ISSN:0026-8976    

DOI:10.1080/00268979609484523

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268979609484524

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268979609484525

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Off-lattice, freely rotating hard rods are a reasonable representation of certain lyotropic liquid crystalline systems. The translational ordering of these rods is compared with that of rods which can point along only one of the three coordinate axes and that of rods on a lattice, using bifurcation analysis of a free energy expression truncated at the second virial coefficient level. Whereas off-lattice freely rotating hard rods form a smectic phase, long rods on a lattice form a columnar phase. Even for off-lattice rods, restricting their orientations changes their behaviour qualitatively, at least if the rods are very long. Disc-like molecules are shown to be affected similarly by the imposition of a lattice. In general, it is not possible to study translationally ordered, liquid-crystalline phases of off-lattice systems by examining their lattice analogues.

ISSN:0026-8976    

DOI:10.1080/00268979609484526

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Die magnetochemischen, optischen und magnetooptischen Eigenschaften von (COT)Pr[HB(Me2pz)3] wurden sowohl bei Raumtemperatur als auch bei tiefen Temperaturen bestimmt. Insbesondere die Absorptions- und Lumineszenzspektren deuten darauf hin, daß die f-Elektronen einem dominanten Kristallfeld (KF) der Symmetrie C8vsowie einem trigonalen Störfeld, das bevorzugt durch den KF-ParameterB66berücksichtigt werden kann, ausgesetzt sind. Auf der Grundlage der optischen Spektren wurde das zugrundeliegende KF-Aufspaltungsmuster abgeleitet und durch Anpassung der offenen Parameter eines empirischen Hamilton-Operators simuliert. Bei 35 Zuordnungen wurde eine RMS-Abweichung von 28 cm−1erzielt. Die erhaltenen Parameter werden diskutiert und mit den Voraussagen früherer Modellrechnungen verglichen.

ISSN:0026-8976    

DOI:10.1080/00268979609484527

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

An extension of the pseudo grand canonical method of Mehta and Kofke to the direct simulation of two-phase coexistence is proposed. The new method samples an ensemble very closely related to the Gibbs ensemble but no longer employs particle transfer moves. Rather, the volumes of the two sub-systems are altered to mimic particle transfer. Convergence of the densities is guided by evaluation of the compressibility factor and chemical potential. The strength of the proposed method is that there is no restriction on how this is achieved. The method is illustrated by application to liquid-vapour equilibria in a cut and shifted Lennard-Jones 12,6 fluid. The liquid-vapour coexistence results compare favourably with existing Gibbs simulation results. The ensembles probed by pseudo grand canonical and pseudo Gibbs methods are discussed. Both methods might be applied most effectively to phase coexistence in dense phases or systems with internal degrees of freedom.

ISSN:0026-8976    

DOI:10.1080/00268979609484528

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The charge-transfer complex formation between iodine as an acceptor and mesitylene as a donor has been investigated using Raman spectroscopy. The iodine was dissolved in dilute (1–2·5 volume%) mixtures of the donor in n-heptane used as an inert solvent. The kinetics of the complex were simulated with a two-state Markov process model for the Raman line-shape of the free iodine-complexed iodine system. The model is formulated on the basis of the theories of Kubo, Gordon and Strauss. The reactive part of the profile can be separated out from the total line-shape using iterative convolution of the Kubo-Gordon line-shape function with a reference spectrum measured at zero donor concentration. The results show that the iodine-mesitylene complex obeys a two-state model well. The lifetime of the complex at 300 K, calculated from the iteratively determined best-fit line-shape function, is 21+10−5ps.

ISSN:0026-8976    

DOI:10.1080/00268979609484529

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The spectral region of the F band of SO2was investigated in crossed supersonic jet and laser beams under conditions of low rotational temperatures. Eight major vibronic bands were identified within the region and their fluorescence spectra were selectively excited and measured. In each spectrum, the relative intensities of the vibrational resonance transitions, particularly for the (n,0,0)″ progressions, were found to change considerably when measured after different time delays following the exciting laser pulse. This indicated efficient collision-induced relaxation processes among the upper vibronic levels, which accounted for the unusual very strong transition into the (1,0,0)″ level. The non-resonance background fluorescence spectrum, which becomes present at the high rovibronic temperatures, was also investigated and discussed in the light of our findings.

ISSN:0026-8976    

DOI:10.1080/00268979609484530

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A two-component model of dimerizing hard spheres in contact with a penetrable hard surface is studied. The associative interaction between the bulk fluid particles and between one of the bulk species and the hard surface is taken in the form of a square-well interaction. The model is studied by means of Monte Carlo simulations. The density profiles of the particles, the distribution of the centres of mass of the dimers, and the number densities of dimers and particles bonded with the surface are calculated. The effect of the strength of the associative interactions and the bonding distance between the bulk fluid particles and the surface is investigated. The adsorption of the adsorbed species is affected appreciably by the strength of the associative bond with the surface. The distance of this surface-molecule well from the surface affects the average orientation of the adsorbed dimers and so mimics orientationally specific association. Simple singlet theories are not very successful when there is associative adsorption or, for that matter, when the interaction with the surface is anything other than a hard repulsion.

ISSN:0026-8976    

DOI:10.1080/00268979609484531

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Molecular dynamics simulations have been carried out of rigid and dynamic solid near-spherical atomistically discrete Lennard-Jones (LJ) clusters in a WCA host liquid. A single cluster consisted of 5–256 LJ particles in systems containing up to 27000 particles in total. The diffusion coefficients were found to be insensitive to the nature of the degrees of freedom of the cluster. Rigid clusters, with no internal degrees of freedom, gave essentially the same self-diffusion coefficients as those composed of thermally interacting LJ atoms. The diffusion coefficients decrease with cluster size and increase with system size. For clusters in excess of 100 particles, system sizes of at least 10000 particles are required to attain the thermodynamic limit. In the thermodynamic limit, the Stokes-Einstein relationship is obeyed approximately, assuming an increase in the local viscosity of the liquid around the cluster, as a consequence of an observed enhanced local order in this region. We have shown that clusters of several hundred atoms exhibit classical Langevin dynamics, with near exponential long-term decay of the force and velocity autocorrelation functions. The large clusters exhibit slow reorientational relaxation compared with that of angular frequency.

ISSN:0026-8976    

DOI:10.1080/00268979609484532

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor