摘要:

AbstractThe nature of relativistic effects in the electronic structure of atoms and molecules is explained and an account of theoretical methods for relativistic calculations in a quantum‐mechanical framework is given. The focus is on the requirement of reducing the number of degrees of freedom in the theory in order to obtain computationally efficient and still highly accurate approximations. Some applications illustrating the relativistic effects in coinage metal atoms and molecules are discusse

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010102

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

年代:1997

数据来源: WILEY

摘要:

AbstractTwo‐dimensional cuts through one‐electron density matrices of three ionic solids in the position representation were calculated from restricted Hartree–Fock wavefunctions. The basis‐set quality was assessed by comparison of calculated Compton profiles/reciprocal form factors with experimental ones. The off‐diagonal regions of the density matrix contain the main information about chemical bonding in the crystal. The decomposition of the total density matrix into band contributions shows that the valence band always dominates in those regions. Furthermore, one‐electron density matrices of small subunits of the crystal and of symmetrically orthogonalised crystal wavefunctions were calculated. Their similarity and differences with respect to the solid ar

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010103

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

年代:1997

数据来源: WILEY

摘要:

AbstractIn a sequence of papers we will systematically address the problem of mass and charge transport through boundaries from the standpoint of irreversible thermodynamics and kinetics. Special emphasis is put on the transport through space charge regions. As a model material we consider a binary crystal (MX1+δ) exhibiting ionic and/or electronic conduction and thus allowing for changes in the nonstoichiometry as well. A typical situation is a mixed conductor sandwiched between two partially reversible electrodes. The boundaries are assumed to be morphologically stable. Driving forces considered are differences in chemical and/or electrical potential. They are assumed to be sufficiently small to allow for a linear response treatment. No reference to ad hoc assumptions such as the local electroneutrality condition is made. We also allow for compositional changes in the material. The continuum approach will be presented in the framework of linear irreversible thermodynamics. The introduction of virtual electric fields significantly facilitates the formalism with respect to electrochemical relationships, boundary conditions and analytical treatment. The instationary state will be formally tackled in Fourier space. A conceptual discretisation is generally of advantage – in particular in cases in which the continuum problem can only be solved numerically – since it takes account of the atomistic situation in a kinetic framework. This paper sets out the fundamental equations which will be applied to specific examples. One application already reveals quantitatively the important result that space charge regions necessarily appear in weakly disordered materials during a chemical diffusion even if one starts from a space – charge free initial situation. The steady state concentration profiles are d

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010104

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

年代:1997

数据来源: WILEY

摘要:

AbstractAfter adding cationic dyes like oxazine 170, malachite green, and crystal violet to a solution of colloidal silver sometimes an absorption band appears at wavelengths>750 nm which is neither caused by the monomeric dye nor by a coagulation of the colloid. Based on electrochemical measurements this new absorption band is assigned to a chinhydron‐like adsorption geometry of the dye. Usually this band is only observed at low concentration of the dye, whereas at higher concentration the formation of H‐aggregates occurs. There seems to be a relationship between the intensity of this band and the SERS activ

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010105

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

年代:1997

数据来源: WILEY

摘要:

AbstractA theoretical investigation of potentiostatic polarization processes in mixed conductors with arbitrary electronic transport numbers has been performed. As the potentiostatic polarization is accompanied by a chemical diffusion process inside the mixed conductor located between blocking electrodes, Fick's second law of diffusion has been solved for asymmetric electrochemical cells in order to obtain concentration profiles of the mobile species, current‐time relationships and the impedance of the asymmetric cell. Ohmic interfacial resistances as well as the ohmic bulk resistance owing to the total conductivity of the mixed conductor are considered. The theoretical results reveal that chemical diffusion processes in mixed conductors with comparable ionic and electronic conductivities show non‐Cottrell behaviour resulting in non‐Cottrell type current‐time relationships. These relations allow the exact description of the short‐time behaviour of potentiostatic diffusion processes occurring during chronoamperometric measurements. In addition, the non‐Cottrell behaviour of potentiostatic processes in mixed conductors with arbitrary electronic transport numbers employed in symmetric electrochemical cells i

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010106

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

年代:1997

数据来源: WILEY

摘要:

AbstractA deep cathodic polarization has been applied to a Platinum/Polycrystalline Yttria Stabilized Zirconia interface under low oxygen pressure. In the temperature range 973–1273 K the Electromotive Force recorded after the current cut off did not show any rest potential at a level corresponding to nucleation of a zirconium metal phase, likely because such process is kinetically unfavoured with respect to that of formation of intermetallic phases, whose stability introduces a limitation of the local oxygen chemical potential depression.Two rest potentials were found at less negative potentials which levels correspond to intermetallic phases which very high stability can be accounted for d–d orbitals bonding, as described by the Engel‐Brewer correlation.In some EMF decays it was observed the occurrence of a third rest potential, located at ∼ −450 mV (reference pure oxygen) that could be attributed to a transitory presence of a Pt

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010107

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe device constituted by two past electrodes: ferrocene and orthochloranil at fixed current potentiometry, can be used as a good sensor for the in‐situ determination of phosphoric acid concentration (2.0–14.7 M). Good agreement was observed regarding the values obtained with our method and the spectrophotometric values in synthetic phosphoric media. Different factors affecting the variation of potential at imposed current such as current intensity, temperature, stirring rate of solution and H+ ion concentrations are studied. The potential variations measured by our device between ferrocene and orthochloranil electrodes have the same values as those obtained by the voltamperometric curves. A new acidity functionRi(H), which represents the determination of the H+ activity has been introduced and compared to StrehlowRo(H) and HammetHofunctions. A good agreement has been observed between theRo(H) andRi(H) functi

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010108

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe structure of ion clusters have been calculated for the nonrestricted primitive model in the low density limit. The investigated systems are symmetric with respect to the charge but not with respect to the ion diameter. The influence of the size ratio on the ion cluster structure has been investigated as a function of the temperature for cluster ranging from the dimer to the octamer. In a certain range of ion diameter ratios all structural results are independent of the size ratio. Outside this range both quantitative and qualitative have been found depending on the cluster size. Comparisons with experimentally obtained cluster structures taken from the literature have been accomplished. Furthermore the temperature dependence of the numerically obtained structural properties have been fitted to analytical functions.

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010109

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

年代:1997

数据来源: WILEY

摘要:

AbstractWe perform computer simulations of methane in a slit shaped graphite pore using the molecular dynamics technique. From the equilibrium density profile across the pore we determine the adsorption isotherms in the pressure range between 20 and 200 bar for the two temperatures −20° and 50°C. The simulated surface excess concentration is found to be in good agreement with the experim

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010110

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe results of Monte Carlo simulation for adsorption of linear trimers from their mixtures with monomers on homogeneous and heterogeneous surfaces are analysed. The lattice model of the liquid mixture is used. The different surface topographies (strip‐like and chess‐board) are considered. An influence of surface topography, size of homogeneous patches and molecular interactions on adsorption and orientational ordering in the mixed fluid near the boundary plane is discus

ISSN:0005-9021    

DOI:10.1002/bbpc.19971010111

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

年代:1997

数据来源: WILEY