The temperature dependences of copper (II) EPR and 17 0 NMR spectra are analyzed in terms of a tetragonally distorted Cu(H20)e2+ ionic species in which only the equatorial water molecules form strong (1' bonds to copper (II). By reconstructing the EPR spectra at temperatures in the range _10° to 100°C the contributions to the linewidth from spin-lattice relaxation, tumbling of an ionic complex having an aclsotropic g factor and an anisotropic hyperfine coupling constant, and from isotropic hyperfine splitting, are separated. It is found that the spin-lattice relaxation time Tlo has components from both spin-rotational and Van Vleck processes. The 17 0 NMR linewidth is due to scalar hyperfine interaction with the copper (n) electron spin, and the spin-exchange correlation time T. for this mechanism is determined over the same temperature range. While Tlo and T. have similar temperature dependences, T. is 6-8 times smaller than T1., suggesting that it may be related to inversion of tetragonal distortion in the complex rather than to electron relaxation.'
Paramagnetic and diamagnetic shifts of the O17 NMR signal in aqueous solutions of the rare-earth ions at room temperature have been observed. The shift arises from the isotropic part of the hyperfine interaction between the O17 nucleus and the thermal average value of the spin of the rare-earth ion. The direction of the shift is in all cases opposed to the spin magnetization of the rare-earth ion. This result is explained through the formation of covalent bonds in the hydrated ion involving the rare-earth 6s orbital.
The temperature dependences of the 17 0 NMR and CU(Il) EPR spectra of solutions of the ethylenediamine complex ions Cu(en) (H20) ,2+ and Cu(en),(H20)22+ are analyzed in terms of an octahedrally coordinated structure with tetragonal distortion. It is found that the 17 0 NMR spectrum is broadened and shifted by Cu(en) (H20).2+ through scalar hyperfine interaction with the copper (II) electron spin, while Cu(en)2(H20j.2+ has no effect. The Cu(II) EPR spectra of both species have linewidth contributions from spin-rotational relaxation, from tumbling of an ionic complex having an anisotropic g factor and an anisotropic hyperfine coupling constant, and from 63CU isotropic hyperfine and 14N isotropic extrahyperfine splitting. The results are discussed in terms of the antibonding molecular-orbital model for the Blg ground state of Cu(II) and compared with the previous study on Cu(H20)a2+.
Complex vibronic structure has been observed in the electric-dipole-forbidden charge transfer absorption bands of solid and matrix-isolated UF 6 in the temperature range 8-14 K. These bands have their maximum intensity near 260 and 375 nm. Associated with the 260 nm band are four electronic transitions with origins at 30331, 31032, 32120, and 32821 cm-" the first two being observed directly. Two more nophonon transitions are associated with the weak band at 375 nm, one at 24564 cm-I and another at 25265 cm-I . These levels are assigned via a weak j-j coupling scheme as excitations from the ligand tluG" orbital to empty uranium Sf orbitals. Uranium spin-orbit coupling in UF 6 charge transfer states strongly resembles that of UF 6 -. Several progressions in the symmetric stretch frequency VI = 580-595 cm-I are present which have as their origins various combinations of the above electronic levels with the bending modes V" vs, and V6 or their overtones 2v •• 2vs, and 2V6' Temperature effects, which account for the principal differences between the gas and solid spectra, are also discussed. A much more intense band at 214 nm is lacking in vibronic structure and is attributed to an allowed charge transfer transition.Although the Cary 14 spectrometer appeared to have more than adequate resolution for the UF 8 spectrum, a
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