Absorption line CW EPR using an amplitude modulated longitudinal field

In standard continuous wave electron paramagnetic resonance (CW-EPR) experiments, the first derivative of absorption lines is detected. This type of a line shape is caused by the magnetic field modulation and is usually an undesired feature, since the sensitivity of CW-EPR drastically decreases with increasing linewidth. A new approach is introduced, which allows for the measurement of absorption line EPR spectra in systems with broad inhomogeneous lines. The method makes use of multiple-photon transitions that are induced in spin systems when a transverse microwave and a longitudinal radio frequency field are simultaneously applied. The absorption lines are obtained by using amplitude modulation of the radio frequency field and slight saturation of the spectral lines. The basics of the new approach are discussed and experimental examples are given.     

Millimeter and submillimeter EPR spectroscopy

For a long time, the electron paramagnetic resonance (EPR) spectrometers have been operated in X and Q bands with wavelengths of microwave radiation about 3 cm and 8 mm. Increasing the operating frequency improves the basic parameters of an EPR spectrometer. In view of this, there has recently been rapid development of high-frequency EPR spectroscopy, including the submillimeter-wave range, related to significant progress in the millimeter-and submillimeterwave technique. This paper discusses characteristic features, application areas, and the state of the art of the experimental technique of EPR spectroscopy in the millimeter-wave range and the short-wavelength region of the millimeter-wave range. The design features of the high-frequency EPR spectrometer operated in the frequency range 65–1500 GHz, which was created at the E. K. Zavoisky Physico-Technical Institute of the Kazan’ Scientific Center of the Russian Academy of Sciences, are presented. The results of studying the structure of the paramagnetic centers formed by impurity Ho³⁺ ions in synthetic forsterite (Mg₂SiO₄), obtained by the method of tunable high-frequency EPR spectroscopy, are reported.     

Amplitude modulated solitary ion motion in solids

A self-consistent, variational formalism of an ion motion in a solid is developed. An amplitude modulated ion wave function and the induced wakeon potential are found to have a soliton solution. The observed large positron diffusion lengths in single crystal metals are attributed to the existence of bound positron to its wakeon potential.     

Microwave modulated polarization spectroscopy

Complex sub-Doppler spectra can be simplified by the application of microwave modulated polarization spectroscopy (MMPS). This new laser spectroscopy technique is based on a combination of Doppler free laser polarization spectroscopy with microwave optical polarization spectroscopy (MOPS). The method has been used to label particular optical lines in the B²σ-X²σ spectrum of SrF.     

Giant transversal particle diffusion in a longitudinal magnetic ratchet

We study the transversal motion of paramagnetic particles on a uniaxial garnet film, exhibiting a longitudinal ratchet effect in the presence of an oscillating magnetic field. Without the field, the thermal diffusion coefficient obtained by video microscopy is D(0) ≈ 3 × 10(-4) μm2/s. With the field, the transversal diffusion exhibits a giant enhancement by almost four decades and a pronounced maximum as a function of the driving frequency. We explain the experimental findings with a theoretical interpretation in terms of random disorder effects within the magnetic film.     

EPR spectroscopy of fullerene adducts

EPR spectroscopy has been used to identify and characterize the paramagnetic adducts of small free radicals with C₆₀ through measurements of the hyperfine interactions of protons and¹³C nuclei. The initially formed mono-radical adducts (RC₆₀) have unpaired spin density localized near the point of attachment of the radical. Generally, they are in thermal equilibrium with their diamagnetic dimer, and have a surprisingly large barrier to internal rotation about the new bond. The tri- and penta-radical adducts have electronic structures similar to those of allyl and cyclopentadienyl radicals, respectively.NRCC No. 35262     

Amplitude correlations in nuclear resonance spectroscopy

Both magnitudes and relative signs of inelastic decay amplitudes have been measured for proton resonances in the compound nuclei ⁴⁵Su, ⁴⁷V, ⁴⁹V, ⁵¹Mn, ⁵⁵Co, and ⁵⁷Co. Resonances with orbital angular momenta 1,2 and 3 and five different values of J^π were studied. For l = 1 and l = 2 resonances, sample sizes are sufficient to perform statistical analyses: distributions of the reduced widths, distributions of the products of reduced width amplitudes, and both amplitude and widt correlations have been determined over energy ranges of ～ 1 MeV. The distributions are compared with the predictions of random matrix theory, and good overall agreement is obtained. These result have provided new tests of the statistical theory of resonances and of the theory of isobaric analogue states. In addition, these data give the first experimental confirmation of the channel coupling required by direct reaction theory. The linear correlation coefficients are often surprisingly large (for these data sets, the average value is >0.5 ), so large in fact that the traditional DWBA treatment of direct reactions must fail in some cases. This failure is discussed with the aid of a simplified model. Tests of the Gaussian nature of reduced width amplitudes are also examined.     

On the energetics of transversal and longitudinal fluctuations of atomic magnetic moments

By constrained spin-density functional calculations we estimate the relative role of the longitudinal and transversal fluctuations of the magnetic moments in the series of 3d metals (bcc Fe, hcp and fcc Co, and fcc Ni) for weak excitations from the ferromagnetic ground state. It is shown that the importance of longitudinal fluctuations strongly varies from relatively small in bcc Fe to large in fcc Ni. This means that a consistent adiabatic treatment of the low-energy spin fluctuations should include independent longitudinal fluctuations.     

Pseudo field modulation in EPR spectroscopy

This paper develops methodology for computer simulation of the effect on an experimental EPR spectrum that would occur if an additional field modulation were applied followed by eventual phase sensitive detection at the modulation frequency or at one its harmonics. The algorithm, which is called pseudomodulation, transforms the digitized spectrum and also filters the noise. If a second harmonic spectrum is desired in order to make subtle changes in curvature more apparent, it is shown that it is always preferable to obtain an experimental second harmonic spectrum. The signals are identical, but because of the filtering properties of the pseudomodulation algorithm, the noise is lower. Pseudomodulation should be applied to simulated spectra prior to fitting a model to data in order more precisely to simulate the experimental signal. It is argued that such fits ought to involve not only first harmonics but also higher harmonics, since the various harmonics are sensitive in different ways to input parameters in the spin Hamiltonian. Application of pseudomodulation to the EPR spectrum of the blue copper-protein azurin is described.     

EPR spectroscopy and imaging of TEMPO-labeled magnetite nanoparticles

The article presents results of a study of TEMPO-labeled polymer coated superparamagnetic iron(II,III) oxide nanoparticles using both Electron Paramagnetic Resonance (EPR) spectroscopy and Electron Paramagnetic Resonance imaging technique (EPRI). The X-band (9.4 GHz) EPR spectroscopy was used to investigate the behavior of TEMPO-labeled polymer coated magnetite nanoparticles in different conditions (temperature and orientation in magnetic field). The broad line, which comes from the core of Fe₃O₄ nanoparticles, shows anisotropy. This signal broadens with decreasing temperature, its intensity increases with increasing temperature and the g factor decreases with increasing temperature. The shape of the signal from nitroxide radical strongly depends on temperature. When temperature is higher than 200 K, a narrow triplet appears, but when it is lower than 200 K the signal consists of broad asymmetric lines. Analysis of the signal allowed characterization of the motion of the spin label attached to nanoparticles. Values of anisotropy parameter ɛ and rotational correlation time τ_c were calculated for TEMPO in the fast rotation regime.The ability of TEMPO-labeled PEG coated magnetite nanoparticles to diffuse within the hydrogel medium was also investigated. The EPR imaging of nanoparticles diffusion in hydrogel was made at room temperature using an EPR L-band (1 GHz) spectrometer. EPRI has been proved effective for evaluation of changes in the spatial distribution of nanoparticles in the sample.     

Orientationally modulated EPR in systems with anisotropic Zeeman and fine interactions

V. I. Ul'yanov (Lenin) Leningrad Electrical Engineering Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 6, pp. 651–660, June, 1991.     

Intracavity spectroscopy with modulated multimode lasers

The output of a cw multimode dye laser with an intracavity narrow-band absorber and its pump power modulated shows spectral condensation on both wings of the absorption line. This indicates phase locking of two groups of laser modes. The dispersion of the absorber modifies the mode spacing of the laser such that mode groups on both sides of the absorption line get into resonance with the modulation. These mode groups feel smaller loss and acquire the total laser power. Spectra of the laser output reveal the total absorption coefficient, the homogeneous broadening of the absorber, and the spectral width of individual laser modes.On leave from Lebedev Physical Institute, Academy of Sciences of the USSR, SU-117924 Moscow, USSR     

Quantum-like approach to the transversal and longitudinal beam dynamics. The halo problem

An interpretation of the formation of halo in accelerators based on quantum-like theory by a diffraction model is given in terms of the transversal beam motion. Physical implications of the longitudinal dynamics are also examined. Received: 18 October 1999     

Kinetic measurements using EPR imaging with a modulated field gradient

EPR imaging with modulated field gradient was applied for the investigation of fast diffusion processes. Three different imaging methods are possible: spectral-temporal, spatio-temporal, and spectral-spatial imaging. The time resolution is on the order of seconds and the spatial resolution is in the micrometer region. The efficiency of this imaging technique is demonstrated for the penetration of the spin probe Tempol in the skin of hairless mice biopsies. The skin is normally protected against the penetration of water soluble substances by the horny layer, a resistive thin lipophilic layer. Overcoming this horny layer for water soluble ingredients is one of the main practical problems for the topical application of pharmaceutics which could be investigated by EPR imaging. Different images represent the penetration behavior of the water soluble Tempol in the skin after treatment with the penetration enhancer DMSO (Dimethylsulfoxide) and after removing the horny layer.