J. A. McMillan

Kinetics of Glass Transformation by Thermal Analysis. I. Glycerol

Thermal analysis of the glass transformation permits the determination of the temperature at which the transformation occurs at a maximum rate. It is found that this temperature depends on the experiments rate of warmup. Appropriate handling of kinetic equations and experimental data permits the evaluation of the thermodynamic functions that characterize the activation barrier. Experimental results on glycerol are comparable to results extrapolated from dielectric relaxation studies.

Electron Spin Resonance Absorption Spectrum of Y3+‐Stabilized CO33− Molecule–Ion in Single‐Crystal Calcite

An electron spin resonance absorption spectrum of effective spin S = 12 exhibiting two hyperfine structure doublet patterns has been observed in naturally occurring single crystals of calcite. The nuclei responsible for these doublets are identified from electron–nucleus double resonance and relative intensity measurements to be 89Y and 13C. From the mean of the spectroscopic splitting tensor values as well as from the 13C hyperfine structure separations, it is deduced that this spectrum is due to the CO33 − molecule–ion which is charge stabilized by a neighboring Y3+ ion. Experimental data suggest the existence of two sets of six equivalent centers each having an orthorhombic g tensor which is diagonal in a coordinate system whose z axis is canted with respect to the crystal [111] direction. The 89Y and 13C hyperfine tensors exhibit orthorhombic and axial symmetries, respectively, with the z axis of each being parallel to the crystal [111] direction. From an analysis of the 89Y hyperfine structure spectr...

Paramagnetic Resonance of Some Silver (II) Compounds

The electron paramagnetic resonance of acidic solutions of silver (II) and several silver (II) solid complex compounds has been investigated. In all cases a strong g anistropy permitted the evaluation of the principal g values. In two cases, the hyperfine splitting could be measured without ambiguity. Parallel measurements of the optical and ultraviolet absorption in the case of silver (II) solutions indicated that the hole is not localized on the paramagnetic ion.

Paramagnetic Resonance of Gamma‐Irradiated Single Crystals of Ice at 77°K

The anisotropy of the paramagnetic resonance spectra of ice crystals irradiated and measured at 77 deg K was studied in- an effort to identify the paramagnetic species indicated by previous experiments. The doses were approximately 1021 ev/cc each, and the spectra were obtained with the c axis parallel and perpendicular to the axis of rotation, which was kept perpendicular and parallel to the static and microwave magnetic fields, respectively. The parallel run showed sixfold symmetry while the perpendicular run showed one canonical orientation with a minimum doublet separation, a maximum g value, and two mirror planes. The spectra show twelve-fold periodicity at 15 deg orientations to each mirror; the results are interpreted in terms of a cylindrically symmetric radical. Polycrystalline ice was also examined, giving two lines with sixfold symmetry in the parallel run; this result indicates the presence of H 2O+.

Motional Effects in the Electron Spin Resonance Absorption Spectrum of CO2– Molecule‐Ions in Single‐Crystal Calcite

The electron spin resonance absorption spectrum of CO2– molecule‐ion in single‐crystal calcite has been reinvestigated as a function of temperature. Between 77° and 250°K the spectrum exhibits orthorhombic symmetry and from the manner in which the widths of the spectral components behave, it is concluded that in this temperature range the CO2– molecule‐ion hops from one to another of three equivalent configurations each being rotationally displaced from the other two by  ± 2π / 3 radians in the (111) plane. Such hops involve the crossing of one of three equivalent potential wells whose depths are estimated to be 0.165 eV and whose widths are not more than 0.1 radians. At 250°K the spectrum associated with the (111) plane is wiped out. Above this temperature an axially symmetric spectrum appears whose parameters are simply related to those of the low‐temperature spectrum, and from the manner in which the widths depend upon temperature, it is concluded that in this temperature region the CO2– molecule‐ion u...

Paramagnetic and optical studies of radiation damage centers in K(H1−xDx)2PO4

Optical and EPR studies of K(H1−xDx)2PO4 (0⩽x⩽1) single crystals irradiated at 77°K with 60Co gamma rays and observed in liquid nitrogen, argon, and oxygen, have permitted not only the identification of two radical species produced as HPȮ−4 and H2PȮ4, but also a description of the annealing processes and their correlation with the ferroelectric transition temperature. Magnetic and kinetic parameters are given.

Electron Paramagnetic Resonance of Dipyridyl‐Coordinated Ag2+(4d9)

The paramagnetic resonance spectrum of solid [Ag dipy2] S2O8 and its solution in nitric acid have been observed at 77°K. The frozen solution exhibits silver hyperfine and nitrogen superhyperfine structure. Due to a strong axial g anisotropy it is possible to determine the principal values of the hyperfine interaction tensors. With these values it is found that the hole in the silver d shell is highly delocalized. Wavefunctions for the unpaired electron are calculated on the basis of the experimental results. Exchange narrowing in the solid wipes out the hyperfine structure.

Electron Spin Resonance Absorption Spectrum of CO2− Molecule Ions Associated with F− Ions in Single‐Crystal Calcite

Single crystals of calcite subjected to γ irradiation exhibit a number of paramagnetic defect centers. One of these has been identified as the CO2− molecule ion which is in close association with an F− impurity ion. An analysis of the ESR superhyperfine structure due to the fluorine nucleus suggests that for 3.3% of the time, negative charge is transferred from the F− ion to the CO2− molecule ion. This transfer of charge creates the diamagnetic CO22− molecule ion and atomic fluorine whose electron configuration is approximately 90% (2s22p5) and 10% (2s2p6). The effective magnetic field at the fluorine nucleus due to core polarization and 2s contact is calculated to be 21 kOe.

Ligand Contribution to the Spin‐Spin Anisotropic Hyperfine Interaction in the Tetragonal Cu2+ Complex Ion

The nondiagonal, first‐order contributions to the hyperfine‐structure anisotropy of EPR spectra of the Cu2+(3d9) ion in tetragonal fields of O, N, S, F−, and Cl− have been calculated. It is shown that such effects are comparable in order of magnitude with some of the effects due to orbital admixture. The ligand s and pz contributions are computed separately and equations for the case of hybrid s–pz orbitals are derived. Tables of values of the nondiagonal term as a function of the metal‐ligand distance are presented. Consideration of the nondiagonal contribution leads to larger values of the electron localization, as exemplified by five cases discussed in this paper.

Experimental Core Polarization of Transition Ions from Electron Paramagnetic Resonance Data

Treatment of available electron paramagnetic resonance data of 2D ions of the 3d and 4d transition series taking into account the transfer of unpaired electronic density to the ligand molecules leads to experimental values of the core polarization within 20% of the theoretical estimates. Experimental values are given for Nb3+, Mo5+, Ag2+, VO2+, and Cu2+. Tentative values are also given for two 5d ions: Pt3+ and Re6+.