摘要:

The dependence of the reduced reorientational correlation times, τn*, for linear and spherical-top molecules on the angular velocity correlation time, τω*, is evaluated and conveniently presented for four different models of molecular reorientational thermal motion—the extended diffusion model, the Langevin model, the Ivanov model, and the strong collision model. In particular the theories of Sack [2] and Fixman and Rider [6] are compared. They are not the same for spherical molecules in the Langevin model. Some new results are also given for the Langevin model for the almost-free-molecule limit. The results are relevant to molecular gases, liquids and crystals.

ISSN:0026-8976    

DOI:10.1080/00268977700101031

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The potential of mean forceWijbetween two solute ions in a dipolar solution at infinite solute dilution is investigated using a potential analysis. The ions are taken to be charged hard spheres of radiiaiandajwith point chargeseiandejat their centres while the solvent molecules are represented by point dipoles fixed at the centre of hard spheres of diameterd. For the separationrof the two ions greater thanai+aj+ 2dwith 1/2dˇ-aiandajwe find that

ISSN:0026-8976    

DOI:10.1080/00268977700101041

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

By considering the variation of charge-transfer energy and of the intensity parameters across isostructural series it is concluded that charge-transfer mixing is of negligible importance in accounting for the intensity of the hypersensitive transitions of the trivalent lanthanides. The experimental relationship between hypersensitive transition intensity and charge-transfer energy found for a particular member of the lanthanide series in various environments can be as satisfactorily explained by the ligand polarization theory as by charge-transfer mixing.

ISSN:0026-8976    

DOI:10.1080/00268977700101051

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The polarized scattering intensity is calculated, in the Einstein-Smoluchowski approximation, for four thermodynamic states of a model diatomic; these are the same states for which the depolarized intensity was calculated in the first article (I) of this series. The polarized intensity is discussed in terms of an ‘effective isotropic polarizability’α0effand the ratio (α0eff/α0)2, whereα0is the gas-phase isotropic polarizability, and is both expressed formally and tabulated for the four states. Similarly in (I), depolarized intensities were discussed in terms of the ratio, (γ/Δα)2, whereγis the ‘effective polarizability anisotropy’ and Δαthe gas-phase anisotropy. We find that (α0eff/α0)2lies much closer to unity than does (γ/Δα)2, in agreement with existing experimental data, which indicates that the introduction of effective polarizabilities is relatively unimportant or important, respectively, as polarized or depolarized scattering is considered.

ISSN:0026-8976    

DOI:10.1080/00268977700101061

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The Kirkwood-Yvon dielectric theory is generalized to the case of fluids consisting of molecules possessing arbitrary polarizability densities. The theory is used to find expressions for the equilibrium dielectric constant, the polarized scattering intensity, and the depolarized scattering intensity, which we have previously calculated under the approximation (PPA) that molecules have point polarizabilities. A simplified version of the general theory, in which each atom in a polyatomic is given a point polarizability (PAPA), is proposed, and worked out in detail for the case of homonuclear diatomics. A discussion is given of how we hope to obtain numerical results in the near future for liquids composed of model homonuclear diatomics considered by us previously.

ISSN:0026-8976    

DOI:10.1080/00268977700101071

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

A theoretical study of the statistical mechanical description of a system composed of interaction-site molecules is made using the site-site correlation function approach. The system of hard dumb-bells is then studied in detail. The problem of excluded volume of a pair of spheres embedded in the dumb-bells is solved, which enables one to evaluate the second virial coefficient and to derive an approximate equation of state in a closed analytical form. The equation of state obtained shows good agreement with Monte Carlo data.

ISSN:0026-8976    

DOI:10.1080/00268977700101081

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

By coupling linear combinations of the |JMket vectors which transform as irreducible representations ofCn*,Dn* andT*, symmetry coupling coefficients for these groups are calculated. Also,⫫coefficients as defined by Golding [1] are evaluated.

ISSN:0026-8976    

DOI:10.1080/00268977700101091

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Previously proposed quantum conditions are used to calculate the higher eigenvalues of a simple two-dimensional (2D) potential from classical trajectories. A new modification to our earlier work is introduced to deal with problems arising from the complicated behaviour of the caustics in certain cases. Results are in excellent agreement with quantum-mechanical calculations. Our methods are shown to be competitive with quantum calculations in their ease of application for these upper levels. However, it is not possible to calculate certain semiclassical eigenvalues near the escape energy because corresponding trajectories are ergodic.

ISSN:0026-8976    

DOI:10.1080/00268977700101101

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Neutron inelastic scattering is introduced as a new experimental technique for the study of exchange interactions in polynuclear transition metal complexes. Measurements were performed on deuterated μ-hydroxo-bis[pentaamminechromium(III)]chloride monohydrate at temperatures ranging from 5 K to 290 K. Transitions between split levels of the electronic ground state were observed in both energy-gain and energy-loss configurations. The values for the splittings and the resulting exchange parameters are found to be temperature dependent. Comparisons are made with values obtained from optical spectroscopic studies and magnetic susceptibility measurements. The observed intensity ratios of the neutron inelastic scattering transitions are in good agreement with values calculated on the basis of a simple spin-spin coupling model for the chromium pair.

ISSN:0026-8976    

DOI:10.1080/00268977700101111

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Potential surfaces have been calculated for ethane and the three lowest-lying states of its positive ion usingab initioSCF and CI methods. The C2H6+states treated consist of two2Agand a single2Bgspecies in the lowest nuclear symmetry considered (C2h) and they are found to possess markedly different equilibrium structures both compared to ethane itself and also to one another. The C2H6+ground state (2Ag) is a pure2A1gspecies (D3dsymmetry) at large CC distances with optimum CCH angles of 100°, but at shorterRCCvalues it becomes a mixture of both2A1gand2Egcharacter through a large diborane-type (v12) distortion. The second2Agspecies is complementary to the first and appears to preferD3dsymmetry both at large CC values, for which it is a2Egspecies, and also at short distances, for which it eventually becomes a2A1gstate. The2Bgspecies correlates with2EginD3dsymmetry but is Jahn-Teller distorted, possessing anRCCvalue of 2·75 bohr and an HCH angle of only 90° (ethane values are 2·91 bohr and 109·47°). A Franck-Condon analysis of the calculated potential curves indicates that the spectrum for ionization to the lowest2Agspecies is too diffuse and of wrong characteristic frequency to be attributed to the fairly regular fine structure observed in the 11·5–12·6 eV region of the ethane PES (with average vibrational spacting of 1170 cm-1). By contrast the analogous results for2Bgionization do compare quite well with the latter experimental system, with both thev3(CC stretch) andv11(CH3deformation) modes showing progressions in the desired frequency range. Finally it is argued that a breakdown of the Born-Oppenheimer Approximation for the2Agstates in the region of vertical ionization coupled with the fact that one of the species dissociates in the same energy region is responsible for the much more irregular and broad appearance of the PES observed in the 12·5–14·0 eV region.

ISSN:0026-8976    

DOI:10.1080/00268977700101121

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor