摘要:

Phosphorescence microwave double resonance experiments are reported on Zn porphin at 1·2 K. In glassy solution very broad resonance transitions are observed. However, for Zn porphin in a crystallinen-octane matrix—a system known for its sharp optical spectra (Shpolskii effect)—three pairs of microwave transitions with widths of a few MHz are found, all of them corresponding to a decrease in phosphorescence intensity. By studying the behaviour of the signals for various methods of preparation of the sample and as a function of the optical bandwidth of excitation and detection, one pair of transitions could be assigned to monomeric solute molecules. The corresponding zero-field splittings are |X-Z| = 1355, |Y-Z| = 806 MHz. It was further established that by ‘pumping’ either of these transitions a third one can be detected at the difference frequency, so that the order of the levels must beX>Y>Z(or reverse). The results indicate that the molecule no longer possesses a four-fold axis in the excited state. What one observes must be the lowest vibronic level of a Jahn-Teller unstable state, the degeneracy of which is removed by an anisotropic crystal field. From some preliminary E.S.R. experiments on zinc porphin in an EPA glass at 77K it is concluded thatZcorresponds to that component where the angular momentum lies in the molecular plane; for aππ* electronic state this is expected to be the lowest in energy of the three.

ISSN:0026-8976    

DOI:10.1080/00268977100103061

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The dynamics of populating and depopulating the phosphorescent triplet state of Zn porphin in ann-octane matrix is investigated by microwave induced delayed phosphorescence experiments at 1·2K. Values for theabsoluterates of decay of the three spin levels are given and also therelativesteady-state populations, radiative decay rates and probabilities for entry through intersystem crossing. Further, it is established that the phosphorescence is inplane polarized. The results are compatible with the decay modes expected for a lowest vibronic state that deviates fromD4symmetry by combined action of the Jahn-Teller effect and crystal field anisotropy.

ISSN:0026-8976    

DOI:10.1080/00268977100103071

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The Karplus-Kolker approximate uncoupled Hartree-Fock perturbation scheme is compared with the corresponding coupled variation-perturbation approach. The first-order perturbation-like corrections to the Karplus-Kolker second-order energies are defined and their meaning and relative importance are discussed. Also a geometric approximation to the coupled Hartree-Fock perturbation theory, based on the Karplus-Kolker method, is examined. To account properly for the coupling effects an alternative approach, called the coupled geometric approximation, is proposed.

ISSN:0026-8976    

DOI:10.1080/00268977100103081

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

It is suggested that the method of Wannier functions could be used advantageously in connection with theπ-electron problem in long polyenes. The question of the localization of the Wannier functions is discussed and formulae are derived for the matrix elements. The use of the method is demonstrated by an application to the benzene molecule.

ISSN:0026-8976    

DOI:10.1080/00268977100103091

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The E.P.R. spectra of the monovalent positive and negative ions of 1,2,3,6,7,8-hexahydropyrene reveal an alternating line broadening, caused by the non-synchronized motion of the two aliphatic bridges in the molecule. When this motion is described by the modified Bloch equations, using a four-sites jump model, spectra are obtained which agree quite well with the experimental ones.

ISSN:0026-8976    

DOI:10.1080/00268977100103101

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

For aromatic hydrocarbon radicals in non-degenerate electronic states there is excellent agreement between theory and experiment for the deviation of thegfactor from the free electron value, but this agreement is not present for degenerate radicals. This work extends the theory to degenerate radicals and it is shown that allowance must be made for the presence of orbital angular momentum and that, in estimating this, account must be taken of a number of factors, notably vibronic coupling. Calculations show that this theory is capable of explaining the anomalousg-factor deviation in the benzene anion.

ISSN:0026-8976    

DOI:10.1080/00268977100103111

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Gas-phase E.P.R. spectra of35ClO have been measured accurately both in theJ=5/2 andJ=3/2 rotational levels, using C-band (4·4 GHz) and X-band (9·4 GHz) microwaves, respectively. Special attention has been paid to separate the spectral lines of35ClO from those of37ClO. Analysis of the spectra has resulted in the simultaneous determination of the hyperfine parametershandband, when combined witha-(b+c)/2 obtained by microwave spectroscopy, the hyperfine parametersa, bandcare all determined. Molecular constants which describe the distribution of the unpaired electron around the chlorine nucleus are derived from them. The moleculargvalues of the rotational levels indicate the mixing of the2Π state both with the2Σ+ and with the2Δ electronic excited states.

ISSN:0026-8976    

DOI:10.1080/00268977100103121

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Dans un article précédent [1] les auteurs ont discuté l'écriture de l'énergie cinétique à l'aide d'opérateurs quasi-moments pour le mouvement deNparticules. Dans cet article, les résultats de [1] sont appliqués à la transcription quantique de l'énergie cinétique des noyaux dans une molécule, écrite à l'aide d'un système d'axes mobile lié à la molécule. Il est montré, en particulier, que, dans le cas des molécules quasi-rigides, la vérification des conditions de Wilson-Howard est nécessaire et suffisante pour l'hermiticité des quasi-moments utilisés et que, dans le cas des molécules non-rigides, elle n'est que suffisante.

ISSN:0026-8976    

DOI:10.1080/00268977100103131

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The definition of the quantity ‘bond order’ is discussed. The molecularorbital (Coulson) definition, the valence-bond (Penney-Dirac) definition and a definition recently proposed by Coulson and Maclagan, involving the two-particle density matrix rather than the one-particle density matrix, are compared using molecular-orbital wavefunctions and valence-bond wavefunctions neglecting ionic structures as two extreme descriptions of theπ-electron structure of molecules, using minimal basis sets. ‘Bond order’ is shown to be a quantity whose numerical values are relatively independent of its definition. The effect on bond order of the non-neglect of overlap is considered. Butadiene and benzene are used in comparing the various definitions. A valence-bond calculation on butadiene using the same integrals as Parr and Mulliken's molecular-orbital calculation is described.

ISSN:0026-8976    

DOI:10.1080/00268977100103141

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A theoretical study is presented of the effects of solvent molecular motion on nuclear spin-spin coupling constants. Solvent molecules are treated as point dipoles arranged around the solute molecule in a cubic closest packed arrangement. Average dipole moment vectors are given by a rotational Boltzmann average and the resulting perturbation is included in the Fock matrices. Calculations of nuclear spin-spin coupling constants were performed by self-consistent perturbation theory in the INDO (intermediate neglect of differential overlap) approximation of self-consistent-field molecular orbital theory. Calculated results are compared with the experimental data as well as the results of previous models.

ISSN:0026-8976    

DOI:10.1080/00268977100103151

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor