ESR Observation Research Articles

ESR Studies of the Cation Radicals Produced by SbCl5 Oxidation of Some Biphenyls with ortho- and para-Dialkyl Substituents

Abstract The cation radicals of some alkylbiphenyls such as 4,4′-bitolyl, 4,4′-di-t-butylbiphenyl, and 2,2′, 4,4′, 6,6′-bimesityl, were generated by SbCl5 oxidation in CH2Cl2. The ESR observation was carried out, and the Q, values of the methyl and t-butyl were estimated based on either the theoretical spin density or the experimentally-determined spin density from the 13C-hyperfine splitting. The Q, value of the methyl in the cation radical was found to be 1.5 times that for the anion radical. The t-butyl groups of the cation radical also showed a much larger Q value than that for the anion radical. The perturbation of the spin density due to the steric hindrance was investigated with reference to the prediction of the McLachlan’s MO calculations carried out for the hindered biphenyl. The experimentally-determined spin density derived from the Q value established for the para-derivative can be adequately interpreted on the assumption that the planar character of the biphenyl would be much reduced, contrary to the tendency found for the anion radicals. This effect suggests that a different delocalization of the unpaired electron may be expected between the cation and the anion radical: that is, the unpaired electron brings about a fair bonding on the central 1–1′ bond in the anion radical, but an antibonding for the cation radical, because the odd π-orbital of the cation has its node between the central 1–1′ bond.

ESR observations of graft polymerization of butadiene onto preirradiated poly(vinyl chloride)

Journal of Polymer Science: Polymer Chemistry EditionVolume 11, Issue 9 p. 2377-2381 Note ESR observations of graft polymerization of butadiene onto preirradiated poly(vinyl chloride) Kazuya Suzuki, Kazuya Suzuki Chemistry Division, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken, JapanSearch for more papers by this author Kazuya Suzuki, Kazuya Suzuki Chemistry Division, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken, JapanSearch for more papers by this author First published: September 1973 https://doi.org/10.1002/pol.1973.170110928Citations: 16AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume11, Issue9September 1973Pages 2377-2381 RelatedInformation

A correlation of esr and radiobiological observations of the temperature and oxygen effects in osmunda regalis spores after irradiation with fast electrons

Dodd N.J.F. and Ebert M. A correlation of ESR and radiobiological observations of the temperature and oxygen effects in Osmunda regalis spores after irradiation with fast electrons. Radiation Botany 13, 89-96, 1973.-Dried spores of Osmunda regalis were irradiated in N 2 with 10 MeV electrons and the influence of temperature and O 2 on the radiation-produced free radicals was studied by ESR. Irradiation produced several different radical groups. The concentration of one of these groups, characterized by a broad ESR signal of line width 25G, could be reduced by 30–40 per cent by heating in N 2 . The apparent activation energy of this process was 20·5 ±2·1 kcal mole −1 . Introduction of O 2 to the irradiated spores resulted in complete decay of this radical group and formation of a new radical group characterized by a narrow signal of line width 9G. The apparent activation energy for formation of this new radical group was 13·1 ±0·7 kcal mole −1 . Although the extent of formation of these radicals was reduced by prior annealment, the rate and apparent activation energy were unaffected. Decay of the broad signal in O 2 and appearance of the narrow signal involved two distinct stages since the rate of decay of the broad signal was significantly faster than the rate of formation of the narrow signal, although both processes had similar activation energies. From these findings a strong quantitative correlation can be made between the radicals giving the broad signal and the precursors of radiobiological oxygen damage and between the radicals giving the narrow signal and the species responsible for post-irradiation oxygen damage.

Dimethylsilyl- and methylene-bridged aromatic groups : II. Phosphorescent triplet states

The zero-field splitting parameters D and E, or D, were measured by electron spin spectroscopy for the triplet states of bis(4-biphenylyl)dimethylsilane, 4,4′-bis-(4-biphenylyldimethylsilyl)biphenyl, 1,2-diphenyltetramethyldisilane, several monosilanes, bis(4-biphenylyl)methane, 4,4′-bis(4-phenylbenzyl)biphenyl, and dimethyldiphenylmethane. The zero-field splitting values of compounds having biphenyl subunits bridged with either SiMe 2- or CH 2-groups, compared with those of mono- and disubstituted biphenyls, show that the triplet electrons are localized mainly on one biphenyl group in each of the bridged compounds on the time scale of the ESR observations.

