摘要:

The Monte Carlo method is used to study three systems of fused hard spheres with length-to-width ratios ranging from 3·5 to 5·2. Spontaneous nematic alignment is observed only for the most elongated molecules. The isotropic data are compared with a theoretical expression due to Boublik and are fitted by ayexpansion in each case. Site-site distribution functions and Legendre coefficients of the total angular distribution function are reported for a representative state point in the nematic phase. These are discussed in relation to the equivalent functions for a system of parallel fused spheres. It is found that the single-particle angular distribution function is represented well byf(γ) =Aexp (- κ cos2γ) +c. The Frank elastic constants are estimated and are in the expected range. At higher densities there is evidence for a smectic phase.

ISSN:0026-8976    

DOI:10.1080/00268979100100191

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Corundum, or α-Al2O3, is investigated at theab initioperiodic Hartree-Fock LCAO level using the program CRYSTAL. A split valence 6–21G basis set is adopted, and the influence of d polarization functions is explored. The four geometrical parameters of the unit cell are optimized, the difference with respect to the experimental data always being less than 1%. The electric field gradient tensor at both nuclei (Al and O) is calculated; agreement with the experimental data is quite satisfactory. Band structure, density of states and charge density maps are also given. The resulting electronic structure is highly ionic.

ISSN:0026-8976    

DOI:10.1080/00268979100100201

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The effects of solvent density on the solute-solute potential of mean force in Lennard-Jones fluids are studied by means of the integral equation method. The solvent density plays an important role in solute-solute correlation in solution: the effect of the solute-solvent attractive interaction is quite different in the medium-density and high-density regions. In the latter the strong solute-solvent attractive interaction destabilizes the contact solute pair, and the strong solvent-solvent attractive interaction stabilizes the contact solute pair, which is expected from both ‘desolvation’ and the ‘solvophobic’ effect. In the medium-density region, however, curious phenomena are observed that cannot be interpreted by a simple picture: for example, the solute-solvent attractive interaction stabilizes both the solvent-separated pair and the contact pair of solute molecules under some conditions. The characteristics of the medium-density region are discussed in terms of the density fluctuation around the solute molecule.

ISSN:0026-8976    

DOI:10.1080/00268979100100211

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

ESR, TSL and fluorescence studies of K2UO2(SO4)2· 2H2O and Rb2UO2(SO4)2· 2H2O and their deuterated compounds subjected to gamma irradiation at 77 K reveal the participation of 5f orbitals in the bonding between uranyl and oxygen (of the sulphate group). Radiation-induced paramagnetic species and thermally stimulated reactions between them are also characterized optically and structurally.

ISSN:0026-8976    

DOI:10.1080/00268979100100221

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We present closed-form expressions for derivatives at contact of the hard-sphere radial distribution function (RDF) in the Percus-Yevick theory. The derivatives of lower order coincide with well-known results. Corresponding expressions are also derived using the Verlet-Weis algorithm. These results are compared with values extracted from recent Monte Carlo data on the HS RDF and an accurate expression for the first-order derivative is given. Expressions for moments of the HS correlation function are also obtained in the Percus-Yevick theory. All of these quantities are useful in the perturbation theory of liquids.

ISSN:0026-8976    

DOI:10.1080/00268979100100231

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Transitions in the fundamental band of the ground state X2Π1/2of the GeH radical are detected by tunable diode laser spectroscopy. Signals are observed for all five naturally occurring isotopes of germanium. A preliminary fit of the vibrational-rotational constants for the ground state is given, in which the vibrational corrections αA, αγand αp+2qto the fine structure constantA, the spin rotation constant γ and the lambda doubling constantp+ 2qare determined from our data.

ISSN:0026-8976    

DOI:10.1080/00268979100100241

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The three-state rotational isomeric state (RIS) model of conformer statistics is used to analyse the 16 independent dipole coupling constants measured in a recent proton NMR study of n-hexane in a nematic liquid crystal solvent by Gochinet al.The orientational ordering of the hexane molecule is treated in the context of the modular formulation of the potential of mean torque developed recently by Photinoset al.This formulation gives a very accurate description of alkane solute orientational order and conformer probabilities in the nematic solvent. Consequently, substantially more accurate calculated dipolar couplings are obtained than in previous calculations and, moreover, this is achieved without the need to resort to unconventionally high values of thetrans-gaucheenergy differenceEgin the RIS model; an optimized fit to the data wherein the location of thegauchedihedral angle RIS state φgandEgare varied yields the values φg= 112° andEg= 0·67 kcal mol-1. The sensitivity of the dipolar couplings to conformational variations of the interproton distances (1/r3) provides a critical test of the accuracy of the RIS model. It is found that the standard RIS model itself (in terms of its intrinsic features: three rotamer states, a single position-independentEgvalue, and rigid geometry), and not its parametrization (φg,Eg), is the impediment to an exact reproduction of the experimental dipolar couplings.

ISSN:0026-8976    

DOI:10.1080/00268979100100261

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

New data on the three-body correlation spectra obtained from collision-induced light scattering by SF6and CF4at 295 K are reported. The experimental zeroth and second moments are compared with calculations based on a pairwise-additive triplet cluster polarizability. Dipole-induced-dipole and electron-overlap contributions to the pair polarizabilities are considered. Comments are made on the adequacy of existing potentials for describing the scattering.

ISSN:0026-8976    

DOI:10.1080/00268979100100271

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Precise measurements of the complex permittivity of acetone at 293 K have been made for frequencies in the range 50–310 GHz. These, when obtained with earlier results, have allowed for a determination of the complex permittivity over the entire 0–6 THz frequency region. The results suggest the presence of a dynamic cooperative motion among the acetone molecules in the pure liquid. The experimental data are fitted to the Budó model and confined rotator models (CRM). Both models are shown to have their own characteristic features. The Budó model provides a better fit for low and high frequencies, whereas the CRM provides a better fit for middle frequencies only.

ISSN:0026-8976    

DOI:10.1080/00268979100100281

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A stochastic model of single-particle motion based on the velocity auto-correlation function is proposed. Recent simulations of the probability density for changes in direction are discussed in terms of this model. In all cases but one the theoretical results are in excellent agreement with the simulations. It is concluded that the measures of directional change proposed do not show any behaviour that cannot be explained in terms of the model and an empirical VACF.

ISSN:0026-8976    

DOI:10.1080/00268979100100291

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor