Hyperfine Structure In EPR Spectra Research Articles

Fluorine-free synthesis and characterization of vanadium-zircon (V–ZrSiO4) turquoise ceramic pigment by a low temperature solid state reaction route

A fluorine-free and low temperature synthetic route derived from in-situ formed mineralizer has been developed to fabricate V–ZrSiO4 turquoise ceramic pigment. When the calcination temperature is 750 °C and mole ratio of Na3VO4 to ZrOCl2·8H2O (NV/Zr) is 0.3, the as-prepared pigment exhibits a cluster-like structure and deep blue hue (L* = 69.28, a* = −12.15, b* = −20.04). The solid state reaction taking place during the mechanical grinding process lead to the in-situ formation of mineralizer NaCl and certain Si–O–Zr bond. The XRD refinement results and hyperfine structure in EPR spectra indicate that vanadium is located at the zircon interstitial site 16g with an isolated V4+ cluster state. The enameled samples exhibit excellent coloring ability, high chemical and thermal stability, suggesting its potential application in ceramic decoration.

Hyperfine structure of EPR spectra of Gd3+ odd isotopes in PbMoO4, Pb5Ge3O11, YVO4, and quadrupole interaction (temperature dependence)

A hyperfine structure of EPR signals of odd isotopes Gd3+ in Pb5Ge3O11, PbMoO4, and YVO4 single crystals has been investigated at different temperatures. The observation of forbidden (with the nuclear spin flip) transitions has made it possible to determine quadrupole interaction P20 associated with the gradient of the electric field of ligands at the impurity. It has been shown for the first time that, under the condition |P20| ≥ |Ax, y| (Ai are the tensor components), not only the magnitudes of splitting but also the observed asymmetry in a hyperfine structure (in perpendicular orientations of the magnetic field) depends on mutual signs of parameters of initial splitting b20 and P20. Results of studying the spectra have demonstrated that |b20(T)|/|P20(T)| ∼ const for a concrete single crystal, which assumes the similarity of physical mechanisms determining these parameters.

Hyperfine structure in EPR spectra of the catalytic system TiCl4 + Al(i-C4H9)3

In an EPR study of the catalytic system TiCl4 + Al(i-C4H9)3 in toluene and isopentane in TiCl4/oligopiperylene + Al(i-C4H9)3 in toluene, we have observed a dependence of the linewidth of the hyperfine structure on the mobility of the complex in solution.

Electronic structure of Zn‐chlorin π‐anions studied by spectroscopic and quantum‐chemical methods

AbstractElectronic structure of neutral Zn‐chlorin complexes and their π‐mono‐ and dianions has been considered. The π‐anions were obtained by reduction of neutral chlorins with a sodium mirror in tetrahydrofuran solution. Results of spectroscopic studies have been compared with semiempirical quantum‐chemical calculations. Characteristic bands in electronic absorption spectra of the uv, visible and near infrared regions are in good agreement with CNDO/S‐CI calculations. Partially resolved hyperfine structure in EPR spectra of π‐radical anions was observed. Parameters of the EPR spectra obtained by using the simulation technique were compared with spin densities calculated by the INDO method. The detailed interpretation of 1H and 13C NMR spectra of neutral and dianion Zn‐octaethylchlorins is presented. All the proton signals in π‐dianions are shifted upfield because of the influence of paramagnetic ring current. The upfield shifts in 13C NMR spectra of the species studied have been observed too, except for two carbon atoms of the pyrrole ring being placed opposite the hydrogenated one. The 13C peak positions correlate with the charge distribution on C atoms in neutral molecules as well as in π‐dianions. © 1995 John Wiley & Sons, Inc.

Hyperfine Structure of EPR Spectra of Rhombic Binuclear Exchange Clusters in Triplet State

Abstract The hyperfine electron-nuclear interaction in antiferromagnetic rhombic binuclear exchange clusters in the triplet state ( S = 1) is considered. The second-order corrections to the hyperfine energy levels and the probabilities of allowed (Δ M = 1, Δ m 1 + Δ m 2 = 0) and different types of forbidden (Δ M = 1, 2; Δ m 1 + Δ m 2 = 0, 1, 2) EPR transitions for canonical orientations of the external magnetic field are calculated. It is shown that the relative line intensities of parallel low- and high-field fine transitions depend on the parameter of rhombicity E i . The hyperfine structure of the low-field transition is predicted to be equally spaced. The EPR spectra of {Cu[(CH 3 ) 2 CHCOO] 2 · 0.5C 4 H 8 O 2 ) 2 single crystals were studied and explained on the basis of the calculated results obtained.

ChemInform Abstract: Ring Pseudorotation in Pyrrolidine N‐Oxyl Radicals: An Analysis of 13C Hyperfine Structure of EPR Spectra

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

19F ENDOR measurements of transferred hyperfine interactions in CsCdF3:Gd3+and CsCaF3:Gd3+

The transferred hyperfine interaction parameters have been measured at 4.2K by ENDOR for five shells of 19F neighbours around Gd3+ in CsCdF3:Gd and CsCaF3:Gd. The parameters for the octahedrally coordinated ligands are rather different from those previously determined from the transferred hyperfine structure of EPR spectra at 300K by Buzare and co-workers (1977). The authors' own EPR measurements show that the separations of the transferred hyperfine-structure lines are rather smaller than those predicted using the ENDOR data. They are only just consistent for CsCdF3, and they are slightly outside the estimated uncertainty of the EPR data for CsCaF3. There is no evidence of temperature dependence of the separation of the transferred hyperfine-structure lines in the EPR spectrum. Local distortions are deduced from 19F second-shell parameters and these distortions and the ligand-shell parameters are compared with those for octahedrally coordinated 19F ligands in CaF2 and CdF2.

Hyperfine structure of EPR spectra of Cr5+ ions in irradiated sodium dichromate crystals

AbstractEPR spectra are studied of X‐irradiated sodium dichromate crystals grown from an aqueous solution by evaporation at 31°C. Doublet lines of EPR‐absorption are attributed to the Cr5+ ions in the CrO43− and CrO3− radicals resulting from radiation decomposition of Cr2O72− and being in the lattice in two unequivalent positions. Hyperfine structure caused by interaction of an unpaired electron with Cr53 nucleus were observed both at liquid nitrogen and room temperatures. For the line, caused by CrO43− radical, gy and Ay directions coincide and angles both between Ax, gx and Az, gz make up ∼ 25°. The spectrum is described by usual spin Hamiltonian for S = 1/2 with following parameters (T = 77 K): for CrO: gz = 1.984, gy = 1.970, gx = 1.961, |Az| = 8.2 · 10−4 cm−1, |Ay| = 13.7 × 10−4 cm−1, |Ax| = 36.1 · 10−4 cm−1; for CrO3−: gz = 1.915, gy = 1.975, gx = 1.985, |Az| = 32.2 · 10−4 cm−1.

A comparison of calculated and measured hyperfine structure of epr spectra of Mn2+ ion in LiNbO3 monocrystal

An outline of numerical calculation of positions and intensities of spectral lines in EPR spectra of Mn2+ ion in LiNbO3 is presented. Results of numerical calculations obtained by means of computers TESLA 200 and SIEMENS 4004 are compared with experimental spectra. A modification of Jacobi's method of diagonalization is described, which was used for exact solution of a secular equation with Hermitian matrix.

Asymmetries in Cu(II) impurity complexes in asparagine monohydrate crystals

A representative form of cupric impurity ion complexes in asparagine monohydrate crystals is a trans bisasparaginato Cu(II) dihydrate, in which the ion is coordinated by two α amino groups, two carboxyl oxygens, and two H 2O. The complex structure characterized by the ligand nitrogen hyperfine structure in EPR spectra has been found to depend on pH of the solution from which the crystals were grown. In asparagine crystals, water molecules of hydration are directly involved in the impurity complexes and therefore considered to be responsible for the observed pH dependence. The EPR results have indicated that the magnetic structure is asymmetrical, depending on the surrounding proton configuration due to charge compensation for divalent impurity ions.

Effect of composition of coordination sphere on value of constant of additional hyperfine structure of EPR spectra

Replacing the oxygen atoms by sulfur atoms in the coordination sphere of nitrogen-containing copper complexes leads to a substantial increase in the constant of the additional hyperfine structure from the nitrogen atoms, and consequently also to an increase in the degree of covalency of the Cu-N bonds.

Direct Confirmation of the A-Center Model in ZnS by Observation of Hyperfine Structure in EPR Spectra

Direct Confirmation of the <i>A</i>-Center Model in ZnS by Observation of Hyperfine Structure in EPR Spectra

Changes in EPR spectrum of free radical species inγ-irradiated polyformaldehyde

We have found that gamma-irradiated polyformaldehyde does not exhibit the effect of the “disappearance” of the hyperfine structure of EPR spectrum as a function of the dose or the time passed since the end of irradiation, as was found earlier for a group of polymers having only C-C-C-C-atoms in the polymer chain. This difference in the change in the EPR of the polyformaldehyde (PFA) spectrum compared with the polymers with a -C-C-C-C- chain is explained by the impossibility of forming a conjugate double bond in the -C-O-C-O- chain in PFA.