摘要:

We construct a gauge-invariant approximation of the energy density of an interacting electron gas in the presence of a non-uniform magnetic field. The interaction is approximated by a slowly varying local potential. The magnetic field is a superposition of a constant fieldBand that due to a magnetic dipoleμ, thus making the energy density suitable for direct calculation of chemical-shift tensors of, for example, interacting closed-shell systems. Unlike a similar theory for the magnetic susceptibility, the field-dependent exchange energy does not diverge.

ISSN:0026-8976    

DOI:10.1080/00268979000101611

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The potential-energy surface of the reactive molecular system HO2is analysed in terms of reaction path and transversal modes, along the line of arguments initially proposed by Milleret al.This is a complicated case because, for any value of the reaction-path abscissa, the minimum-energy configuration of the system is non-symmetric (i.e. Csand not C2vor C∞v), and therefore corresponds to several points in configuration space through what can be called ‘transversal isomerization’ (rotation of H around O2). It is shown that the reaction-path description is nevertheless possible in this case, and can be used as a starting point for dynamical investigations of the system. A thorough discussion of the branching of the reaction paths for both the exchange reaction and the isomerization process is presented.

ISSN:0026-8976    

DOI:10.1080/00268979000101621

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The electronic spectrum of the NCS radical is obtained following UV excimer-laser photolysis of C2H5NCS in a large excess of inert gas in a supersonic free jet expansion. The spectrum is complicated by the presence of Renner-Teller and spin-orbit coupling and a Fermi resonance between the doubly excited bending vibration andv3, the CS stretching vibration. Bending vibronic level structure in the X2Π ground state of the radical is determined from a variety of laser-induced-fluorescence techniques, including stimulated-emission pumping. These energy levels are used to determine vibronic-coupling parameters for the radical. Coupling between close-lying bending levels with differentv2andK(= Λ +l) is found to be important because some of these levels are close together in NCS owing to the very large spin-orbit coupling. A parameter representing this effect is related to the dipolar contribution ε1to the Renner-Teller coupling parameter ε by applying perturbation theory to a simple model involving the X2Π and B2Σ+electronic states of NCS. This procedure results in an estimate for ε1that agrees approximately with that determined from the vibronic-coupling parametergK, assuming the same model for the interacting electronic states.

ISSN:0026-8976    

DOI:10.1080/00268979000101631

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Detailed far-infrared dilution measurements on DMF in carbon tetrachloride provide data on which to base an assessment of the way in which both the short-ranged and long-ranged dynamics are dependent on the surrounding molecular interactions. While there is an obvious increase in the rate of the long-time reorientational motion on dilution, the short-time dynamics appear to be relatively weakly affected. This is considered to be due to competing effects of removal of solute-solute interactions and the addition of solute-solvent interactions. The data are interpreted with the aid of the Gaussian-‘cage’ model of Lynden-Bell and Steele, which reflects the large intermolecular mean-squared torques and the collective intermolecular dynamic origins of the high-frequency spectral density in the region of 80–120 cm-1.

ISSN:0026-8976    

DOI:10.1080/00268979000101641

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This paper continues a previous investigation of the three-atom potential (3AP) of xenon, where the number of adjustable parameters has been varied. This time, the parameters are restricted to make the 3AP deviate as little as possible from the multipole expansion at long range, while their number is kept fixed at 26. To find the minimum deviation that is necessary to satisfy the experimental data, a statistical criterion is derived and applied. A few tests show that the 3APs thus obtained possess considerable predictive power. The method yields a 3AP that shows overlap effects at short range and that can be regarded as the ‘best’ many-body potential available for xenon.

ISSN:0026-8976    

DOI:10.1080/00268979000101651

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Corrections to the dipole-induced-dipole theory coming from both electronic overlaps and dispersion-force effects are introduced into the self-consistent equation for the effective atomic polarizability and applied to the case of rare-gas crystals. We show that the one-phonon expansion for Brillouin-scattered intensities can be rigorously solved, with the difference from a pure dipole-induced-dipole theory that Brillouin intensities now contain three microscopic quantities of the system. In the case of krypton crystals these quantities, which are related to the corrections to elasto-optic coefficients, are estimated by using experimental data. A comparison with theoretical predictions and experimental results is discussed. In the case of neon, argon and xenon available experimental data are not sufficient to estimate the three quantities, so just the rates of the elasto-optic coefficients are discussed. A slight discrepancy might be due to an overestimate of the anisotropic short-range contribution coming from the self-consistent-field calculations.

ISSN:0026-8976    

DOI:10.1080/00268979000101661

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A new analytical equation of state for fluid mixtures is presented, which is both simple and accurate enough to describe the thermodynamic properties of a general fluid mixture over its entire density range. It is derived by statistical-mechanical perturbation theory for hard-sphere mixtures, as a generalization of Song and Mason's equation for pure fluids. Agreement with computer simulations for Lennard-Jones binary mixtures is quite remarkable. The equation of state can be calculated if all the intermolecular potentials are known, but for practical purposes knowledge of just the second virial coefficients is sufficient to determine the whole equation of state.

ISSN:0026-8976    

DOI:10.1080/00268979000101671

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The value of the shear-viscosity coefficient in fluids is controlled by the dynamical processes affecting the time decay of the associated Green-Kubo integrand, the stress autocorrelation function (SACF). These processes are investigated in monatomic liquids by means of a microscopic approach with a minimum use of phenomenological assumptions. In particular, mode-coupling effects (responsible for the presence in the SACF of a long-lasting ‘tail’) are accounted for by a simplified approach where the only requirement is knowledge of the structural properties. The theory readily yields quantitative predictions in its domain of validity, which comprises ordinary and moderately supercooled ‘simple’ liquids. The framework is applied to liquid Ar and Rb near their melting points, and quite satisfactory agreement with the simulation data is found for both the details of the SACF and the value of the shear-viscosity coefficient.

ISSN:0026-8976    

DOI:10.1080/00268979000101681

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The quantum corrections to the properties of a densev-dimensional fluid of hardv-spheres are estimated at high temperature. Explicit expressions for the first quantum corrections to the free energy and equation of state are given. Numerical results are reported for hardv-spheres with 1 ˇ-vˇ- 5. The behaviour of the radial distribution function near the hard core is also studied. A significant feature is the large increase in quantum correction with increasing dimensionality.

ISSN:0026-8976    

DOI:10.1080/00268979000101691

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A simple expression for the mean-spherical-approximation (MSA) solution of the Ornstein-Zernike (OZ) equation in the Baxter formalism is presented for the case withncomponents and a single Yukawa term with factorizable prefactor: all coefficients of the MSA solution are given in terms of simple rational functions of a parameter that is defined as the acceptable solution of a non-linear equation. The manifold of solutions of the nonlinear equation and the choice of the acceptable solution are discussed. A thermodynamic theory is also presented in terms of simple rational functions of the above-mentioned parameter, and the effect of the ‘charge-non-neutrality’ condition on thermodynamic functions is discussed.

ISSN:0026-8976    

DOI:10.1080/00268979000101701

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor