W. Burton Lewis

Oxygen‐17 NMR Shifts in Aqueous Solutions of Rare‐Earth Ions

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.

Magnetic Resonance Studies on Copper(II) Complex Ions in Solution. I. Temperature Dependences of the 17O NMR and Copper(II) EPR Linewidths of Cu(H2O)62

The temperature dependences of copper (II) EPR and 17O NMR spectra are analyzed in terms of a tetragonally distorted Cu(H2O)62+ ionic species in which only the equatorial water molecules form strong σ 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 anisotropic g factor and an anisotropic hyperfine coupling constant, and from isotropic hyperfine splitting, are separated. It is found that the spin—lattice relaxation time T1e has components from both spin—rotational and Van Vleck processes. The 17O NMR linewidth is due to scalar hyperfine interaction with the copper (II) electron spin, and the spin‐exchange correlation time τe for this mechanism is determined over the same temperature range. While T1e and τe have similar temperature dependences, τe is 6–8 times smaller than T1e, suggesting that it may be related to inversion of tetragonal distortion in the complex, rather than to electron relaxation.The temperature dependences of copper (II) EPR and 17O NMR spectra are analyzed in terms of a tetragonally distorted Cu(H2O)62+ ionic species in which only the equatorial water molecules form strong σ 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 anisotropic g factor and an anisotropic hyperfine coupling constant, and from isotropic hyperfine splitting, are separated. It is found that the spin—lattice relaxation time T1e has components from both spin—rotational and Van Vleck processes. The 17O NMR linewidth is due to scalar hyperfine interaction with the copper (II) electron spin, and the spin‐exchange correlation time τe for this mechanism is determined over the same temperature range. While T1e and τe have similar temperature dependences, τe is 6–8 times smaller than T1e, suggesting that it may be related to inversion of tetragonal distortion in th...

Magnetic‐Resonance Studies on Copper(II) Complex Ions in Solution. II. Oxygen−17 NMR and Copper(II) EPR in Aqueous Solutions of Cu(en)(H2O)42+ and Cu(en)2(H2O)22+

The temperature dependences of the 17O NMR and Cu(II) EPR spectra of solutions of the ethylenedi‐amine complex ions Cu(en)(H2O)42+ and Cu(en)2(H2O)22+ are analyzed in terms of an octahedrally coordinated structure with tetragonal distortion. It is found that the 17O NMR spectrum is broadened and shifted by Cu(en)(H2O)42+ through scalar hyperfine interaction with the copper (II) electron spin, while Cu(en)2(H2O)22+ 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 B1g ground state of Cu(II) and compared with the previous study on Cu(H2O)62+.

Properties of lithium hydride—III. Paramagnetic resonance of color centers☆

Concentrations of F-centers in excess of 1017cm3 have been produced in single crystals of LiH by neutron irradiation at 78°K. The ESR absorption of the F-centers has been observed at g = 2.004 ± 0.001. The saturation parameter of the ESR absorption (T1T2)12 is dose to that for F-centers in KC1. From r.m.s. line width measurements on LiH crystals of various isotopic compositions (Li7H, Li7D, Li6H and Li6D), spin densities of the F-center electron at the Li+ and H− sites have been estimated.

A study of the kinetics of the reaction between H2 and F2 by EPR methods

Abstract Attesting to its interest for laser-related studies, the reaction between hydrogen and fluorine has recently been studied by a variety of experimental approaches in laboratories throughout the world. An EPR superheterodyne X-band spectrometer was used in the present work in conjunction with a fast flow gas mixing system to obtain both hydrogen and fluorine atom concentrations. The reactant hydrogen atoms were produced by the dissociation of molecular hydrogen in a 2450 MHz microwave discharge unit; the product fluorine atoms were produced by the reaction of hydrogen atoms with molecular fluorine. The changes in both atom concentrations were followed as fluorine was added incrementally to the helium-diluted reactants, H + H 2 . Values of the specific rate constants for the H + F 2 and F + H 2 reactions at 300°K have been found to be 2.5 ± 0.2 × 10 12 cm 3 mole −1 sec −1 and 4 ± 1 × 10 12 cm 3 mole −1 sec 1 , respectively. Under the conditions of our experiments, i.e., at pressures of ca. 2 Torr and with quartz flow tube walls coated with boric acid, the contribution of a branched-chain step to the reaction mechanism appears to be minimal.

Magnetic Resonance Studies on Copper (II) Complex Ions in Solution. III. NMR and EPR in Concentrated Ethylenediamine Solutions

Measurements of the proton and 14N NMR linewidths in ethylenediamine—water solutions of Cu(II) combined with EPR studies of Cu(II) in these media demonstrate that the first sphere relaxation and residence times both make singificant contributions to the over‐all relaxation of protons and 14N by Cu(II). Moreover, the results are consistent with the view that protons and 14N both experience the Cu(II) evironment through exchange of the ethylenediamine molecule as a whole between the bulk solvent and the Cu(II) first sphere. From the temperature dependence of the Cu(II) EPR linewidth it is further concluded that the relaxation of the electron spin occurs predominantly via the spin—rotational process at higher temperatures. At lower temperatures the EPR linewidth is broadened both by tumbling of a tetragonally distorted complex with an anisotropic g factor and hyperfine coupling constant and by the same fast chemical exchange process which provides 14N and proton relaxation in ethylenediamine.

Analysis of the CsNpF6 optical spectrum

A new analysis is given of the CsNpF6 optical spectrum, which removes several features of a previous analysis which were questionable. Possible vibronic structure, SCF–Xα–SW calculations, and analyses of related compounds have been used as a basis for the present investigation. It was found that configuration interaction effects are significant and cannot be neglected. By inclusion of linear CI terms, a fit to 33 assigned levels gave an rms deviation of 140.6 cm−1 in a least‐squares refinement. The parameters determined are F2=202.2, F4=14.26, F6=1.517, ζ=2137, A4〈r4〉=1431, A6〈r6〉=112.6, α=195.2, β=−5798, and γ=9582 cm−1.

Electron Resonance Powder Spectra for Systems with S > 12

A qualitative interpretation, ignoring nuclear hyperfine effects, of the line shapes and positions of all the lines occurring in the ESR powder spectra for S = 32, 52 systems with rhombic environments is presented. The formulation of the problem assumes the zero‐field tensor is dominant in determining the angular dependence of oriented crystal spectra. In favorable cases, g factors and zero‐field splitting parameters can be determined, and results from powder spectra are compared with spin‐Hamiltonian parameters obtained from a single crystal study of Cr3+: (NH4)2[In(H2O)Cl5].

Magnetic Susceptibilities of Some Pu+4 Compounds

The magnetic susceptibilities of Pu(SO4)2·4H2O, Rb4Pu(SO4)4·2H2O, Pu(C2O4)2·6H2O, [(CH3)4N]2‐PuCl6, and PuF4 have been measured over the temperature range 77–334°K. The large departures from the Curie‐Weiss law observed in these salts are discussed in terms of the crystalline field symmetry.