摘要:

The gas phase electron resonance spectra of NCO in its ground2Π3/2vibronic state and in two excited vibronic states are described. Theoretical analysis of the spectra yields effectivegvalues for the three states. In additon the14N magnetic hyperfine and electric quadrupole coupling constants and the electric dipole moment are determined. The theory of the Renner coupling of electronic and vibrational motion is extended, and shown to account for anomalous contributions to thegvalues. The theory also shows that these contributions are closely related to the Renner coupling constant.

ISSN:0026-8976    

DOI:10.1080/00268977100100971

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Nuclear magnetic double resonance experiments were performed on the strongly coupled two-proton system (AB) in 2-chloroacrylontirile to study the spin relaxation processes. The single resonance parameters of the AB spectrum are (operating frequency 100 MHz): |vA -vB|=9.85±0.1 Hz andJAB=2.8±0.1 Hz. Frequency-sweep double resonance spectra were obtained by irradiating each of the four transitions at different strengths of irradiation in the range 0.015 Hz to 2.35 Hz. These spectra were analysed by using the ‘Bloch approximation’ in the rotating frame for the ‘high’ irradiation strengths and the ‘simple line’ approximation for the ‘low’ irradiation strengths. The analysis showed that the proton relaxation in this molecule can be described by interaction with isotropic random fields of nearly equal strengths at the two nuclei with no appreciable correlation between them. Internal dipole-dipole interaction is not a significant mechanism (at room temperature). It is shown that for analysing ‘low’ irradiation spectra the choice of certain functions of intensity changes would lead to a marked distinction between the different relaxation mechanisms.

ISSN:0026-8976    

DOI:10.1080/00268977100100981

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Upon prolonged alkali reduction in ethereal solvents 1,3,5-triphenylbenzene (Tpb), 2,4,6-triphenyl-sym-triazine (Tpt) and 2,4,6-tritolyl-sym-triazine (Ttt) can be reduced to their dinegative ions. Dissolved in rigid solvent matrices these ions produce E.S.R. spectra which are characteristic for randomly oriented triplet systems. Hückel and SCF MO calculations indicate that these dianions have a twofold degenerate lowest anti-bonding level.

ISSN:0026-8976    

DOI:10.1080/00268977100100991

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The well-known Kaplan-Alexander equations for chemical exchange are generalized to include Heisenberg exchange of high spins (S> 1/2). General expressions are obtained for the effect of the exchange on the shape and width of lines and on the population of spin eigenstates. The broadening action of an arbitrary spin on a spin of 1/2 is taken as an example.

ISSN:0026-8976    

DOI:10.1080/00268977100101001

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A phenomenological site hamiltonian is constructed for molecular crystals whose lowest electronic excitations involve an electron transfer, as in many donor-acceptor and free-radical crystals. When only the lowest chargetransfer states are retained, a fermion representation of the site hamiltonian is obtained which leads to a typical many-body problem. The model reduces in special cases to the Hubbard and the Pariser-Parr-Pople models. However, instead of a one-electron, frozen core model, the site representation includes core rearrangements and polarization.

ISSN:0026-8976    

DOI:10.1080/00268977100101011

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The observed change in the phosphorescence decay of the spin-aligned triplet state of pyrazine at 1·6K upon application of a magnetic field is examined both experimentally and theoretically. Experimentally, the decay curve is resolved into the three decay components of the three triplet sublevels in the field range of 0–6000 G. Both the decay constants and the fraction of total initial intensity of each decay component are determined for each field strength. Theoretically, the observed change in the decay characteristics is assumed to be solely due to the Zeeman mixing of the zero-field levels in the absence of spin-lattice relaxation processes. This has the effect of distributing the radiative strength of the strongly radiative zero-field level among the other two weakly radiative zero field levels. A simple approximate calculation gives excellent and encouraging agreement with experimental quantities in the range of validity of the approximations made (below 1000 G). A rigorous calculation was then performed using the exact solution of the secular equation resulting from the Hamiltonian including the spin-spin and Zeeman interactions. Due to the difficulty in finding a host of known crystal structure in which pyrazine can dissolve substitutionally and uniquely, the comparison between theory and experiment is made using a polycrystalline sample. A special averaging procedure is used in calculating a theoretical decay curve for each magnetic field strength used. The theoretical decay curve is then decomposed into three components employing the same computer programme used for decomposing the experimental decay curve. The agreement between the observed and the more rigorous calculated decay quantities is excellent up to 2000 G, but observed disagreement appears above 3000 G and increases with field strength. The calculated lifetimes above 3000 G are found to be longer than the observed ones. The difference is due to other relaxation mechanisms at these high fields, for example, in spin-lattice relaxation processes between the Zeeman sublevels of the lowest triplet state.

ISSN:0026-8976    

DOI:10.1080/00268977100101021

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

At high temperatures the dominant relaxation process which determines the linewidths in the electron resonance spectra of flexible biradicals is modulation of the scalar electron-electron exchange interaction. In systems of high viscosity, the modulation of the exchange interaction is often quenched, and the rotational modulation of the anisotropic magnetic interactions now constitutes the principal relaxation mechanism. In this paper we derive a theoretical expression for the broadening which results from this relaxation process. The applications of the theory to the determination of molecular configurations, electron-electron separations and the sign of the exchange interaction are illustrated by comparison with the electron resonance spectrum of bis(2,2,6,6-tetramethyl-piperidinol-1-oxyl)carbonate. The theory is also of value in understanding the spectra of partially immobilized biradical spin labels.

ISSN:0026-8976    

DOI:10.1080/00268977100101031

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A perturbation calculation of the interaction between close-lying2σ and2II states of diatomic molecules has been carried out to the fourth order. The formula for the spin-splitting of the2σ states thus obtained has been found to yield a proper explanation for the large anomalies encountered in the spinsplitting of theB2σ states of the hydrides and deuterides of Ca, Sr and Ba. Especially for CaH, CaD, SrH and SrD good agreement between theoretical and fitted values has been found for the higher-order correction terms to the spin-splitting.

ISSN:0026-8976    

DOI:10.1080/00268977100101041

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Within the context of pi-electron theory an expression for the proton chemical shifts in conjugated molecules is derived via a current density approach. Using London integral approximations the method is applied to benzene and naphthalene. Provided a particular form of the London Approximation is used, theoretical values in good agreement with experiment are obtained.

ISSN:0026-8976    

DOI:10.1080/00268977100101051

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Calculations are presented of the non-local pi-electron (ring current) contribution to the magnetic anisotropy of benzene and to the chemical shift experienced by an attached proton. The usual London Approximation (to simplify the integral evaluation) is not made, and the method thereby permits of a more detailed analysis of this approximation than has hitherto been possible.

ISSN:0026-8976    

DOI:10.1080/00268977100101061

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor