ESR Line Research Articles

ESR in conducting polymers: Oxygen-induced contribution to the linewidth.

The oxygen-induced ESR line broadening has been investigated in the case of the conducting polymer polyaniline in powder and in film form. Pumping under vacuum results in a narrowing of the ESR linewidth. After initial pumping various oxygen containing gases have been applied to the sample (pure ${\mathrm{O}}_{2}$, ambient air, dry air) and the linewidth has been measured as a function of time. The residual water in these gases was found to seriously affect the narrowing behavior of the linewidth. A theoretical calculation is proposed showing that the line broadening is proportional to the oxygen concentration and to the polaron mobility. Considering the linewidth dependence upon applied oxygen pressure an evaluation of the polaron mobility is obtained. This value is consistent with the values estimated from previous spin dynamics studies. An evaluation of the exchange integral is also given.

Esr of heavily neutron-transmutation-doped germanium

Integrated electron spin resonance is used to monitor the magnetic properties of the electron spin in a sample of NTD Ge using temperatures down to 40 mK and uniaxial stresses up to 0.36 GPa. The sample density is just below the critical density at ambient stress for the metal-non-metal transition. The electron spin susceptibility under stress shows no temperature variation; a small broadening as T is lowered is matched by a similar decrease of intensity. Further, uniaxial stress enhances the intensity of the esr line. The contrast with Si∶P is discussed. A large ‘stress-tuning’ effect is inferred.

Magnetic interactions between Gd ions in Gd xY 1− xBa 2Cu 3O 7−δ: An ESR investigation

We analyse the ESR line width of Gd in Gd x Y 1− x Ba 2Cu 3O 7−δ as a function of the Gd concentration x and temperature in the normal state. The powder samples were oriented in a magnetic field of 7 T. An orientation dependence of the line width was found. The experimentally observed change of the ESR line width with Gd concentration x is compared with a model calculation based on the Gd-spin dipole-dipole and exchange interaction. The absence of resolved fine-structure splitting is explained by a dominance of the dipole-dipole and exchange interaction.

Microwave magnetoabsorptions of Bi 2(Ca,Gd,Bi) 3Cu 2O z superconductor

Microwave magnetoabsorptions were observed for a Bi 2(Ca,Gd,Bi) 3Cu 2O z superconductor over a temperature range from 6 K to room temperature. A broad absorption slope of Gd 3+ was observed with the external static field from 0 to 6 kOe, because a weak antiferromagnetic order occurred in the Gd 3+ sublattice. When each particle is small in a powder specimen, a usual ESR line of Gd 3+ was observed due to superparamagnetism. Nonresonant microwave absorptions due to superconductivity were observed below 56 K, and the lower critical field as well as the diamagnetic susceptibilities were determined.

Thermoluminescence and Electron Spin Resonance of Atomic Hydrogens in Coesite and Stishovite, High Pressure Phases of SiO2

Thermoluminescence (TL) of coesite and stishovite has been measured after γ-ray irradiation at room temperature from 60 Co. Analysis of the first TL peaks at 205°C indicates an activation energy, E I =1.20 eV and a pre-exponential frequency factor, s =1.3×10 12 Hz; the second peaks are at 240°C and at 255°C giving E II =1.27 eV and 1.32 eV for coesite and stishovite, respectively. ESR lines at g =2.002 with A ⊥ =46 mT and A ∥ =59 mT show the same isochronal annealing behavior with the same parameters of thermal stability as those of the first TL peaks. Other ESR lines at g =2.002 with A ⊥ =50 mT and A ∥ =53 mT are stable to high temperature. Atomic hydrogens, H 0 , in densified amorphous and in crystalline parts are responsible for the ESR signals and the release of trapped H 0 leads to recombination with a hole center emitting the TL light.

Mixing of the sideband lines from an ESR absorption. Proposed technique of the modulation-frequency sweep curve

Experimental and theoretical studies have shown that a mixing occurs for the sideband-lines from a modulated ESR absorption. This suggested a new technique which enables one to measure the lifetime of the Zeeman state, or true T 2 of the individual spin packet of an inhomogeneously broadened ESR line.

Far-infrared spectroscopy in high magnetic fields

A far-infrared spectrometer. which can be used in the energy range between 3 and 40 cm −1, has been constructed to measure magneto-optical spectra with the Tsukuba Magnet Laboratories hybrid magnet system. The spectrometer was examined by measuring ESR of the inorganic spin-Peierls (SP) compound CuGeO 3 with a superconducting magnet instead of the hybrid magnet. ESR lines were observed at steady fields for both the SP phase and the field-induced incommensurate M phase.

Allowed Values of Ratios of the Rotational Diffusion Constants for a Radical with Four Equivalent I = 1/2 Nuclei

The ESR line widths of a radical (S = 1/2) with four equivalent I = 1/2 nuclei divided into two completely equivalent pairs can be used to obtain ratios of the elements of the rotational diffusion tensor when it is not possible to determine the individual tensor elements, Di. Two nuclei are equivalent if the zero-order spin Hamiltionian, H0, is invariant with respect to their interchange; the nuclei are completely equivalent if the time-dependent spin Hamiltonian responsible for the relaxation, H1(t), is also invariant with respect to their interchange. The anion radicals of para-disubstituted benzenes are examples of this type of spin equivalence; the ratio of the reorientational line width parameters C/B can be used to obtain a second degree equation that gives two values of ρx = Dx/Dz for a given ρy = Dy/Dz ≥ 0. The analysis of C/B for p-benzosemiquinone (PBSQ) in ethyl alcohol (EtOH) shows that one of the values of ρx is always positive while the other is always negative (and physically unacceptable)....

Bistable Magnetic Resonance of Conduction Electrons in Solids

The phenomenon of bistable hysteresis in magnetic resonance of conduction electrons in solids is discussed, particularly the case of gallium oxide β-Ga2O3. This memory effect is a consequence of the dynamic polarization of nuclei by the Overhauser effect and manifests itself by a hysteresis of the ESR line provided that particular conditions for the external (or control) and internal (or material) parameters are satisfied. The influence of all these parameters on bistability is studied in detail. It is shown that magnetic resonance of conduction electrons in solids containing nonzero nuclear spins is an intrinsically bistable phenomenon. The reasons why bistability is so strong in gallium oxide even at room temperature, compared to other identified compounds where bistability exists only at very low temperature, are discussed in terms of electronic and crystallographic structure.

Orientation and Dynamics of NO2 in a N2O4 Host Matrix Prepared on a Plane Surface Investigated by ESR Line Shape Analysis

Thick films (approximately 100 μm) of NO2/N2O4 were prepared in a combined ultrahigh-vacuum ESR apparatus by adsorption of gaseous NO2 through a dosing system on a single-crystal surface (NiAl(110)). The adsorption temperature was in the range from 35 to 65 K. The line shapes of the ESR spectra are dependent on the adsorption conditions and show remarkable changes in heating processes. These observations can be explained in terms of geometrical rearrangements and molecular dynamics of the NO2 monomers. The line widths vary from 2 to 10 G depending on the concentration of ESR-active molecules through magnetic dipolar interactions. In all cases the observed line shape itself cannot be described by a simple distribution of randomly oriented molecules. The analysis of the spectra indicates a preferred molecular orientation with the NO2 C2 axis perpendicular to the surface plane of the substrate. The spectra are fitted by computer simulation using a line width that depends on the z component of the nuclear spi...

Simultaneous ESR measurements of the kinetics of oxygen consumption and spin label reduction by mammalian cells

AbstractNitroxide spin labels and probes were applied to measurements of cell redox activities and oxygen concentration by ESR. Current experimental methods often require large numbers of cells and monitoring of only the amplitude of the ESR signal. This can result in experimental artifacts and data misinterpretation. An improved method is described for accurate measurement of nitroxide intensity and linewidth, which in turn provides information about cell redox activities and oxygen concentration. The method is based on fitting of ESR spectra using a fast convolution least‐squares algorithm suitable for inhomogeneously broadened ESR lines. All fitting parameters, including the Lorentzian component of the linewidth and the double integrated intensity, are extracted from the experimental spectra directly. The experiments were carried out at cell concentrations of 5 × 106 cell ml−1 or less to prevent cell crowding and at initial nitroxide concentration of 1 mM or 100 μM to ensure that nitroxide metabolism by the cells was not diffusion limited. Examples include experiments with cultured baby hamster kidney and adenovirus transformed hamster cells using the nitroxide radicals TEMPOL (2,2,6,6‐tetramethylpiperidine‐N‐oxyl‐4‐ol) and 15N‐labeled perdeuteriated TEMPONE (15NPDT) (2,2,6,6‐tetramethylpiperidine‐N‐oxyl‐4‐one). Under these experimental conditions, the rates of nitroxide metabolism derived from changes in nitroxide intensity are independent of oxygen concentration.

Kinetics of free radical decay reactions in lactic acid homo and copolymers irradiated to sterilization dose

The kinetics of free radical decay reactions of poly(L-Lactic acid), poly(DL-Lactic acid) and random copolymer of lactic and glycolic acid have been investigated for decays taking place in air and in vacuum. The change in ESR lines of γ-irradiated polymers have been followed over a long time period. The decay has been found to follow neither simple first-order nor second-order kinetics. Various kinetic approaches including composite first or second-order mechanisms and diffusion-controlled first or second-order equations were determined to be also unsatisfactory. The decay of radicals in bulk irradiated lactic acid homo and copolymers was found to be best described when the second-order non-classical equation with time dependent rate constant approach was used.

On the antiphase structure of the ESR spectra of spin-correlated radical pairs. Dependence on dimensionality

The ESR lineshape of spin-correlated radical pairs (RP) diffusing in a small volume is calculated within the sudden perturbation approach for space dimensionalities D = 1, 2, 3. It is shown that in 2D and 3D models the RP spin dynamics are described by a Bloch-type equation quite accurately. A simple formula for the antiphase structure of the ESR lines is derived. The results obtained differ essentially from those predicted in the quasistatic approximation.

The Electrical and Magnetic Properties of a Novel Two-Dimensional Antiferromagnet Based on BEDT–TTF: θ-(BEDT–TTF)2Cu2(CN)[N(CN)2

Abstract A crystal-structure analysis and a band calculation, as well as conductivity, thermoelectric power, ESR, and static susceptibility measurements were performed on the new BEDT–TTF salt, θ-(BEDT–TTF)2Cu2(CN)[N(CN)2]2. This salt has a unique polymerized anion comprising infinite Cu–N(CN)2–Cu double helices bridged by disordered CN groups. Although the two-dimensional arrangement of crystallographically equivalent BEDT–TTF+0.5 cations provides a two-dimensional closed Fermi surface within the tight-binding approximation, this salt is semiconductive even at room temperature, probably due to a strong electron correlation in this system. A semiconductor–semiconductor transition has been observed around 220 K. Below 220 K the electronic system is represented as a Mott insulator and a two-dimensional Heisenberg antiferromagnet. Rapid decreases in the ESR line width and spin susceptibility below 50 K indicate the existence of an additional magnetic transition.

An E.S.R. study of penetration depth in high- Tc BiSrCaCuO superconductors

X-band microwave penetration depth has been measured in two sol-gel synthesised BiSrCaCuO superconductors (A) 2212 and (B) Pb - doped 2223 in the range 77 K – 300 K by conventional ESR using DPPH decorated pellet samples. The T c ′s were found to be 84 K for A, and 104 K for B which were confirmed by the low field microwave absorption. The widths of observed (Gaussian) ESR lines were related to the penetration depth below T c using Brandt's model for a triangular vortex lattice. From an analysis of the temperature dependence of λ, we found λ o for A as 2400 ± 100 A ̊ and for B as 2582 ± 100 A ̊

A quantitative electron spin resonance line shape study of the order-disorder transition in the lamellar phase of the palmitoyllysophosphatidylcholine-water system

A quantitative slow-motional ESR line shape study is reported of the lamellar phase and the micellar phase of the palmitoyllysophosphatidylcholine (PaLPC)-water system. The lamellar spectra are simulated using the microscopic order-macroscopic disorder (MOMD) model developed by Meirovitch, E., Nayeem, A., and Freed, J. H., 1984, J. phys. Chem., 88, 3454, whereas the micellar spectra are interpreted in terms of a two-dynamics model developed in this laboratory (Liang, Z., and Westlund, P.-O., 1993, J. chem. Phys., 99, 7098). For the lamellar phase, an order-disorder transition is observed from the temperature dependence of the spectra and quantized in terms of the model parameters, yielding a transition temperature of about 45°C. A comparison of the model parameters is made between the lamellar and the micellar phases, which indicates a phase independence of the local orientational order. A similar comparison is made also between the oleoyllysophospatidylcholine-water and the PaLPC-water systems in the lam...

The photoreduction of methylviologen via electron transfer from aluminosilicate zeolites

The photoreduction yields of methylviologen and various alkylated homologues in zeolite-X, Y and A were determined at 77 K in the absence of any reducing counteranion. Upon irradiation at 77K, dehydrated samples turned light blue and a single line ESR spectrum was observed with a g-factor identical to that of the methylviologen radical cation. Samples that were not dehydrated produced ESR spectra about 10% as intense as those that had the water removed. The photoreduction yield was largest in zeolite Y, less in zeolite X which has more cations and hence more crowding in the cages, and very small in zeolite A which has much smaller cages. The electron donor in these systems is believed to be the anionic aluminosilicate framework of the host zeolite.

ESR study on the charge transfer complexes of N-salicylideneanilines containing NHO hydrogen bond as a dynamic function

Summary form only given. N-Salicylideneaniline derivatives have intramolecular NHO hydrogen bond. We have found that the barrier height for the proton transfer in the NHO hydrogen bond of these compounds is relatively small in the crystalline state and the proton transfer is accompanied by a configurational change of the /spl pi/-electron system, showing thermochromism in some cases. Thus in the charge transfer complexes of these N-salicylideneaniline derivatives (NN, NPY and DNP shown in the figure) with TCNQ and with F/sub 4/-TCNQ, a dynamic interaction between the hydrogen bond and the electronic state of the mixed stacking column of donor and acceptors may be expected. The ESR line shape of (NPY)/sub 2//F/sub 4/-TCNQ and NN/(TCNQ)/sub 2/ was simple lorentzian near 20 K and the line width decreased remarkably as temperature increased up to 300 K. This behavior is similar to that of t-polyacetylene and suggests a motion of the spin. A deuteration of the hydrogen bond of NN/(TCNQ)/sub 2/ led to a reduction of ESR line width. Delocalization of the proton in the hydrogen bond in the NPY and NN complexes was suggested by X-ray structure analysis. NMR measurements were also performed on the complexes.

Molecular mobility in polyaniline studied by ESR method

For emeraldine salts of polyaniline (ES), segmental motions in precipitated ES and large-scale rearrangements of ES globules in solutions of polyaniline in N-methylpyrrolidinone (NMP) were found, in spite of the formation of salt bridges between polyaniline chains. For precipitated ES it was found that the asymmetry of the Dysonian ESR line correlates with macroviscosity of solvent. This observation reveals the important role of segmental motions of polyaniline chains in conductivity of ES at microwave frequency. For solutions of ES in NMP the broadening of the ESR lines at room temperature and 77 K was found at dilution of the solutions. This observation shows the increase of the distances between paramagnetic centres of ES with the dilution.

Oxygen-induced ESR line broadening in conducting polymers

The oxygen-induced ESR line broadening has been investigated in the case of the conducting polymer polyaniline in powder and film form. Pumping under vacuum results in a narrowing of the ESR linewith. After initial pumping various oxygen containing gas has been applied to the sample (pure O 2, O 2 + N 2, O 2 + He), and the linewidth has been measured as a function of time. At first, the linewidth increases similarly in the various cases. Then, different behaviors are observed, which are discussed according to the relative velocity of the sorption / diffusion process of oxygen and its partner. The connection of the line broadening with the samlpe conductivity is also discussed.