bluuebunny/crossref_metadata_2025 huggingface dataset:
Der thermische Zerfall von C2F4 in der Gasphase. Zur Bildungsenthalpie von Difluorcarben
Authors: Schug K. P. , Gg. Wagner H.
Published: September 2012

Der thermische Zerfall von C2F4 wurde im Temperaturbereich von 1150 bis 1600 K und bei Drücken von 0,07 bis 46 bar in stark verdünnten Gemischen mit Argon als Trägergas hinter einfallenden und reflektierten Stoßwellen untersucht. C2F4 zerfällt unter Bruch der C‐C‐Doppelbindung in zwei CF2‐Radikale. Die Reaktion folgt einem einfachen Dissoziations‐Rekombinations‐Mechanismus. Aus der Druckabhängigkeit der Geschwindigkeitskonstante k1.0. des Zerfalls erhält man unter Anwendung von Theorien unimolekularer Reaktionen für die Grenzbereiche sehr niedriger und sehr hoher Drücke die Arrhenius‐Ausdrücke chemical structure image.

Eine Auswertung der chemischen Gleichgewichte ergibt in übereinstimmung mit dem Ergebnis der kinetischen Messungen eine Reaktionsenthalpie von δHR2980 = (290,8 ± 5) kJ mol−1. Daraus wurde für die Bildungsenthalpie des CF2‐Radikals ein Wert von δHt2980 = (‐184 ± 4) kJ mol−1 bestimmt.
Transport of Isotopes in Systems with Reversibly Reacting Species. II: Binary and Ternary Nonelectrolyte Solutions with Association Reactions
Authors: Schönert H.
Published: September 2012

Binary solutions with the association reactions nA → An and ternary solutions with the complex forming reactions A + B → AB and 2A + B → A2B are treated with respect to diffusion and tracer diffusion. In some cases these systems exhibit unusual transport behaviour.
The Interaction of Molecules with Field Emitter Surfaces Studied by Field Ion Appearance Spectroscopy
Authors: Ernst N. , Bozdech G. , Block J. H.
Published: September 2012

On rhodium and tungsten field emitters the integral ion energy distribution is measured. The high energy onset of distribution curves is correlated to critical energy deficits with respect to the emitter potential. For gas phase field ionization of noble gases, H2, NH3, H2O the critical energy deficit is related to the ionization potential I of the neutral species without observable temperature or field dependence. Energy deficits of H+ from H2 and NH3, measured at Rh confirm the model of associated pair field ionization. – H3+ is generated by a protonation reaction with a critical energy deficit of 3.0 eV below that of H2. For NO on tungsten a strong layer formation is observed and investigated in respect of formation rates. Energy deficits of protonated noble gases (XeH+, KrH+, ArH+) from a NH3/NH4+ layer are the same as for NH3+. Protonation of noble gases also by water at tungsten and rhodium has no correlation to the heat of formation of XeH+, KrH+, and ArH+. Protonation occurs during a fast (< 10−12 s) proton stripping process. A field dependence of critical energy deficits for NH4+ car be explained by ion image attraction. Protonated water ions (H3O+) yield different critical energy deficits at different metal emitters (Rh and W), due to stronger interaction of water with tungsten. For the hydrazine parent ion N2H4+ at rhodium the increase of the critical energy deficit with increasing field strength is explained by field desorption of a field stabilized adsorption state, with a binding energy of 1.4 eV of N2H4 to the Rh field emitter. The field dependency of critical energy deficits of N2H5+ is similar to NH4+, taking in addition the dipole of the ion into account.
13C1H Intermolecular Relaxation Rate and Molecular Pair Distribution Function in Liquid Acetonitrile
Authors: Kratochwill A.
Published: September 2012

The13C relaxation rate of the nitrile carbon and the self‐diffusion coefficient have been investigated for liquid acetonitrile in the temperature range from −40 to 25 °C. The13C –1H intermolecular part of the total relaxation rate was determined by isotopic substitution‐dilution experiments. – Combined with the known intermolecular proton relaxation rate the orientation dependent molecular pair distribution function was studied. In the first coordination sphere the molecules are arranged most probably in an antiparallel manner, in accordance with a previous x‐ray investigation.
Experimentelle Prüfung von approximativen Chiralitätsfunktionen [1, 2] am Beispiel der induziert cholesterischen Lösung chiraler Methan‐Derivate
Authors: Richter W. J. , Korte C. H.
Published: September 2012

Die R‐Cotton‐Effekte von cholesterischen Lösungen, die durch chirale Methan‐Derivate in nematischen Phasen induziert werden, stellen Chiralitätsbeobachtungen dar, die durch approximative Chiralitätsfunktionen in guter Näherung beschrieben werden können. Die untersuchten Systeme sind Schiffsche Basen, gelöst in EBBA/MBBA sowie in Licristal®. Nur für die Lösung der Schiffschen Basen in EBBA/MBBA lassen sich bei Anwendung von Chiralitätsfunktionen ligandenspezifische Zahlen ermitteln.
Calculation of the Structure of Laminar Flat Flames III: Structure of Burner‐Stabilized Hydrogen‐Oxygen and Hydrogen‐Fluorine Flames
Authors: Warnatz J.
Published: September 2012

The development of proper boundary conditions permits the solution of the conservation equations for burner‐stabilized laminar flat flames. Hence, comparison is possible with corresponding experimental results. The examples considered are burner‐stabilized H2– O2and H2– F2– Ar flames. In both cases there is satisfactory agreement of calculation and experiment.
Photochemical and Thermal Reactions of Porphyrins and Organic Surfactants in Monolayer Assemblies. Modification of Reactivity in Condensed Hydrophobic Microenvironments [1]
Authors: Whitten David G. , Eaker David W. , Horsey Barbara E. , Schmehl Russell H. , Worsham Paul R.
Published: September 2012

This paper summarizes a number of investigations of reactions occurring in organized monolayer assemblies, monolayer films, and at monolayer assembly or film‐solution interfaces. In several cases, the reactions involve chromophores localized in relatively hydrophobic sites and pronounced differences in reactivity can be ascribed to the microenvironment. Metallation of free base porphyrins has been examined in assemblies and at film‐solution interfaces. Although several divalent metal ions can be incorporated, the order of reactivity varies from that observed in solution. Several porphyrins residing in highly hydrophobic sites are resistant to metallation while those lying near the hydrophilic interface react rapidly. Photooxidation of surfactant protoporphyrin esters residing in hydrophobic regions occurs in both micelles and monolayers but the product distribution is quite different from that obtained in solution. Iron and ruthenium porphyrins isolated in assemblies undergo ligand substitution reactions not readily observable in solution. The photoreactions of some surfactant styrenes has been examined; close packing of the styrene unit, which lies at the end of a hydrocarbon chain, leads to substantial ground state interaction and rapid and selective dimerization on irradiation. Different products are obtained from those formed on irradiation of the same compound in solution, micelles, and crystals. The photoreactivity of a surfactant phenyl ketone has been investigated in condensed monolayers. In solution the primary reaction of the ketone is the “type II” photoelimination which proceeds via α‐hydrogen abstraction. In condensed monolayers the required conformation for this reaction can evidently not be readily attained. Thus in the assemblies dramatic reduction in the efficiency of the type II process occurs concurrent with the onset of new reaction paths.
Three‐Phase Contact Line Motion in the Deposition of Spread Monolayers
Authors: Petrov J. G. , Kuhn H. , Möbius D.
Published: September 2012

A monolayer of a water insoluble surfactant can be transferred with some maximum rate vmax from a water surface to the surface of a solid being taken out. This rate was measured by observing the motion of the three‐phase‐contact line (detecting fluorescence quenching or change of light reflection by water entrained). The rate vmax was found to be determined by the reactivity between the monolayer head groups and the solid surface. vmax is particularly large in the case of opposite sign of the charges of the immobile groups on the solid surface and in the monolayer. In the case of equal sign vmax is strongly increased by the presence of divalent counter‐ions in the solution. The hydration of the head groups decreases vmax and therefore optimal transfer is found when the charged head groups are separated from each other by uncharged head groups. Particularly large values of vmax are observed when the monolayer head groups and the solid surface interact by zipper like hydrogen bonding between undissociated carboxyl groups.
Alignment of Liquid Crystals by Amphiphilic Monolayers
Authors: Hiltrop K. , Stegemeyer H.
Published: September 2012

The action of solid surfaces coated with monomolecular films of amphiphilic compounds (especially lecithins) on adjacent liquid crystal phases resulting in an uniform homeotropic orientation has been investigated. The quality of orientation was found to be effected by molecular structure of the amphiphilics as well as the liquid crystals, the packing density of the film, and the temperature. The experimental results can be understood in terms of the following model: Lecithins form brush‐like films with the hydrophobic alkyl chains pointing off the glass surface. Under suitable conditions holes of molecular dimensions exist in the films into which nematogenic molecules can penetrate. By means of elastic interaction forces between these anchored molecules and the adjacent nematic bulk the homeotropization is induced.
Interactions between Lipid Monolayers and Band 3‐Protein from Human Erythrocyte Membranes
Authors: Klappauf E. , Schubert D.
Published: September 2012

Lipid monolayers at the air‐water interface were used as a model system to study the specificity of protein‐lipid interactions of band 3, the main integral protein (the anion transport protein) of human erythrocyte membranes.

Band 3‐protein was isolated by zonal electrophoresis (in acetic acid/H2O/sucrose mixtures) of erythrocyte membranes preextracted in 10% acetic acid and solubilized in 92% acetic acid. Afterwards, the protein was transferred into aqueous solutions and injected into the aqueous subphase of monolayers of different lipid classes. The changes in monolayer surface pressure following protein addition were used as a measure of the strength of protein‐lipid interactions.
Calorimetric Investigations of Phosphatidic Acid Bilayers
Authors: Blume Alfred
Published: September 2012

Differential scanning calorimetry is a sensitive method for studying the phase transition of phospholipid bilayers. Up to now only few calorimetric investigations of the phase transition of charged phospholipids have been carried out [1–3]. We studied the phase behaviour of dihexadecyl‐phosphatidic acid (DHPA) as a function of the pH of the dispersion [4, 5]. Varying the pH induces different degrees of ionization of the phosphatidic acid head group. At high pH the head group has two negative charges leading to a decrease of the transition temperature to 49°C compared to 70°C at pH 9.0 and a decrease in transition enthalpy to 21.8 kJ/mol compared to 31.4 kJ/mol at pH 9.0. Lowering the pH below 9.0 leads to a gradual protonation of singly charged DHPA. With increasing protonation Tm rises to 74°C at pH 3.5 and then drops to 62°C at pH 1.5.

The results obtained by calorimetry indicate, that probably two different phases can exist between pH 9.0 and 1.0. At half protonation at pH 3.5 a particular stable phase with high transition temperature and low transition enthalpy (11.3 kJ/mol) can be observed. Complete protonation leads to a phase, which has the same transition temperature as the melting point of dry crystalline protonated DHPA.

The observed variation of the transition enthalpy with pH cannot be explained by assuming, that only the electrostatic potential of the bilayer surface is changed [6]. An influence of the degree of ionization of the head group on the hydrocarbon chain interactions has to be taken into account.

From these experiments conclusions can be drawn upon the intermolecular interactions between the head groups of phosphatidic acids.
Raman Spectroscopic Investigations on Binary Lipid Mixtures
Authors: Knoll Wolfgang
Published: September 2012

Raman spectra in the C‐H and C‐C stretching vibration region for dipalmitoyl‐phosphatidic acid and mixtures of dimyristoyl‐, dipalmitoyl‐ and distearoyl lecithin are reported. Suitable peak height ratios show characteristic changes with temperature. From the data of the pure lipids one can derive ordered‐fluid transition temperatures that are in good agreement with the values from other methods: 57°C for DPPA at pH 9, 23.5°C for DML, 42°C for DPL and 55°C for DSL. – For the DML/DPL mixture a somewhat broadened transition at intermediate temperature is found (33.5°C for DML: DPL = 1:1). – For a mixture of DPPA and polylysine‐bound DPPA two distinct transition temperatures can be seen, which reflect the immiscibility of the two components. – For mixtures of DML and DSL more complicated transition curves are found. The peak height ratios of C – H vibrations at 2880 and 2850 cm−1 nevertheless can be used to construct a phase diagram. The transition curve of C‐C stretching vibrations at 1130 and 1100 cm−1 seems to monitor a complex phase separation behaviour which cannot be explained for the moment in full detail without additional experimental results.
Formation and Some Properties of Micelles
Authors: Mukerjee Pasupati
Published: September 2012

The relationship of micelles to other types of organized structures formed by amphipathic monomers such as monolayers, bilayers, membranes, and adsorbed layers is pointed out. The patterns of self‐association followed by micelle‐forming surfactants is examined in terms of a general association model. The interactions responsible for micelle formation and the characteristic features of the local microenvironments of micelles are reviewed. The nature of solubilization by micelles is discussed in terms of the forces of interaction involved and problems of location, distribution and orientation.
Light Initiated Electron Transfer in Functional Surfactant Assemblies I: Micelles with Transition Metal Counterions
Authors: Moroi Yoshikiyo , Braun André , Grätzel Michael
Published: September 2012

The photo induced reduction of cupric ions by organic donors (D) was studied in functional surfactant assemblies in which the Cu2+ ions constitute the counterion atmosphere of the micelle. The donors employed were N‐methyl‐phenothiazine (MPTH) and N,N'‐Dimethyl‐5,11‐dihydroindolo‐[3,2‐b]carbazol (DI). Laser photolysis, steady state illumination and fluorescence techniques were used to investigate the photoredox processes. The transfer of an electron from the excited donor inside the micelle to the counterion occurs so rapidly that it cannot be resolved kinetically by nanosecond laser techniques. In the case of DI, the reactive excited state was found to be the first excited singlet state whose lifetime in the Cu2+ micelles is 1.2 · 10−9 s. The cuprous ion formed in the photoredox process escapes from the micelle into the bulk solution before back transfer of electrons to D+ can occur. There it may be used for a second redox reaction with a negative ion or a zwitter ion. In such a system, the back reaction between reduced acceptor ion and oxydized donor is prevented by the micellar surface potential allowing for storage of light energy. The dynamics of excited state interaction with micellar counterions was investigated also in aggregates with Co2+ and Ni2+ counterion atmospheres, respectively.
Free Tenside Radicals and Micellar Equilibria
Authors: Henglein A. , Proske H.
Published: September 2012

Three tensides (1‐(6‐dodecylbenzene‐sulfonate)‐Na; myristyltriethyleneglycol‐ether‐sulfonate‐Na; cetyl‐21‐ethyleneglycol‐ether) were σ− and electron irradiated in aqueous solution. The OH radicals produced in the radiolysis of water attacked the tensides to form organic radicals either by hydrogen abstraction or addition to the aromatic ring. The decay of the organic radicals was followed optically and the rate constant for bimolecular deactivation measured at different tenside concentrations.

In these case of the two anionic micelles, mutual deactivation of radicals in micelles is not possible because of the Coulombic repulsion between the micelles. Deactivation can occur after the exit of a radical from its micelle. The kinetics of radical‐radical deactivation is therefore strongly ruled by the dynamics of the micellar equilibrium Mn → Mn+1 K M. All rate constants of this equilibrium can be obtained from the analysis of the kinetic data.

In the case of the neutral micelles, radicals in micelles do activate each other. In these micelles, more than one radical could be produced. Intramicellar radical‐radical deactivation was observed in the microsecond range, intermicellar deactivation in the millisecond range. σ‐irradiation led to crosslinking of the tenside molecules.
Nuclear Magnetic Resonance Studies of the Arrangement of Benzene Molecules in the Cavities of the Zeolite NaX
Authors: Lechert H. , Wittern K.‐P.
Published: September 2012

The second moments of the proton resonances of benzene in the cavities of a zeolite NaX with Si/Al = 1.32 have been measured for C6H6and C6H3D3, between 100 K and 200 K, and the intra‐ and intermolecular contribution extracted from the results. From the intramolecular contribution for coverages above four molecules in a large cavity below 150 K a rotation around the hexagonal axis of the benzene molecule can be concluded. For the explanation of the intermolecular contribution, model calculations have been carried out, showing that for four molecules in a large cavity the molecules are arranged flat on the walls above the S2‐sites with a distance of about 0.32 nm from the ions in these sites. The intermolecular second moment for a coverage above five molecules in a cavity can be explained only by arranging the fifth molecule in the window between two cavities parallel to the plane of the window. This arrangement explains the limiting coverage of about six molecule in a large cavity as well as the possibility of a motion of the molecules at higher temperatures.
Dependence of the Intensity of Fluorescence on the Quencher Concentration in Micellar Systems
Authors: Henglein A. , Scheerer R.
Published: September 2012

The quenching of the fluorescence of 2‐(4‐aminophenyl)‐3‐methylbenzothiazol solubilized in micelles of sodium dodecylsulfate by duroquinone was investigated. The decay constant k0, in the absence of quencher is 6.9·108 s−1. At constant concentrations of the fluorescing and the quenching compounds the fluorescence intensity decreases with decreasing surfactant concentration. This effect is explained by the changes in the distribution of the emitting and quenching molecules among the micelles. A relationship is given which takes into account the statistical distribution of solubilized molecules. The first order rate constant is km = m·k1, for quenching in a micelle carrying m molecules of the quencher. k1, the rate constant for quenching in a micelle containing 1 molecule of the quencher, was found to be 3.5·108 s−1. – The ion pair formation in micelles containing 2‐(4‐aminophenyl)‐3‐methylbenzothiazol and duroquinone, the biphotonic ionization of 2‐(4‐aminophenyl)‐3‐methylbenzo‐thiazol in anionic micelles and in methanol solution, and the formation of the triplet state of this compound in toluene and in acid aqueous solutions were studied by laser flash photolysis.
Fragmentierung von Halogenmethanen beim Stoß mit monochromatischen Elektronen niedriger Energie (0 – 10 eV)
Authors: Illenberger E. , Scheunemann H.‐U. , Baumgärtel H.
Published: September 2012

Mit Hilfe eines Trochoidal‐Elektronenmonochromators (δE ≈︁ 0.13 eV) und eines Quadrupol‐Massenfilters wird die energieselektive Fragmentierung von CF3Cl, CF2Cl2 und CFCl3 im Bereich niedriger Elektronenenergien (0 – 10 eV) untersucht. Innerhalb einer Anzahl verschiedener negativer Fragmente ist die überaus intensive Bildung von Cl− aus CFCl3 – das bereits bei 0.0 eV entsteht – besonders auffällig. Die hohen Bildungsquerschnitte machen deutlich, daß bereits niederenergetische Elektronen, ganz im Gegensatz zu Photonen. die chemisch sehr stabilen Gase zu dissoziieren vermögen. Es wird diskutiert, ob dieser Effekt die troposphärischen Lebensdauern der Halogenmethane beeinflußt.
Dynamics of Physisorbed Hydrogen on Charcoal and Microcrystalline Graphite
Authors: Stockmeyer R. , Stortnik H. , Wagner R.
Published: September 2012

The molecular motion in monolayers of hydrogen adsorbed on charcoal and on the basal planes of microcrystalline, partially oriented graphite have been studied by neutron spectroscopy at temperatures between 40 K and 140 K. At high temperature the H2 molecule is dominantly found in gas‐like states. At low temperature the adsorbed molecules populate mainly localized states, in which the molecules diffuse over the surface like in a surface lattice gas. The o‐H2 rotation is only slightly hindered. The localized states are separated from the non‐localized states by a band gap of about 12 meV.
Electrochemical Solar Cell Based on the d‐Band Semiconductor Tungsten‐Diselenide
Authors: Gobrecht J. , Gerischer H. , Tributsch H.
Published: September 2012

In a search for corrosion resistent electrode materials for electrochemical solar cells the covalent, layered semiconductor WSe2, has been investigated. Its photoactivity in the visible spectral region (band gap 1.57 eV) involves d‐d electron transitions which do not lead to an immediate photocorrosien. An energetically favourable energy band position makes it possible to operate p‐type material as photocathodes for energy conversion. Photocell outputs in the order of 15 mA/cm2 and 0.5 V were obtained in 100 mW/cm2 illumination (Xenon‐lamp). It is shown that the produced photovoltage is not systematically dependent on the redox potential of the redox agents but influenced by their chemical reactivity due to a specific interaction with the electrode surface.
Enhancement of the Proton Exchange Rate in Aqueous Solution by Small Amounts of Hydrophobic Substances, as Determined from Ultrasonic Relaxation
Authors: Nicola C. U. , Labhardt A. , Schwarz G.
Published: September 2012

The kinetics of the proton transfer reaction between dihydrogen phosphate and imidazole in water with some added methanol, ethanol, and dioxan, respectively, was investigated by means of ultrasonic absorption and velocity dispersion measurements in the frequency range from 0.5 to 36 MHz. The system exhibits a single chemical relaxation time. It reflects a diffusion controlled direct transfer mechanism. The two rate constants have been evaluated as a function of the volume percentage of the added solvent. Both show a sharp maximum at about 0.5%. This effect turned out to be the more pronounced the more hydrophobe the foreign molecules are. Comparatively few molecules of such material therefore seem to appreciably increase the hydrogen bonded water structure in the hydration shells through which proton transfer is mediated.
Neuere Untersuchungen zur Bindung von Ethidiumbromid an DNA 2. Mitteilung: Vergleich der Bindungskonstanten von Ethidiumbromid und verwandten Verbindungen. Diskussion der kompetitiven und nicht‐kompetitiven Bindung
Authors: Pauluhn Jürgen , Zimmermann Herbert W.
Published: September 2012

Die Bindung einiger Derivate des Ethidiumbromids (2,7‐Diamino‐9‐phenyl‐phenanthridin DPP, DPPH⊕, 7‐Amino‐9‐phenyl‐10‐äthyl‐phenanthridinium‐bromid APEP, 9'‐Phenyl‐10‐äthyl‐phenanthridinium‐bromid PEP) an Kalbsthymus‐DNA wurde absorptionsspektroskopisch untersucht. Aus Scatchard‐Bindungsisothermen wurden die Bindungskonstanten für die kompetitive und die nicht‐kompetitive Bindung bestimmt und mit denen von Ethidiumbromid E verglichen. ‐ Die Bindung der Base DPP an DNA ist pH‐abhängig. In alkalischem Medium liegt die freie Base vor, die nicht an DNA gebunden wird. In saurem Medium wird die Base protoniert. DPPH⊕ kann ebenso wie E kompetitiv und nicht‐kompetitiv an DNA gebunden werden. Bei mittleren pH‐Werten existiert in Lösung ein Gleichgewicht zwischen freier Base und gebundener protonierter Base. Die freie Enthalpie der Bindung von DPPH⊕ an DNA erzwingt unter diesen Bedingungen die Protonierung der Base. — Die Monoaminoverbindung APEP wird kompetitiv und nicht‐kompetitiv gebunden. Der Wert der Bindungskonstante der kompetitiven Bindung KS2 ist im Vergleich zu E etwa halbiert. ‐ Das Kation PEP, das keine Aminogruppen enthält, wird nur noch sehr schwach kompetitiv gebunden. KS2 ist gegenüber E etwa um eine Zehnerpotenz erniedrigt. Die nicht‐kompetitive Bindung konnte nicht beobachtet werden. ‐ Aus dem Vergleich der Bindungskonstanten geht hervor, daß für ausgeprägte kompetitive und nicht‐kompetitive Bindungen eine positive Ladung und wenigstens eine Aminogruppe erforderlich sind. Intercalation und externe Bindung werden unter diesen Gesichtspunkten diskutiert.
Comparative Study of Adsorbate Systems and Corresponding Compounds Using X‐Ray and UV‐Photoemission I. Hexagonal (0001) Co/CO, O2 versus Oxides and Carbonyls
Authors: Freund Hans‐Joachim , Hohlneicher Georg
Published: September 2012

Photoemission studies using XPS and UPS (HeI, HeII) on clean and gas‐covered hexagonal (0001)‐Cobalt‐single‐crystal surfaces are reported (300 K). To interpret the results on the adsorbates namely Co/CO and Co/O2, compound systems, such as CoO, Co3O4 and Co2(CO)8 are studied parallel and comparison is made. It is shown that the emission from Co/O2 is similar to that from CoO and not to that from Co3O4 and that the Co/CO‐systems resembles the Co2(CO)8‐photoemission characteristics. Assignment of CO‐peaks as far as the sequence of the 4σ, 1π and 5σ is concerned is shown to be the same as in free CO. The C1s spectrum of the carbonyl is analysed using theoretical predictions of atomic populations, which show the bridging ligands to carry more electron density than terminal ones. From comparison with adsorbate systems it follows that the differences in the adsorbate system are not as pronounced as in the case of the carbonyls.
Nature of the Electron‐Hole Pair in the System Anthracene Crystal/Rhodamine B Adsorbed from Aqueous Solution. Dependence of Kinetics and Spin‐Dynamics on External Parameters. Part I: External Electric Field
Authors: Müller N. , Papier G. , Charlé K.‐P. , Willig F.
Published: September 2012

We have studied the influence of an applied electric field (up to 5 · 105 Vcm−1) and of a small applied magnetic field (up to 2 · 10−2 Tesla) on the irreversible separation of electron‐hole pairs (measured as sensitized hole current SHC) and on their geminate recombination (measured as sensitized delayed fluorescence SDF) at the interface between an organic crystal and an aqueous solution. The electron‐hole pairs have been generated via electron transfer from the surface of an anthracene crystal to the excited singlet state of adsorbed rhodamine B molecules. There is a steep decrease in the magnitude of the SDF and in the magnetic hyperfine modulation (HFM) of the SHC with rising applied electric field strength. The experimental results can be described with a theory taking into account the repeated dissociation and re‐formation of the bound electron‐hole pair. The magnetic field effect on the kinetics of the electron‐hole pair develops almost exclusively during the periods when the hole is released from the bound state and moves about at the crystal surface. The hitherto accepted model of Groff et al., in which only the bound state of the electron‐hole pair has been considered, cannot account for the behaviour of the system.
Mass Spectrometric Determination of the Dissociation Energies of CuTb(g), CuDy(g), and CuHo(g)
Authors: Hilpert K.
Published: September 2012

The enthalpy changes of the reactions

magnified image

(M = Tb, Dy or Ho) could be determined by Knudsen effusion mass spectrometric studies vaporizing pure Cu and M‐Cu alloys. The following dissociation energies at 0 K were obtained for Cu2(g), TbCu(g), DyCu(g) and HoCu(g) in kJ mol−1: 190.2 ± 5.4, 187 ± 19, 140 ± 19 and 139 ± 19. The appearance potentials of the single charged ions of these molecules could be determined as 7.8 ± 0.4, 5.3 ± 0.3, 5.4 ± 0.4 and 5.3 ± 0.3 eV, respectively. The experimental dissociation energies for the heteronuclear diatomic molecules are compared with the theoretical predictions of the Pauling model of the polar bond.
Rotational Diffusion of Prolate and Oblate Molecules from Absorption Relaxation
Authors: Von Jena A. , Lessing H. E.
Published: September 2012

The complex interplay of anisotropic rotational diffusion, ground‐state population recovery and intersystem‐crossing involved in a transient absorption experiment is treated theoretically via balance equations for the angular‐dependent population densities. An approach to the solution of this problem is presented that avoids the formalistic Green's function method and provides an analytical expression for the time course of the absorption relaxation in the small‐signal case with sin2‐pulse excitation and interrogation. The approach from first principles allows a straightforward discussion of the large‐signal case. It can be shown that a rotation‐free measurement is possible by the 54.7°‐method irrespective of the excitation intensity and anisotropy of the molecular rotator. — Experiments are performed with a cw pulse photometer which delivers precise absorption‐relaxation plots that are amenable to computer evalution by least‐square methods. Even though the dye molecules Rhodamine 6 G, Erythrosine B and Pyronine G, Acridine Orange are definitely oblate and prolate rotators, respectively, their rotational behaviour is dominated by a single‐exponential decay. From this it is concluded that rotational diffusion obeys the “stick” boundary condition and that the transition moment for the S0 → S1 transition lies in the molecular plane pointing along the long axis. This agrees well with a simple free‐electron model of the molecular π‐electron system.
Profilanalyse der OH‐Streckschwingungsbanden von Alkoholen im Oberschwingungsbereich — Infrarot‐Fourierspektrometrische Untersuchungen —
Authors: Kirchner H.‐H. , Richter W.
Published: September 2012

Die Beobachtung der Obertonspektren der OH‐Streckschwingung von Alkoholen ‐ einschließlich solcher, die intramolekulare Wasserstoffbrücken bilden ‐ liefert weitere Informationen über die Moleküstruktur und trägt zur experimentellen Bestätigung bislang bekannter Vorstellungen über den Zusammenhang zwischen den Spektren von Molekülschwingungen und den zwischenmolekularen Wechselwirkungen sowie der Moleküldynamik in flüssiger Phase bei. Durch Verwendung von Kohlenwasserstoffen als Lösungsmittel wird die Streckschwingung der OH‐Gruppe in gauche‐Stellung als separate Bande beobachtet. Ein Vergleich mit dem Grundschwingungsspektrum zeigt, daß die Zeitauflösung des Beobachtungsmittels erst bei den Obertönen zur Abtrennung dieser Bande ausreicht. Daraus wird eine Lebensdauer dieser Struktur von mindestens 3 ps abgeschätzt. Aus der Zunahme und der Angleichung der Profilbreiten beim Übergang in den Obertonbereich wird gefolgert, daß eine inhomogene Störfeldverteilung (Phasenrelaxation im Zeitbild) der dominierende Verbreiterungsmechanismus in diesen Spektralbereichen ist. Das besondere Verhalten der durch Wasserstoffbrücken beeinflußten OH‐Schwingungen unterstreicht diese Vorstellung. Der hohe Gaußformanteil in den Profilen der zweiten Obertonspektren wird als Abnahme der durch die Moleküldynamik bewirkten Verzerrung des Spektrums gedeutet.
Product Quantum Yields from the Photolysis of NO2 at 366 nm in the Presence of Ethylene. ‐ The Role of NO3*
Authors: Canosa C. , Penzhorn R.‐D. , Von Sonntag C.
Published: September 2012

Nitrogen dioxide (1.3 · 10−4, 4.0 · 10−4, and 7.2 · 10−4 mol/l) has been photolysed (λ = 366 nm) at room temperature in the presence of ethylene (3.7 · 10−2 mol/l). Quantum yields of N2O, NO, CO, CO2, O2, CH2O, (CH2)2O, CH3CHO, CH3ONO, CH3ONO2, CH3NO2, C2H5ONO2, and C2H5NO2 were determined (NO2 actinometry). Satisfactory N, O, and H material balances were obtained. ‐ The O atoms from the photolysis of NO2 react with NO2 to give NO3*, as well as with ethylene to yield C2H4O*. It is concluded that the excited NO3*, rather than being deactivated to thermal NO3, essentially reacts chemically with ethylene. The excited C2H4O* may either become collisionally deactivated into (CH2)O and CH3CHO, or decay to CHO and CH3 radicals. The observed products can be explained via subsequent reactions of these radicals. A number of rate constants and ratios of rate constants pertinent to this system have been estimated.
The NO Yield of O(1D) + N2O as Function of Kinetic Energy
Authors: Marx W. , Bahe F. , Schurath U.
Published: September 2012

The photolysis of pure N2O and of N2O in a large excess of He at 184.9 nm and at 206.2 nm was used as a source of O(1D) atoms, to study the branching ratio of reactions (2a) N2O + O(1D) → N2 + O2 and (2b) N2O + O(1D) → NO + NO, as function of kinetic energy of O(1D). The mole fraction b = k2b/(k2a + k2b) of O(1D) atoms reacting with N2O via (2b) governs the source strength of NO in the stratosphere. The products N2, O2, and NO were measured every 3 minutes by automated gas chromatography, and continuously by a chemi‐luminescence detector as function of time during the photolysis of N2O. Back extrapolation of the product ratios to zero conversion yielded the correct stoichiometry. The value of b derived from initial product ratios was b = 0.617 ± 0.015, independent of kinetic energy in the range 11.3 to 184 kJ/mol. The result is in excellent agreement with a theoretical model of reaction (2) proposed by Tully. The new value of b = 0.617 increases the source strength of NO in the stratosphere by 23% relative to current model calculations based on b = 0.50.
Electrochemical and Photoelectrochemical Properties of the Semiconducting SrTiO3 Single Crystal Electrode
Authors: Kerchove F. Vanden , Vandermolen J. , Gomes W. P. , Cardon F.
Published: September 2012

The photoelectrochemical behaviour of several reagents at the SrTiO3 anode has been investigated. Current‐doubling was found with several reducing agents. By competitive reaction experiments, hole capture was detected with some other reagents. Quantitative data on relative hole reactivities were obtained for several reducing agents, including water. The position of the band edges at the semiconductor surface was deduced from capacitance measurements. The reactivity data are interpreted in terms of the position of electron energy levels at both sides of the surface, and the applicability of the direct electron transfer model to the reactions observed is discussed.
Thermodynamics of Mn3O4 — Co3O4, Fe3O4 — Mn3O4, and Fe3O4 — Co3O4 Spinels by Phase Diagram Analysis
Authors: Pelton A. D. , Schmalzried H. , Sticher J.
Published: September 2012

High temperature phase equilibrium data are compiled from the literature for the Mn—Co—O, Fe—Mn—O, and Fe—Co—O systems. These data are then analyzed with a view to examining the thermodynamics of the spinel phases. It is shown that the results are consistent with a simple “ideal” model of cation distribution in the spinel phases. The representation and subsequent analysis of the phase equilibria are greatly facilitated through the use of isothermal log po,‐composition phase diagrams and through the use of a computer program to calculate these diagrams.
Electric Transport Phenomena in Mixed Electrolyte Solutions. I. General Phenomenological Aspects
Authors: Timmermann E. O.
Published: September 2012

The electric transport phenomena in mixed electrolyte solutions (of more than two ion constituents) are analysed from the phenomenological point of view. The expressions for the equivalent conductivity and the stoichiometric transport numbers are derived using the equivalent fractions, the total equivalent concentration and the conventional ionic conductivities of the ion constituents. Limiting values and limiting laws under several conditions are studied. General expressions for the ionic conductivities and the excess conductivity of ternary electrolyte solutions are given.
Electric Transport Phenomena in Mixed Electrolyte Solutions. II. Experimental Examples
Authors: Timmermann E. O.
Published: September 2012

