ISSN:0005-9021    

DOI:10.1002/bbpc.19790830502

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

年代:1979

数据来源: WILEY

摘要:

AbstractNuclear spin‐lattice relaxation rates and nmr absorption linewidths of1H and7Li in solid LiH have been measured up to 620 C. For both species motional narrowing is observed which is shifted under the influence of MgH2additions in opposite directions. Above 300°C spin‐lattice relaxation is exclusively determined by dipole interactions originating from translational diffusion. The calculated peak relaxation rates are in excellent agreement with the observed ones. ‐ For LiH containing Li2O or small additions of MgH2, the mean jump frequency of hydrogen by far exceeds that of lithium in the whole temperature range. Between 400 and 620°C for LiH in equilibrium with Li2O the mean jump frequencies are given byFor the “pure” material investigated (with an estimated oxygen content of 300 ppm) the activation energy forv(H) is (0.97 ± 0.07) eV. The numerical values ofv(H) andv(Li) are not very sensitive to variations in oxygen content. With large additions of MgH2(>1000 ppm),v(Li) by far exceedsv(H) in the whole temperature range; the activation energy forv(Li) above 250°C is 0.55eV in agreement with results derived from conductivity data for LiH doped with MgH2. — For LiH without MgH2additions, the nmr results are in agreement with diffusion data but deviate from conductivity measurements in temperature dependence and in numerical value. — The present results are interpreted on the basis of Schottky disorder with an enthalpy of formation of 2eV and migration enthalpies of 0.3–0.4eV and 0.55 eV for H−and Li+ions, respectively. Strong association between O2−impurities and anion vacancies must be assumed. With O2−impurities present, the H−jumps by means of associated vacancies probably play an important role for the diffusion process. For this type of diffusion a nmr correlation factor is to be expected which differs by a factor of 0.5 from the corresponding correlation

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830503

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe kinetics of an organic solid‐state reaction is studied by a flash‐photochemical experiment. A set‐up is described which allows the detection of a photoreaction monitoring the change in reflectivity of a polycrystalline sample reacting upon photoinitiation with a laser light pulse. The time scale of the measurement extends from 5 ns to several hundred ms. The topochemical polymerization of two different diacetylenes is investigated measuring the formation of the polymer as a function of time after the initiating light pulse of wavelength λ = 337.1 nm. The first polymer is formed after a timelag of 300 ns. The total conversion per light pulse is less than 1 percent. The time conversion curve is described by an exp √t‐law for virgin samples suggesting a kinetic model which includes a strongly scattering random walk of photo‐excited states to randomly distributed reaction centers as the rate determining factor of the photopolymerization. The average life time of the photoexcited state is 758.5 ps. The overall quantum yield of the polymerization is approximately 10 and the frequency of addition of a monomer unit to a reactive chain end is va,

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830504

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

年代:1979

数据来源: WILEY

摘要:

AbstractCopper phthalocyanine (CuPc) films vacuum‐deposited on SnO2electrodes develop photocurrents by illumination with monochromatic light. Their action spectra reflect the absorption spectrum of the CuPc film. The effect of the thickness of the CuPc film and the illumination direction dependence of photocurrent action spectra are observed. Anodic photocurrents arise from excitons generated near the SnO2/CuPc interface and are consistent with the ordinary dye sensitization scheme. Cathodic photocurrents are attributable to excitons which are generated and dissociate in the bulk of CuPc. Hydroquinone, p‐quinone, and O2act as a reducing or an oxidizing agent. p‐Quinone interacts with CuPc preferentially. Transient behaviors and open circuit photovoltages are also disc

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830505

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

年代:1979

数据来源: WILEY

摘要:

AbstractBy evaluating potential‐shifts and slopes of the anodic polarographic wave which is associated with the azide‐anion oxidation in acetonitrile, standard charge transfer rates for N·3⇌ N3+ e−were determined at graphitic carbon, glassy carbon and platinum electrodes. This standard exchange rate decreases from carbon to platinum by more than an order of magnitude. Furthermore the rate constants for the consecutive irreversible radical‐dimerization (2N·3→ N6) and competing addition reaction to olefinswere evaluated by the same means. Dimerization as well as addition reaction are essentially of heterogeneous nature and are heterogeneously catalyzed at carbon electrodes. They are however of a homogeneous character at platinum electrodes due to a relatively poor adsorbability of azide‐and carbon‐radicals at platinum anodes compared to carbon anodes. — It is this special non‐catalytic nature of platinum anodes which favours typical radical dimerization reactions in Kolbe‐synthesis as well as in anodic radical‐addi

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830506

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

年代:1979

数据来源: WILEY

摘要:

AbstractA phenomenological theory of the photovoltage at a semiconductor/electrolyte interface is proposed. This theory was found to explain well the dependence of the photovoltage on the light intensity. The validity of the theory was proved experimentally. The slope of the curve of the photovoltage plotted against the logarithmic light intensity was found to be inversely proportional to the sum of the transfer coefficient and the corresponding coefficient of the photocurrent, which can explain the dependence of the slope on the kind of electrode and redox system.

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830507

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe formation, reduction, and the properties of “sandwich oxides” of the type metal/oxide 1/oxide 2/electrolyte were investigated by potentiostatic and potentiodynamic techniques, using the system Au/Au2O3/γy‐FeOOH/borate buffer, pH = 7.2.Gold oxide layers (up to 5 Å) were formed by anodic oxidation, the γ‐FeOOH‐layers (up to 200 Å) by anodic deposition from a 10−3M Fe2+‐solution. The two oxide layers could be formed in arbitrary sequence and varied independently in layer thickness. ‐ Kinetic investigations of formation and reduction were completed by capacity and redox measurements. The results are explained by a model of a semi‐conducting γ‐FeOOH‐layer with an underlying i

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830508

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

年代:1979

数据来源: WILEY

摘要:

AbstractESR spectra of a number of methyl‐substituted N‐hydropyridinyl, N, N′‐dihydropyrazinyl, and N, N′‐dihydropyrimidinyl radicals have been measured in solution at room temperature. The radicals were produced by in‐situ photolytic reduction of the parent azaaromatic compounds. The hyperfine coupling constants have been analyzed in terms of the Karplus‐Fraenkel relation and the McConnell‐type relations for the CH, CH3, and NH proton splittings and using the condition for conservation of π‐spin population. Consistent values of the spin polarization parametersQN,QNCN,QHCH, andQHCCH3, but not ofQHNH, were obtained virtually independently of calculated spin populations. Experimental and calculated π‐spin populations have been compared for the N‐protonated azaaromatic radicals from this and other work. There is no correlation between the NH proton coupling constant and the experimental π‐spin population on the nitrogen atom in substituted N‐hydropyridinyl radicals. The non‐transferability of the McConnell‐type parameterQHNHis attributed to a contribution of the out

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830509

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe electronic absorption spectra of trans‐4‐stilbenecarboxylic acid HTSC, its sodium salt NaTSC, [Rh(NH3)5TSC]2+, and [Ir(NH3)5TSC]2+dissolved in different solvents, all show a nearly identical long wavelength absorption band at 319 nm. This band is assigned to the first spin‐allowed (So→ S1)ππ* transition of TSC−and appears as an isolated intraligand chromophore in the complexes. Whereas HTSC and TSC−emit a fluorescence, this emission is completely quenched in the complexes. Not only HTSC, but also [Rh(NH3)5TSC]2+, and [Ir(NH3)5TSC]2+undergo trans/cis photoisomerization of the stilbene moiety upon So→ S1intraligand excitation. While the S1state of the free ligand is assumed to initiate the isomerization, the results support the first triplet (T1) of the coordinated TSC−as the photoactive excited state. In the complexes, the heavy metals seem to induce S1→ T1i

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830510

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

年代:1979

数据来源: WILEY

摘要:

AbstractThe triplet state processes in thioindigo have been investigated with respect to the mechanism of the trans → cis photoisomerization by laser flash photolysis. According to our experimental results the intersystem crossing takes place from the trans singlet to the trans triplet. This is also the only transient, which is detected spectroscopically. An activation energy barrier between the trans‐ and a twisted triplet determines the internal rotation. The twisted triplet decays nonradiatively to the cis and trans groundstates. A model for the mechanism of the trans → cis photoisomerization is proposed. — Preliminary results for the cis → trans photoisomerization indicate an internal rotation in the excited singlet state to a transoid configuration followed by intersystem crossing to the trans triplet from which the molecule decays into the gro

ISSN:0005-9021    

DOI:10.1002/bbpc.19790830511

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

年代:1979

数据来源: WILEY