The hyperfine structure has been resolved in the optically detected electron spin resonance (OD ESR) spectra of radical ion pairs generated by ionizing radiation at a low dopant concentration in a solid polyethylene matrix at room temperature. The different organic molecules that can capture electrons and holes were used as the dopants. The spin-lattice relaxation times T (1) for radical ions of dopants were estimated to be tens of microseconds. The temperature dependence of OD ESR signal intensity indicates the diffusion-assisted mechanism of recombination of radical ion pairs in polyethylene.

Resolved hyperfine structure is observed for the first time in the OD EPR spectra of charge pairs recombining in a solid polymer matrix at room temperature.

A setup for recording optically detected electron paramagnetic resonance spectra of radical ions involved in geminate recombination and generated by vacuum ultraviolet is described. The setup allows registration of EPR spectra from short-lived radical ions in polymeric films at room temperature by recombination fluorescence modulated by a resonance microwave field.

The paper discusses the dependence of the singlet product yield in the recombination of radical ion pairs vs. external magnetic field in a situation when hyperfine couplings in one partner are much greater than those in the other partner. The theoretical calculations performed for the case of equivalent magnetic nuclei demonstrate a considerable effect of small hyperfine couplings on the shape of this dependence. In particular, the width of the low-field magnetic field effect (referred to as the ‘zero-field’ MARY line) is determined by weak hyperfine interactions along with spin coherence lifetime. The predictions are in a qualitative agreement with experimental results.

A new version of the optically detected electron spin resonance (OD ESR) technique using vacuum ultraviolet radiation to generate radical ion pairs is discussed. The technique can be used to study the spin-correlated processes of charge recombination in thin films that can be useful in spintronics. Distinctive features of photoionization and high-energy (including X-ray) ionization are discussed. The first results obtained by the technique in the study of charge recombination in polymeric and liquid crystal films are presented. The results of the concurrent observation of the OD ESR and electron cyclotron resonance (ECR) in the low-pressure gas over the sample are outlined. A possible application of ECR in the context of the OD ESR spectroscopy is suggested.

A setup for recording optically detected electron paramagnetic resonance (OD EPR) spectra of radical ions involved in geminate pair recombination is described. Unlike the previously developed setups of this kind, vacuum ultraviolet (VUV) radiation is used to generate radical ion pairs. The setup allows registration of EPR spectra of short-lived radical ions in liquid and solid samples by recombination fluorescence modulated by a resonance microwave field. The spectra are recorded in the mode of direct detection of the fluorescence intensity or using the phase-sensitive detection. The advantages of the photochemical generation of radical ion pairs compared to the use of X rays and fast-electron radiation are as follows: the lack of track effects on the recombination process, the possibility of studying recombination processes in thin films of nanometer thickness, the small size, low cost, and radiation safety of VUV sources.

Microwave pulses at a frequency of 2.45 GHz with a duration of 30–55 ns (at the base level) were obtained using the effect of fast energy transfer in a pair of coupled cavities. The pulse repetition rate reached 40 kHz, and the maximum magnetic-induction amplitude was 0.32 mT at a 20-W generator power.

A method using the effect of external electric field on the delayed luminescence of solutes was applied to measure the drift mobility of geminate radical ions. The mobilities of a number of radical ions in alkanes with viscosities varying from 0.24 to 35.4cP were determined. Mobilities of radical ions were found to correlate with their molecular size but for similar species only. As a specific case, radical cations of polycyclic aromatic molecules were found to exhibit significantly lower mobilities than the olefin and alkane radical cations.

Spin-lattice relaxation times of radical cations were measured by the decay of the time-resolved magnetic field effect in the recombination fluorescence of radical ion pairs in liquid hydrocarbons at high concentrations of solvent holes acceptor. The dependences of spin-lattice relaxation time on the magnetic field strength and solvent viscosity were studied. The results could not be explained in terms of the model of ion-molecular charge transfer involving monomeric or dimeric radical cations. The paramagnetic relaxation observed in a weak magnetic field is attributed to internal reorganizations of aggregates that originate from radical cations at high acceptor concentration.

A resonator and pulsed microwave 2.45-GHz generator are described. The system operates at a 40-kHz pulse repetition rate and 900-ns pulse duration. At a 150-W pulse power, the circularly polarized component of the magnetic induction in a sample is 1.2 mT.

A novel experimental setup to study the effect of microwave field on the kinetics of recombination fluorescence from nonpolar solutions irradiated with nanosecond X-ray pulses is described. Experiments on the observation of the microwave field effects in dodecane and hexane solutions are presented. The most favorable conditions for observation of the microwave induced quantum oscillations are found. The effect of spin locking was observed for the first time in the time-resolved microwave field effects. An efficient method to calculate the spin evolution of a radical pair in a microwave field taking into account relaxation is suggested. Analytical expressions for the microwave field effect in the limiting cases of large and small hyperfine splittings are given.

The fractions Θβ and ΘX of spin-correlated singlet radical-ion pairs in alkane solutions irradiated by β-particles and X-rays were got from experiments on magnetic field effects and quantum beats in recombination fluorescence. The ratio Θβ/ΘX values of 1.3−2.8 for the solvent series studied were found both from magnetic effect and quantum beats. The Monte Carlo calculations were made to explain the variations of Θβ/ΘX in different solvents. The high value of Θβ/ΘX = 2.8 for isooctane is probably due both to large separation between ions in pair and to high concentration of neutral radical in the spur.

A new approach is proposed to identify the recombining particles in irradiated hydrocarbon solutions. It is based on the observation of time-resolved effects of an electric field in recombination fluorescence. The experiments demonstrate the possibility of observing molecular ions, electrons and holes that participate in radiation track recombination. The recombination processes involving the aforementioned particles can be reasonably distinguished in summary fluorescence kinetics by choosing the corresponding field strength.

The optically detected ESR spectra (OD ESR) of naphthalene radical ion pairs in squalane show inversion near the glass formation point of the solvent. A similar inversion of OD ESR spectra is also observed for some other additives, such as biphenyl and tetrafluorobenzene in glassy nonpolar solvents (squalane, 3-methylpentane). A theory of radical pairs can be used to account for the observed inversion of signal amplitude as a result of adiabatic passage of the anticrossing point of radical pair S and T-levels upon counter ion recombination. The comparison between the shapes of experimentally observed and theoretically calculated spectra qualitatively confirm this hypothesis.

Foreign body (FB) ingestion is a common problem especially in children below the age of 5 years. This is fueled by their curiosity to explore their surroundings. The ingested foreign body finds its way out of the gastrointestinal tract without any serious consequences most of the time. On the other hand, disc battery ingestion has been reported to cause serious harm when ingested including death. We report two patients who had ingested disc batteries and their respective outcomes.

In the framework of the isolated cluster model for radical-ion recombination, the survival probability, recombination rate, escape probability and the ratio of the geminate recombination rate to the total recombination rate have been calculated using the Monte Carlo method. This ratio is important for interpreting the magnitude of magnetic field effects in recombination fluorescence. The results are compared with experiment.

The temperature dependence of the ESR linewidth of excess electrons in squalane and 3-methylpentane has been measured by the OD ESR technique. When the temperature dependence of the linewidth is fit by a model which includes a temperature-dependent jump frequency, Ef, it is found to be smaller than the activation energy, Eμ, for the electron mobility. For 3-methylpentane the activation difference is small and the jump length calculated from the Einstein formula, λ ≈ 10 Å, therefore has weak dependence on the temperature. In squalane the difference between Eμand Ef is greater, and the calculated large values of at high temperatures indicate a wide depth-distribution of trap energies.

It is well known that an external magnetic field can affect the rate of singlet-triplet transitions in a radical pair and hence its recombination probability in liquid. Resonance radiofrequency (RF) radiation induces quantum beats in the kinetics of radical pair recombination. At high RF field amplitudes the singlet-triplet transitions in radical pairs can be efficiently suppressed.