ISSN:0005-9021    

DOI:10.1002/bbpc.199500016

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

年代:1995

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.199500017

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

年代:1995

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.199500020

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

年代:1995

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.199500021

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

年代:1995

数据来源: WILEY

摘要:

AbstractAn overview over currently available methods for the calculation of NMR chemical shifts is given. After a brief discussion of the basis aspects, i.e. definition of the shielding tensor and gauge‐origin problem in the calculation of magnetic properties, recently developed methods for calculating NMR chemical shifts based on electron‐correlated quantum chemical approaches will be discussed. The importance of electron correlation effects for the accurate determination of absolute shielding constants and relative shifts is demonstrated and the accuracy of various approaches assessed by a careful comparison with experiment, before a few representative applications will be presented. In case of the carboranes C2B3H5and C2B3H7, electron‐correlated calculations were essential to resolve discrepancies between SCF calculations and experiment, while for the vinyl‐substituted vinyl cations CH2= C+–CH = CHCH3correlated NMR chemical shift calculations – but not the SCF calculations – allow the unequivocal assignment of the measured13C signals to the Z and E isomers formed in superacid solutions. Finally, an outlook with respect to pending problems in the area of NMR chemical shift calculat

ISSN:0005-9021    

DOI:10.1002/bbpc.199500022

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

年代:1995

数据来源: WILEY

摘要:

AbstractTemperature dependences of NMR spin‐lattice relaxation timesT1, of15N,14N,85Rb and87Rb, spin‐spin relaxation timesT2of14N and87Rb, and NMR spectra of15N and87Rb in RbNO, were observed in the plastic phase (Phase 1) and the low‐temperature phase (Phase II) obtainable below 264 K. We showed the presence of a new NO−2motion in Phase II with an activation energy of 12‐ 15 kJ mol−1. This motion was assigned to NO−2reorientation about its C2‐axis by referring to the temperature dependence of the15N chemical‐shift anisotropy and the reported data of the dielectric dispersion. In the plastic phase, we detected the NO−2isotropic reorientation with an activation energy of 6.2 kJ mol−1and the ionic self‐diffusion with 110 kJ mol−1, which was confirmed by measurin

ISSN:0005-9021    

DOI:10.1002/bbpc.199500023

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

年代:1995

数据来源: WILEY

摘要:

AbstractA complete set of thermodynamic functions was determined for the palladium‐rich solid solution and for the intermetallic compounds Pd5Nd, Pd3Nd, Pd2Nd, Pd4Nd3, and PdNd from electromotive force measurements between 700 and 800°C. A CaF2single crystal was employed as the solid electrolyte. The activity of Nd in Pd‐rich alloys shows pronounced negative deviations from Raoult's law with a relative partial excess Gibbs energy of Nd at infinite dilution of −305 kJ/mol. Two effects are discussed to account for the non‐ideal properties of the solid solution: the transfer of the valence electrons of Nd to the electron gas of the alloy and the lattice distortion brought about by the size difference of the components. Remarkably exothermic values were obtained for the heats of formation of the intermetallic compounds. The results are compared with predictions of the Miede

ISSN:0005-9021    

DOI:10.1002/bbpc.199500024

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

年代:1995

数据来源: WILEY

摘要:

AbstractElectronic properties of passive films (d≤20 nm) on single grains of polycrystalline Titanium were investigated by micro‐ellipsometry and electrochemical methods using photoresist microelectrodes with defined areas. A number of experimental improvements are reported here: i) The minimisation of the electrochemical active area down to 3×10−6cm2, ii) the determination of the crystallographic orientation of single grains by anisotropy microellipsometry, as well as iii) the determination of local film thicknesses under potentiostatic control by in‐situ micro‐ellipsometry. iv) The capacity C of the microelectrodes was measured applying a new droplet technique. Anodisation of Ti single grains up to the same potentialUyields different oxide thicknesses, anodic charges, donor densities and oxygen evolution. Thin passive layers need less anodic chargeqOxfor the oxide formation and have a higher donor densityNd. The great extent of oxygen evolution at these grains can be explained by an increased tunnel probability for the transition to the conduction band. The properties vary with the substrate orientation in a systematic manner, indicating a change of the properties at the (0111) o

ISSN:0005-9021    

DOI:10.1002/bbpc.199500025

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

年代:1995

数据来源: WILEY

摘要:

AbstractDiffusion layer imaging (DLI), time‐resolved spectroelectrochemical methods and electrochemical impedance spectroscopy (EIS) were applied to determine the influence of the solvent and the supporting electrolyte on reaction parameters for the benzophenone/benzophenone radical anion redox couple (BP/BP*−) formed at a Hg‐covered Au wire in aprotic solvents.Results are reported for the solvents acetonitrile (AN) and N,N‐dimethylformamide (DMF) using two different tetraalkylammonium salts as supporting electrolytes. Heterogeneous rate constants for the electron transfer reaction and diffusion coefficients of the neutral BP and the radical anion BP*−obtained with the different methods are discussed and

ISSN:0005-9021    

DOI:10.1002/bbpc.199500026

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

年代:1995

数据来源: WILEY

摘要:

AbstractNetwork approach has been used to analyse the electrical properties of a system consisting of three ionic species having different charges in contact with blocking electrodes. A network model for the electrodiffusion process taking place in such a system has been proposed. With this model and the electric circuit simulation program PSPICE, the transient response of the system to a step‐function applied potential difference and the small‐signal ac response of this system subject to a steady external voltage bias have been simulated. Nyquist plots for the electrochemical impedance, and the time evolution of the surface charge density stored in the electrical double layers at the electrode/electrolyte interfaces as well as the electric current density through the system, are given. The ionic concentration, the electric charge density, and the electric potential profiles across the cell were also obtained as a function of t

ISSN:0005-9021    

DOI:10.1002/bbpc.199500027

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

年代:1995

数据来源: WILEY