摘要:

An effective hamiltonian ℋeffis developed for the treatment of exchange interactions in a pair of transition metal ions with orbitally degenerate ground states. In contrast to a Heisenberg-Dirac-van Vleck (HDvV) hamiltonian ℋeffretains a partial degeneracy of singlet and triplet pair states. The hamiltonian is applied to Ti2X93-(X=Cl, Br) dimers. The gross experimental features of Cs3Ti2Cl9and Rb3Ti2Br9are well reproduced by the theoretical model. The coupling is strongly antiferromagnetic and the exchange parameters can be rationalized by an approximate MO calculation.

ISSN:0026-8976    

DOI:10.1080/00268978400100011

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Molecular dynamics has been used to simulate a high density fluid of homonuclear diatomic molecules in the presence of a rigid planar wall. The molecular interactions were modelled by Lennard-Jones (12, 6) site-site potentials and (17, 3) wall-site potentials. The relative influence of attractive and repulsive forces on the interfacial orientational structure was studied by comparing with simulations in which the attractive components of either or both the site-site and wall-site potentials were absent. The results, presented as contour plots of the density-orientation profile ρ(z, θ), show that parallel orientation of the molecules is favoured when the centre-of-mass distancezis very close to the wall, but that perpendicular orientation is favoured at slightly larger distances. The presence of weakly attractive wall-site forces slightly increases the relative degree of parallel alignment compared with that in the absence of such forces. The presence of attractive site-site pair interactions diminishes considerably the amplitude of oscillations in ρ(z, θ) compared with their amplitude in the absence of such interactions, but does not modify the orientational preferences. This is attributed to increased cohesion of the liquid phase when the pair attractions are present, leading to a non-wetting state of the liquid-solid interface and a corresponding reduction in the density and wall-induced orientational anisotropy of the fluid layers near the wall. Site-wall density profiles were also obtained from the simulations and compared with the results of an interaction site approximation, integral equation theory: the agreement is only fair at best.

ISSN:0026-8976    

DOI:10.1080/00268978400100021

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Third order polarizabilities for fluorinated methanes and sulphur hexafluoride, derived from three non-linear optical processes are compared. Significant differences beyond those estimated for dispersion are ascribed to vibrational effects. Estimates of the vibrational mode contributions using spectroscopic data, while crude, are consistent with the experimental values. It is concluded that vibrational contributions to third order polarizabilities are significant in specific cases.

ISSN:0026-8976    

DOI:10.1080/00268978400100031

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The values of the deuterium quadrupole coupling constants (DQCC) obtained from2H N.M.R. spectra of nitromethane-d3in liquid crystalline phase are reported. Different values are obtained in different nematogens. In a mixture of EBBA and ZLI 1167 a variation from 128 kHz to 161 kHz is observed as a function of the composition of the mixture. A similar variation has been found for the isotope effect on the dipole-dipole couplings in the monoprotonated molecule.

ISSN:0026-8976    

DOI:10.1080/00268978400100041

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A modified cell theory using both cell size fluctuations and random packing is extended to hard convex body fluids. The equation of state is obtained and is found to be a reasonable approximation for the dense fluid range. A simple universal relation between the equation of state of hard spheres and of hard convex particles is derived, permitting the construction of accurate hard convex body equations of state from hard sphere data.

ISSN:0026-8976    

DOI:10.1080/00268978400100051

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The infrared spectra of the monoisotopic species H374Ge79Br and H374Ge81Br in the 750–1000 cm-1region covering the vibrationsv2,v5andv3+v6have been recorded with a resolution of 0·04 cm-1and rotationally analysed. In addition, information concerning the hot band (v3+v5) -v3has been obtained and data onv6and (v3+v6) -v3have been used. Fermi resonance betweenv5andv3+v6has been established with |W356| = 4·4067(7)/4·3055(8) cm-1(79/81Br) and the Coriolisx,yresonance linkingv2withv5has been evaluated.

ISSN:0026-8976    

DOI:10.1080/00268978400100061

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The depolarized rotovibrational band in fluid N2has been measured in a wide temperature and density range. The behaviour of normalized second moment versus temperature and density is analysed in order to clarify the role played by the various non-rotational contributions. Practically no dependence on temperature is found while a net increase with density is present. Induced effects are carefully analysed in the dipole-induced-dipole approximation. In particular exact formulas are derived for both the intensity and second moment of induced cross contributions. Good agreement with experimental data is obtained. The cross contributions are responsible for the observed second moment increase with density.

ISSN:0026-8976    

DOI:10.1080/00268978400100071

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A simple, intermolecular potential function has been derived empirically to yield good thermodynamic and structural results for liquid hydrogen fluoride. The function was tested in Monte Carlo statistical mechanics simulations for the liquid at temperatures of 0°C and -70°C at 1 atm. The average errors in the computed densities and energies are 1 and 5 per cent, respectively. The temperature dependence of the structural results is also analysed by means of radial distribution functions and hydrogen bond distributions. As expected, hydrogen bonded chains dominate the liquid's structure. Enhanced structure and hydrogen bonding are evident as the temperature is lowered. In view of the simplicity of the potential function and the quality of the results, the potential is well suited for simulations of dilute solutions including studies of the solvation of carbonium ions in a model superacid solvent.

ISSN:0026-8976    

DOI:10.1080/00268978400100081

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The microscopic evolution of a one parameter reaction system in a dense phase is represented, in the diffusion limit, by a Smoluchowski equation with a bistable potential. The WKB techniques recently developed are applied to the calculation of the time dependent reactive fluxk(t), defined as a derivative of the correlation function of the number of particles, in the case of a simplified model of n-butane isomerization already studied by Chandler and other authors. The reactive flux is expressed as a sum of decreasing exponentials; the larger characteristic times and corresponding numerical coefficients are computed explicitly. The results confirm the validity of the phenomenological rate law for times larger than 10-12s.

ISSN:0026-8976    

DOI:10.1080/00268978400100091

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The effects of first order Coriolis interactions and vibrationalltype resonances in the infrared spectrum of the band system 2ν9±2, ν9±1+ν10±1, 2ν10±2of gaseous allene-d4have been studied at a resolution near 0·05 cm-1. Sets of spectroscopic constants for each of the vibrations are determined, as well as the Coriolis interaction parameter which couples all three levels. The relative magnitudes and signs of the intensity parameters of the band system have been derived from contour simulations. A number of local perturbations are discussed qualitatively.

ISSN:0026-8976    

DOI:10.1080/00268978400100101

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor