ISSN:0005-9021    

DOI:10.1002/bbpc.19730770102

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1973

数据来源: WILEY

摘要:

AbstractThe relatively long lived ascorbic acid radical or the ferrihexacyanide anion were produced by a 20 ns pulse of high energy electrons in N2O saturated, 10−3molar solutions of ascorbic acid or ferrohexacyanide anion, respectively. Their cathodic currents at a hanging mercury drop electrode were recorded as function of time in the micro to millisecond range. The analysis of current‐time curves at constant potential was carried out in the same way as in the single potential jump experiments of conventional electrochemistry. Absolute values of the rate constant of the transfer processes could be obtained for various potentials. The transfer coefficient was found to be 0.23 for the ascorbic acid radical and 0.15 for the ferrihexacyanide anion. The exchange current density at the standard potential of the system [Fe(CN)6]3‐[Fe(CN)6]4‐was calculated as 3.5 mA · cm−2at a concentratio

ISSN:0005-9021    

DOI:10.1002/bbpc.19730770103

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1973

数据来源: WILEY

摘要:

AbstractElectrode processes of free radicals formed by a short pulse of high energy electrons are influenced bya) diffusion of the radicals,b) second order disappearance of the radicals,c) hindrance of the transfer reaction.Approximations for the evaluation of polarographic current‐time curves are discussed. The Birk‐Perone approximation developed for flash photo‐polarography is applied to describe the kinetics of electrode processes which have a large transfer rate constant. Experiments are carried out on the oxidation of the radical anions C6H5COCH3and CH3COCH3and on the reduction of CH3COCOCH3(at potentials where the transfer reaction is fast). The second order rate constants for radical‐radical reactions derived from the polarographic current‐time curves agree to within 20% with the optically determined rate constants. The reduction of CH3COCOCH3(at potentials where the rate of the transfer reaction is slow) is investigated as an example for electrode processes which depend on all three effects a), b), and c) mentioned above. The absolute rate constant of the transfer reaction was obtained for various potentials. The transfer coefficient amounts to 0.21 atpH = 6 for the reduction of C

ISSN:0005-9021    

DOI:10.1002/bbpc.19730770104

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1973

数据来源: WILEY

摘要:

AbstractThe ethanol radical was produced in N2O saturated, 2 · 10−3molar aqueous ethanol solutions by a 20 ns pulse of high energy electrons. The anodic current of the radical was recorded as a function of time at various potentials of the mercury electrode and at variouspH‐values of the solution. The concentration of the radical in the bulk of solution as a function of time was simultaneously recorded by optical measurements. Analysis of the data shows that the electrode process is reversible in the 10−5s range atpH>12, i.e. when the base form of the radical is mainly present. Transfer rate constants of more than 1.0 cm s−1are calculated. BelowpH = 12, the electrode process becomes more irreversible with decreasingpH. The kinetics of the oxidation of the acid form of the radical is strongly influenced by its adsorption at the mercury electrode. The influence of electrochemically inactive adsorbed solutes is also investigated: Adsorbed sulfate ions strongly decrease the anodic current at potentials more positive than ‐ 0.5 V. Fluorid ions exert a less pronounced effect. Adsorbed alcohol molecules have a promoting effect on the oxidation of the ethan

ISSN:0005-9021    

DOI:10.1002/bbpc.19730770105

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1973

数据来源: WILEY

摘要:

AbstractMathematical solutions for the polarographic current as a function of time are given for the case of two‐step electrode reactions: R → Ra → P (R: radicals produced homogeneously in solution by a short pulse of high energy electrons; Ra: radical adsorbed at the electrode; P: product of oxidation or reduction). If R is long‐lived or disappears according to first order kinetics, the differential equations involved are amenable to solution. If R disappears by second order kinetics, an explicit solution cannot be given; the solution for first order disappearance, however, may well be applied to such cases at times shorter than the first half‐life time of the radical. The current‐time curves exhibit a maximum whose magnitude and position with respect to time can be expressed in terms of the ratioV=k/k1wherekis the transfer rate constant in s−1and k1the time constant of the disappearance of the radicals in the solution, k1is measured by recording the optical absorption of the radicals as a function of time.The current‐time curves obtained for the oxidation of the ethanol radical at a mercury electrode are described by the above two‐step electrode reaction,kis obtained at different electrode potentials. The transfer coefficient for the oxidation of the ethanol radical

ISSN:0005-9021    

DOI:10.1002/bbpc.19730770106

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1973

数据来源: WILEY

摘要:

