bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Spectral Sensitization and Supersensitization by Means of the Rotating Ring‐Disk Electrode Technique
Authors: Watanabe Tadashi , Nakao Masashi , Fujishima Akira , Honda Kenichi
Published: July 2012

Rotating ring‐disk electrode (RRDE) technique, using a ZnO single crystal as the disk electrode, was applied to the study of spectral sensitization by rhodamine B (RhB) and supersensitization by hydroquinone (HQ) in acetonitrile. The primary product of spectral sensitization, i. e., RhB radical cation (RhB+·), was detected electrochemically at the Pt ring electrode. Upon addition of HQ to the electrolyte solution, the sensitized photocurrent was enhanced (supersensitization), and concomitantly the collection efficiency for RhB+· at the Pt ring electrode showed a decrease. Assuming that the supersensitization results from the reduction of RhB+· by HQ, the rate constant for this process was calculated to give 106 − 107 M−1 s−1. Taking into account the singlet lifetime of RhB* as well as the rate constant for the quenching of RhB* by HQ, the mechanism of spectral sensitization and supersensitization is discussed.
A Thermodynamic Analysis of Phase Transitions of Crystals with Structural Disorder
Authors: Schmalzried H.
Published: July 2012

Crystals with high point defect disorder exhibit on overexponential increase of their defect dependent properties with temperature, sometimes combined with phase transitions. It is shown that these experimental facts may be interpreted by explicitly taking into account the dependence of the defect formation energy and entropy upon the molar volume of the crystal.
Hydrogen Diffusion through the Semiconductor‐Liquid‐Junction on TiO2 (Rutile) Electrodes
Authors: Schumacher Rolf
Published: July 2012

Reduction of TiO2 (rutile) single crystals with hydrogen at temperatures considerably higher than room temperature leads, in addition to the formation of oxygen vacancies, to crystal structures where hydrogen is chemically bound inside the crystal. Investigations on such crystals have revealed that bound hydrogen becomes sufficiently mobile at temperatures above 450°C so that it can leave the crystal. In contrast to that, the mobility of unbound interstitial hydrogen ions is much higher even at room temperature. It was shown that unbound interstitial hydrogen leaves the crystal by two different mechanisms: above an internal electric field strength, Es, close to the surface of 106 V cm−1 as protons, whereas below that value as atoms.
Charge Transfer across Organic Photoconductor/Insulating Liquid Interfaces. Part II: Metal Free Phthalocyanine/Dodecane Containing Electron Donor/Acceptor Molecules
Authors: Ahuja R. C. , Hauffe K.
Published: July 2012

The phenomenon of charge transfer through the metal free Phthalocyanine/Dodecane interface has been investigated using a transient technique. It is reported that the photoinjected charge, interfacial charge transfer efficiency and overall quantum yield are mainly controlled by the presence of foreign molecules in Dodecane. The effect of about 30 different molecules (electron donor/acceptor) on the relevant parameters is presented. The results are discussed qualitatively and an attempt has been made to correlate the results to the relevant molecular parameters.
Charge Transfer across Organic Photoconductor/Insulating Liquid Interfaces. Part III: Copper Phthalocyanine, Chlorinated Copper Phthalocyanine/Dodecane Containing Electron Acceptor/Donor Additives
Authors: Ahuja R. C. , Hauffe K.
Published: July 2012

The results on the charge transfer processes at the Copper phthalocyanine/Dodecane interfaces are described. The photocharge injection was investigated (using a transient measurement technique) as a function of electric field, intensity and wavelength of light and the nature and concentration of various electron donor/acceptor additives. While CuPC demonstrates positive and negative charge injection, no negative charge injection could be detected with Cl‐CuPC. The photocharge injection follows the order H2PC > CuPC > ClCuPC. The results have been explained qualitatively.
Investigation of the Phase Transition Kinetics Liquid ⇌ Vapour by a Pressure‐jump Relaxation Technique
Authors: Schulze Friedrich‐Wilhelm , Cammenga Heiko K.
Published: July 2012

The construction and performance of an apparatus for the kinetic study of mass transfer processes between gaseous and condensed phases is described. In this method, phase equilibrium is suddenly disturbed by the generation of a pressure jump in the gaseous phase after which the establishment of the new equilibrium state is followed by a sensitive pressure gauge. The application of the method to the kinetics of evaporation and condensation of liquids is described. For water at 20.0°C the evaporation coefficient is found to be α = 1.00 ± 0.037 and the condensation coefficient αc = 0.98 ± 0.067. This is the first unambiguous proof that for resting water α = αc = 1.
Photopolymerization of a Diacetylene‐Phenazine Mixed Crystal
Authors: Braunschweig F. , Bässler H.
Published: July 2012

Photopolymerization of mixed crystals of 2,4‐heptadecadiynoic acid and phenazine was studied under optical excitation of either the phenazine at 420 nm or the diacetylene monomer at 280 nm. Polymer absorption at 514 nm or dark‐ and photoconductivity were used as a probe to continuously monitor product formation. The reaction velocity is constant up to about 10 percent conversion and decreases in a linear fashion for 0.15 ≲ c ≲ 0.4. Consequently, energy transfer from the primarily excited state to polymer molecules must be negligible for c < 0.1. This yields a upper limit of 10−11 s for the lifetime of the optical precursor state which must be of singlet character. At 290 K the quantum efficiencies are E(420) = 0.1 and E(280) = 0.5 for phenazine and diacetylene excitation, respectively. The activation energies for photopolymerization are E(420) = 0.21 ± 0.02 eV and E(280) = 0.17 ± 0.02 eV. E(280) is attributed to chain growth whereas E(420) − E(280) ≈︁ 0.04 eV has to be associated with formation of a chain initiation species as a result of sensitizer excitation. Electron transfer between diacetylene and the excited phenazine is excluded as the rate‐determining step for the sensitized reaction.
Experimentelle Prüfung von approximativen Chiralitätsfunktionen am Beispiel induziert cholesterischer Lösungen: Chirale Methan‐Derivate II
Authors: Richter W. J. , Heggemeier H. , Schrader B. , Krabbe H. J. , Korte E. H.
Published: July 2012

Die induzierten HTP‐Werte von 27 chiralen Methan‐Derivaten, zusammengefaßt in 6 Pentupeln, werden auf ihre Beschreibbarkeit durch approximative Chiralitätsfunktionen untersucht. Der qualitative Aspekt dieser Chiralitätsbeobachtungen wird durch Chiralitätsfunktionen angemessen erfaßt; zur Bestimmung von ligandenspezifischen Parametern sind diese Funktionen nur in wenigen Fällen eine gute Näherung. Als Basis zur Bestimmung des Zusammenhanges von absoluter Konfiguration der Gastmoleküle und dem Vorzeichen des induzierten HTP‐Wertes sind diese Parameter bisher weniger geeignet als das Sequenzregelverfahren.
Molare Entropien von Salzschmelzen zwischen 600 K und 3000 K
Authors: Richter J. , Vreuls W. , Winthagen W.
Published: July 2012

Die molare Entropie geschmolzener Salze einer Gruppe des Periodensystems mit einem gemeinsamen Anion hängt in sehr guter Näherung linear vom Kationenradius ab. Die Extrapolation der molaren Entropie für gegen Null gehenden Kationenradius (rk → 0) liefert den Anteil der molaren Entropie für dieses gemeinsame Anion, aus dem sich mit experimentellen Daten die zugehörigen Kationenanteile der Entropie und weitere Anionenanteile berechnen lassen. Mit diesen Ionenanteilen läßt sich die molare Entropie einer großen Anzahl von geschmolzenen Salzen in einem Temperaturbereich von 600 K bis 3000 K je nach dem Schmelz‐ und Siedepunkt bzw. der Zersetzungstemperatur mit einer Abweichung von etwa 2,5% abschätzen.
Pressure Effect on the Two‐Phase Region and the Electrical Conductivity in Liquid Bi  BiBr3 Mixtures
Authors: Tamura K. , Hoshino H. , Endo H.
Published: July 2012

The pressure variation of the two‐phase region in liquid Bi  BiBr3 mixtures was studied by measuring the conductivity as a function of temperature up to 17 kbar using an internally heated autoclave and a piston‐cylinder apparatus. The retrograde solubility region disappears at about 1.5 kbar. The two‐phase region disappears at about 16 kbar and the liquidus curve with S‐shape appears at about 17 kbar. Around 55 mol‐% Bi the electrical conductivity changes sharply at high pressures where the two‐phase region diminishes.
Physikalisch‐chemische Untersuchungen an geordneten Histon/Polynukleotidkomplexen
Authors: Klump H. , Hütig H.
Published: July 2012

Es ist heute allgemein akzeptiert, daß native DNA in den Chromosomen als hochgeordneter Komplex aus DNA und dem Histonoktamer (H2A, H2B, H3, H4)2 vorliegt. Diese Komplexe können isoliert und aufgereinigt und in einzelne Nukleosomen zerlegt werden. Durch Erhöhung der Ionenstärke läßt sich der Komplex dissoziieren und bei sorgfältiger Erniedrigung der Ionenstärke läßt sich die native Struktur wieder reassoziieren. In dieser Arbeit wird für eine Reihe von Polynukleotiden gezeigt, daß für die Ausbildung der geordneten Histon‐komplexe das Vorhandensein einer doppelhelikalen Struktur, entweder in Form einer DNA‐Helix oder einer RNA‐Helix, ausreichend ist. Einzelsträngige Polynukleotide wie Poly A oder Poly C bilden mit den Histonen keine geordneten Strukturen. Aufgrund der Ergebnisse dieser Untersuchung kann man schließen, daß die Histone ausschließlich zur dichten Packung der DNA in den Chromosomen gebraucht werden.
Temperature‐Dependent Hyperfine Coupling Constants. An ESR Study of Some Substituted N‐Hydropyridinyl Radicals in Solution
Authors: Sander Ulrich , Dohrmann Jürgen K.
Published: July 2012

The hyperfine splittings of the radicals N‐hydro‐4‐methylpyridinyl (1), N‐hydro‐2,6‐dimethylpyridinyl (2), and N‐hydro‐4‐cyanopyridinyl (3) have been measured as a function of temperature in propanol(‐2)/acetone. The temperature coefficients of the NH proton splitting in radicals 1 and 2 are exceptionally large. The temperature‐dependence of the ring proton splittings has been analyzed using the model of localized out‐of‐plane vibrations of the protons. The estimated frequencies are given. The NH proton frequencies, ṽ1, increase in the following order: ṽ1 (2) < ṽ1 (1) < ṽ1, (3). The contributions to the NH proton splitting from out‐of‐plane vibration and σ‐π spin polarization have been determined. A value of — 3.1 ± 0.2 mT is obtained for the spin polarization parameter of the NH bond in the fixed planar structure of the radicals.
Die Adsorption von Benzonitrilen an der Quecksilberelektrode in wasserfreiem Acetonitril
Authors: Wegert H. , Baumgärtel H.
Published: July 2012

Mit Hilfe der phasenselektiven Wechselstrompolarographie wird die Adsorption von Benzonitrilen an einer Quecksilberelektrode in wasserfreiem Acetonitril gemessen. ΔGads, ΔHads und ΔSads des Adsorptionsprozesses werden bestimmt. Das Adsorptionsverhalten von Benzonitrilen wird durch die Langmuir‐Isotherme beschrieben. Durch Substitution von Benzonitril mit CH3‐, CH3O‐ und weiteren Nitrilgruppen kann gezeigt werden, daß das Dipolmoment der Moleküle keinen Einfluß auf deren Adsorptionsverhalten ausübt. Zunehmende π‐Elektronendichte des aromatischen Rings erhöht die Fähigkeit der Moleküle, spezifisch an der Elektrode zu adsorbieren. Es wurde eine lineare Energiebeziehung zwischen der Freien Adsorptionsenthalpie und der Zahl der Substituenten gefunden.
Investigation of the Fluorescence Behaviour and the Primary Step in the Photoreaction of Various 3‐ and 4‐Substituted Sydnones
Authors: Eber G. , Schneider S. , Dörr F.
Published: July 2012

The quantum yields of fluorescence and photochemical reaction, as well as fluorescence decay times of several sydnone derivates were measured in dependence on temperature. It was found that not only the rate of radiationless transitions was temperature dependent but also the one of the radiative decay. Furthermore, evidence is given that the photochemically reactive state is a 3ππ*‐state.
Excess Enthalpies of Liquid α,ω‐Dichloroalkane + n‐Hexane Mixtures. A Group Contribution Study of the Cl  Cl Proximity Effect
Authors: Polo Carmelo , Gutierrez‐Losa Celso , Kechavarz Mohammad‐Reza , Kehiaian Henry V.
Published: July 2012

Enthalpies of mixing at 298.15 K are reported for the following binary mixtures: 1,2‐dichloroethane +, 1,3‐dichloropropane +, 1,4‐dichlorobutane +, 1,5‐dichloropentane +, and 1,6‐dichlorohexane + n‐hexane. — These experimental results, along with literature data on enthalpies of mixing of dichloromethane + n‐hexane or + n‐heptane, 1‐chlorobutane + n‐hexane or + n‐nonane, and 1‐chlorooctane + n‐hexane or + n‐octane, are interpreted in terms of molecular surface interactions between the groups Cl, CH3, and CH2 in the quasichemical approximation. — Comparison of the enthalpy of the Cl/aliphatic‐interchange parameters reveals a decrease of the inter‐molecular interactions with decreasing intramolecular ClCl distance in the various α,ω‐dichloroalkanes (proximity effect).
Der Einfluß von Temperatur und Zusammensetzung auf die Art von Phasenübergängen cholesterischer Flüssigkristalle bis zu Drücken von 2,5 kbar
Authors: Pollmann P. , Scherer G.
Published: July 2012

Seit 1973 ist bekannt (Keyes et al.), daß ein Wechsel der Art eines Phasenübergangs nicht nur durch Variation des Mischungsverhältnisses von Zwei‐Komponenten‐Systemen bei Normaldruck erreicht werden kann, sondern im Fall reiner Stoffe auch durch Anwendung von Druck. — Eigene Untersuchungen an Cholesterylmyristat (CM) und Cholesterylnonanoat (CN) haben jetzt gezeigt, daß der trikritische Punkt der reinen Stoffe bei hohen Drücken für den Phasenübergang smektisch‐A/cholesterisch kontinuierlich gegen die Normaldruckebene durch Zumischen einer geeigneten zweiten Komponente verschoben wird. Auf diese Weise wird eine trikritische Linie gebildet. — Bei der Prüfung der McMillan‐Theorie aufgrund der experimentell erhaltenen reduzierten Temperaturen der trikritischen Punkte — diese haben Werte zwischen 0,83 und 0,96 — ergab sich, daß die Vereinfachung, den Modellparameter δ = 0 (bzw. δ = const.) zu setzen. aufgegeben werden muß. Dazu mußten die Modellgleichungen der McMillan‐Theorie vollständig gelöst werden. — Die Veränderungen der McMillan‐Parameter entlang der trikritischen Linie werden diskutiert. — Die Phasenübergänge smektisch‐A/cholesterisch und cholesterisch isotrop von CM und CN sowie ihrer Mischungen mit p‐Pentylphenyl‐2‐chlor‐4‐(p‐pentylbenzoyloxy)benzoat wurden bis 2,5 kbar bestimmt.
Combined Ruthenium Lead Surface Treatment of Gallium Arsenide Photoanodes
Authors: Heller A. , Lewerenz H. J. , Miller B.
Published: July 2012

An increase in the solar‐to‐electrical conversion efficiency beyond that due to chemisorption of ruthenium results from subsequent adsorption of lead from alkaline solutions on both single crystal and polycrystalline n‐GaAs photoanodes. An efficiency of 7.8% is reached with thin film, chemically vapor deposited polycrystalline GaAs in the cell n‐GaAs/0.8 M K2Se0.1 M K2Se21 M KOH/C.
Electron Transfer through the Space Charge Barrier on TiO2 (Rutile) Electrodes via Interstitial Protons
Authors: Schumacher Rolf
Published: July 2012

It is reported on charge transfer reactions on n‐TiO2 electrodes in electrochemical experiments. The electrodes used were cleaned prior to treatment in oxygen and/or air at room temperature by a standardized procedure with H2SO4. The experiments showed that hydrogen interstitials located close to the electrode surface influence the charge transfer reaction. These states were introduced by the surface reaction with the acid. As the experiments showed the typical feature of the oxidation current peak changed dramatically to an unpronounced shape when using samples loaded with very little unbound hydrogen. Investigations on the influence of electrolyte‐pH on the charge transfer reaction revealed that a potential drop in the depletion region of around 2.1 V is needed to initiate this anodic process. The existence of the anodic peak is discussed in terms of resonance tunneling via states created by the pre‐treatment procedures in the charge barrier and at the surface.
Dielectric Measurements at High Pressures and Low Temperatures. II. The Dielectric Constant of Acetonitrile
Authors: Würflinger A.
Published: July 2012

The dielectric constant of acetonitrile is studied at temperatures between −60°C and +30°C up to pressures of 3 kbar. The electrode set developed is described. The dielectric constant of liquid acetonitrile together with recently determined PVT‐ data allow the calculation of the Kirkwood correlation factor g. This g‐factor decreases on approaching the melting curve to a constant value of approximately 0.7, independent of the pressure. On freezing the dielectric constant falls off from 49 to about 4 at atmospheric pressure and from 45.5 to about 4 at 3 kbar. In the solid state the dielectric constant is fairly independent of temperature and pressure, however, a small change is observed at a lower solid‐solid transition.
Study of a Fluid/Solid Interface over a Wide Density Range Including the Critical Region. I. Surface Excess of Ethylene/Graphite
Authors: Specovius J. , Findenegg G. H.
Published: July 2012

The surface excess amount of ethylene adsorbed on graphitised carbon black has been measured over a pressure range from 1 to 120 bar using a high pressure microbalance technique. The data span a range of temperatures from 263 to 323 K (0.93 ≤ T/Tc ≤ 1.14) and a range of bulk densities up to ρ/ρc=1.7. The results show the transition from the low‐temperature behavior (T < Tc) with multilayer adsorption on approaching the saturation pressure, to the situation above the critical temperature Tc when the surface excess isotherms Γσ(P) exhibit a pronounced maximum at a pressure Pmax > Pc. The dependence of Pmax on temperature, and the variation of Γσ with temperature along the critical isochore, is determined quantitatively. The surface excess is discussed in terms of an operationally defined exponential density profile of the fluid at the interface. The dependence of the decay length of this profile on the bulk density and on temperature is shown.
Der Isotopieeffekt bei der Verdampfung von Ammoniumchlorid
Authors: Virnich H.‐H. , Höpfner A.
Published: July 2012

Normales und deuteriertes Ammoniumchlorid zeigt bei seiner irreversiblen Verdampfung recht unterschiedliche Verdampfungsgeschwindigkeiten. Je nach Verdampfungstemperatur wurde im Verhältnis der Sublimationsraten eine bis zu 10fach gesteigerte Verdampfung des normalen Salzes gegenüber der deuterierten Substanz beobachtet. — Eine theoretische Deutung dieses Phänomens kann im Rahmen eines Modells gefunden werden, in welchem der geschwindigkeitsbestimmende Schritt in der an die Kristalloberfläche gebundenen Dissoziation von Ammoniumchlorid zu Ammoniak und Chlorwasserstoff gesehen wird. Dies befindet sich im Einklang mit der seit längerem bekannten Tatsache, daß der Dampf von Salmiak aus den genannten Komponenten besteht. — Die am Modell in harmonischer Oszillator‐Approximation entwickelten Rechnungen liefern für beide Substanzen mit den Experimenten übereinstimmende Aktivierungsenergien.
Rotational Diffusion Tensor of Cyclohexene Molecule Determined from Selective Measurements of T1
Authors: Pajak Z. , Latanowicz L. , Jurga K.
Published: July 2012

Performed analysis of the experimental data obtained from selectively measured proton spin‐lattice relaxation times T1 for cyclohexene solutions in carbon tetrachloride at various temperatures is shown to be a method for determining the rotational diffusion coefficients of the molecule, treated as a symmetrical top since Ix ≅ Iy ≠ Iz. The evidenced anisotropy of the rotational motion is of a gas‐like nature — the reorientation about the axis of the greatest moment of inertia i. e. the symmetry axis of the diffusion tensor is the slowest and has the largest activation energy. The rotational diffusion model with small‐angle reorientations describes adequately the motional behaviour. The values of the rotational diffusion coefficients obtained for the neat liquid at room temperature D‖ = 8.3 · 1010 s−1 and D⟂ = 13.9 · 1010 s−1 are in agreement with calculations based on the modified Nora Hill model.
On the Approach to Steady States of Reacting Systems in the Continuous Stirred Tank Reactor
Authors: Heinrichs M. , Schneider F. W.
Published: July 2012

A theoretical investigation is presented of the approach of chemical reactions to their steady states in a continuous stirred tank reactor (CSTR). We define a approach time tϵ which is a measure of the time required for any perturbation to decrease below a certain value where ϵ = 1/e is a convenient choice for linear networks. We shown analytically for any first order network that the approach time is less than or equal to the average residence time but never longer regardless whether „overshoot”︁ or „false start”︁ occurs if the sum of the initial CSTR concentrations does not exceed the sum of the input concentrations. For higher order single step CSTR reactions we present analytical solutions for small perturbations from their steady states. We show that the longest relaxation time is equal to the average residence time for all non‐autocatalytic higher order reactions in the CSTR. For autocatalytic reactions, however, the relaxation time constant in the CSTR may become infinite at critical flow rates. This interesting phenomenon is called critical slowing down and it has an analogy in second order equilibrium phase transitions. We show that critical slowing down may occur also in higher order autocatalysis. It may act as a tunable low pass filter i.e. the open autocatalytic reaction may resemble a kinetic buffer system that absorbs even large perturbations. As illustrations a number of examples of reaction types are presented.
Crystal Structure and Phase Transformation of Trichloroethylidene Trichlorolactic Ester (Chloralide), Cl3CCHOCOCHOCCl3. An X‐Ray and NQR Study
Authors: Hashimoto M. , Paulus H. , Weiss Alarich
Published: July 2012

Trichloroethylidene trichlorolactic ester (Chloralide), Cl3CCHOCOCHOCCl3, crystallizes at room temperature (T ≈︁ 298 K) monoclinic, space group C52h — P21/c, with 4 molecules in the unit cell. The lattice constants are a = (619.94 ± 0.20) pm, b = (1716.3 ± 0.6) pm, c = (1037.0 ± 0.3) pm, β = 95.083° ± 0.010°. The crystal structure was determined with a reliability factor R = 0.044 (1638 symmetry independent reflexes with I > σ(I)). At 343 ≦ T/K ≦ 344 a phase transformation occurs, which shows super heating phenomena. — In the 35Cl‐NQR the 6 line low temperature spectrum 38.178 ≦ v/MHz ≦ 40.178 at T = 77 K is in accordance with the crystal structure. By intensity considerations an assignment of the spectrum of the two different CCl3 groups in the molecule was possible. The high temperature phase of Chloralide shows the fade out phenomenon in the NQR‐spectrum due to hindered rotations of one of the two CCl3 groups. The kinetics of the transformation phase II → phase I is of first order.
Analytische Diskussion des Austauschs von Kohlendioxid zwischen Atmosphäre und Ozean an Hand eines Advektions‐Diffusions‐Modells
Authors: Kohlmaier G. H. , Siré E. O. , Kratz G. , Fischbach U. , Bröhl H.
Published: July 2012

Eine analytische Behandlung des Kohlenstoffaustauschs zwischen der Atmosphäre und der Oberflächenschicht des Meeres sowie zwischen dieser und der Tiefsee wird vorgestellt. Anhand der daraus gewonnenen Ergebnisse wird diskutiert, inwieweit die Festlandbiota (im Rahmen der bisher konstruierten Ozeanmodelle) als Quelle oder als Senke für zusätzliches atmosphärisches CO2 in Frage kommen. Außerdem werden die Auswirkungen verschiedener Szenarien des fossilen Kohlenstoffinputs auf den CO2‐Gehalt der Atmosphäre für die nächsten Jahrzehnte abgeschätzt.
Thermodynamic investigations of Ag2Se
Authors: Oehsen U. V. , Schmalzried H.
Published: July 2012

With the help of coulometric titrations, using the solid state galvanic cell Ag/Ag4RbI5/Ag2+δSe/C between 75°C and 190°C, the following parameters have been determined in addition to the phase diagram: Point defect concentrations, Fermi‐level and width of band gap, effective mass of electrons and holes, partial molar enthalpies and entropies of electrons.
Density, viscosity, and electrical conductivity of acidic AICI3 ‐ LiCl ‐ NaCl melts
Authors: Carpio Ronald A. , Kibler Fred C. , King Lowell A. , Brockner W. , Tørklep Knut , Øye Harald A.
Published: July 2012

Densities, viscosities, and specific conductivities were measured for ternary AlCl3‐LiCl‐NaCl melts in the range 0.5 ≤ XAlCl3 ≤ 0.8, 0 < XLiCl/(XLiCl + XNaCl) < 1. In addition, specific conductivities were measured for AlCl3 ‐ NaCl binary melts. The behavior of molar volume, viscosity, and equivalent conductivity of the ternary melts was rationalized in terms of a shift in the equilibrium 2Al2Cl−7 ⇄ 2AlCl−4 + Al2Cl6 as the composition of the ternary is changed, as well as a stronger interaction between Li+ and AlCl4− than between Na+ and AlCl−4.
Desaktivierungsverhalten von Arenen und Heteroarenen XIX. Die Temperatur‐ und Lösungsmittelabhängigkeit der Desaktivierung des Benzo[g]chinolins
Authors: Bendig J. , Henkel B. , Kreysig D.
Published: July 2012

The energetic lowest excited singlet and triplet states, the quantum yields of fluorescence, intersystem crossing, and internal conversion, the singlet life times, the fluorescence anisotropy and the dipol moments of the ground and the excited states of benzo[g]quinoline are determined. The dependence of the fluorescence quantum yield on temperature is attributed to a thermal activated deactivation process of the first excited singlet state by intersystem crossing. Considering a contribution of temperature independent radiationless deactivation this temperature dependence obeys the Arrhenius equation. ‐ At increasing acceptor behaviour and ET‐values of the solvent the activation energy of temperature dependent intersystem crossing is increasing too. A linear relationship between the experimental determined activation energies and the solvent parameter (ET + b · NA), (NA = Acceptor number, b = 8.3 J · mol−1), is obtained. The rate constants of the temperature dependent intersystem crossing process are different in the cases of investigated solvents and correlate with the above‐mentioned solvent parameter, provided heavy atomes are absent. These results are explained by the different solvation of S1 (π π*‐character) and T3 (π π*‐with partial nπ*‐character). — At 77 K no phosphorescence can be observed (øp ≤ 0.01). It follows that the temperature independent intersystem crossing process is negligible. — The quantum yields of internal conversion decrease at increasing solvent parameter. This fact is attributed to the weaker coupling of the S1 (π π*) and S2 (n π*) states in the case of increasing energy distance and, connected with this, smaller Franck‐Condon‐factors of the internal conversion.
Electrolytic separation of ions of different valency by ion‐exchange membranes
Authors: Chakravarti A. , Langer P. , Wiedner G. , Bojadzijev Z.
Published: July 2012

The transport properties through a cation‐exchange membrane were investigated for ions of different valency, using an electric field as driving force. In agreement with theoretical considerations a distinct preference of the higher valent ions was found.
Solid‐liquid equilibria in n‐alkylbenzene + n‐alkane mixtures. A group contribution study of phase diagrams
Authors: Kehiaian Henry V. , Guieu Raymond , Faradjzadeh Abolhassan , Carbonnel Luce
Published: July 2012

The solid‐liquid equilibrium diagrams of following 11 binary systems were determined: benzene, toluene, ethylbenzene, n‐propylbenzene, and n‐butylbenzene + n‐heptane or n‐tetradecane and benzene + n‐dodecane. All these diagrams could be calculated accurately (maximum deviation ca. 1 K) in terms of the group‐contribution theory (in the random mixing approximation) developed by Kehiaian et al. [7], which is essentially the surface version of the Guggenheim‐Barker lattice theory. Most interchange parameters were identical to those derived previously [7, 31, 33] from experimental data (liquid‐vapor equilibria, excess enthalpies, excess heat capacities). Where experimental data were lacking, the parameters were estimated and finely adjusted to the observed equilibrium diagrams.
Termination rates by time‐resolved ESR. The N‐hydro‐4‐acetylpyridinyl radical in solution
Authors: Krohn Holger , Leuschner Rainer , Dohrmann Jürgen K.
Published: July 2012

The second‐order rate constants for the self‐termination reaction of the N‐hydro‐4‐acetylpyridinyl radical in propanol(‐2) and propanol(‐2) acetone have been measured by time‐resolved ESR during intermittent photolysis. The radical was generated from 4‐acetylpyridine via different photochemical reactions. The rate constants were measured in the temperature range ‐10 to 26°C. The frequency factor and the activation energy from the Arrhenius plot are (1.1 ± 0.4) · 1010M−1· s−1and 16.6 ± 0.6 kJ · mol−1, respectively. The Arrhenius parameters were independent of the solvent composition and the method of radical generation. The termination reaction is attributed to the formation of the respective pinacol by the combination of two radicals. The reaction rate is not diffusion‐controlled. Possible mechanisms are proposed and discussed.
Mechanism of the reaction of H atoms with methanol
Authors: Hoyermann K. , Sievert R. , Wagner H. Gg.
Published: July 2012

