摘要:

The light-scattering spectrum of liquid triphenyl phosphite (TPP) has been studied over a temperature range in which the parameter (k2η/Γoρ) varies from 0·17 to 50, wherekis the scattering vector, η the shear viscosity, ρ the mass density and Γ0the rotational correlation frequency determined from the HH spectrum. The VH spectrum changes markedly in character over this temperature range and can be explained in terms of molecular rotations coupled to shear modes. A single coupling parameter, dependent upon a time-dependent correlation function, is required to fit the spectrum; this parameter (R) is about equal to 0·45 and is independent of temperature and ofk. The spectrum is a function of the parameter (k2η/Γ0ρ) which includes variations with viscosity, temperature and scattering angle. A statistical theory is presented which yields a different explicit expression for the spectrum from that obtained previously; the difference is essential at large values of (k2η/Γ0ρ). The coefficient of shear viscosity is independent of frequency, and the rotational relaxation frequency Γ0obeys an extended Debye formula with an effective rotational radiusaκ1/3, whereais the ‘true’ molecular radius obtained by means of molar refraction and κ = 0·55 is independent of temperature and is a measure of the coupling between rotations and translational shear modes. κ is closely related to the coupling parameterR, and ηRis the rotational contribution to the shear viscosity. A relation is obtained between the multiparticle parameter κ and its single particle equivalent κs; it is likely that κs< κ for TPP.

ISSN:0026-8976    

DOI:10.1080/00268977500100021

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The theory of the low-frequency depolarized light-scattering spectra from liquids composed of two components, both of which are symmetric tops, is developed. The rotational motion is assumed to be diffusional, and the expressions for the linewidths are related to the single-particle orientational autocorrelation times. The concentration dependence of these single-particle correlation times is also discussed.

ISSN:0026-8976    

DOI:10.1080/00268977500100031

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Electron paramagnetic resonance spectra have been obtained of tetramethylpyrazine in its lowest (ππ*) triplet state in several rigid matrices. Some unusual observations were made :1.(1) In a durene crystal host the in-plane zero-field principal axes are not parallel to the molecular symmetry axes.2.(2) In rigid glass solution the zero-field parameters are strongly dependent on solvent polarity.

ISSN:0026-8976    

DOI:10.1080/00268977500100041

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Using microwave induced phosphorescence techniques we determined the rate constants for populating and decay of the lowest triplet state of tetramethylpyrazine (TMP) in a durene crystal. The dynamic behaviour of the spin statesTy′andTz′corresponding to the in-plane spin axes (principal axes of the dipolar coupling tensor)y′andz′proves to be identical :ky′r=kz′r(radiative decay),ky′=kz′(absolute decay rates) andPy′=Pz′(populating rates). This result supports the suggestion of de Grootet al., based on E.S.R. experiments, that for the phosphorescent state of TMP in the durene host the in-plane spin axesy′andz′have undergone an appreciable (≈45°) rotation with respect to the in-plane molecular axesyandz.

ISSN:0026-8976    

DOI:10.1080/00268977500100051

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

This paper examines the consequences of a strong vibronic coupling on orbitally triply degenerate levels in a cubic environment for the three cases in which spin-orbit coupling is weaker than, comparable with, or stronger than the vibronic coupling. It is shown that vibronic orbital reduction factors may be strongly temperature dependent. The consequences of this temperature dependence for the interpretation of magnetic susceptibility measurements are briefly discussed. An Appendix details a method for the evaluation of overlap integrals between harmonic oscillator eigenfunctions.

ISSN:0026-8976    

DOI:10.1080/00268977500100061

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Some second-order properties like the electrical polarizability, magnetic susceptibility and proton magnetic shielding, computed by the coupled-perturbed SCF method for H2O NH3CH4and CH3F were analysed in terms of localized orbital contributions. For the magnetic observables the gauge transformation introduces some ambiguities in the definition of orbital contributions, besides the well-known difficulties of yielding results which are not gauge invariant for limited bases. These problems are examined in detail and a method is proposed to overcome the effect of the limitation of the basis. Conditions are also stated under which the ambiguities may be resolved. By assuming that the localized orbital contribution may be transferred from one molecule to another, estimates are made for second-order properties of CH2F2, CHF3and CF4molecules. The agreement of these estimates with the available experimental data is better than expected.

ISSN:0026-8976    

DOI:10.1080/00268977500100071

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The absorption spectrum at room temperature and liquid helium temperature and the magnetic circular dichroism (MCD) spectrum at liquid helium temperature are reported for ∼15 per cent Mn2+in CdF2. The results indicate that even at these concentrations the Mn2+ions occupy undistorted cubal symmetry sites. The intensity is entirely vibronic with at least onet1uvibration of 155 cm-1active. Crystal-field calculations have been used to assign the gross features of the spectrum and the use of MCD has allowed an almost complete elucidation of the fine structure observed. In the two4T2gstates this structure is assigned to the various spin orbit components. The MCD results indicate that vibronic mixing to theground state, rather than to excited states, produces the observed spectrum and that both4T1uand4T2ustates probably mix.

ISSN:0026-8976    

DOI:10.1080/00268977500100081

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

All electronab initioSCF MO calculations of Cr(C6H6)2and C6H6Cr(CO)3are described. In both complexes the benzene ligand bears a net negative charge and in the carbonyl complex the -CO ligands accept more electron density than in unsubstituted carbonyls. The He(I) and He(II) p.e. spectra of both complexes are reported and interpreted with the aid of these calculations. For ionization from mainly ligand MO's, Koopmans' theorem allows a satisfactory interpretation of the measured I.P.'s and the change in intensity between He(I) and He(II) spectra may be correlated with the atomic orbital character of the M.O.'s. However, for ionization from these MO's having substantial metal character the relaxation energy is dependent upon their degree of localization and direct calculation of the energy of the ion states is necessary to interpret this region of the p.e. spectra.

ISSN:0026-8976    

DOI:10.1080/00268977500100091

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The1H N.M.R. spectra of the anions of anthracene, pyrene and triphenylene and the2D N.M.R. spectra of the anions of anthracene-d10and partly, randomly deuterated triphenylene have been measured in ethereal solutions. The hyperfine splitting constants derived from the measured Fermi contact shifts are presented and compared with E.S.R. data and predictions from theory. From the measured1H and2D linewidths the electron spin and rotational correlation times have been calculated. It is shown that the derived rotational correlation times are not very sensitive to anisotropic rotation.

ISSN:0026-8976    

DOI:10.1080/00268977500100101

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The application of perturbation theory to a fluid of non-spherical molecules of arbitrary symmetry is considered. The influence of a large number of angle-dependent pair interactions and three-body non-additive interactions on the Helmholtz free energy and on the pair and triplet distribution functions, in some cases through the third order of the perturbation theory, is evaluated. Explicit expressions are given for the Helmholtz free energy for molecules possessing axial and tetrahedral symmetries in terms of molecular parameters and the reference systems pair and triplet distribution functions. The contributions of the various terms discussed in this paper are expected to be substantial at low temperatures for a real fluid.

ISSN:0026-8976    

DOI:10.1080/00268977500100111

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor