摘要:

Nuclear magnetic resonance has been carried out on all nuclei with nonzero magnetic moments present in the alkali ion pairs of deuterated and nondeuterated naphthalene radical anion in 1,2-dimethoxyethane. Both the sign and magnitude of the hyperfine splitting constant (h.f.s.c.) were measured, the alkali h.f.s.c. being studied as a function of the temperature. The Li and Na h.f.s.c. appear to be positive, those of Rb and Cs are negative, whereas that of K changes sign with temperature.

ISSN:0026-8976    

DOI:10.1080/00268977100100201

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The synthesis of three nitroxide radicals labelled with13C in the α position makes possible the unambiguous determination of the corresponding13C nuclear-electron contact coupling constant: di-t-butyl nitroxide (1) (quaternary13C), N-methyl13C,N-t-octyl nitroxide (2), and N-methyl13C,N-phenyl (d5) nitroxide (3). The order of magnitude of this interaction is consistent with a polarization of the N-Cα bond by the nitrogen spin density ρnπ. Variations of nitrogen and carbon hyperfine splittingsan,acαandacβ have been studied through the solvent effect on radical (1). For radicals (2) and (3),acαhas the same value. In order to interpret these results (and the similar variation ofahαin H-NO-R nitroxides) we propose to take into account the influence of oxygen spin density ρoπand of the non-planarity of the CNOC system, at least in non-aromatic nitroxides. Study of selective broadening of particular lines in the hyperfine spectra shows that α-carbon interactions are probably negative.

ISSN:0026-8976    

DOI:10.1080/00268977100100211

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The experimental and theoretical literature on the molecular Zeeman effect is surveyed. The observation of the linear (H) and quadratic (H2) Zeeman effect leads to a direct determination of the moleculargvalues, magnetic susceptibility anisotropies and molecular quadrupole moments. The recent results are discussed and the available moleculargvalues, magnetic susceptibility anisotropies, and molecular quadrupole moments are tabulated.

ISSN:0026-8976    

DOI:10.1080/00268977100100221

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The Kerr, Faraday and Cotton-Mouton terms are derived by considering the first-order dispersion relations in static electric and magnetic fields.

ISSN:0026-8976    

DOI:10.1080/00268977100100231

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The assumption that the electric field gradient at the nucleus of a Mössbauer atom is an additive function of the ligands leads to correlations between Mössbauer quadrupole splitting and the coordination geometry. These correlations are associated with a situation known as intermediate symmetry, in which the electric field gradient has higher symmetry than that required by the point symmetry of the complex. The theory of additive electric field gradients is developed by use of cartesian tensors, irreducible tensors, and Shubnikov antisymmetry operators. Underlying symmetry features responsible for the intermediate symmetry are elucidated, and particular models for rationalizing the correlations are seen as manifestations of these symmetries. On making the convenient (but not indispensable) assumption that the metal-ligand bonds have cylindrical symmetry, the so-called ‘point-charge model’ is obtained.

ISSN:0026-8976    

DOI:10.1080/00268977100100241

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The electric dipole moments of the diatomic radicals IO, SF, SeF and SeO (1Δ) have been determined by studying the Stark splitting in their gas phase electron resonance spectra. Previous measurements for several other diatomic radicals are repeated and, in particular, earlier results for NS and SO (1Δ) are corrected.

ISSN:0026-8976    

DOI:10.1080/00268977100100251

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

We report here measurements of the static permittivity as a first step in a dielectric study of rotational motion in liquids up to the critical point. The decrease of the static dielectric constant has been measured along the liquidgas coexistence curve for the liquids C6H5Cl, C6H5F, C6H6, CHCl3, CFCl3, CCl4, SCO and CS2.

ISSN:0026-8976    

DOI:10.1080/00268977100100261

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

An electron-nuclear-double-resonance (ENDOR) study has been made of pentaphenylcyclopentadienyl (PPCPD) and a series ofpara-methylated PPCPD radicals in liquid solution. The hyperfine splitting (hfs) constants in PPCPD and pentamethyl PPCPD (MPPCPD) do not show a significant π-σ spin delocalization effect. This indicates that the phenyl substituents are twisted less than 60° out of the plane of the five-membered ring. A MO calculation based on σ-π separability using the McLachlan approximation gives good agreement between experimental and theoretical hfs constants for a twist angle of 40°. The ring proton hfs constants in PPCPD and MPPCPD are practically identical, indicating a negligible effect of the methyl groups on the spin density distribution. Moreover, the hfs constants in both radicals are not affected noticeably by temperature variations. The ring proton splittings in the partially methylated PPCPD radicals, on the other hand, vary widely and show a marked temperature dependence. The same is true for the methyl proton splittings in these compounds.

ISSN:0026-8976    

DOI:10.1080/00268977100100271

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The nuclear magnetic resonance line width and second moment for the molecular crystal hexamethylethane have been measured from 85°kto the melting point, 374°k. The spin-lattice relaxation timeT1and the spinlattice relaxation time in the rotating frameT1σhave also been measured over the same temperature range. The results have been interpreted in terms of the various molecular motions occurring in the crystal. Below the thermal transition point at 152·5°kmethyl group reorientation and anisotropic molecular reorientation appear to occur simultaneously and with the same correlation time. The activation enthalpy for this motion is 13·4±0·5 kJmole-1. Above the phase transition, the second moment measurements indicate isotropic molecular reorientation, and relaxation time measurements give an activation enthalpy of 9·2±0·5 kJmole-1for this process. Above 250°kmolecular self-diffusion becomes the dominant controlling mechanism for line width andT1p. The activation enthalpy for this process is found to be 82±2 kJmole-1. TheT1presults allow the associated correlation frequency for self-diffusion to be followed from 20 hz to 6 Mhz. The results are consistent with a vacancy diffusion mechanism.

ISSN:0026-8976    

DOI:10.1080/00268977100100281

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The relative signs of all the coupling constants involving1H,29Si and31P in (28SiH3)2P29SiH3and (28SiH3)2Sb29SiH3have been determined by1H-{29Si} and1H-{31P} ‘tickling’ experiments. With the exception of1K(29Si-31P), the reduced coupling constants are probably positive over one and three bonds, and negative over two and four bonds.

ISSN:0026-8976    

DOI:10.1080/00268977100100291

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor