摘要:

We have studied two model nematogenic solutions composed of biaxial solutes dissolved in a solvent of uniaxial particles using the Monte Carlo simulation technique. The nematogenic solvent consists of cylindrically symmetric particles located on the sites of a face centred cubic lattice and interacting only with their nearest neighbours through a soft anisotropic potential. The solution is formed by replacing a small number of solvent molecules, chosen at random, with biaxial solute particles. The second rank order parameter of the solvent and the Saupe ordering matrix for the solute have been determined as a function of temperature for the two solutions which differ solely in the biaxiality of the solute. These results are found to be in good qualitative agreement with the predictions of a molecular field theory for such nematogenic solutions.

ISSN:0026-8976    

DOI:10.1080/00268978500103021

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A model for calculating the structural and dynamical properties of the plastic phase of adamantane is described. The simulation is performed with the molecular dynamics technique. A pairwise additive potential function (exp -6) is used to calculate the molecular interactions. The molecules are considered rigid and their equations of motion are integrated using a method of constraints. The temperature dependence of the structure is investigated in the range 310–425 K. An expansion in terms of symmetry adapted functions yields the molecular orientational probability density. The results obtained by simulation are in good agreement with experimental values.

ISSN:0026-8976    

DOI:10.1080/00268978500103031

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The perturbative configuration interaction approach based on non-orthogonal bond-orbitals previously used for dealing with rotational barriers is applied to the study of the hydrogen bonding in the linear water dimer. First and second-order interaction energies are obtained in terms of static and transition charge distributions fully accounting for intermolecular overlap. Neglecting electron correlation, the second-order calculations include all single excitations from bonding to antibonding orbitals accounting for induction including exchange and giving results close to the corresponding supermolecular SCF-MOs in the same basis.Ab initiocalculations using different gaussian minimal bases show that Clementi's GTO basis MEDIUM is the most suitable for describing molecular interactions. Detailed component analysis of the energy up to second order is possible and reveals the main features of the intermolecular hydrogen bonding occurring between the water molecules.

ISSN:0026-8976    

DOI:10.1080/00268978500103041

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The mechanism responsible for the numerous perturbations affecting localized groups ofJ-components in the rotational structure of thev4perpendicular fundamental of H374Ge35Cl, observed almost at every value ofK″ΔK, has been clarified. These perturbations are caused byJ-level crossing of the branches ofv4and those of neighbour vibrational states with markedly smaller values ofBor local effectiveB, due to the excitation of quanta ofv3(αB3∼ 6·886 · 10-4cm-1) and to the strongx-yCoriolis coupling with vibrational states differing by (v2-v5). The complex interaction scheme involves 10 vibrational states in the rangev4± 50 cm-1, and we have determined parameters of the seven vibrational states 3v3+v5,v2+v3+v5,v2+ 3v3, 2v2+v3,v3+ 2v05,v3+ 2v±25, and 5v3, in addition to the threev1,v4andv∓15+ 2v±26which were considered in a previous work [1]. Improved vibration-rotation parameters ofv1have been estimated.

ISSN:0026-8976    

DOI:10.1080/00268978500103051

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The N.M.R. relaxation times of liquids in heterogeneous systems, where a molecule is either close to an interface, or has diffusive motions which are in some way geometrically bounded, often show features such as spin-lattice relaxation time (T1) minima resembling those found in bulk solids. These measurements have nearly always been interpreted using the theory of relaxation for bulk materials. This frequently leads to the conclusion that there is, as a result of proximity to the interface, a reduction in the molecular mobility of several orders of magnitude compared to the bulk liquid. This conclusion often conflicts with those derived from other measurements such as quasielastic neutron scattering. Another interpretation which takes into account the restricted nature of the diffusion is given. The effects that bounded two dimensional motion has on proton relaxation times are discussed in detail and the theory applied to a number of real cases. Calculations using the diffusion constants determined by neutron scattering give values ofT1andT1minima in agreement with experiment. In our opinion these results place a doubt on the correctness of the conclusions of the majority of proton N.M.R. relaxation time measurements in heterogeneous systems.

ISSN:0026-8976    

DOI:10.1080/00268978500103061

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The use of hole and particle distributions on equal footing is shown to give rise to the PY approximation, as well as to associated rigorous inequalities. The approximation is extended to third- and higher-order distributions.

ISSN:0026-8976    

DOI:10.1080/00268978500103071

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

We study the approach to complete wetting by gas at the interface between a repulsive wall and dense liquid, paying particular attention to the basic model consisting of a hard-wall system approaching bulk liquid-vapour coexistence. This class of wetting phenomena is of special interest from the point of view of the compressibility route to interfacial statistical mechanics and for its suitability to direct observation by computer simulation. On the theoretical side, there exists a battery of exact sum rules that are of direct relevance to the problem and it is possible to make use of capillary wave fluctuation theory in almost the same form as has been developed for the study of liquid-vapour interfaces.

ISSN:0026-8976    

DOI:10.1080/00268978500103081

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The spectra of the radicals obtained by flash photolysis of solutions of two related organic anhydrides have been observed using the time-integration spectroscopy method. It is shown that the chemistry is complex, with several radicals observable under different conditions. The anions of the parent anhydrides exhibited spin-polarized spectra which were affected by electron exchange in the intermediate and fast ranges. They have been used to test the theory of the effect of electron exchange on observed polarized spectra.

ISSN:0026-8976    

DOI:10.1080/00268978500103091

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The high frequency deflection technique has been applied to the PHA3Π-X3Σ-transition for measurements of the fluorescence lifetimes of individual rotational levels of thev′= 0 vibrational level of theA3Π state. The onset of a rotationally dependent predissociation is observed at aboutJ′= 11 as a decrease in the measured lifetimes. The predissociation is interpreted in terms of a first-order spin-orbit interaction between theA3Π state and a repulsive5Σ-state arising from the ground state dissociation products. The average radiative lifetime of low rotational levels is 450 ns and the observed predissociation gives an upper limit of 3·74ev to the PH dissociation energy.

ISSN:0026-8976    

DOI:10.1080/00268978500103101

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A series of Monte Carlo simulations has been carried out to characterize the temperature and size dependence of the results for liquid water using the TIP4P potential function. Five temperatures from -25 to 100°C and four system sizes from 64 to 512 molecules have been studied. Comparisons are made with experimental thermodynamic and structural data as well as results of prior simulations.

ISSN:0026-8976    

DOI:10.1080/00268978500103111

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor