 5sp bands of the alloy and the lattice distortion brought about by the different molar volumes of the components. The rise of the Fermi energy, as determined from the activity data, indicates a strict adherence of the alloys to the rigid band model.
Defects and Cation Diffusion in Magnetite (III.) Tracerdiffusion of Foreign Tracer Cations as a Function of Temperature and Oxygen Potential
Authors: Dieckmann R. , Mason T. O. , Hodge J. D. , Schmalzried H. 
Published: September 2012

AbstractTracer diffusion coefficients of60Co (T= 906–1210°C) and51Cr (T= 1210–1410°C) in magnetite (Fe3‐O4) were measured by the rest‐activity method as a function of temperature and oxygen activity. For both tracers minima were obtained at all temperatures in logDversus logacurves within the existence range of Fe3‐δO4. At high oxygen activities the slopes d logD/d logpare 2/3; at low oxygen activities the slopes are ‐2/3. According to point defect analysis, diffusion is dominated by vacancy mechanism at high oxygen activity while at low oxygen activity an interstitial or interstitialcy mechanism dominates. Comparison is made with Fe‐ and Al‐diffusion data for magnetite.
Triple Helix Formation of Poly dA · Poly dT · Poly rU
Authors: Klump H. 
Published: September 2012

AbstractThe enthalpy of the triple helix formation of polydeoxythymidylic acid (poly dT), polydeoxyadenylic acid (poly dA), and polyribouridylic acid (poly rU) has been measured by the help of an isothermal mixing calorimeter. The reaction can be split under proper condition into two consecutive steps, the double helix formation of poly dA · poly dT and the addition of the poly U strand to form a trip · helix poly dA · poly dT · poly rU. The interaction energy of poly dA and dT has been determined to 34.3 kJ per mole base pairs and the interaction energy of a poly U single strand with the poly (dA‐dT) double helix has been determined to 9.8 kJ per mole U. The formation energy of the triple helix thus amounts to 44.3 kJ per mole base triplet. The stoichiometry of the complex formation of poly dA · poly dT and of poly dA · poly dT · poly rU was derived from the continuous mixing curves of the constituents. The intrinsic sedimentation coefficient of the components has also been used as an independent method to check the base ratio. Thermal denaturation of the helices has been followed by recording the UV‐absorbance as a function of temperature. Finally the template activity of the triple helix has been tested.
Electrical Conductivity and Thermoelectric Power of Concentrated Lithium‐Ammonia Solutions
Authors: Hirasawa Masahiro , Nakamura Yoshio , Shimoji Mitsuo 
Published: September 2012

AbstractThe electrical conductivity and thermoelectric power of solutions of lithium in liquid ammonia have been measured as a function of composition and temperature. The transition from the semiconducting to the metallic state has been observed in the intermediate concentration range, around 4.5 mole percent lithium. The obtained results are discussed in terms of the models put forward by Mott and others.
Cyclic‐Voltammetric Study of n‐ and p‐Type GaP Electrodes
Authors: Madou M. J. , Cardon F. , Gomes W. P. 
Published: September 2012

AbstractCyclic‐voltammetric electrochemical studies were performed on n‐ and p‐type GaP single crystal electrodes in indifferent aqueous electrolytes. The n‐type GaP cathode was observed to show quasi‐metallic behaviour and the p‐type cathode to be a stable photoelectrode. In this connection some thermodynamic considerations are held. It was found that the potentiodynamic current‐voltage characteristics exhibited additional currents as compared to the potentiostatic curves. The additional currents were attributed to surface redox reactions and reactions with oxidation products accumulated at the surface.
Rate Constant for the Reaction of NH (X3Σ−) with O2 Determined by Pulsed Vacuum UV Photolysis of NH3 and Resonance Fluorescence Detection of NH
Authors: Zetzsch C. , Hansen I. 
Published: September 2012

AbstractThe kinetics of NH (X3σ−) was studied using resonance fluorescence of NH (A3 →II Σ X3Σ−). From the pulsed vacuum uv photolysis of mixtures containing NH3, O2, and He the rate constant for the reaction magnified image. was found to be (at 296 K): magnified image.
Light Induced Electron Transfer between Spatially Separated Donor and Acceptor
Authors: Möbius Dietmar 
Published: September 2012

AbstractQuenching of fluorescence due to electron transfer is observed in monolayer assemblies when electron donor and electron acceptor, both immobile, are either in the same monolayer or in adjacent monolayers. When the donor and acceptor monolayers are separated by two fatty acid interlayers no fluorescence quenching is detected.Two types of light induced electron transfer have been observed.The donor is excited and the electron is transferred from the S1 state of the donor into the lowest unoccupied orbital of the acceptor. The donor fluorescence is quenched.The acceptor is excited and the electron is transferred from the S0 state of the donor into the highest occupied orbital of the acceptor. The acceptor fluorescence is quenched.In both processes the initial situation is recovered by back transfer of an electron from the reduced acceptor to the highest occupied orbital of the donor.These electron transfer processes have been studied by varying the concentration of the acceptor. The fluorescence quenching depends on the average distance R̃ between acceptor molecules and values of R̃1/2 (average distance in the acceptor layer at which the fluorescence intensity is half of the intensity without electron transfer) have been determined.The value of R̃1/2 depends on the energetic position of both the electron donating level and the electron accepting level as calculated from electrochemical and spectroscopic data.
Sensitized Photocurrent through a Semiconductor Electrode by Consecutive Energy and Electron Transfer in Dye Monolayers
Authors: Arden Wolfgang , Fromherz Peter 
Published: September 2012

AbstractElectron injection from photoexcited cyanine dyes into the conduction band of a thin film semiconductor (indiumoxide) is investigated in an electrochemical cell. The sensitizing dyes are incorporated into tenside monolayers covering the electrode. Separation of the chromophores from the electrode by two tenside layers suppresses sensitized photocurrent. Insertion of an appropriate second dye at the semiconductor surface recovers the sensitizing yield of the distant dye. The distant dye absorbs light, transfers energy to the second dye at the semiconductor surface which transfers an electron into the electrode. The processes in this concerted energy‐electron‐transfer system are characterized by simultaneous measurement of photocurrent and fluorescence emission.
Adsorption of Polar Molecules on the Surface of Water
Authors: Baumer Doris , Mang H. , Findenegg G. H. 
Published: September 2012

AbstractThe adsorption of fluorobenzene, chlorobenzene, and benzonitrile on the surface of water has been determined by measurements of the surface tension as a function of the vapor pressure of the organic vapor. The standard thermodynamic quantities of adsorption, δGo, δHo, and δSo, were calculated at the zero‐coverage limit. δHo is less negative than the enthalpy of condensation of the respective pure vapor. Near the saturation vapor pressure chlorobenzene forms a single monolayer whereas fluorobenzene tends to multilayer formation. The stability of adsorbed films on water is predicted by the Lifshitz formula in the correct sequence fluorobenzene > benzene > chlorobenzene.
The Effect of Chain Length Compatibility on Molecular Area, Intermolecular Spacing, Dispersion Energies and Evaporation Resistance of Mixed Monolayers
Authors: Shah D. O. , Shiao S. Y. 
Published: September 2012

AbstractUsing mixed monolayers of alkyl alcohols, it was established that the unequal chain lengths cause an expansion in the area/molecule in mixed monolayers. Assuming the cross‐sectional area of molecules to be circles, it was shown that a difference of two methylene groups between the two components of the mixed monolayer causes an increase in the intermolecular spacing of about 0.05 A. The small increase in intermolecular spacing strikingly decreases the resistance of mixed monolayers to evaporation of water. The surface viscosity was found to be maximum when the chain‐lengths of the components were equal. The dispersion energy between alcohol molecules in the mixed monolayer was calculated using Salem's approach. It was found that a small increase in intermolecular spacing (0.05Å) can decrease the dispersion energy by 6.7 kJ/mol. The magnitude of this decrease is about 1/4 of the energy of a hydrogen bond. It was further shown that the small increase in intermolecular spacing, decreases the melting point of mixed crystals by about 9°C. The chainlength compatibility of mixed surfactants also influences the bubble size, bubble stability, emulsion stability, lubrication, contact angle and wettability. In summary, using the monolayer approach, it was experimentally shown that a small change of 0.05 Å in intermolecular spacing, brought about by a difference of 2 methylene groups between the two surfactant molecules, can strikingly influence the dispersion energy between the molecules. The small change in dispersion energy influences the characteristics of many engineering processes such as bubbles, foams, emulsions, lubrication and wettability.
Vergleich des Polymorphismus in Phospholipid‐Mono‐und geordneten Multischichten
Authors: Albrecht O. , Jürgens E. 
Published: September 2012

Abstract1. Durch direkte Messung von Isobaren mit einer konventionellen Langmuir‐Filmwaage konnten in mehreren Lipiden (Lecithine, Phosphatidsäuren), neben dem bekannten Phasenübergang 1. Ordnung und dem Gas‐Fluüssigkeitsübergang bei sehr niederen Drücken, zwei weitere Phasenübergänge 2. Ordnung nachgewiesen werden.Es wird auch eine Zuordnung zwischen der Hauptumwandlung von Multischichten und Monoschichten angeboten, die nicht die Phasenumwandlungstemperatur gleichsetzt, sondern die Umwandlungsenthalpie und die Flächenänderung beim Phasensprung.2. Geordnete Multischichten wurden nach der Methode von L. Powers und N. A. Clark hergestellt. Der Polymorphismus wurde mit Hilfe der Spinlabel‐Technik und optischen Methoden untersucht.
The Association of Water on Molecular Layers
Authors: Steinbach H. , Sucker ChR. 
Published: September 2012

AbstractHydrocomplexes which form around the hydrophilic group of surface‐active compounds are one of the basic requirements for the colloid‐chemical behaviour of these compounds. According to our conception, the complex in which four water molecules are attached to the hydrophilic group is in equilibrium with the one‐water‐molecule‐complex while compressing a myristic acid monolayer by a Langmuir‐balance. The space requirements of these complexes can be calculated from the size of the hydrophilic group and from the space requirement of the water molecules, which amount to 7.3 Å2 for each one. Polymeric substances follow the same laws, as will be demonstrated by the example of polydimethyl‐siloxane.Depending on the surface area available, a discrete number of water molecules per (CH3)2SiO unit attach themselves to polydimethylsiloxane spread upon water. When such films are compressed, four defined states of orientation will result.This concept is transferred to surfaces of solids. It is shown that when silicone‐treated glass plates are sprayed with water, four defined states of wetting will form which are to be co‐ordinated with the states of orientation.Glass plates with these different states of silicone coating are prepared; they are subjected to measurement of contact angles which they form with various fluids. Informative relationships of adhesion energy, surface tension on solids, wettability, etc. to the interfacial coating are shown when the surface tension of the fluid is plotted versus the adhesion energy.Pronounced polarization of the molecules within the complexes is found while they are adsorbed on the interface of the solid.The heat of association, which is the same whether the poly‐dimethylsiloxane films are adsorbed on water or glass, is calculated from the adhesion energy. Finally, the heat of association allows conclusions to be drawn as to the tensile strength of silicone rubber.
Studies of Lipase and Phospholipase A2 Acting on Lipid Monolayers
Authors: Verger R. , Pieroni G. , Rietsch J. , Pattus F. , Ferrato F. , De Haas G. H. , Desnuelle P. 
Published: September 2012

AbstractThe penetration process of various lipolytic enzymes into lipid monolayers was studied by the use of a surface barostat technique. The induction time, measured during pre‐steady state conditions, increased abruptly for a given value of the surface pressure. This appears to be due to a degree of lipid packing above which the enzyme no longer can penetrate the lipid film.Pancreatic lipase and phospholipase A2 have been shown by the monomolecular film technique to be progressively inactivated when adsorbed at the interface of their respective substrates. This inactivation is faster for lipase than for phospholipase. It is also enhanced by low film pressure and film transfer.The use of radioactive phospholipase and lipase samples offered the possibility to measure for the first time the amount of enzyme adsorbed at a monomolecular film. This adsorption was found to be relatively slow under the conditions of the assays.The existence of an optimum in the velocity versus surface pressure profile is the result of at least two counterbalancing factors. As the surface pressure increases, the amount of enzyme present in the interface decreases, whereas the minimal specific activity of the enzyme increases.Using radioactively labelled lipase, we have shown for the first time in a bile salt free system that the critical surface pressure above which lipase can no longer penetrate a negatively charged monolayer is around 23 dynes/cm. This critical surface pressure is shifted up to 30 dynes/cm in the presence of colipase. The 23 to 30 dynes/cm range may be the critical region where colipase displays assistance during the penetration process of lipase under physiological conditions.From this study with monolayers, we can conclude that activity of lipolytic enzymes used as tools for probing biological membranes will be greatly influenced by the physicochemical nature of the membrane‐water interface.