The description of the electric transport quantities in mixed electrolyte solutions given in Part I is illustrated with experimental data for several systems. The use of the excess conductivity functions is shown on the basis of Longsworth's data for HCl(1)‐KCl(2)‐H2O at c = 0.1 mol dm−3. The ionic conductivities of the three ion constituents are non‐linear with respect to the equivalent fraction y,1. A quadratic term has to be added to reproduce the experimental data. The excess conductivity AE at constant total equivalent concentration for NaCl(1)—KCl(2)—H2O (molality scale) and NaCl(1)—MgCl2(2)—H2O (molarity scale) responds to the simple and symmetric formula over a wide range of concentration. A correlation between the constant A and the difference of the equivalent conductivities of the corresponding binary solutions for nine ternary mixtures of uni‐univalent electrolytes is discussed. Within the experimental error and with the few experimental data available for four alkali‐metal chloride mixtures the limiting law of the transport number is confirmed. Limiting ionic conductivities of the trace ion constituents are calculated and compared with their ionic conductivities in the binary solutions and with the values predicted by Van Rysselbergh's approximation. The latter are consistent with the experimental results.
The Viscosity and Diffusion Coefficients of the Mixtures of Light Hydrocarbons with Other Polyatomic Gases
Authors: Abe Y. , Kestin J. , Khalifa H. E. , Wakeham W. A.
Published: September 2012

The paper presents new measurements of the viscosity of binary, gaseous mixtures of the three saturated hydrocarbons ethane, propane, and normal‐butane with other polyatomic gases. Specifically, the systems studied are: C2H6‐N2, C2H6‐CO2, C2H6‐CF4, C2H6‐SF6, C3H8‐N2, C3H8‐CO2, n‐C4H10‐N2, and n‐C4H10‐CO2. The measurements have been carried out near atmospheric pressure in the temperature range 25 — 195 °C in a high precision oscillating‐disk viscometer. The accuracy of the reported values of viscosity is estimated as one of ±0.3%. — Our previous work has proved that each of the pure components conforms to the extended law of corresponding states formulated by Kestin, Ro, and Wakeham. The present measurements demonstrate that the same is true for the interactions among unlike pairs of molecules of the pure components. The experimental viscosities are employed to determine the scaling factors σ12 and 12 which secure the optimum representation of the data with the aid of the universal functional of the law of corresponding states. — The measurements also provide values of the binary diffusion coefficients for the eight mixtures studied. For those systems for which direct measurements of the diffusivity are available, the agreement between the two sets of data is within the mutual uncertainty. For the mixtures C2H6‐CF4, C2H6‐SF6, and n‐C4H10‐CO2 the present measurements represent the first determination of the binary diffusion coefficients.
Low Temperature Luminescence Spectra of the Antiferromagnetic Complexes (CH3NH3)2MnCl4 and (C2H5NH3)2MnCl4
Authors: Lignou F.
Published: September 2012

The luminescence spectra of (CH3NH3)2MnCl4 and (C2H5NH3)2MnCl4 were studied in the temperature range 4.2 K < T < 100 K. The shape of the spectra at constant temperature is very similar to that of the paramagnetic (C5H6N)2MnCl4. With increasing temperature the total intensity of the luminescence decreases strongly. In contrast to paramagnetic complexes the maximum wavelength and the width of G(1/λ) are not increasing with increasing temperature. The anomalous behavior is due to the magnetoelastic effect.
Auflösungsgeschwindigkeit von Polymeren
Authors: Asmussen F.
Published: September 2012

Die Kinetik des Auflösungsprozesses eines polymeren Stoffes in einem strömenden Lösungsmittel wird von thermo‐ und hydrodynamischen Eigenschaften des Polymer‐Lösungsmittel‐Systems beeinflußt. Es können verschiedene Mechanismen unterschieden werden:

Normale Auflösung: Die Auflösungsgeschwindigkeit wird durch gegenseitige Diffusion der Komponenten innerhalb einer Quellschicht gesteuert.

Auflösung ohne Quellschicht: Unterhalb der Geltemperatur wird der Auflösungsprozeß durch eine behinderte Konformationsumwandlung der Makromoleküle vom Glas‐ in den Gleichgewichtszustand kontrolliert.

Auflösung mit Entmischung in der Quellschicht: Die Quellschicht zerfällt in Gel‐ und Solschicht. Der Lösungsprozeß verläuft nicht‐stationär.

Auflösung mit Rekristallisation in der Quellschicht: Die Auflösung von glasigen, aber kristallisationsfähigen Polymeren (Beispiel: Polycarbonat) führt zu einer quasistationären Kristallisationszone innerhalb der Quellschicht.

Auflösung von teilkristallinen Polymeren: Die Wachstumsbedingungen der sphärolithischen Struktur sind für den Löseprozeß geschwindigkeitsbestimmend.

Der Auflösungsprozeß hat in der Röntgen‐Lithographie große Bedeutung. Zur Abbildung kleinster Strukturen wird ein Polymer‐Resist durch Strahlung partiell abgebaut und mit einem Lösungsmittel selektiv entwickelt. ‐ Das Ausmaß der Strahlenschädigung im Polymerresist kann über die Kinetik des Auflösungsprozesses erfaßt werden.
Sorption und Diffusion von Acrylnitril in Polyacrylnitril
Authors: Roth W.
Published: September 2012

Im Temperaturbereich von 25 °C bis 90 °C wurden die Sorptionsisothermen und Diffusionskoeffizienten von Acrylnitril in Polyacrylnitril‐pulver ermittelt. Die Sorption läßt sich durch nicht‐lineare Isothermen kennzeichnen, die Diffusion ist durch sehr kleine Diffusionskoeffizienten bestimmt (25 °C: D = 4 · 10−16 cm2/s; Aktivierungsenergie 67.7 kJ/mol). Durch eine gleichzeitig mit der Eindiffusion beobachtete Adsorption von Acrylnitril an der Polyacrylnitril‐Oberfläche bedingt konnte eine Abschätzung des freien Volumens im verwendeten Pulver zu 1,8% vorgenommen werden.
Diffusion, Löslichkeit und Permeation niedrigmolekularer Verbindungen in Polymeren
Authors: Horacek H.
Published: September 2012

An den Beispielen, Mehrschichtfolien, Kunststoffschäume und Polymergemenge, werden Anwendungsmöglichkeiten von Diffusions‐, Löslichkeits‐ und Permeationswerten auf Probleme der Praxis aufgezeigt. Bei Mehrschichtfolien wird die Schicht mit der geringsten Permeablität für die Sperreigenschaften der Kombination bestimmend, hingegen wird bei Polymergemengen das Eigenschaftsbild durch die kohärente Phase dominierend beeinflußt. Bei “ verpackten” Kunststoffen, das sind Polymergemenge, bei denen die kohärente Phase nur einen kleinen Gewichtsanteil der Gesamtprobe ausmacht und in Polyederstruktur vorliegt, wird die Phase in Überschuß wie die Gaskomponente in einem geschlossenzelligen Schaum verpackt. Sowohl in solchen Gemengen als auch in Schäumen wird die kohärente Polyederphase eigenschaftsbestimmend. Für die Biomedizin sind Polymergemenge aus Polyelektrolyten mit sehr spezifischer Morphologie von Interesse. Über ihr Quell‐ und Permeationsverhalten schlagen sie eine Brücke zu den Biomembranen, so daß die Behauptung, daß Diffusion, Löslichkeit und Permeation niedrigmolekularer Verbindungen in Polymeren lebensnotwendig sind, nicht übertrieben ist.
Physikalische Grundlagen des Energie‐ und Ladungstransports in eindimensionalen Systemen
Authors: Sixl Hans
Published: September 2012

Mit diesem Beitrag soll in die Physik des Energie‐ und Ladungstransports eingeführt werden. Als Modellsubstanz zum Studium der elektronischen Eigenschaften in Theorie und Experiment dienen niederdimensionale organische und anorganische Festkörper. Im Mittelpunkt stehen die lokalisierten und delokalisierten elektronischen Anregungszustände in kristallinen Festkörpern, ihr Energieniveauschema und ihre Bandstruktur mit Schwerpunkt auf freie Ladungsträger (Elektronen und Löcher) und Exzitonenzustände (Mott‐Wannier, Frenkel). Der kohärente und inkohärente Energie‐ und Ladungstransport, der durch das Wellenmodell und das Hüpfmodell beschrieben wird, sowie die dafür verantwortlichen Wechselwirkungen werden diskutiert.
A kinetic study of the formation of aluminium formate in aqueous solution
Authors: Rauh Hannelore , Knoche Wilhelm
Published: September 2012

The formation of the aluminium formate complex has been studied using chemical relaxation and stopped‐flow techniques. The results are explained by the Eigen‐Tamm two‐step association mechanism. The outer‐sphere and inner‐sphere stability constants are determined to be K0 = (60 ± 15) dm3 mol−1 and Ki = 6 ± 1 at 25°C. The rate constant for the formation of the innersphere complex is found to be k23 = (9 ± 1)s−1.
Redoxkinetik von Metallkomplexen in nichtwäßrigen Lösungen VI. Die Reduktion der Acetylacetonate des Mn(III) und Co(III) mit Fe(II) in Propandiol‐1,2‐carbonat
Authors: Schmid R.
Published: September 2012

Die Elektronenübertragung von Fe(DMF)2+6 auf M(acac)3 in PDC erfolgt intramolekular in einem zweikernigen Zwischenprodukt (acac)2M‐acac‐Fe(DMF)2+5 dessen Bildung durch M(acac)2, eines der primären Reaktionsprodukte, katalysiert wird (M = Co, Mn). Der autokatalytische Effekt von M(acac)2 wird durch überschüssiges M(acac)3 gehemmt. Die Übertragung von Acetylacetonat‐Ionen von M(acac)2 auf Fe(acac)2+ erfolgt schneller als die Dissoziation des primären Zwischenprodukts. In einem zweiten Reaktionsabschnitt dissoziiert ein weiteres Zwischenprodukt M‐acac‐Fe(acac)2+2 in die Endprodukte M2+ und Fe(acac)3. Diese Reaktion wird durch vom Eisen(II)‐solvat stammenden DMF‐Molekülen katalysiert. ‐ Außerdem wird ein Mechanismus für die Ligandentauschreaktion von Mn(acac)3 mit Fe(DMF)3+6 in PDC vorgeschlagen.
On the micellation kinetics of sodium‐decylsulphate
Authors: Diekmann Stephan
Published: September 2012

The kinetics of micellation of sodium‐decylsulphate (NaDeS) in aqueous solutions were investigated using the ultrasonic relaxation technique for the fast relaxation process and the pressure‐jump technique with conductivity detection for the slow relaxation process. No relaxation process was found below the critical micelle concentration. The ultrasonic measurements give a hint to the existence of a third very fast relaxation process. The dependence of the relaxation time and amplitude of both processes on the NaDeS‐concentration are discussed.
Rate measurements for the reactions H + I2→ HI + I and H + HI → H2+ I by Lyman‐α‐fluorescence
Authors: Lorenz K. , Wagner H. Gg. , Zellner R.
Published: September 2012

Rate constants for the reactions of hydrogen atoms with I2(k1) and HI(k2) have been determined in a discharge flow system using the detection of H‐atoms by Lyman‐α resonance fluorescence. Temperature dependent measurements in the range 250–420 K for H + I2show an extremely weak variation with temperaturek1,(H + I2) = (6.6 ± 3) 10−10exp(‐20 K/T) cm3/molecule · s. which is equally well represented by the temperature independent expressionk1, = (6 ± 2.5) 10−10cm3/molecule · s. — From rate measurements for H + HI in the range 250–370 K the Arrhenius expressionk2(H + HI) = (7.4 ± 2.0) 10−11exp(‐290 K/T) cm3/molecule · s is obtained.