摘要:

We present an analysis of pair correlation data of a Lennard-Jones fluid (argon), covering a wide range of thermodynamic states, in terms of structural diffusion (SD) models. These are based on the notion of a locally observed ordered structure and of spatial disorder as an outcome of a random spatial process. A general recipe is developed for analysing structural data by such models. First, we analyse fluid argon in terms of the simple SD model (SDM1). Nine lattices are chosen for the description of the local order in the fluid. It is found that close packed lattices are better suited for describing the high density fluid structure while open lattices are better suited for the description of the low density fluid. The SDM parameters obtained by constrained optimization describe the dependence of the pair correlation on density and temperature, and constitute a structural map of the fluid in the (ρ,T) plane. Two possible ways are presented for improving the fitting ofg(r) data: (1) distortion of a chosen symmetric lattice (FCC in our case) by varying the basic cell angles and optimizing within the SDM1. It is found that the higher symmetry lattices, BCC and FCC, give the best fitting to the experimentalg(r); (2) use of an extended version of the model (SDM2) that enables us to obtain a refined fitting through a built-in contraction function,f(r). A simple choice forf(r) in the model expression ofg(r), applied to the four most dense lattices, gives an improved fit for high densities. The best results are obtained with the hcp lattice.

ISSN:0026-8976    

DOI:10.1080/00268979100101491

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

For the first time inelastic neutron scattering measurements on a poly-crystalline sample of D2O up to the O-D stretching region are presented. The data have been analysed, treating the coherent scattering contribution within the incoherent approximation. The O-D density of states for the deuterium sites has been extracted and compared with the available Raman and neutron spectra of ice Ih.

ISSN:0026-8976    

DOI:10.1080/00268979100101501

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The rigorous treatment of light scattering effects in dense dielectric media can be achieved only by accounting fully for the dipolar induction appearing in the microscopic Maxwell equations. The starting point, namely the expression for the local microscopic electric field, is here cast in a new form which allows us to deduce, rigorously, for a system of point polarizable atoms, a tractable self-consistent equation for the effective atomic polarizability. The main implications of this equation, which have already been used successfully in evaluating the Brillouin scattering intensity in rare gas crystals, are briefly discussed.

ISSN:0026-8976    

DOI:10.1080/00268979100101511

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Results from Monte Carlo calculations on dense fluids of heteronuclear hard dumbbells are presented. In all cases theg1factor, related to dielectric properties, is one, within statistical error. The results forg2, related to light-scattering properties, are also close to one.

ISSN:0026-8976    

DOI:10.1080/00268979100101521

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Simulation data for the compressibility factor of 4000, 864 and 108 hard-sphere (HS) particles, obtained from different research groups, are analysed to yield empirical equations of state. A continued fraction technique, that allows information on the virial coefficients known from theoretical grounds to be included, yielding irreducible rational functions (IRF), is used. The virial expansion each IRF produces is included. For the HS systems with 864 and 108 particles these IRF are the quotient of two quadratic polynomials. We present very accurate empirical equations of state.

ISSN:0026-8976    

DOI:10.1080/00268979100101531

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We present new Monte Carlo calculations of the third and fourth virial coefficients for isotropic systems of different two-dimensional hard convex bodies: ellipses, rectangles and spherocylinders for various aspect ratios, and needles. Our results differ significantly from previously published values. The accuracy of our Monte Carlo method is tested by comparison with theexactvalue ofB3for unaligned hard needles, which we have obtained analytically. Finally, the validity of some approximate equations of state is investigated.

ISSN:0026-8976    

DOI:10.1080/00268979100101541

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Tarazona's weighted density approximation (WDA) to the intrinsic free-energy functional is used to investigate the equilibrium structure of a uniform hard-sphere fluid. The WDA results for the radial distribution functiong(r), obtained by fixing one particle at the origin and computing the resulting density profile, are close to those of simulation for all bulk (fluid) densities. Moreover, the cavity functiony(r) and the bridge functionb(r) are in good agreement with simulation for separationsrinside the hard-core. Our results provide further evidence that the WDA provides an accurate description of highly inhomogeneous hard-sphere fluids.

ISSN:0026-8976    

DOI:10.1080/00268979100101551

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The mechanism of the sensitization of the photoconductivity in poly-N-epoxypropylcarbazole (PEPC) films by the dye Rhodamine 6G is discussed. Sensitization through the exiplex state is shown to be a two-stage process which accompanies the main sensitization mechanism. In the latter the dye molecules act as photogeneration centres. On excitation of a dye molecule, a hole passes to the carbazole nucleus of the PEPC and a bound electron-hole pair is formed; this electron-hole pair dissociates in an external electric field with generation of free carriers according to the Poole-Frenkel model.

ISSN:0026-8976    

DOI:10.1080/00268979100101561

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Hyperfine splittings in several bands of the A-X system of TlI were measured using laser excitation spectroscopy on a highly collimated molecular beam. The quadrupole coupling constant in the A state and its dependence on the vibrational quantum number ν′ was derived. The results are discussed in a simple model with the assumption of an avoided crossing.

ISSN:0026-8976    

DOI:10.1080/00268979100101571

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In NaBp.2Tg (Bp = biphenyl; Tg = triglyme = CH3O(CH2CH2O)3CH3) layers of paramagnetic biphenyl anions are separated by layers of alkali-glyme complexes. EPR showed that this layered system behaves as a pseudo-two-dimensional magnetic system. It was also suggested that in the plane of the paramagnetic biphenyl anions exchange coupling constants of different signs may be found. In this paper we prove the presence of these exchange couplings with different sign by theoretical calculations. First of all, the EPR resonance field shifts below 4 K are explained on the basis of a localized and delocalized point-dipole approximation. It is concluded that positive as well as negative exchange constants are present and that the positive interactions follow a zig-zag path parallel to theb-axis. Second, the powder susceptibility measured from 11 to 260 K was calculated using mean field theory for a cluster of three spins. A satisfactory agreement was reached between the experimental and calculated susceptibilities withJ1= 0 K,J2= 13·8 K andJ3= -6.9 K. Finally, the exchange coupling constants between the three discernible biphenyl anion pair configurations have been calculated. Qualitative agreement with the above mentioned exchange constants was found. All results, therefore, confirm the idea of a magnetic lattice with exchange couplings of positive as well as negative sign.

ISSN:0026-8976    

DOI:10.1080/00268979100101581

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor