摘要:

The second-order hyperfine energy in the 1s and 2s states of the hydrogen atom is calculated analytically using the Dirac equation for an electron in a Coulomb potential perturbed by a point nuclear magnetic moment. The (divergent) result is compared with the calculation using the non-relativistic form of the hamiltonian. It is emphasized that in this comparison all the contributions to the non-relativistic second-order energy must be included. It is shown that, at least for the Fermi contact interaction, the results are the same to ordermc2α6, so that for this case the reduction of the Dirac equation to non-relativistic form is not suspect, contrary to previous assertions.

ISSN:0026-8976    

DOI:10.1080/00268977500102851

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Various finite nucleus models are used in the calculation of the Fermi contact part of the second-order hyperfine splitting in the ground state of the hydrogen atom. It is shown that any reasonable model successfully avoids the divergence associated with the calculation using the point magnetic moment model. This result should have application to molecular calculations that involve the use of the contact operator to second order.

ISSN:0026-8976    

DOI:10.1080/00268977500102861

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Magneto-optical parameters useful for the interpretation of magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) spectra of high spin d5complexes in tetrahedral or octahedral crystalline fields have been calculated. Two possible intensity borrowing mechanisms—one involving spin-orbit (s.o.) interaction of the ground sextet with the excited quartet states and the other involving the s.o. interaction of an excited charge transfer sextet with the excited quartet states—have been considered for electric dipole transitions inTdsymmetry and for magnetic dipole transitions inOhsymmetry. Of the numerous other mechanisms which may induce electric dipole oscillator strength inOhsymmetry complexes, eight (those in involving odd parityT1uorT2ustates vibronically induced viat1uort2uvibrational modes) have been investigated in detail. In each of these mechanisms, parameters have been calculated for transitions to all individual s.o. components of all excited quartet states. It is shown how the MCD and MLD techniques, if used in combination, may provide specific information on the mechanism of intensity borrowing and on the spectroscopic assignments of individual s.o. components.

ISSN:0026-8976    

DOI:10.1080/00268977500102871

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Most molecular theories of nematic liquid crystals assume that the constituent molecules are cylindrically symmetric. However, although this may be a useful approximation the molecules of real nematogens are of lower symmetry; here we develop a theory for an ensemble of such particles based on a general expansion of the pairwise intermolecular potential together with the molecular field approximation. The dependence of the orientational properties of the uniaxial mesophase on the deviation from molecular cylindrical symmetry is calculated from the series expansion of the pseudopotential. In these calculations the number of arbitrary parameters in the orientational pseudo-potential is reduced by assuming that the anisotropic intermolecular potential originates solely from dispersion forces. The theoretical predictions for the values of the ordering matrix and the entropy change at the nematic-isotropic transition are found to be in good agreement with those observed for 4,4′-dimethoxyazoxybenzene. In addition, the theory provides a reasonable account of the temperature dependence of the order parameter at constant volume for this nematogen. The allowance for deviations from molecular cylindrical symmetry appears to remove many of the discrepancies between the Maier-Saupe theory and experiment.

ISSN:0026-8976    

DOI:10.1080/00268977500102881

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The possibility of applying ENDOR in studies of hyperfine interactions in stable biradicals in liquid solution has been explored. The ENDOR spectra of two phenoxy biradicals are reported. Attempts to record ENDOR of some nitroxide and verdazyl biradicals were unsuccessful. The general structure of biradicals spectra and the relaxation processes which may affect the ENDOR effect are briefly discussed.

ISSN:0026-8976    

DOI:10.1080/00268977500102891

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

E.S.R. spectra of PF4radicals were investigated with single crystals of PF3made at a low temperature and irradiated with γ-rays. The angular dependence of the spectral lines was satisfactorily analysed in terms of the second-order equations for large couplings of one31P nucleus and two magnetically equivalent19F nuclei and of the first-order equation for two19F nuclei with small couplings. We conclude that the two magnetically equivalent fluorine nuclei occupy the axial positions of the trigonal bipyramidal structure of the PF4radical and the other two fluorine nuclei are in the equatorial positions. Furthermore, the unpaired electron of the PF4radical was shown to occupy an orbital consisting mainly of the 2porbital of each of the two axial fluorine atoms along the F-P-F axis and the 3sand 3porbitals, directed towards the vacant equatorial position of the central phosphorus atom. The orbital of the unpaired electron can be reasonably represented as a Rundle three-centre non-bonding orbital. The results obtained for the PF4radicals not only strongly support the results given for POCl3-radicals, but also allow us to discuss the electronic structure of phosphoranyl radicals in more detail.

ISSN:0026-8976    

DOI:10.1080/00268977500102901

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The Van Vleck transformation as previously described is generalized so that it can isolate several levels simultaneously. It is shown that the contact transformation involves projectors in an implicit way and that it can be considered as a special case of the generalized Van Vleck transformation. We discuss to what extent the recursion relations (for further transformation of theNth transform) given in part I can be carried over to the generalized Van Vleck transformation and to the contact transformation. An effective hamiltonian for a particular ‘cluster’ of zeroth-order levels can be obtained in several ways. We compare the results of the usual Van Vleck transformation, Soliverez's transformation and the contact transformation.

ISSN:0026-8976    

DOI:10.1080/00268977500102911

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Simplified inversion techniques are described which enable the potential energy functions of molecules to be determined directly from thermophysical data without recourse to additional information. The accuracy of the methods is confirmed by applying them to the data for krypton, a substance for which the potential energy function is well established.

ISSN:0026-8976    

DOI:10.1080/00268977500102921

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The intermolecular potentials which were recently proposed for neon are examined as to their ability to predict dilute gas bulk properties. The ESMSV III potential due to Farraret al.is found to characterize dilute gas behaviour best.

ISSN:0026-8976    

DOI:10.1080/00268977500102931

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Close-coupling calculations in natural collision coordinates on the reactive scattering of H + H2are reported. A procedure for allowing for anharmonic motion perpendicular to the reaction path is described. The results suggest that the discrepancy between results obtained by Wu and Levine [1] and by other workers is not due to a failure of their method but to their neglect of anharmonic terms in the potential surface.

ISSN:0026-8976    

DOI:10.1080/00268977500102941

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor