Electron spin echo envelope modulation from trapped electrons in a glassy medium

An amplitude modulation of the electron spin echo envelope has been observed for radiation-produced trapped electrons in 10 M NaOD/D₂O at 77°K but not in 10 M N₂OH/H₂O. The modulation has been simulated theoretically by generalizing the single crystal model of Rowan et al. to disordered systems. The modulation has been interpreted as due to dipolar interactions with deuterons in molecules of the second solvation shell around the trapped electrons.     

Electron spin echo envelope modulation spectroscopy with g-value and orientation filters

Two new electron spin echo envelope modulation (ESEEM) experiments, electron-Zeeman (EZ) ESEEM and right-angle wiggling (RAW) ESEEM, are introduced. The experiments are based on the combination of a one- or two-dimensional ESEEM sequence with an EZ-EPR or RAW-EPR detection scheme. The approaches provide considerably enhanced g-value and orientation filters as compared to the standard ESEEM experiments. EZ-ESEEM facilitates the disentangling of overlapping nuclear frequencies along a g-value dimension for systems with anisotropic g-matrices, whereas with RAW-ESEEM overlapping frequency components along a dimension that is related to the change in resonance frequency when the orientation is varied, can be separated. The underlying concepts are outlined and the new experiments are illustrated by numerical simulations and examples of applications.     

Comparative modulation analysis of electron spin echo signals from oxidized chlorophyll a in vitro and P 700 centres in chloroplasts

A comparative analysis of electron spin echo modulation effects from ¹⁴N nuclei of pyrrole rings for Chla⁺ and P 700⁺ has been performed, yielding parameters of quadrupole and isotropic hyperfine couplings with nitrogen nuclei in these paramagnetic centres.     

Electron spin echo of CH2OH radicals adsorbed in A-type zeolites

Data on the trapping site of radicals in zeolite α-cages have been obtained by the analysis of modulation effects in the electron spin echo of CH₂OH radicals produced by irradiation in A-type zeolite with adsorbed methyl alcohol.     

Electron spin emission spectra from pairs of radicals

Electron spin emission from both radicals of a pair has been observed. It is demonstrated that it is possible to explain the polarization by the radical pair mechanism if nuclear relaxation is fast enough. The extent of ST_?1 mixing induced by an anisotropic g-factor is deduced.     

Electron spin echo study of long-lived radicals which cause mutation in gamma-ray irradiated mammalian cells

Long-lived radicals, produced by gamma-ray irradiation of mammalian cells at room temperature, cause mutation and morphological transformation in the cells. The local environment near the long-lived radicals in irradiated cells was investigated here by the analysis of electron spin echo envelope modulation (ESEEM) spectra. The number of hydrogen (deuterium) atoms surrounding the long-lived radical, which may correspond to the number of water molecules, was estimated roughly as one or two. It is postulated that the long-lived radicals are generated in the interior of biopolymers. The radicals are not produced by the reaction of OH radicals, but mainly by the decomposition of biopolymer which absorbed directly the energy of the ionizing radiation.     

Electron spin echo as a method of ESR tomography

The electron spin echo method combined with pulsed gradients of an external magnetic field has been proposed for studies on the spatial distribution of paramagnetic centres. The relationship has been found between the distribution function of paramagnetic centres and the dependence of the spin echo signal on the parameters of the applied gradients. The resolution of the method depends on the ratio of the inverse phase relaxation time (T₂⁻¹) to the magnetic field-gradient and may be much higher than the resolution of standard ESR tomography. The method has been applied to a model system.     

Quadrupole effects in the electron spin echo from pairs of diphenylnitryl radicals

Conclusions This analysis of ESE modulation effects for DPN pairs indicates that the frequencies are those of quadrupole resonance for the nitrogen atoms in the DPN in the external magnetic field, and this has enabled us to determine the quadrupole splitting parameters. However, an exact calculation on the NQR transition frequencies in the partially oriented system requires a knowledge of the directions of the electric field gradient tensor axes, which cannot be derived from these experiments. For this reason, in a study of this type one must make the fullest possible use of data from other experiments or from quantum-chemical calculations, which should enable one to restrict the possible directions for the EFG tensor axes.Translated from Zhurnal Strukturnoi Khimii, Vol. 26, No. 1, pp. 43–48, January–February, 1985.     

Electron spin resonance spin trapping of thiyl,radicals from the decomposition of thionitrites

Alkyl thiyl radicals produced by the homolytic decomposition of thionitrites are detected by ESR spin trapping using 5,5-dimethyl-1-Δ-pyrroline-N-oxide (DMPO).     

Electron spin resonance of radical cations in nafion membranes

Studies of radical cations in solution at room temperature are still relatively rare and require very strongly acidic media; we report here the novel use of the superacidic membrane Nafion (having properties similar to trifluoroacetic acid) for the generation and stabilization of several radical cation species. E.s.r. spectroscopy permitted not only the detection and characterization of the radical cation species so generated but also the qualitative comparison of the effects of the semi-rigid membrane environment on radical mobility as compared to that in solution.     

Chlorine nuclear quadrupole resonance spectral line asymmetry and spin echo envelope modulation in gold(III) chloride

The ³⁵Cl pure quadrupole resonance bands in AuCl₃ at 36.094 and 33.401 MHz studied both by Fourier transform spectroscopy and by the observation of modulation of the spin-echo envelope shows a partially-resolved asymmetric structure. Possible sources of this structure are discussed.     

Electron spin relaxation of radicals in weak magnetic fields

The review summarizes the results of studies on specific features of spin relaxation of radicals in liquids in weak magnetic fields. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1642–1654, October, 2006.