摘要:

AbstractWe present a numerical study of the electronic structure of a simple model of molten salts, with application to alkali halides. The geometry of the model is simulated using the primitive model of charged hard spheres, the electronic structure is described by a tight‐binding Hamiltonian. We study the influence of the topological and Madelung potential disorder on the evolution of the density of states upon melting and the optical absorption, the latter directly comparable to experiments. A population analysis of the cationic conduction band is performed, the results are discussed with respect to the possible formation of dipolar atoms in the corresponding metal‐molten salt soluti

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000202

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

年代:1996

数据来源: WILEY

摘要:

AbstractWe present a numerical study of the electronic properties of simple models of expanded alkali metals. An Anderson‐Hubbard model incorporating on‐site electron‐electron repulsion and liquid‐like disorder is solved within the unrestricted Hartree‐Fock approximation. We focus on the proper determination of the localization properties deciding the metallic or nonmetallic character of the model and on the computation of the electrical conductivity within the random phase model.With a realistic set of parameters we obtain good quantitative agreement with experiments on expanded Cs for i) the density at which the metal‐nonmetal transition occurs and ii) the electrical conductivity throughout the entire density interval accessible by experiments. The transport properties thus computed give additional support to recent claims that the description of liquid expanded metals requires the incorporation of both disorder and interact

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000203

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe aim of this work is to understand how the chain orientational order in monolayers depends on intramolecular connectivity. Therefore monolayers of one‐, two‐, three‐, and four‐chain flexible molecules have been simulated using the Monte Carlo technique. The chains are linked up in the head group region. Three‐ and four‐chain molecules can have both: linear rigid as well as flexible head groups. The simulations were carried out within a lattice model on the simple cubic lattice. Only the excluded volume effect was taken into account. For the calculation of the orientational order we used end‐end vectors of each chain in the molecule and vectors pointing from the centre of mass of the whole molecule to the centre of mass of the head group. If the chains in the molecules have equal lengths the degree of order calculated from end‐end vectors is neither influenced by connectivity in the head group region nor by the flexibility of the head group. The degree of order based on the centre of mass vectors clearly indicates an effect of the intramolecular connectivity and for short chains also an influence of the flexibility of

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000204

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

年代:1996

数据来源: WILEY

摘要:

AbstractOne of the foremost objectives in the search for improved catalysts is the promotion of molecule dissociation, which in many catalytic reactions is the rate limiting step. It is shown that modification of electronic surface states by surface dopants allows to control the dissociation barrier. The relation of this new type of promotion mechanism to the effect of surfactants in metal epitaxy opens a new perspective in the search for both, promoters and surfactants.

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000205

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

年代:1996

数据来源: WILEY

摘要:

AbstractRaman scattering experiments were performed on single optically levitated microparticles. In comparison with bulk experiments an dramatic enhancement of the Raman scattering relative to the fluorescence scattering was observed. Tworeal‐worldsamples, a monomer for use in laser stereolithography and an engine lubricant, were investigated. Furthermore Dioctylphthalat (DOP), doped with fluorescent dye Coumarin 6, was studied by Raman spectroscopy in a droplet chain, on an optically levitated particle and in a cuvette. The combination of Raman spectroscopy and optical levitation could be a new offspring for analytical applications of Raman spectroscopy. Liquid and solid microparticles with a few nanograms in mass can be investigated by this technique with excellent signal‐to‐noise

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000206

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe widely accepted concept of introducing a fictive temperature (Tf) to describe the structural relaxation below the glass transition temperature is transposed to explain the orientational dynamics of nonlinear optical (NLO) active chromophores in poled polymer systems. The influence of different thermal histories on the results of differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC) gives evidence for a direct connection between the structural relaxation as measured by DSC and the relaxation of polar order as measured by TSDC. With the fictive temperature being determined from the DSC experiments it is possible to relate the equilibrium dynamics of the NLO chromophores above the glass transition temperature as determined by dielectric spectroscopy to the nonequilibrium relaxation times of polar order relaxation belowTgover 12 decades in time. The obtained time‐temperature dependence for the relaxation times, based on Scherer's extension of the Adam‐Gibbs theory (AGV), shows a Vogel‐Fulcher behavior aboveTgand an Arrhenius‐like behavior far belowTg. BelowTgthe temperature dependence of the relaxation times of polar order is in excellent agreement with an empirically found modified Vogel‐Fulcher equation, which modeled the relaxation of polar order of different poled polymer systems in an universal manner. The AGV theory further offers a direct approach to introduce the influence of the thermal history on the time‐temperature characteristics of polar order

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000207

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

年代:1996

数据来源: WILEY

摘要:

AbstractA phenomenological description for the formation of cylindrolites in cooperative 2d‐(bio)polymeric systems in terms of the modified normal grain growth concept and stretched exponential kinetics in a linear regime is offered. As the principal result, a linear dependence of the cylindrolite radius as a function of time has been obtained which is in excellent accord with experimental data reporte

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000208

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe photolysis of aerated aqueous solutions of 4‐chlorophenol in the presence of Ru(bpy)2+3and peroxydisulphate has been followed by UV/visible absorption spectroscopy, and reveals a relatively rapid oxidative decomposition of the phenol. Confirmation of the formation of benzoquinone and dihydroxybenzene as the principal products comes from product separation and spectroscopic characterization, HPLC, and TLC. 4‐Chlorocatechol is also produced, while the main inorganic products are shown to be chloride and sulphate ions. Ru(bpy)2+3is regenerated in the reaction scheme, making this an overall catalytic process. Prolonged irradiation leads to further degradation into CO2and HCL. From the study of the kinetics of the reactions and considerations of literature data, a mechanistic scheme is presen

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000209

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe formation of a film at the electrode in aqueous electrolytes with organic ligands is shown. This film is presumed to be an intermediate product in the overall mechanism of the reduction or oxidation of metal ions. It consists of oxide‐hydroxide compounds with mixed conductivity as it takes place in electrolyte with inorganic ligan

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000210

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe viscosity of n‐pentane, n‐heptane and their mixtures has been measured with a capillary flow method between 298 K and the critical temperatures at the saturation vapor pressure. The concentrations studied were 0.259, 0.419 and 0.745 mole fraction of n‐heptane. The maximal error of the experimental values of the viscosity is estimated to be ± 1.2% in the region far from the critical point and ± 5% in the immediate vicinity of the critical point. The viscosity obtained was compared to data by other authors with satisfactory agreement. The validity of the method has been confirmed by the measurement of the viscosity of standard liquids as water and

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000211

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

年代:1996

数据来源: WILEY