摘要:

The reaction of adiabatic electron transfer in a polar solvent with two relaxation periods is studied. The dynamics of the process is described by a stochastic non-Markovian equation with memory. This equation reduces to a system of two Markovian equations. Calculations of the rate constant within the framework of generalized transition-state theory (equivalent to the Grote-Hynes theory) are not satisfactory if the relaxation periods differ greatly. The non-equilibrium rate constant is obtained by reducing the appropriate Fokker-Planck equation to the Sumi-Marcus equation. Various kinetic regimes are examined for the latter equation, depending on the ratio of relaxation periods. Rate constants are estimated for the reactions of outer-sphere electron transfer in aliphatic alcohols.

ISSN:0026-8976    

DOI:10.1080/00268979000101911

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A novel solid-state deuteron NMR method for spectroscopic imaging is presented. It employs information about molecular orientation and dynamics obtained from broad2H-NMR lineshapes governed by the anisotropic quadrupole interaction without sacrificing spatial resolution. To this end, double-quantum coherence is created, which is independent of the strength of the quadrupole coupling. In a Fourier-imaging scheme magnetic-field gradients are applied for spatial encoding during the evolution of double-quantum coherence. In the detection period single-quantum coherence is recorded, providing a spectroscopic dimension with a wide-line spectrum. Its lineshape contains spatially resolved information about molecular orientation and dynamics. Experimental results are presented for orientation imaging of drawn polyethylene and molecular-dynamics imaging in a composite sample of glassy polystyrene and glassy polycarbonate, where the two species can be discriminated based on both the NMR lineshape and the spin-lattice relaxation timeT1.

ISSN:0026-8976    

DOI:10.1080/00268979000101921

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Second-order perturbation theory is applied to a Stockmayer fluid to obtain its static dielectric constant over a range of temperatures, densities and dipole moments. A discrepancy in the literature, associated with this calculation, is identified and explained. An explanation is also provided for the fact that the theory predicts the dielectric constant accurately for low to moderately high dipole moments, while it is very inaccurate in its prediction of angular structure.

ISSN:0026-8976    

DOI:10.1080/00268979000101931

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We present results, for three different temperatures, of a Monte Carlo simulation of the equilibrium electrical response of the inner region of the electrical double layer. The model chosen for the inner layer is a hexagonal monolayer of two-state point dipoles. The dipole-dipole interactions of all dipoles are calculated exactly within the full computation cell. We compare extrapolated simulation results with previous Monte Carlo results in which the dipole-dipole interactions were restricted to nearest neighbours. We find a significant difference between these two treatments of the dipole-dipole interaction and show that dipole-dipole interactions beyond nearest neighbours should not be neglected.

ISSN:0026-8976    

DOI:10.1080/00268979000101941

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Using the transient hot-wire method, thermal conductivity and heat capacity per unit volume are measured for solid and liquid phases and glassy crystal states of cyclooctanol, and information is provided on the phase diagram under high pressure. A new solid phase (III) is detected and characterized as a normal crystal phase, whereas all other solid phases (I, II, IV, V) are characterized as plastic crystal phases. We find evidence that the plastic crystal phases I, II and IV could each be the source for a distinct glassy crystal state. It is argued for phase II that its possession of both a low thermal conductivity and a low dielectric permittivity could be accounted for by assuming restricted reorientational motion of the molecules. The unusual (although small) decrease of thermal conductivity observed through the glassy to plastic crystal transitions may indicate that phonons can couple to reorientational motion in the plastic crystal phases I, II and IV.

ISSN:0026-8976    

DOI:10.1080/00268979000101951

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We present molecular-dynamics simulation results for the equation of state of one-component fluids containing freely jointed hard chains of lengths 2, 4, 8, 16 and 32, and compare these results with the predictions of the generalized Florydimer theory. In addition, we present the predictions of a modification to the generalized Flory-dimer theory which uses accurate values for the exclusion volumes of hard chains. Using a Monte Carlo integration technique, we obtain the conformationally averaged exclusion volumes, mean-squared radii of gyration and mean-squared end-to-end distances of isolated freely jointed hard chains of lengths 3, 4, 5, 6, 7, 8, 15, 16, 17, 31, 32, 33 and 64. This modification to the generalized Flory-dimer theory improves the agreement with simulation results for the longer chains at high densities, but has negligible effect at intermediate densities.

ISSN:0026-8976    

DOI:10.1080/00268979000101961

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We study a system of hard parallel cylinders in the framework of the smoothed-density approximation (SDA). Using a bifurcation analysis, we argue that, apart from the nematic phase, smectic-A, solid (or crystalline smectic-B) and columnar phases should also occur in this system. We predict the following sequence of phase transitions: nematic-smectic-A at η* = η/ηcp= 0·31, smectic-A-solid (or smectic-B) at η* ≈ 0·59 and solid (or smectic-B)-columnar at η* ≈ 0·84, where ηcp= 0·9069 is the close-packing density. In our approach we cannot distinguish between a solid phase and a crystalline smectic-B phase.

ISSN:0026-8976    

DOI:10.1080/00268979000101971

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Clusters containing the K+or Cl-ion at the centre with 14 or 26 water molecules are investigated by means of computer experiments. For two models of water, the profiles for atomic density, the local energy per molecule, the normal component of the pressure tensor, the polarization vector, the volume and molecular polarizabilities, the local electric potential and the electric field affecting a water molecule are obtained. The most probable configurations of water molecules in the hydration shells are studied in detail. The lifetime τ of a molecule in the first hydration shell and the coefficients of the normal (transversal),DN, and tangential (longitudinal),DT, self-diffusion are estimated. The size dependence of the cluster properties is considered. The grand potential of a liquid cluster around an ion is calculated. The thermodynamic conclusion regarding the difference in the work of formation of clusters on oppositely charged cores is verified.

ISSN:0026-8976    

DOI:10.1080/00268979000101981

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Computer simulations by the molecular-dynamics method are used to study the physical properties of liquid water. Two three-point-charge models (SPC and TIPS) are analysed and compared using the Ewald-Kornfeld summation method to calculate long-range electrostatic interactions. Although these two models are not very different considering their geometry and energy parameters, they lead to different physical properties of liquid water. Simulations with the SPC water model and the Ewald-summation method are then used as a reference against which different termination functions for Coulombic interactions are compared. The largest discrepancies between simulations performed using the truncated potentials combined with termination functions and those performed using the non-truncated one occur in the radial distribution functions and in the diffusion coefficients. The origin of these discrepancies is analysed and it is shown that the termination function of the form 1 - 2(r/rc)n+ (r/rc)2nwithn= 1 provides results most resembling those obtained using the Ewald summation.

ISSN:0026-8976    

DOI:10.1080/00268979000101991

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268979000102001

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor