The simple amino acid l-α-alanine (ala) in polycrystalline form was among the first substances to be proposed and subsequently developed for Electron Paramagnetic Resonance (EPR)-based solid state radiation dosimetry. One disadvantage with ala is a relatively low sensitivity for doses below a few gray (Gy) which is a dose range of particular interest in medical, accident and environmental applications. A number of other compounds have been screened and some of these have shown a better sensitivity to radiation exposure than ala, in some cases up to a factor of 7–8. In particular ammonium tartrate (AT) and lithium formate (LiFo) have been taken into practical use. The present work was initially aimed to investigate the low-temperature radical products in AT, and the reactions leading to the product of dosimetric interest at room temperature. As a part of these studies, the previously characterized major room temperature radical product was re-investigated using single crystal electron magnetic resonance (EMR) techniques combined with periodic density functional theory (DFT) -type quantum chemical calculations. Surprisingly, this study showed that the molecular structure of the dominant radical at room temperature is somewhat different from that previously proposed. Furthermore, a second room temperature radical, previously not well characterized, was carefully investigated and three hyperfine coupling tensors were determined. These three tensors were sufficient to simulate all experimental observations for the second radical but not alone sufficient to permit an unambiguous molecular structure of the defect to be determined. It appears that the EPR resonance from this radical does not influence the dosimetric potential of AT.

Exact and perturbation methods were employed in simulations of powder ENDOR spectra to obtain the anisotropic hyperfine (hfc) and nuclear quadrupole (nqc) coupling constants of certain organic radicals of interest in fundamental research and in applications in radiation research, surface chemistry and biophysics. The principal hfc values of the ring protons and methyl substituents for several aromatic cations trapped in disordered matrices might be more accurate than those previously reported using regular EPR. Only one of the earlier assignments of the naphthalene cation spectrum was in acceptable agreement with the simulations. The proton couplings at the beta-position of alkyl radicals were deduced by simulations while the spectrum due to alpha-couplings with appreciable anisotropy was weak. Accurate simulation of the 14N (I = 1) spectra in bio-radicals was obtained by adjustment of the relative orientation of the principal hfc and nuclear quadrupole coupling (nqc) tensors as well as the principal values. Adjustment of the excitation width parameter employed in the software was also required in a few cases to improve the agreement with the experimental spectra. The hfc patterns due to matrix nuclei (1H and 7Li) around the radicals of X-irradiated samples were simulated to elucidate the nature of the trapping sites in materials used for EPR dosimetry. ENDOR simulation programs known to us are presented in an Appendix. The performance of the ENDORF2 program used in previous works was examined by comparison with exact treatment. Input and output examples, source and executable codes used in this work can be downloaded at https://github.com/EndorF2/Simulation.

Coronene (C24H12), a charge transfer complex with low-cost and high-performance energy storage, has recently attracted attention as a model molecule of graphene nano-flakes (GNFs). The stacking structures of the trimer radical cation correlate strongly with the conduction states of the GNFs. In the present paper, the structures and electronic states of the monomer, dimer and trimer radical cations of coronene were investigated by means of density functional theory calculations. In particular, the proton hyperfine coupling constants of these species were determined. The radical cation of coronene+ (monomer) showed two structures corresponding to the 2Au and 2B3u states due to the Jahn-Teller effect. The 2Au state was more stable than the 2B3u state, although the energy difference between the two states was only 0.03 kcal mol-1. The dimer and trimer radical cations took stacking structures distorted from a full overlap structure. The intermolecular distances of the molecular planes were 3.602 Å (dimer) and 3.564 and 3.600 Å (trimer). The binding energies of the dimer and trimer were calculated to be 8.7 and 13.3 kcal mol-1, respectively. The spin density was equivalently distributed on both coronene planes in the dimer cation. In contrast, the central plane in the trimer cation had a larger spin density, ρ = 0.72, than the upper and lower planes, both with ρ = 0.14. The proton hyperfine coupling constants calculated from these structures and the electronic states of the monomer, dimer, and trimer radical cations of coronene were in excellent agreement with previous ESR spectra of coronene radical cations. The structures and electronic states of (coronene)n+ (n = 1-3) were discussed on the basis of the theoretical results.

The analysis of single crystal electron magnetic resonance (EMR) data has traditionally been performed using software in programming languages that are difficult to update, are not easily available, or are obsolete. By using a modern script-language with tools for the analysis and graphical display of the data, three MatLab (R) codes were prepared to compute the g, zero-field splitting (zfs) and hyperfine coupling (hfc) tensors from roadmaps obtained by EPR or ENDOR measurements in three crystal planes. Schonland's original method was used to compute the g- and hfc-tensors by a least-squares fit to the experimental data in each plane. The modifications required for the analysis of the zfs of radical pairs with S = 1 were accounted for. A non-linear fit was employed in a second code to obtain the hfc-tensor from EPR measurements, taking the nuclear Zeeman interaction of an I = 1/2 nucleus into account. A previously developed method to calculate the g- and hfc -tensors by a simultaneous linear fit to all data was used in the third code. The validity of the methods was examined by comparison with results obtained experimentally, and by roadmaps computed by exact diagonalization. The probable errors were estimated using functions for regression analysis available in MatLab. The software will be published at https://doi.org/10.17632/ps24sw95gz.1, Input and output examples presented in this work can also be downloaded from https://old.liu.se/simarc/downloads?l=en. (C) 2021 The Author(s). Published by Elsevier Inc.

The structures of the free radicals formed by the irradiation of potassium dithionate (K2S2O6) with 60Co γ-rays and 14N7+ ions were investigated by EPR to further examine a recently proposed LET effect in this material. Two types of SO3− radical ions were identified in X-irradiated single crystals by measurements at X- and Q bands. One of these (S1) exhibited 33S hyperfine couplings A⊥ = 12.49, A|| = 15.60 mT, the other (S2) A⊥ = 11.29, A|| = 13.92 mT. The g-factors were nearly isotropic, g⊥ = 2.0010, g|| = 2.0003; and g⊥ = 2.0026, g|| = 2.0008, respectively. The 33S hyperfine coupling tensors and g-tensors were axially symmetric about the trigonal -axis, coinciding with the direction of the S–S bonds of the two non-equivalent S2O62− ions in the crystal. A model for the radiation damage was proposed in which the SO3− radical ions retain the orientation of the SO3 groups, aligned along the trigonal axis. The structure of a third main radical species (S3) with g⊥ = 2.0026, g|| = 2.0052 could not be unambiguously assigned, due to undetected 33S features. The relative integrated intensities of S1, S2 and S3 depended on the radiation quality and were approximately estimated as 0.18: 0.65:0.17 for 60Co γ-rays and 0.47: 0.38: 0.15 for 14N7+ ions. Additional weak lines on the low field side of the main signal were tentatively attributed to SO2− radical ions. An even weaker strongly anisotropic pair of lines was attributed to SO3− radical pairs separated by 0.93–0.95 nm along the trigonal axis.

Single crystals of Rochelle salt, [-OOC-CHOH-CHOH-COO-, Na+ K+]center dot 4H(2)O, X-irradiated at 10 K, have been examined using EPR, ENDOR and EIE spectroscopic techniques to characterize the radiation induced radicals stable at that temperature and their reactions upon warming. The one-electron gain product was observed and from the hyperfine interaction with a beta-proton it was unambiguously centered at the C-4 position of the tartrate moiety. An additional nearly isotropic hyperfine structure of about 21 MHz was tentatively assigned to interaction with a sodium ion exhibiting a close contact to O-3 in the crystal. Evidence was obtained that the one-electron reduced radical had become protonated at one of the C-4 bonded carboxyl oxygens, most probably O-4. No evidence for the corresponding C-1-centered reduction product was found. Two resonance lines (R2, A1) were shown by EIE to belong to a species formed by decarboxylation at C-3, a secondary oxidation product. Two other resonance lines (K1, K2) were assigned to two varieties of another decarboxylation radical, centered at C-2, distinguished by differences in the potassium ion coordination. Furthermore, one other resonance line (A2) was tentatively ascribed to a third decarboxylation radical, centered at the opposite end of the tartrate moiety. The precursor of these products, that is, the one-electron loss product, was not observed after X-irradiation at 10 K. Thermally induced free radical reactions followed by EPR in the temperature range of 12-119K indicate that a water molecule or a hydroxyl ion is eliminated from the one-electron reduction product radical and that a C-3-centered radical is formed. The reduction and oxidation reaction pathways of hydroxy acid derivatives are discussed. (C) 2011 Elsevier Ltd. All rights reserved.

Electron paramagnetic resonance (EPR) spectroscopy was applied to study the paramagnetic species formed from styrene, 1,1-diphenylethylene, α-methylstyrene, β-methylstyrene and methylmethacrylate adsorbed on amorphous silica gel after γ-irradiation at 77 K. Radicals formed by the hydrogen atom addition at the vinyl group of the monomers were observed in all samples. The hydrogen atoms were shown to originate to a large extent from the adsorbent by using silica gel with deuterated silanol groups. An EPR spectrum assigned to a propagating radical was observed at increased temperature for samples containing methylmethacrylate (MMA). The structures of the adsorption complexes, the respective hyperfine splitting constants and the adsorption energies were calculated by applying DFT quantum chemical methods. The reaction between an MMA molecule and the MMA radical and the structure of the propagating radical was modeled. The calculated hyperfine splitting constants for all radicals confirmed the assignment of the experimental spectra.

CW-ESR spectroscopy combined with matrix isolation method and ionizing radiation is applied to investigate structure and reactions of intermediate radicals in low temperature solid matrices. ESR parameters are predicted with considerable precision by computations, affording a valuable bridge between experiment and theory. Cyclic-CnF2n- radicals (n = 3-5) have a planar structure with an entirely delocalized singly occupied MO. Unsaturated CnF2n-2- radicals have a distorted pyramidal structure occurring by mixing the pi* and sigma* orbitals. The acetylene anion has a trans-bent structure. Structural distortion occurs in methane cation from original T-d to C-2v symmetry due to the Jahn-Teller effect. A similar symmetry lowering from D-3h to C-2v is discussed for the trimethylenemethane cation. High-resolution ESR spectra of D-labelled methyl radicals in solid Ar are discussed in terms of nuclear spin-rotation couplings. The formation of "H---CH3" radical pairs and of a "H---H-2" complex" in solid Ar is presented. The structure of [H-2(H-2)H-2](+) formed in para-H-2 is discussed based on the ESR spectra of D-substituted samples and on computations.

Electronic and geometrical structures of NO-Na+ and Cu(I)-NO complexes formed in zeolites are discussed based on the g and the N-14 and Na-23 hf values evaluated by multi-frequency ESR, pulsed ENDOR and HYSCORE methods. The structure of (NO)(2) bi-radical formed in zeolites is discussed based on X-and Q-band ESR spectra. Microenvironment effects on the molecular dynamics and the thermal stability of triethyl- and tripropyl-amine radical cations as spin probes are presented referring to the CW-X-band ESR results and theoretical DFT calculations. X- and Q-band ESR studies on nitrogen-doped TiO2 semiconductor reveal that the diamagnetic N- ion in the system absorbs visible light so as to excite an electron of N- to the conduction band. The photo-catalytic reactions of TiO2 are modified by introducing O-2 molecules which scavenge a fraction of photoexcited electrons to generate O-2(-). ESR spectral characteristics of adsorbed O-2(-), g-tensor and hf structure of labeled O-17 (I = 7/2), are presented.

Multi-resonance involves ENDOR, TRIPLE and ELDOR in continuous-wave (CW) and pulsed modes. ENDOR is mainly used to increase the spectral resolution of weak hyperfine couplings (hfc). TRIPLE provides a method to determine the signs of the hfc. The ELDOR method uses two microwave (MW) frequencies to obtain distances between specific spin-labeled sites in pulsed experiments, PELDOR or DEER. The electron-spin-echo (ESE) technique involves radiation with two or more MW pulses. The electron-spin-echo-envelope-modulation (ESEEM) method is particularly used to resolve weak anisotropic hfc in disordered solids. HYSCORE (Hyperfine Sublevel Correlation Spectroscopy) is the most common two-dimensional ESEEM method to measure weak hfc after Fourier transformation of the echo decay signal. The ESEEM and HYSCORE methods are not applicable to liquid samples, in which case the FID (free induction decay) method finds some use. Pulsed ESR is also used to measure magnetic relaxation in a more direct way than with CW ESR.

The analysis of ESR, ENDOR, and ESEEM data to extract the resonance parameters is treated. Free radicals in solution are mainly identified by their hyperfine couplings (hfc). The analysis of ESR and ENDOR spectra by visual inspection and by computer simulation is discussed. The Schonland method to obtain the principal values and directions of the anisotropic g- and hfc- tensors from single crystal ESR and ENDOR data is presented. The modifications needed when S > 1/2 or I > 1/2 to obtain zero-field splitting (zfs) or nuclear quadrupole coupling (nqc) tensors are considered. Examples of simulations to extract g-, hfc-, zfs-, and nqc-tensors from ESR and ENDOR spectra of disordered systems are presented. Simulation methods in pulsed ESR (1- and 2-dimensional ESEEM) studies are exemplified. Internet addresses for down-loading software for the simulation of ESR, ENDOR, and ESEEM spectra are provided. Software for the analysis of single crystal data by the Schonland method is also available.

With an increasing interest in using protons and light ions for radiation therapy there is a need for possibilities to simultaneously determine both absorbed dose (D) and linear energy transfer, LET, (L-Delta). Potassium dithionate (K2S2O6) tablets were irradiated in a conventional 6 MV linear accelerator photon beam and a N7+ beam (E = 33.5 MeV/u) respectively. The EPR spectrum of irradiated potassium dithionate is a narrow doublet consisting of two signals, R-1 and R-2, with different microwave power saturation properties. On the basis of identification in related substances by EPR and ENDOR, these two signals are assigned to two non-equivalent SO3- - radicals. Our experiments showed that the ratios of these two lines (R-1/R-2) were clearly connected to beam LET. Irrespective of the mechanistic details this investigation suggests a new method for measurement of absorbed dose and beam LET by using potassium dithionate EPR dosimetry. (C) 2011 Elsevier Ltd. All rights reserved.

ESR applications concerned with the measurement of the amount of paramagnetic species are the common theme of the chapter. Procedures to obtain absolute concentrations are outlined. Error sources are discussed and procedures to reduce the uncertainties are reviewed. The principles of ESR-dosimetry are presented. Strategies to increase the dose response by using materials other than L-alanine, by isotopic substitution, metal ion doping, and instrumental developments are briefly described. The measurement of the spatial distribution of radiation dose by the ESR imaging (ESRI) method is discussed. Geological dating by ESR using the additive dose method is applicable for periods up to two million years. Procedures to estimate doses by ESR in contaminated areas and after radiological accidents are described as well as ESR analyses for test of irradiated food and of medical equipment. Methods to analyze the ESR line-shapes are considered in the context of obtaining the integrated spectral intensity.

ESR measurements at high microwave frequency and corresponding high field increase the resolution between species with different g-factors and of g-anisotropies in a single species. Field-independent spectral features due to hyperfine couplings (hfc) and zero-field splittings (zfs) can be separated from g-factor effects by multi-frequency measurements. The zfs for S >= 1 species is obtained directly when the microwave frequency is much larger than the zfs. Very large zfs (larger than the microwave energy available) can be indirectly determined by multi-frequency measurements of the effective g-factor. The sign of the zfs (D) can be deduced by high field ESR measurements of the relative intensities of the lines due to zfs. The conditions for obtaining the Heisenberg exchange energy (J) between two species forming a coupled system are considered. Examples of applied studies in the solid state are presented. The influence of forbidden transitions and nuclear spin flip lines frequently complicating the analysis of anisotropic hfc clue to H-1 is discussed.

The ESR (electron spin resonance) method is employed for studies of paramagnetic substances most commonly in liquids and solids. A spectrum is obtained in continuous wave (CW) ESR by sweeping the magnetic field. The substances are characterized by measurements of the g-factor at the centre of the spectrum and of line splittings due to hyperfine structure from nuclei with spin I not equal 0. Zero-field splitting (or fine structure) characteristic of transition metal ion complexes and other substances with two or more unpaired electrons (S >= 1) can be observed in solid samples. Concentration measurements with the CW-ESR method are common in other applications. High field and multi-resonance (e.g. ENDOR) methods employed in modern applications improve the resolution of the g-factor and of the hyperfine couplings, respectively. Pulse microwave techniques are used for measurements of dynamic properties like magnetic relaxation but also for structural studies.

ESR spectroscopic applications to polymer science are presented. ESR parameters used for the molecular and material characterization of polymer materials are reviewed. It is emphasized that ESR studies of the polymer science are particularly effective in three areas. (1) Intermediate species such as free radicals produced in chemical reactions of polymer materials can be directly detected. (2) The temperature dependent ESR spectra of free radicals trapped in the polymer matrices are very effective for the evaluation of molecular mobility (molecular motion) of polymer chains. (3) The mobility of electron, the structure of solitons, and the doping behavior in conduction polymers can be observed in detail in order to clarify the mechanism of conduction.

Measurements of temperature dependent ESR spectra of spin labels trapped in the polymer matrices is very effective for the evaluation of molecular mobility (molecular motion) of polymer chains. We can characterize the molecular motion of the particular sites in different region by the ESR method. It is possible to detect the mobility of polymer material at the segment or atomic level. ESR studies help to relate the features of the nanometer scale to macroscopic properties of the polymer materials. We present examples of spin labeling studies in the polymer science to help readers new to the field understand how and for what areas the method is effective. In the first part, we give a simple review of the spin labeling method and present applications in the polymer physics related to relaxation phenomena in various systems. In the second part applications to biopolymer system are introduced to help the clarification of various mechanisms of bio-membranes.

Density functional theory (DFT) calculations were applied for the modeling of the adsorption sites of nitric oxide in Li+ exchanged zeolite A previously studied experimentally. Two model clusters, a 6T six-membered ring, and a 3T fragment of an octagonal structure were examined. The obtained results showed that the geometry of the formed [Li–NO]+ complex depended on the coordination of the exchangeable cation with the oxygen atoms of the zeolite framework. Calculated anisotropy of the g-factor and the magnetic parameters of 14N and 7Li are in the range of experimental values observed for those types of complexes.

Electron spin relaxation behaviours of radiation induced radicals were studied by the continous microwave saturation method of electron spin resonance (ESR) spectra. Radiation induced radicals in nutmeg yielded a sharp and intense ESR signal at g = 2.0. By the progressive saturation procedure, we could evaluate relaxation times (T1 and T2). The computer program to analyze the ESR line shape using all data points on a saturation curve was applied. Based on the theoretical analysis, the relaxation behaviors of radiacals were revealed. Radiation induced radicals of the specimens yielded relaxation times, T1 in the μsec and T2 in nsec ranges, respectively. Upon the irradiation, T1 shortened, and T2 lengthened. The progressive saturation curve was changed by the irradiation.