The reactions of normal and deuterated methanols with H/D atoms have been studied in an isothermal discharge flow reactor (500 ≤ T(K) ≤ 680) at low pressures (2–8 mbar). Samples were withdrawn by a molecular beam sampling system directly into the ion source of a mass spectrometer. Concentration measurements with calibration procedures and the knowledge of secondary radical + atom reactions establish the reaction route

The reaction route

was found to be negligible (ratio of efficiencies (I)/(II) > 10). ‐ The rate constants for the reactions H + CH3OH, H + CD3OH, and H + CD3OD were measured in the temperature range 500‐680 K, leading to

.
Pressure induced reorientation and aggregation of pheophytin in monomolecular layers
Authors: Fischer A. , Heithier H. , Knoll W. , Möhwald H.
Published: July 2012

Monomolecular layers of pheophytin were investigated by absorption spectroscopy, by thermodynamic, and by light‐ and electron microscopical measurements. — It is shown, that a pressure increase induces reorientations of the porphyrin rings. At pressures above a critical value pk pheophytin aggregates in an arrangement with coplanar stacking of the porphyrin rings. Size and shape of the aggregates are determined microscopically. The diameters amount to 2 μm, the thickness to 500 Å. — The results prove the stability of the monolayers for pressures below pk = 15 dyn/cm and the existence of instable phases at higher pressures.
Component self‐diffusion in liquid binary solutions
Authors: Hawlicka E. , Reimschüssel W.
Published: July 2012

Component self‐diffusion coefficients in solutions: n‐hexane‐cyclohexane, n‐hexane‐benzene, benzene‐nitrobenzene, and n‐hexane‐nitrobenzene have been determined as a temperature function over the entire composition range. The activation energies of component self‐diffusion have been calculated. The excess self‐diffusion coefficients as a useful way to determine a solution structure have been discussed.
Cyclische Voltammetrie an dünnen Elektrolyt‐ und Chemisorptionsschichten beim Vorliegen eines reversiblen Semichinon‐ und Dimerenbildungsgleichgewichts
Authors: Huck H.
Published: July 2012

The paper presents the derivation of equations for the determination of semiquinone formation and dimerization constants from the half peak width and the peak distance of a double peak by means of thin layer and adsorbat voltammetry. As an experimental example flavin adenine dinucleotide adsorbed on a roughened glassy carbon electrode was chosen, for which a semiquinone formation constant of 2.6 (0.77 in solution) was found at pH 7.
Zum Mechanismus der Induktionsperioden bei der Oxidation N‐substituierter p‐Phenylendiamine
Authors: Nickel Ulrich
Published: July 2012

The appearance of induction periods when oxidizing p‐phenylene diamines may be due to different reasons. In acidified aqueous solution distinct induction periods are observed for the formation of semiquinonediimine as well as quinonediimine with nearly all oxidizing agents employed. In this case primary oxidation is very slow because of the low concentration of oxidizable unprotonated p‐phenylenediamine. After the formation of some semiquinonediimine which is unprotonated, however, its subsequent oxidation accelerates the reaction in an autocatalytic way. Under different conditions of reaction either formation of quinonediimine or semiquinonediimine is retarded. Certain foreign substances give rise to a significant shortening or prolongation of the induction period, although the actual oxidation reaction is not noticeably. The different mechanisms are discussed and the reaction rates for the autocatalytic reaction are presented for some redox systems.
Thermodynamics of Al — Si and Al — Ge — Si liquid alloys: Enthalpies of formation by high temperature calorimetry
Authors: Bros J. P. , Eslami H. , Gaune P.
Published: July 2012

The enthalpies of formation of Al — Si and Al — Ge — Si liquid alloys were investigated by high temperature calorimetry. A new mixing and stirring device was designed in order to take into account the physicochemical properties of the metals involved. — The enthalpy of formation of the ternary alloys were found satisfactory using the Kohler's equation; the quasi‐ideality assumption for the binary Ge — Si revealed verified within the experimental accuracy.
Evidence of Hydrophobic Effects from Critical Phenomena
Authors: Pelger M. , Klein H. , Woermann D.
Published: July 2012

Data of the temperature dependence of partial molar quantities (heat capacity and temperature derivative of partial molar volume) of perfluoromethylcyclohexane and carbon tetrachloride in a mixture of critical composition are reported. It is found that for both components the signs of the critical amplitudes of the partial molar quantities are positive. Using these data a thermodynamic relation between the critical amplitudes of specific head capacity, partial molar heat capacity, temperature derivative of specific volume and temperature derivative of partial molar volume is tested. — Analogous experiments on the system isobutyric acid/water give results which are characteristically different: (1) the sign of the critical amplitude of the partial molar heat capacity of isobutyric acid is positive whereas that of water is negative, (2) the opposite is true for the sign of the critical amplitude of the temperature derivative of the partial molar volume of the two components. The characteristics of the system isobutyric acid/water are interpreted by assuming that in a critical mixture, approaching the critical point from the one fluid phase region, the extent of hydrogen bonding between water molecules in the vicinity of the hydrophobic part of isobutyric acid molecules increases with decreasing temperature difference from the critical temperature.
Unusual Thermodynamic and Electrical Properties of Metallic Solutions Near the Critical Point of the Almost Pure Solvent
Authors: Schönherr G. , Hensel F.
Published: July 2012

The paper presents experimental results of the electrical conductivity σ, the equation of state data and different related properties such as excess volumes of mixingVExand partial molar volumes V̄Infor dilute amalgams of In as a function of pressurep. temperatureTand compositionXInto 2700 bar, 1900 K and 2.85 at‐% In, respectively. Particular attention is given to the behaviour of these properties in the metal‐nonmetal transition range and close to the critical point of pure Hg. It is found that the divergence of the compressibility χTof pure Hg at the critical point is reflected in the behaviour ofVEx, V̄Inand in the concentration dependenceof the conductivity. The limiting values of the negative partial molar volume V̄Inand offor infinitely dilute solutions become extremely large as the critical point of pure Hg is approached. — An attempt is made to separate the different effects of temperature, volume and concentration and to analyze the data in terms of existing models for the electrical transport in expanded Hg and the critical behaviour of fluid dilute solutions.
Thermodynamische Messungen der Bindungsenthalpien kleiner Liganden mit Nukleinsäuren I. Anlagerung von Ethidiumbromid an DNA und Apurinsäure
Authors: Burkart W. , Klump H.
Published: July 2012

The enthalpy of binding of ethidiumbromide (EB) to double‐ and single‐stranded DNA of two different species and to apurinic acid has been measured by means of an isothermal mixing calorimeter. Equilibrium dialysis served as a tool to determine the extent of binding of EB. — At 5, 20, and 35 °C the binding enthalpies were −20.3, ‐23,6, and −33.5 kJ/mol EB, respectively, for the binding to single‐stranded calf‐thymus DNA (ssCT) in SSC‐buffer and −21.4, 28.5, −36.4 kJ/mol EB for the binding to dsCT. In a tenfold diluted buffer the values were ‐39.4, −62.8, −72.0 kJ/mol EB for ssCT and −21.4, −30.8, and 36.0 kJ/mol EB for dsCT.
Thermodynamische Messungen der Bindungsenthalpie kleiner Liganden mit Nukleinsäuren II. Anlagerung von Oligopeptiden an DNA
Authors: Burkart W. , Klump H.
Published: July 2012

The enthalpy of binding of different amines and oligopeptides to double‐ and single‐stranded DNA has been measured by means of an isoperibolic mixing calorimeter. Measurements were performed in diluted Citrate buffer at 25 °C. The binding of the peptides to double‐stranded DNA did not result in any measurable enthalpy change (except LysTrpLys), binding of the peptides could be demonstrated by equilibrium techniques. Binding to single‐stranded DNA yielded enthalpies up to ‐30 kJ/mol of peptide bound. The binding enthalpy of some of the peptides depends markedly of the degree of binding, which has been determined by equilibrium dialysis
The Viscosity of Mixtures of Hydrogen with Three Noble Gases
Authors: Clifford A. A. , Kestin J. , Wakeham W. A.
Published: July 2012

The paper reports new absolute measurements of the viscosity of hydrogen and its binary, gaseous mixtures with neon, argon and krypton at 25 °C and 35 °C and at a pressure of 0.1 MPa. The measurements were carried out in a high‐precision oscillating‐disk viscometer and their accuracy is estimated as one of ±0.2%. — The results have been compared with predictions based on recent intermolecular pair potentials for the interactions of hydrogen with the monatomic gases derived from spectroscopic and molecular beam studies. The calculations, which have been carried out with second‐order kinetic theory expressions, are not entirely consistent with the experimental results. The experimental results have been employed to determine binary diffusion coefficients for the three systems. The viscosity data have also been employed to predict the thermal conductivity of the mixtures with the aid of the most accurate kinetic theory formulae available for systems containing polyatomic components. A comparison with accurate thermal conductivity data indicates that the equations, which are first‐order approximations, are not sufficiently accurate for systems containing components of widely disparate mass.
Spectral Sensitization of ZnO Film Electrodes by the J‐Aggregate of Cyanine Dyes
Authors: Hada H. , Yonezawa Y. , Inaba H.
Published: July 2012

Magnetron sputtered ZnO film electrodes were sensitized to visible light by using the J‐aggregates of four cyanine dyes. Both the sensitized anodic and cathodic photocurrents are observed but the magnitude of them considerably changes according to the kind of dyes employed. The action spectra of both photocurrents are fairly in accord with each other, not to speak of a distinct J‐band. Characteristics of carrier injection from the J‐aggregates are discussed.
Neutron Scattering Study on Three Different Phases of Toluene Adsorbed on Graphite Surfaces
Authors: Monkenbusch M. , Stockmeyer R.
Published: July 2012

The structure and dynamics of toluene layers adsorbed on microcrystalline graphite have been investigated by thermal neutron scattering. The structure determination by diffraction from a C6D5—CD3 layer reveals three different phases at temperatures between 40 K and 200 K. — We observed a registered 3 × 3 structure below 70 K, an incommensurate phase in the temperature interval between 70 K and 140 K and a fluid phase above 140 K. — The dynamics has been studied by inelastic incoherent scattering due to the protons of a C6H5 — CH3 (C6H5 — CD3) layer. The fluid phase shows quasielastic scattering, at 200 K the effective diffusion coefficients have been determined as D1 = 4 · 10−5 cm2/s for the ring protons and D2 = 2 · 10−4 cm2/s for the CH3 protons. The registered 3 × 3 phase shows a spectrum with features as expected from the corresponding data from 3‐dim. toluene crystals. The incommensurate phase exhibits a pseudo quasielastic scattering, which has been attributed to the scattering intensity from a 2D‐Debye solid in the low frequency region.
Investigation of Photoinduced Bond Cleavage by Time‐Resolved Resonance Raman Spectroscopy
Authors: Hub W. , Melzig M. , Schneider S. , Dörr F.
Published: July 2012

The photochromic behaviour of 2,3,4,4‐Tetrachloro‐1‐oxo‐1, 4‐dihydronaphthalene (“β‐TKN”) was studied by means of time‐resolved resonance raman spectroscopy in various solvents. It is shown that the results confirm the interpretation of a photoinduced homolytic rather than the one of a heterolytic cleavage of a C‐Cl bond, leading to the 2,3,4‐Trichloronaphthoxyl‐radical as the colored species.
Time‐Resolved Resonance Raman Spectroscopy: Excited Triplet States of Biological Polyenes
Authors: Wilbrandt R. , Jensen N.‐H.
Published: July 2012

In this paper we give an account of our studies of the excited triplet states of the biological polyenes all‐trans‐retinal, all‐trans‐β‐carotene and canthaxanthin by time‐resolved resonance Raman spectroscopy. The spectra indicate increased π‐electron delocalisation and twisting of inner double bonds of these molecules in their relaxed triplet states. The results on canthaxanthin, which are discussed in length, indicate an additional isomerisation equilibrium involving the cyclic end groups.
Transport Properties of Liquids I. Self‐Diffusion, Viscosity and Density of Nearly Spherical and Disk Like Molecules in the Pure Liquid Phase
Authors: Vogel Herbert , Weiss Alarich
Published: July 2012

Self‐diffusion coefficientD, viscositynand densitypof nearly spherical molecules (Tetraalkyl‐, Tetraalkoxy compounds) and of nearly disk like molecules (crown ethers) were measured (250 ≦T/K< 370). ‐1H‐NMR spin‐echo spectroscopy was applied for the measurements ofD. nwas determined via a Ubbelohde micro‐viscosimeter andpvia a vibrating densimeter. ‐Dandnfollow the Stokes‐Einstein‐Gierer‐Wirtz relation. The free‐volume theory of Cohen and Turnbull (CT) was applied to describe the experimental data quantitatively. By introducing geometrical relations for the mean free path λ and the critical free volumev*fthe CT‐model was extended and applied to the experimental results. Thereby a very satisfactory description of the measurements is attained.Dof the substances investigated can be calculated as function of the melting point andp (T). Empirically the temperature dependence ofD (T)follow an Arrhenius law. Application of the hybrid equation of Macedo and Litovitz to the experimental data shows that the temperature dependence of the transport properties in van‐der‐Waals liquids composed of spherical or disk like molecules is mainly determined by the creation of the free volume with increasing temperature.
Raman Spectrometric Investigation of the Molecular Structure of Alcohols; Conformational Dynamics of Ethanol
Authors: Richter W. , Schiel D.
Published: July 2012

The Raman scattering profiles of the OH stretching vibrations of methanol, ethanol, and n‐propanol in the gas phase and of ethanol in alkane solution are measured and analyzed with regard to the conformational behaviour of the molecules. — The fine structure of the profiles is largely resolved because rotational motions do not appreciably contribute to the band width as the scattering tensor is almost isotropic. In the case of ethanol, the assignment of the two sub‐bands to the trans and gauche conformers follows from the intensity ratio. An assignment to the five possible conformers is proposed for the complex profile structure of propanol. A weak satellite on the high frequency wing of the methanol profile can be assigned to a vibrational transition in the first excited torsional state. — Quantitative information on the conformational dynamics can be gained from the temperature dependence of the ethanol profile observed in solution. By applying a theoretical consideration used in NMR spectrometry to explain the dependence of the spectra on molecular dynamics to the present problem on vibrational spectrometry, the following values of the trans ⇌ gauche transition rate are determined: (3.6 ± 0.6) · 1010 s−1 at 20°C and (9.0 ± 1.5) · 1010 s−1 at 137°C.
Temperature and Viscosity Effects on an Excited State Equilibrium as Revealed from the Dual Fluorescence of Very Dilute Solutions of 1‐Dimethylamino‐4‐cyanonaphthalene
Authors: Ayuk Atu Ausaji , Rettig W. , Lippert E.
Published: July 2012

It is shown that polar solutions of 1‐dimethylamino‐4‐cyanonaphthalene display dual fluorescence, closely related to that of p‐dimethylaminobenzonitrile. — The kinetic model introduced by Grabowski et al. has been used. This involves a temperature dependent excited state equilibrium, B → A, which is responsible for the characteristic maximum observed for the fluorescence quantum yield ratio ϕA/ϕB as a function of temperature. — With the help of the degree of polarization of the short wavelength fluorescence band, FB, as a function of temperature, an inversion of the 1La and 1Lb fluorescent states is shown to occur in propylene glycol at room temperature. This fluorescence level inversion is assumed to arise from reorientation effects of the solvent molecules. — The long wavelength fluorescence band, FA, is emitted from a third state which is formed via an adiabatic photoreaction along a reaction coordinate involving solvent reorientation as well as solute geometrical relaxation (intramolecular twisting).
Formation and Fate of NH(X3Σ−) in the Pulsed Vacuum UV Photolysis of NH3
Authors: Zetzsch C. , Stuhl F.
Published: July 2012

The formation of NH(X3Σ‐) from the pulsed vacuum uv photolysis (λ > 105 nm) of NH3 was investigated. Using resonance fluorescence detection the kinetics of NH was studied at room temperature. NH could be observed for up to 2 s; the efficiency of removal of NH by collisions with the walls of the reactor is estimated to be of the order of 10−4. A reaction of NH with its parent molecule NH3 or with N2 was not detected. Upper limits for the rate constants of the reactions magnified image.
Analyses of Vibrational Progressions in Luminescence Spectra of Platinum‐Group d6Complexes
Authors: Eyring Gerd , Schmidtke Hans‐Herbert
Published: July 2012

Low temperature (10 K) luminescence spectra of powder samples and single crystals of various Rh(III), Ir(III), and Pt(IV) complexes have been recorded. Some of these show vibrational fine structure which is explained by several progressions arising from different promoting modes. Band analyses carried out by decomposing the emission profile into a series of lorentzian or gaussian distributions lead to accepting mode frequencies which match frequencies in vibrational spectra. By comparing intensity distributions in the progressions with theoretical line shape functions from recent vibronic theories, some optical and geometrical parameters pertaining to the excited electronic states (potential minima shifts, changes in oscillator frequencies with respect to the ground state) have been calculated. For this analysis the quality of the vibrational resolution is of importance. Broad band vibronic spectra which cannot be resolved at low temperature can also be used to a certain degree for determining excited state properties. The results obtained from simple models seem to agree well with the data obtained from the narrow line spectra.