摘要:

A previously presented [1] equation of motion of a reduced density matrix for a system of spins coupled to a second system of spins, the latter being strongly relaxed on account of their coupling to a thermal reservoir, is rederived without recourse to coarse-grained methods. It is shown that the procedure developed here, in contrast to the earlier approach [1], can be extended to corrections of fourth and higher orders in the strength of the coupling between the two groups of spins. The fourth-order terms are presented and applied to the2A2B3X spin system, the expression derived being compared, for the first-order limit, with the result of an exact calculation. It is shown that the approach [1] becomes invalid in cases for which there is more than one eigenoperator of the Liouville operator appropriate to the rapidly relaxing spins whose eigenvalues are zero or very small. This is shown to occur when the rapidly relaxing group of spins possesses nuclear permutation symmetry and the relaxation of different spins in this group is strongly correlated. An equation of motion of the density matrix is derived for such cases and applied to the2A3X3Y spin system.

ISSN:0026-8976    

DOI:10.1080/00268977100102131

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The general method of calculating the high resolution nuclear magnetic resonance band shape of a group of spin -½ nuclei scalar coupled to more than one quadrupolar nucleus is described, the2A3X3Y case considered in detail, and computed spectra presented. The detailed treatment is carried out with the assumption that molecular reorientation is sufficiently rapid for the extreme narrowing approximation to be applicable. The relationship between the relaxation matrix method of conducting such band-shape calculations and that based upon analogy with chemical exchange is investigated and it is concluded that the latter approach is inadequate. The band shapes resulting in the limit of rapid quadrupole relaxation are discussed and it is shown that these can be understood using a theory [6] of scalar relaxation of the second kind.

ISSN:0026-8976    

DOI:10.1080/00268977100102141

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Electron spin resonance spectra of the six symmetrical diazanaphthalene anions in N,N-dimethylformamide have been measured. The anions were generated within the microwave cavity by electro-reduction of the parent compound. The McConnell equationaH=QCCHρChas been tested for the diazanaphthalenes withρCvalues calculated by the Hückel method and by the Pariser-Parr-Pople S.C.F. method with variable resonance integrals.

ISSN:0026-8976    

DOI:10.1080/00268977100102151

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268977100102161

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The lowest excited triplet state of diphenyl and of six fluorinated derivatives has been investigated by optical and E.S.R. spectroscopy in ethanol solutions at 77 K. Phosphorescence spectra, lifetimes, zero field energies and hyperfine splittings of Δm=2 and Δm=1 stationary peaks are reported. The principal axes of the zero field splitting tensors were determined by magnetophotoselection. The data are interpreted using a model for the effects of fluorine substitution introduced in Part I and the fluorine hyperfine coupling tensor derived in that paper. The results are: (i) a clear indication of the planarity of phosphorescent diphenyl; (ii) a spin density map of the diphenyl triplet state. The further application of the fluorine labelling method to determine simply the electronic structure of phosphorescent hydrocarbons is outlined.

ISSN:0026-8976    

DOI:10.1080/00268977100102171

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

whereMI(N) is the magnetic quantum number for the set of three equivalent14N nuclei. A simple molecular orbital model of thetrisamino-cyclopropenium system satisfactorily accounts for some physico-chemical properties of I⊕. The E.S.R. results for I2⊕are compared with those for the iso-π-electronic hexamethyl[3]radialene radical anion (II⊖).

ISSN:0026-8976    

DOI:10.1080/00268977100102181

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

In a recent paper, Beveridge and Miller conclude that for the calculation of isotropic hyperfine interactions in simple planar hydrocarbon radicals, a semi-empirical molecular orbital method has some advantages over a semi-empirical valence bond method. In the present work we examine this conclusion and find that the arguments which support it are questionable. Our own critical comparison of the two methods does not lead to a clear conclusion. In addition, we report a method for calculating the degree of orbital following in a spin-unrestricted Hartree-Fock molecular orbital wave function and give numerical results for CH3in its out-of-plane bending mode.

ISSN:0026-8976    

DOI:10.1080/00268977100102191

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

An electron spin resonance study of ClO2and Cl2-adsorbed on faujasite and mordenite has shown that the surface environment can cause significant changes in the spin hamiltonian parameters describing these systems. In the case of faujasite, two distinct adsorption sites are observed. It is shown that the experimental hyperfine shifts can be explained by the presence of strong electric fields, presumably due to the cations in the zeolite structure.

ISSN:0026-8976    

DOI:10.1080/00268977100102201

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The even alternant hydrocarbon pairing theorem is used to justify a new recommended choice for electron placement in radical cations when using the McLachlan α-correction method.

ISSN:0026-8976    

DOI:10.1080/00268977100102211

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Vicinal proton couplings in cyclopropane have been calculated using Dirac-Van Vleck and variational methods in valence bond formalism. The couplings may be considered as taking place along a path comprising either three or four intervening bonds. Inclusion of all exchange integrals in the appropriate fragment models leads to a satisfactory ratio ofJcis/Jtrans. In this respect valence bond results appear to be superior to those obtained using a molecular orbital approach. The present valence bond results on couplings in cyclopropane are not affected by the choice of models for bonding in cyclopropane, namely the Coulson-Moffitt model or the Walsh model.

ISSN:0026-8976    

DOI:10.1080/00268977100102221

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor