摘要:

AbstractThe dynamics of unimolecular dissociation of small polyatomic molecules is discussed in the light of exact quantum mechanical calculations. The central quantities are vibrational resonances, that is quasi‐bound states embedded in the continuum. The main concepts are illustrated with two prototypes, HCO and HNO, both in their ground electronic states. While HCO is a system with an extremely low density of states, a mostly regular internal vibrational dynamics and a ‘tight’ transition state, HNO has a higher density of states, behaves more chaotically and has a ‘loose’ transition state. In both cases the resonance widths and hence the dissociation rates strongly fluctuate, as functions of energy, about the average. In addition to the rates, the final state distributions of the products and their relationship to the dynamics beyond the transition state are also discussed in detail. These systems are well suited to elucidate the contrast between state‐ and mode‐specificity in molecular breakup. An essential aspect is the test of approximations like classical mechanics and stati

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020402

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

年代:1998

数据来源: WILEY

摘要:

AbstractKossel rings of colloidal dispersions obtained with colloids at rest and under flowing conditions are described. When flowing only Kossel rings of planes with a component in the direction of the flow do not vanish. Compared with the dispersion at rest the number of Kossel rings of the dispersions under flow is reduced. Experimental examples are presented.

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020403

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

年代:1998

数据来源: WILEY

摘要:

AbstractStatistical mechanical calculations with the extended reference interaction site model (XRISM) and Monte Carlo simulations are performed on fluid CF4. The parameters of a five‐center (12‐6) Lennard Jones potential with added point charges are deduced. The results are compared with total atom pair correlation functions recently determined by neutron diffraction experiments at three supercritical densities. Apart from the good agreement between experimental and theoretical results, we found that depending on the method used, different potentials are able to describe the investigated system. The atom pair correlation functions and angular distribution functions indicate a completely disordered arrangement of the molecules in fluid CF4with no significant short‐range orientational order except for very close distances. The comparison of the results with former Reverse Monte Carlo (RMC) simulations allows the conclusion that the RMC method is an effective tool, equivalent to the well established Monte Carlo and XRISM methods, in determining the microscopic structure of fluid CF4, but without the exact knowledge of intermolecular poten

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020404

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe quasielastic neutron scattering from H2O and D2O in harmotome, a natural zeolite with the unit cell content Ba2(AlO2)4(SiO2)12nH2O, has been measured at temperatures between 294 and 423 K with loadings ofn= 2, 4, and 12 water molecules per unit cell. From the observed coherent scattering relaxation times for D‐D correlations from 2 to 11 ps were deduced. Fitting the incoherent quasielastic peaks from H2O to a two‐site jump model yielded residence times of the protons in the range from 4 to 6

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020405

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe magnetic susceptibility χ and the1H‐Knight shiftKHfor the ternary hydrides Pd0.6Ag0.4Hr(0.05 ≤r≤ 0.16), Pd0.7Ag0.3Hr(0.08 ≤r≤ 0.26), and Pd0.936(RE)0.064H0REGd (0.04 ≤r≤ 0.47), Dy (0.06≤r≤0.50), and Lu (0.02 ≤r≤ 0.59) are studied as a function of the hydrogen content\documentclass{article}\pagestyle{empty}\begin{document}$$ r = \frac{{n({{\rm H}})}} {{n({{\rm Me}})}} $$\end{document}using high resolution1H‐NMR spectroscopy. Additionally, the temperature dependence of χ for the hydrogen free host alloys Pd0.936(RE)0.064is measured using a SQUID magnetometer and the local f magnetic moments of Gd and Dy are determined. In all systems considered, χ is decreasing with increasingrandKHis negative and increasing with increasingr.The various contributions to χ andKHare discussed on the basis of augmented spherical wave (ASW) supercel

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020406

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe electronic conductivity of gadolinia doped ceria (Ce0.8Gd0.2O1.8) was measured as a function of oxygen activity (aOz=1 corresponding to a gas with oxygen partial pressurepO2= 1.013 bar) in the range from aOz≈︁101to aO2≈︁10−13for temperatures between 600 and 750°C. The Hebb‐Wagner polarization technique was used with an encapsulated Pt‐microcontact in N2atmosphere and a Cu2O/CuO reference electrode. For instance, a minimum value of 3.10−7S/cm was found for the electronic conductivity at 600°C and an oxygen activity of 9.10−7. The minimum is shifted to higher activity with increasing temperature. The activity dependence of the electronic conductivity in the n‐type and p‐type range agrees well with the theoretically expected values (p‐type range σp≈︁a, n‐type range σn≈︁a). Extrapolation of the measured electronic conductivities, the electrolytic domain boundaries of Gd‐doped CeO2were obtained as log aO2= 13 to log aO2=‐24.7 at 600°C and log aO2=11 to log aO2=‐20.1 at 700°C (the oxygen ion conductivity being 4.05.10−3S/cm at 600°C and 1.29.10−2S/cm at 700°C).The activation energy was determined from the temperature dependence of the electronic conductivity givingEA,e=(2.59±0.07) eV for electrons in the n‐type range andEA,h=(1.16±0.04) eV for the holes in the p‐type rang

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020407

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

年代:1998

数据来源: WILEY

摘要:

AbstractMeasurements of1H,19F, and31P NMR, differential scanning calorimetry (DSC) and X‐ray powder diffraction were carried out in piperidinium hexafluorophosphate ([C5H10NH2]PF6). Three solid phases were observed by DSC in the range from 150 K to the melting point of 517 K. The highest‐temperature phase was determined to form a CsCl‐type cubic lattice with a=6.21(3) Å, Z=1,V=240(4) Å3, and Dx= 1.60(3) Mg m−3. From the NMR measurements in this phase, both cation and anion were revealed to perform self‐diffusion as well as isotropic rotation. These molecular motions and thermal properties indicate that this phase is an ionic pl

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020408

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

年代:1998

数据来源: WILEY

摘要:

AbstractMeasurements of the electrical conductivity, magnetic susceptibility and thermoelectric power have been carried out on liquid Ag‐As2Te3and Ag‐As2Se3systems. The liquid Ag‐As2Te3system exhibits a deep minimum of the electrical conductivity, diamagnetic peak of the magnetic susceptibility and rapid drop of the positive thermoelectric power at the stoichiometric composition of Ag6As2Te3, reflecting the occurrence of the metal‐semiconductor transition. The liquid Ag‐As2Se3system also has the diamagnetic peak of magnetic susceptibility and sign reversion of thermoelectric power near the composition of Ag6As2Se3. However, the electrical conductivity in the selenide system indicates a negative temperature dependence like metals and takes a maximum value at this composition. The observed results have been discussed with the help of the pseudogap model developed by Enderby and Barnes. In this result, the unusual behavior of electrical conductivity in the selenide system has been deduced to be associated with the conduction and valence band edge‐parameters rather than the pseu

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020409

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

年代:1998

数据来源: WILEY

摘要:

AbstractZirconium isotopes were fractionated by liquid‐liquid extraction system using dicyclohexano‐18‐crown‐6. The experimental enrichment factors showed failure from the Bigeleisen‐Mayer approximation, which had been believed since their article of 1947. The nuclear size and shape and the nuclear spin result in the additional isotope effects on the Bigeleisen‐Mayer approximation. The contributions of the nuclear mass and of the field shifts of s‐orbital and d‐orbital to the chemical isotopic enrichment factors were calculated by adding the correction terms onto the Bigeleisen‐Mayer approximation. The scaling factor ratios which represent weight of contributions of the mass effect and the field shift effect in the separation factors were independent of the initial condition of aqueous phase and indicated constant values throughout every condition, while the scaling factors themselves had individual values. The scaling factor of the nuclear spin was also calculated by means of the hyperfine splitting spectra of91Zr;w'=−0.118±0.003. The constant value ofw'showed that the nuclear magnetic field was not disturbed in the chemic

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020410

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe electric conductivity of a suspension of unilamellar lipid vesicles of phosphatidylcholine and phosphatidylglycerol, filled with electrolyte, increases after exposure to external field pulses. The electrolyte efflux through the electropores is described in terms of volume decrease under Maxwell stress at constant membrane surface area. Applying the Hagen‐Poiseuille Ansatz, the exact analytical solution for the kinetics of the electromechanical vesicle deformation is obtained in terms of a LambertW function. The initial and final phases of the volume decrease can be approximated by exponential functions with the time constants τ and 2τ, respectively. It is found that τ is proportional toE2·a9, describing the extreme sensitivity of the deformation to the vesicle radiusain electric field of strengthE.The kinetic analysis yields the membrane bending rigidity κ = 3.0±0.3·10−20J. At the field strengthE= 1.0 MV m−1and in the range of pulse duration 5 ≤tE/ms ≤ 60, the number of water‐permeable electropores is found to beN=35±5 per vesicle of radius rp= 50 nm with mean pore radiusrp=0.9±0.1 nm.The kinetic analysis developed here for vesicles is readily applied to cell membranes, aiming at physicalchemical guidelines to optimize the membrane electroporation techniques for the direct transfer of drugs and gen

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020411

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

年代:1998

数据来源: WILEY