ESR study of vanadyl ion in tripotassium citrate

ESR spectra of VO²⁺ doped tripotassium citrate are recorded at room temperature. The observed spectra are fitted to a spin Hamiltonian of orthorhombic symmetry with g_x = 2.001 ± 0.001, g_y = 1.997 ± 0.001, g_z = 1.945 ± 0.001, A_x = (49.0 ± 1) × 10⁻⁴ cm⁻¹, A_y = (66.8 ± 1) × 10⁻⁴ cm⁻¹ and A_z = (168.4 ± 1) × 10⁻⁴ cm⁻¹. The covalency and Fermi contact terms are evaluated and compared with those of other lattices.     

Orientational (EPR) study of vanadyl ion in potassium hydrogen oxalate lattice

The EPR spectra of VO²⁺ doped KHC₂O₄ crystals revealed two sites with intensity ratio 2:1 and indicated two nearly parallel orientations of the ion in the lattice. On the basis of comparison of the experimentally determined and the calculated direction cosines, only one of the sites could be identified as the substitutional. The other site is suggested to be due to the interstitial occupation of VO²⁺ in the lattice. While the g? tensor is axially symmetric, the à tensor does not show such perfect axial character. The features are explained in terms of the covalency effects arising from hydrogen bonding in the lattice.     

Zero-field EPR of the vanadyl ion in ammonium sulfate

Zero-field EPR measurements of the vanadyl ion in ammonium sulfate have allowed accurate determination of the hyperfine principal values for three physically distinct sites. This has shown that the rhombic distortions in these sites are almost constant, in contrast to results from a previous EPR analysis. Analytical expressions and polarizations are given for the zero-field resonances for the case of axial hyperfine and nuclear quadrupole terms. These, along with calculations using exact diagonalization for the rhombic case, show certain features of the spectrum to be highly sensitive to certain parameters. Line narrowing is explained by analyzing the effect of small local magnetic fields on the energy levels.     

Electron paramagnetic resonance of vanadyl ion impurities in crystalline solids

The electron paramagnetic resonance of VO²⁺ ion impurities has been studied in certain crystalline solids at ~ 9.45 GHz. VO²⁺ shows an isotropic spectra in Mg(ClO₄)₂·6H₂O, RbBr, RbI, CsCl, thiourea, NH₄HC₂O₄·$\text{1}\text{2}$H₂O and urea oxalate at room temperature, and has preferential orientation in MgSeO₄·6H₂O, KHC₂O₄, Rb₂SO₄ and (NH₄)₂M″(SeO₄)₂·6H₂O (M″ = Zn, Co) single crystals. The line broadening of the EPR spectra of VO²⁺ in (NH₄)₂Co(SeO₄)₂·6H₂O observed on cooling the crystal is explained on the basis of host spin lattice relaxation narrowing. The EPR spectra have been analysed and the spin-Hamiltonian parameters evaluated.     

Spectroscopic studies on vanadyl ion in rubidium magnesium sulphate hexahydrate

The optical absorption spectrum of VO²⁺ ion in a single crystal of Rb₂Mg(SO₄)₂6H₂O has been investigated both at laboratory and liquid nitrogen temperatures. The electron paramagnetic resonance (EPR) spectrum of the polycrystalline sample has also been investigated at the laboratory temperature. Both optical absorption and EPR spectra are characteristic of the VO²⁺ ion in tetragonal symmetry. Molecular orbital coefficients have been evaluated by correlating the optical absorption and EPR data.     

Hyperfine interaction parameters and ground-state wavefunctions of vanadyl ion complexes

Using crystal field approach a theoretical estimate of the ground-state wavefunctions of vanadyl ion doped in various crystals have been made using ESR data and is found to bed _xy in our coordinate system with slight admixture of the excited states ,d _xz andd _yz. The hyperfine interaction parameterP and Fermi contact coupling parameterK have also been estimated for these vanadyl-doped crystals. Results agree with similar studies made earlier.     

Covalent binding parameters and the ground state wavefunctions of vanadyl ion complexes

The Steven’s method of molecular orbitals for octahedral complexes containing transition metal ions has been used for estimating the binding parameters and interpreting theg factors of VO ₂ ⁺ ion in single crystals. The expressions forg factors have been given in terms ofK _‖ andK _⊥ taking into account the tetragonal crystalline field and covalent binding effects. Computations show thatK _⊥ should be less than 0.066 in order to fit the experimentalg values. The ground state wave function (GSWF) of VO ₂ ⁺ ion doped in different single crystals has been estimated using crystal field theory. The GSWF is found to be ind _xy state with slight admixture of the excited states ,d _xz andd _yz. The hyperfine interaction parameterP and Fermi contact termX have also been estimated.     

ESR study of fullerene black

Fullerene black before and after annealing at 850°C has been studied by electron spin resonance (ESR). For initial fullerene black, the ESR line exhibits wide wings and its shape is caused by magnetic dipole-dipole interactions between radicals localized randomly on the carbon surface. Dioxygen decreases reversibly the amplitude of the ESR line without changes in its shape, width (0.19 mT) andg-factor (2.0022). This is explained by the assumption that dioxygen molecules adsorbed on the surface broaden strongly ESR lines only of neighboring radicals. For annealed fullerene black, the ESR line is Lorentzian, dioxygen reversibly broadens the line, and theg-factor decreases with the broadening of the line by dioxygen. This is explained by radical-radical and radical-dioxygen spin exchange interactions via conjugated bonds formed in the course of annealing. Flattening of curved carbon surfaces after annealing explains in a uniform way changes in parameters of ESR lines and in reactivity and catalytic activity of fullerene black.     

EPR study of monomeric and dimeric vanadyl ions in SbVO 5

A new compound, SbVO 5 , formed in the V-Sb-O system, has been synthesized and investigated using the electron paramagnetic resonance (EPR) technique. SbVO 5 has been prepared by two methods: by heating equimolar mixtures of V 2 O 5 and f -Sb 2 O 4 in air and by oxidation of the known phase (SbVO 4.5 ) of rutile type obtained in pure argon at temperatures between 550 v C and 650 v C. At room temperature only a weak EPR signal from the powder sample of SbVO 5 was detected corroborating the absence of bulk V(IV) ions in the structure. Comparison with the CuSO 4 reference sample revealed that only 0.02% vanadium ions are EPR active. Intense EPR spectra obtained in the low temperature range, below 100 v K, showed a well resolved hyperfine structure typical of isolated vanadium ions in axial symmetry, present as VO 2+ species, and a broad line attributed to V 4+ -O-V 5+ bonds. The hyperfine structure lines could be analyzed by an axial spin Hamiltonian with g =1.9311, g =1.9425 and A =181 ‐ 10 m 4 v cm m 1 , A =54 ‐ 10 m 4 v cm m 1 . The spectrum recorded at the lowest obtainable temperature T=3.65 v K contains yet another component which is typical of a triplet state indicating the presence of two interacting VO 2+ nuclei with spin 1/2 giving a singlet S=0 and a triplet S=1 state. The appearance of a low-field line (B～1600 v Gs at g , 4) is another diagnostic for the presence of dimeric species and is attributed to the forbidden j M S = - 2 transition.     

ESR studies on Mn(II) ion in Chinese limnetic pearls

The X-band and Q-band ESR spectra of Mn(II) ion in Chinese limnetic pearls have been studied. No ESR signal of melanin-like radical has been detected. A method of theoretical treatment on ESR spectrum of Mn(II) ion has been modified. Using it, the parameters of zero field splitting D=224 Gs, E=74 Gs and E/D=0.33 for Chinese limnetic pearls with bright pearlite colour have been calculated. The computer simulation has been done using experimental ESR spectra parameters, and satisfactory results have been obtained.     

Schottky mass spectrometry at the heavy ion storage ring ESR

Schottky mass spectrometry is a novel method of precision nuclear mass spectrometry based on the measurement of the revolution frequencies of cooled ions in storage rings performed by non-destructive frequency analysis of the beam noise, the well-established Schottky diagnosis technique. The method was applied for the first time at the Experimental Storage Ring ESR at GSI observing electron cooled highly charged ions up to bare nuclei at relativistic energies around several hundred MeV/u. To demonstrate the performance and feasibility of the method at the ESR, experimental tests have been carried out using beams of nuclear fragments produced in the ring itself by the interaction of different primary beams with the internal gas jet target. Futhermore, first Schottky mass measurements of secondary nuclear beams produced by projectile fragmentation of Au and Bi primary beams in a thick Be-target were carried out in order to determine the masses for numerous heavy neutron deficient nuclei which had not been measured before. Relative accuracies for the measured mass values in the order of 1×10^–6 and below can be achieved. The method is briefly discussed and some early results are presented.     

Comparative study of ESR spectra in incommensurate antiferromagnets

The electron spin resonance is studied for noncollinear low-dimensional antiferromagnets RbMnBr₃ and RbFe(MoO₄)₂ in a wide range of frequencies and fields. Both compounds have incommensurate spin structures appearing due to a low-symmetry distortion of an ideal hexagonal crystal lattice. Magnetic field applied in the spin plane induces a first-order transition into the commensurate phase. The low-energy resonance branch corresponding to a uniform oscillation of the spin system in the easy plane is observed in the two compounds in both incommensurate and commensurate phases, with a dramatic change of the spectra taking place near the transition field. The resonance spectrum of a nearly commensurate spin structure with long-wave modulations is analyzed in clean and dirty limits in the framework of a hydrodynamic approach. The resonance branch with steep field dependence in the incommensurate state is attributed to the acoustic mode with the gap resulted from pinning of local domain walls (discommensurations) on defects of the crystal structure.     

ESR study of impurities in strontium titanate films

The paper reports on an ESR study of Cr-and Ca-codoped SrTiO₃ films, 1700 and 350 nm thick, before and after UV irradiation (λ=365 nm). The spectrum of the thick film (1700 nm) exhibits two ESR lines with g factors of 1.977 and 1.974, which belong to the Cr³⁺ centers. In the spectrum of the thin film (350 nm), one observes only one line, which is due to the chromium center with a g factor of 1.974. Calculations showed that the line with the smaller g factor belongs to the Cr³⁺ center located close to the film surface. The weak line observed in the spectrum after UV irradiation (g factor = 2.012) is most likely due to the O^? center. The regions of thermal stability of the observed centers were studied. A comparative analysis of the characteristics of impurities in bulk samples and films was carried out.     

An investigation of the surface-enhanced Raman scattering (SERS) effect from laser irradiation of Ag nanoparticles prepared by trisodium citrate reduction method

By irradiating a Ag colloid solution, produced by trisodium citrate reduction method, employing the active Quanta Ray Nd:YAG laser system, λ = 1064 nm, we prepared relatively small, spherical Ag nanoparticles with a narrow size distribution. The irradiated particles not only improve the configuration, but also the spectroscopy properties to some extent. The influence of the laser fluence on the irradiated energy was studied, via transmission electron micrograph (TEM) images, surface plasmon absorption (SPA) spectra, and surface-enhanced Raman scattering (SERS) spectra. Those benefit to understanding the spectroscopy properties of irradiated particles to obtain precise understanding of the mechanism. And probably the reasonable explanations are given.     

ESR study of color centers in yttria stabilized zirconia

The ESR of single crystals of yttria stabilized zirconia (YSZ), containing color centers due to reduction in a flowing H₂ atmosphere, has been measured at room temperature. The spin density is about 3 × 10¹⁷ cm^?3 and the strong ESR line displays axial symmetry with principal values g₆ = 1.989, g_⊥ = 1.860.The behaviour of the ESR spectra when the magnetic field is rotated about the 〈1 0 0〉 and 〈1 1 0〉 directions shows that the centers have axial symmetry, the symmetry axis being along the 〈111〉 and equivalent directions. The derivative peak to peak envelope width is g-dependent and varies from 18 Gauss at g = 1.989 to 65 Gauss at g = 1.860. The results are interpretable in terms of an electron trapped at an oxygen vacancy adjacent to an yttrium ion.     

ESR study of exchange coupled pairs in copper diethyldithiocarbamate

ESR investigations on exchange coupled pairs of Cu ions in single crystals of Cu(dtc)₂, isomorphously diluted with the corresponding diamagnetic zinc salt, are reported. The spin Hamiltonian parameters for the coupled species (S=1) are:g _‖=2.1025,g ₊=2.031,A=75.1×10⁻⁴ cm⁻¹,B=14.8×10⁻⁴,D=276.0×10⁻⁴ cm⁻¹ andE=46.7×10⁻⁴ cm⁻¹. While theg andA tensors show tetragonal symmetry, the zeor-field splitting tensor is rhombic and has principal axes different from those of theg andA tensors. Intensity measurements made down to 4.2 K indicate that the exchange is ferromagnetic with |FFF| ∼ 10 cm⁻¹. Direct dipole-dipole interaction appears to be the major contribution to the zero-field splitting. A calculation on the distributed point dipole model shows that dipolar interaction is considerably modified by the high covalency of the Cu-S bond and accounts for the rhombic nature of the tensor. The possible exchange mechanisms in Cu(dtc)₂—direct exchange and superexchange through the bridging sulphurs—are discussed.