AbstractThe temperature dependence of refractive indices of three compensated cholesteric mixtures has been measured using a commercial Abbe‐refractometer. At compensation temperatureTna homeotropic nematic texture was achieved indicated by exchange of ordinary and extraordinary ray and strong increase of birefringence. A comparison is given between nematic and cholesteric birefringence yielding good agreement with the de Vries model of cholesteric structur

ISSN:0005-9021    

DOI:10.1002/bbpc.19730770107

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1973

数据来源: WILEY

摘要:

AbstractNach der Theorie des aktivierten Komplexes werden spezifische Geschwindigkeitskonstantenk(E)für Zerfallsreaktionen bei verschiedenen AnregungsenergienEberechnet. Zur Lokalisierung der Lage aktivierter Komplexe wird das Prinzip des Minimums der Zustandsdichte systematisch angewandt. Wegen der starken Kopplung zwischen Reaktionskoordinate und Molekülrest liegen die aktivierten Komplexe weit vor den Zentrifugalmaxima. Ihre Lage hängt stark von der Anregungsenergie, jedoch nur schwach vom Rotationszustand ab. Bei zu hohen Anregungsenergien existieren aktivierte Komplexe im definierten Sinne nicht mehr. Die Berechnungen vonk(E)stehen in guter Übereinstimmung mit Experimenten zur Photolyse von NO2sowie zur thermischen Dissoziation und Rekombination O + NO  NO2im Hochdruckbe

ISSN:0005-9021    

DOI:10.1002/bbpc.19730770108

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1973

数据来源: WILEY

摘要:

AbstractDie spezifischen Leitfähigkeiten der geschmolzenen Alkalinitrate mit Ausnahme des Cäsiumnitrats wurden in einer Belt‐Apparatur bis 700°C und maximal 55 kbar gemessen. Die Leitfähigkeiten von Natrium‐, Kalium‐ und Rubidiumnitxat zeigen logarithmisch als Funktion des Druckes bei konstanten Temperaturen aufgetragen in einem schmalen Bereich bei mittleren Drücken eine starke Krümmung. In diesem Bereich, der sich mit zunehmender Kationengröße zu niedrigeren Drücken verschiebt, fällt das Aktivierungsvolumen auf etwa die Hälfte seines Niederdruckwertes ab. Bei den gleichen Bedingungen ändert die isochore Aktivierungsenergie, die mit Hilfe extrapolierterPVT‐Daten berechnet wurde, ihre Volumabhängigkeit drastisch. Beim Lithiumnitrat wurden beide Erscheinungen nicht gefunden. Die experimentellen Beobachtungen, die auf einen Wechsel im Mechanismus des Ladungstransports bei hohen Drücken hindeuten, lassen sich qualitativ mit einem von Fürth entwickelten Flüssigkei

ISSN:0005-9021    

DOI:10.1002/bbpc.19730770109

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1973

数据来源: WILEY

摘要:

AbstractThe mixing behavior of the binary systems Pd ‐ H and Pd ‐ B was previously interpreted in terms of three effects:1.The solute atoms H and B, respectively, occupy octahedral sites.2.They donate their valence electrons to the 4d and 5s bands of the palladium, raising its Fermi energy.3.There exists an energy of attraction between the interstitial particles.This model is now applied to the ternary system Pd ‐ B ‐ H. The Fermi energy contribution to the thermodynamic properties is treated strictly as a known function of the total valence electron concentration, which is in agreement with magnetic susceptibility measurements on these systems.The quasichemical approach, which was used to calculate the thermodynamic properties connected with the energy of attraction in the binary systems, is extended to the three‐component system Pd ‐ B ‐ H. In addition to the known energies of attraction between two like particles there appears a third parameter, the energy of attraction between unlike particles.The method is applied to hydrogen absorption measurements on Pd ‐ B alloys. Good fit is obtained with one adjustable parameter, the interaction energy between unlike particles. An interpretation is given for the three energies of attraction in terms of a lowering of the lattice strain energy for nearest neighbor int

ISSN:0005-9021    

DOI:10.1002/bbpc.19730770110

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1973

数据来源: WILEY

摘要:

AbstractThis investigation reports three damping peaks in V caused by dislocation motion constrained by several types of atmospheres. Deformed wires of pure V showed a well‐known damping peak called the α‐peak. This peak is presumed to be caused by depinning of dislocations by an oscillatory stress. Increases in immobile oxygen or nitrogen atoms gradually suppress the peak. Hydrogen, which forms a mobile atmosphere, produces two additional peaks of the Snoek‐Köster type. These latter peaks can result from either externally imposed deformation or from internal deformation produced by misfit of precipitated h

ISSN:0005-9021    

DOI:10.1002/bbpc.19730770111

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1973

数据来源: WILEY