摘要:

The van Kampen analysis of condensation in a fluid of hard spheres with long-range attractions is extended to investigate the statistical mechanics of a fluid of rigid rod-like molecules which interact through both short-range repulsive and long-range attractive forces and which assume only a restricted set of three mutually orthogonal orientations. The thermodynamic properties are derived for the fluid near the liquid-gas critical point and at the nematic-isotropic transition. The model predicts that both isotropic and anisotropic attractive and repulsive interactions contribute to the stabilization of the nematically ordered fluid when a density change accompanies the transition. However, when the transition occurs at constant density, only the anisotropic contributions of the long-range dispersion energy and short-range repulsions are found to stabilize the transition in partial accord with the Maier-Saupe theory. Numerical results for a rigid-rod fluid with length-to-breadth ratio 3 at various packing fractions are presented for the order parameter, entropy and the density change at the nematic-isotropic transition. The results obtained give reasonable agreement with the experimental results for 4,4′-dimethoxyazoxybenzene and compare favourably with the calculations of Cotter and Ypma. The Landau-de Gennes treatment of the nematic-isotropic transition is also discussed in the framework of the present model. Order-parameter fluctuations, the properties of the nematic-isotropic interface and thermodynamic stability of co-existing nematic and isotropic phases at the transition are also considered.

ISSN:0026-8976    

DOI:10.1080/00268977800101361

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Anisotropic crystalline potentials for N2and O2trapped in β-quinol clathrates have been deduced from atom-atom Lennard-Jones and electrostatic multipolar potentials. It was made clear that the multipolar interactions due to the hydroxyl groups and benzene rings constituting the cage of β-quinol are essential. The dipole moment of the OH group has been estimated by use of an obtained theoretical relation between the dipole and quadrupole moments of the atomic groups, μOH= 0·1233 ¢ 108Q2benzene+ ξ, where the value of ξ was determined from magnetic resonance data on zero-point libration. According to recent N.Q.R. data of N2, one has μOH= 0·96 × 10-18e.s.u. cm forQ2benzene= -5·6 × 10-26e.s.u. cm2. The temperature dependence of the order parameter for molecular orientation was also examined. The calculated order parameter was found to be in good agreement with experimental one in the case of N2, and the E.P.R. case of O2was predicted.

ISSN:0026-8976    

DOI:10.1080/00268977800101371

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The thermal conductivity has been measured for the phases; liquid, Ib, II, III and IV of CCl4using the transient hot-wire method. Measurements were made at pressures up to 2·2 GPa, and in the temperature range 166–413 K. The thermal conductivity of the plastic crystal phase Ib was found to have features which are closely similar to those found for the plastic crystal phases of cyclopentane and cyclohexane. Phase IV of CCl4was found to form at pressures in the region of 1 GPa—substantially lower than reported in previous work.

ISSN:0026-8976    

DOI:10.1080/00268977800101381

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The exact Fokker-Planck-like equation of motion for the singlet phase space density derived by Lebowitz and Resibois has been investigated with the objective of improving on the usual replacement of the exact translational collision operator by the Fokker-Planck operator. The exact collision operator is expressed in terms of a projected force correlation operator which acts on the position and momentum of the tagged particle. The lowest order operator dependence of this correlation function is exposed, resulting in an improved FP collision operator that contains third and fourth-order momentum derivatives and a streaming term, which, roughly speaking, allows free translation during the correlation time of the fluctuating forces. The improved FP operator is used to obtain a short time expansion (up tot4) for the velocity correlation function. Through a cumulant expansion technique, theK-space singlet density is also obtained and a criteria, based on force correlation functions, is devised for the existence of the super Burnett coefficient.

ISSN:0026-8976    

DOI:10.1080/00268977800101391

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A rotational FP-like equation is derived for the motion of a tagged diatomic molecule in a bath of diatomics possessing rotational and translational degrees of freedom. The torque correlation operator in the FP-like equation has contributions from (1) rotation-translation coupling; (2) collisions which change the orientation of the molecule as well as its momentum; and (3) non-linear momentum relaxation. An approximate improved FP collision operator is suggested and is employed in the calculation of the orientational distribution function and correlation time,τl, for a high density fluid in the strong collision regime. A translational FP equation for non-spherical molecules is also obtained by analogy with the rotational case.

ISSN:0026-8976    

DOI:10.1080/00268977800101401

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A functional based on the hydrodynamic model ansatz for the total time-dependent wave function is discussed and used to determine the first-order 2l-pole functions of H, He+, He and Li+in the presence of a time-varying electric field. From the first-order corrections dynamic multipole polarizabilities of the atomic systems are determined. The functional is shown to give lower bounds to the dynamic multipole polarizabilities and upper bounds to the imaginary frequency multipole polarizabilities for all frequencies.

ISSN:0026-8976    

DOI:10.1080/00268977800101411

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The functional based on the hydrodynamic model ansatz for the total time-dependent wave function is used to determine imaginary frequency multipole polarizabilities for the ground states of H, He+, He and Li+. The long-range dispersion terms for pairs of these atoms are also given. The functional is shown to give a convenient alternative to the determination ofα2l(iω).

ISSN:0026-8976    

DOI:10.1080/00268977800101421

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Monte Carlo calculations have been carried out for model systems consisting of 324 ions (108 cations and 216 anions). The aims were: (a) to study the thermodynamic and structural properties of liquid and solid alkaline earth halides; (b) to test the rigid ion model.

ISSN:0026-8976    

DOI:10.1080/00268977800101431

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The solvent dependence of the indirect Hg-H, Hg-C and C-H coupling constants in dimethyl mercury has been studied. The measurements show an increase of about 2 per cent in the absolute values of the Hg-H and Hg-C coupling constants on passing from neat dimethyl mercury to a solution in deuterated acetone. Solvent dependence is also observable in comparing the values of the coupling constants in different thermotropic nematogens. This study shows, in accordance with earlier works, that the indirect contribution to the Hg-H coupling is negligible, while the Hg-C coupling is more anisotropic than was earlier predicted. Substituting13C for12C causes a downfield isotope shift of about 7 Hz in the199Hg chemical shifts.

ISSN:0026-8976    

DOI:10.1080/00268977800101441

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

It is pointed out that the σ-bond connectivity of the carbon atoms in a hypothetical, neutral, conjugated hydrocarbon predetermines whether or not it is possible, on the basis of theAufbauPrinciple, to establish a unique, ground-state, π-electronic configuration from energy levels calculated via simple molecular-orbital theory. Such ‘molecular topology’ is relevant because it influences the relative ordering amongst the eigenvalues of the associated molecular graph. It is speculated that certain hypothetical conjugated-systems may not exist because their very topology precludes their having an energy-level family which will lead to a unique, ground-state configuration, on application of theAufbauPrinciple.

ISSN:0026-8976    

DOI:10.1080/00268977800101451

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor