[en] The ¹⁹F NMR of single crystals of TbF₃ and HoF₃ is reported. For both crystals the shift tensor is determined at room temperature for the two different fluoride ion sites in the orthorhombic crystal lattice. The shift tensor for Type I sites in TbF₃ is also determined at 548 K. The temperature dependence of both the isotropic and traceless shift tensors is separately determined for each site in the temperature interval of 175 to 370 K for HoF₃ and 175 to 548 K for TbF₃. Comparison of the experimental traceless shift tensor of TbF₃ and ErF₃ with that calculated from a point dipole model, using experimental susceptibility data from single crystals, shows systematic differences that cannot be attributed to spin transfer mechanisms or defects in the point dipole model. The differences are most probably due to errors in the crystal structure used to calculate the point dipole contributions. It is shown that the pseudo-contact term contributes only 10% of the observed isotropic shift and that the isotropic shift exhibits remarkable changes as we go across the periodic table from TbF₃ to ErF₃. ¹⁹F resonances from one site in TbF₃ are observed to broaden and disappear in the interval 420 to 490 K owing to some type of diffusional motion whose activation energy is estimated to be 40 to 60 kJ/mole. (author)

[en] A fluorine-19 NMR study of single crystals of NdF₃ and PrF₃ is reported. The shift tensors are determined, at 97 K for NdF₃ and 103 K for PrF₃, for the three types of fluorine in the trigonal unit cell. Point-dipole interaction accounts for only 45% of the traceless part of the shift tensors, the rest being a contribution from two spin-transfer mechanisms: a covalent and a spin-polarization mechanism. Expressions are derived and used to estimate the contributions from both. The lowest-symmetry fluorines undergo diffusional motion in the range 280 to 360 K for NdF₃ with an activation energy of 26.5 kJ/mole and in the range 240 to 300 K for PrF₃ with an activation energy of 4.8 kJ/mole. This diffusion is discussed and compared with similar behavior in other lanthanide fluorides. (author)

No abstract available

No abstract available

[en] The ESR spectrum of ¹⁷0-labeled N0₃^2- radical ions formed by γ-irradiation of KN₃ crystals doped with ¹⁷0-enriched KN0₃ was studied. The room-temperature spectrum exhibits hyperfine splitting due to ¹⁴N and three equivalent ¹⁷0 nuclei. The hyperfine tensors for both nuclei and for the g tensor are axially symmetric, with principal components: Asup(N) (parallel) = 60.8 G, Asup(N) (perpendicular) = 31.6 G, A⁰ (parallel) = 33.0 G, A⁰ (perpendicular) = 4.4 G, g (parallel) = 2.0018, g (perpendicular) = 2.0060. On cooling the sample the oxygen-17 satellite spectrum broadens and below about 90⁰C it sharpens again, yielding a complicated many-line spectrum. These results are interpreted in terms of a dynamic process in which the N0₃^2- radical undergoes rotational motion about its C₃ symmetry axis. At room temperature this motion is sufficiently fast to average the hyperfine tensor of all three oxygen nuclei, while at low temperatures the motion is frozen out and the oxygen nuclei become magnetically inequivalent. (author)

[en] Electron spin resonance spectra of γ-irradiated NaN0₃ show the presence of a peak due to the neutral N0₃ radical. It has an axial g tensor with components g (parallel) = 2.0047, g (perpendicular) = 2.0231. No hyperfine splittings due to ¹⁴N nuclei are observed in its spectrum but in ¹⁷0-labeled crystals a single set of ¹⁷0 satellites is observed. The oxygen-17 hyperfine tensor components are A⁰ (parallel) = 39.2 G, A⁰ (perpendicular) = 3 G. These results suggest that the N0₃ radicals occupy the sites of the parent N0₃^- ions in the crystals and are rapidly rotating about their C₃ symmetry axis. (author)