摘要:

AbstractThe following is an investigation on the influence of polyethylenglycol on the two‐dimensional phase transition of 2‐thiohydantoin. The two‐dimensional phase at the interface mercury/aqueous electrolyte has been characterised by measuring the potential as well as the time dependence of the differential capacitance.In the absence of polyethylenglycol, the irreversible phase transition is indicated by a discontinuous change of the capacitance with the potential. The condensed film is formed by two‐dimensional nucleation according to an exponential law and a constant growth rate.However in the presence of polyethylenglycol, the reversible phase transition is connected with a continuous change of the capacitance‐potential dependence. At the state of equilibrium different capacities have been observed. Different equilibrium states also can well be described theoretically as two‐dimensional instantaneous nucleation and growth of 2‐thiohydantoin, too. But in the case of reversible phase transitions of adsorbates a polyethylenglycol induced desorption being proportional to the area of 2‐thiohydantoin centres has t

ISSN:0005-9021    

DOI:10.1002/bbpc.19940981202

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe electrochemical reduction of CO2to CO in aqueous NaClO4solution saturated with CO2, at polycrystalline Ag cathodes was investigated as a function of the potential, temperature and electrolysis duration. A poisoning process has been found to occur in parallel with the CO formation. Building‐up of the surface species closely similar to the detected poison has been observed at a Ag electrode immersed (at open‐circuit) in a solution containing small amounts (10−4mol dm−3) of formaldehyde. A periodic anodic stripping of these inhibiting species was shown to produce stable current densities and faradaic efficiencies of CO over 4 – 5 h electrolysis runs. A tentative reaction pathway for CO2reduction to CO, taking into account the experimentally determined onset potential, is

ISSN:0005-9021    

DOI:10.1002/bbpc.19940981203

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

年代:1994

数据来源: WILEY

摘要:

AbstractSimple expressions for the transport coefficient in the mean spherical approximation (MSA) have been derived. We study the self‐diffusion, conductance and apparent charge of simple electrolytes, where we find good agreement for the concentration dependence. Associated electrolytes are also well described by a natural extension of this theory. The MSA equations extend the concentration range of the chemical model (CM) calculations which, in turn, are a reliable source for the input parameters of the MSA calculation

ISSN:0005-9021    

DOI:10.1002/bbpc.19940981204

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe stability constants of Ag+complexes with macrocyclic diaza‐crown ethers of constant ring size [18], but with different donor atom distributions in the ligand bridges, are strongly dependent upon solvent. The effect of solvent, however, is essentially independent of the ligand involved, and this extends even to bicyclic cryptand ligands. Thus, the stability constants of any one ligand are linearly related to those of the other ligands across a wide range of polar solvents. A more detailed analysis of the results in terms of the free energies of solvation and transfer of the species involved in the complexation reaction shows that, although the dominant influence is normally the solvation of Ag+, specific solvation of either the complexed cation or the free ligand can influence complex stabilities in some cases. Effects due to the former, although relatively weak, are evident in complexes of monocyclic diaza‐ligands in strongly coordinating solvents, such as dimethylformamide and dimethyl sulfoxide, and the latter is quite marked in solvents possessing acidic hydrogen atoms, such as water, methanol, and nitrometh

ISSN:0005-9021    

DOI:10.1002/bbpc.19940981205

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe enthalpies of complexation of Ag+with diaza‐18‐crown ethers containing various combinations of donor atoms have been determined in polar organic solvents using calorimetric and potentiometric techniques. Enthalpies of complexation are also reported for two silver ion cryptates. The results are combined with previously determined free energies of complexation to obtain the corresponding entropies. In dipolar aprotic solvents, the enthalpies of transfer of the complexes are very similar to those of the free ligands, so that changes in enthalpies of complexation are dominated by the enthalpies of solvation of the silver cation. The thermodynamics of ligation, i.e., of complex formation between the gaseous silver ion and the diaza‐crown and cryptand ligands in solution, are calculated and, for the free energies, partitioned into contributions from each of the donor atoms (N, O, and S). Among the aprotic solvents, contributions of oxygen and sulphur atoms in the ligand bridges to the stabilities of diaza‐crown and cryptand complexes are additive and independent of solvent. In methanol, hydrogen bonding between methanol molecules and the free ligands reduces the magnitudes of both the free energies and enthalpies of formation of the silver co

ISSN:0005-9021    

DOI:10.1002/bbpc.19940981206

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe show at the example of noble gases, using the Lennard‐Jones potential to approximate the interactions between the atoms, that the global minimisation of the energy through variation of both the basis vectors of the simulation cell and the relative positions of the atoms within the cell leads to structures that are good candidates for the actual structure of the material. During this optimisation, no restrictions were imposed on size, shape, or symmetry of the simulation cel

ISSN:0005-9021    

DOI:10.1002/bbpc.19940981207

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

年代:1994

数据来源: WILEY

摘要:

AbstractBy pulse FT‐NMR we investigated the resonance of the69Ga isotope with nuclear spinI= 3/2 in single crystals of CdGa2S4, CdGa2Se4, HgGa2S4, and powders of CdGa2S4, CdGa2Se4, ZnGa2S4, ZnGa2Se4, HgGa2S4, and HgGa2Se4. Only the signal of the transitionmI= ‐ 1/2 tomI= + 1/2 was analyzed by its second order shift. In case of crystals we used angular variation to obtain the electric field gradients (EFG). For CdGa2Se4a small difference of the chemical shifts of about 70 ppm was revealed due to the different Ga positions. A characteristic twinning of many crystals was confirmed. Line broadening was different for annealed and quenched crystals and depended very strongly on the orientation of the crystals. This could be assigned to a partially disordered cation sublatt

ISSN:0005-9021    

DOI:10.1002/bbpc.19940981208

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

年代:1994

数据来源: WILEY

摘要:

AbstractMethods for the approximate numerical integration of the time dependent Schrödinger equation with given initial conditions (the initial wave packet) are presented. The methods are based on the Schrödinger representation of the quantum dynamic system. The quantum dynamic equations are transformed into Hamilton‐Jacobi type equations of motion as they occur in multi particle classical dynamics, i.e. standard techniques in molecular dynamics can be applied for the integration. The dynamics of minimum uncertainty Gaussian wave packets in strongly non‐harmonic, nonlinearly coupled oscillators are studied as examples. The numerically exact solutions are compared to time dependent SCF approximations of the wave p

ISSN:0005-9021    

DOI:10.1002/bbpc.19940981209

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

年代:1994

数据来源: WILEY

摘要:

AbstractCompact approximate equations for rovibrational densities of statesρ(E,J) for harmonic oscillator‐rigid rotor molecular systems are derived. Linear molecules, spherical tops, prolate and oblate symmetric tops are considered. Vibrational densities of states are represented by the Whitten‐Rabinovitch approximation which then is convoluted with the contribution from theK‐rotor (for a symmetric top). Likewise, numbers of statesW(E,J) are approximated for prolate symmetric top molecules. The derived expressions allow for quick calculations of specific rate constantsk(E,J) of unimolecular rea

ISSN:0005-9021    

DOI:10.1002/bbpc.19940981210

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe present results of molecular dynamics simulations of water at supercritical conditions that correspond exactly to those of an experimental study performed by Postorino et al. (P. Postorino, R.H. Tromp, M.‐A. Ricci, A.K. Soper, and G.W. Neilson, Nature366, 668 (1993)). The discrepancy between simulation and experiment raised by these authors is partly removed simply by considering corresponding thermodynamic states. The careful analysis of the contributions of neutron scattering experiments on the atomic radial distribution functions of water gives strong evidence that the neutron‐scattering experiment on non‐deuterated water plays a key role in determining the essential features of gOH(r) and gOO(r) and is a potential source of arti

ISSN:0005-9021    

DOI:10.1002/bbpc.19940981211

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

年代:1994

数据来源: WILEY