Electron Spin Resonance Studies and INDO MO-Calculations of Electron Irradiated Peptides. A Single Crystal of N-Acetylglycine

The radicals induced by radiation in single crystals of N-acetylglycine, grown from both H2 O and D2 O solutions, were studied using both ESR spectroscopy and INDO MO-calculations. At room temperature the radical ${\rm H}_{3}{\rm C}\cdot {\rm CO}\cdot {\rm NH}\cdot \dot{{\rm C}}{\rm H}\cdot {\rm COOH}$ was formed as previously demonstrated. In these experiments the detailed distribution of the unpaired spin density was studied both through the ESR observations and by MO-calculations. The two methods were in satisfactory agreement. It was found that the unpaired electron was largely delocalized and even δ-proton interaction was found. Furthermore, the observation that unpaired spin density can migrate through the peptide group may have some bearing with regard to the processes taking place in irradiated proteins.

ESR observation of transient acyl radicals in polyethylene irradiated in the presence of CO

ESR observation of transient acyl radicals in polyethylene irradiated in the presence of CO

Krypton Monofluoride and Its Positive Ion

Nonempirical quantum mechanical calculations have been carried out on KrF and KrF+. A large basis set of Slater functions was used, and the self-consistent-field (SCF) total energies for both diatomics are estimated to lie no more than 0.005 hartree above the exact nonrelativistic Hartree—Fock energies. The KrF SCF potential curve is repulsive and dissociates smoothly to Kr+F atoms. The KrF+ potential curve displays a minimum at 1.68 Å and spectroscopic constants De=−0.02 eV, and ω e=810 cm−1. The importance of polarization functions (d and f orbitals) in the single configuration wavefunctions is discussed. Electron correlation in both molecules has been investigated using first-order wavefunctions, which have yielded dissociation energies in excellent agreement with experiment for several smaller diatomic molecules. A 158-configuration correlated wavefunction predicts a flatter but nevertheless repulsive potential curve for KrF. We conclude that, except for the van der Waals interaction, KrF is unlikely to exist in the gas phase. The relation between this work and the observation of the KrF ESR in crystals of KrF2 is discussed. First-order wavefunctions containing 210 configurations for KrF+ yield the following predictions: re=1.75 Å, D0=1.90 eV, ω e=621 cm−1. Chupka and Berkowitz report the experimental value D0≥1.58 eV for KrF+. Several molecular properties are predicted for KrF+.

ESR Observation of Methyl Radical–Halide Ion Pairs Produced by Dissociative Electron Capture in a Crystalline Matrix

First Page

The distribution of damage produced by ion implantation of silicon at room temperature

Abstract Experiments designed to determine the damage distribution produced by energetic heavy ions in Si are described. For low ion doses (1011 to 1013 cm−2), the location of the damage peak was determined by changes, which were produced by ion damage, in the electrical properties of thin (0.6 μ), uniformly doped Si layers as a function of depth. The ratio of the peak position in the damage distribution to the peak position in the ion distribution was determined to be approximately 0.6 ± 0.1 for Si29 (150 keV), P31 (70, 140, 200 keV), B11 (60 keV), and As75 (280 keV). A comparison of carrier removal rates and the number of displaced lattice atoms previously reported from back-scattering experiments with He ions indicates that the nature of damage produced by Si29 and B11 are different. In the former case, cluster damage (amorphous disordered regions) appears to be an important form of radiation damage, while in the latter case, isolated defects are the dominant form of radiation damage for room temperature implantations. Isochronal annealing studies of Si29 and B11 ion damage provide further support for the different nature of radiation defects produced by these species. For high doses (1014 to 1016 cm−2), the growth of a continuous amorphous Si layer was studied with ESR, optical transmission, and visual observation and stripping studies. The ratio of the location of the damage peak to that of the peak ion concentration was determined to be approximately 0.7 for P31 (140, 280 keV) and 0.8 for As75 (280 keV). From the ESR studies, the number of displaced atoms in amorphous clusters was estimated to be 2800 per 280 keV P31 ion.

ESR observation of Frenkel defect production by post-irradiation electron-hole recombination in KC1

Abstract Experiments are described in which the creation of H centers is detected as a result of electrons recombining with Vk-type centers. The results are interpreted as evidence favoring the excitonic mechanism for radiation damage in alkali halides.

Is age-dependent genetic damage in seeds caused by free radicals?

In dry seeds of several kinds stored for up to 48 yr, no significant changes in electron spin resonance patterns (neither signal amplitudes nor shapes) vs. age were found, although four classes of signals were observed. This result is counter to some crude notions of how genetic damage from aging of seeds might arise from free radical reactions, and differs from ESR observations related to radiation-induced damage.

Effect of Oxygen on Radiation-Induced Free Radicals in Proteins

The effect of oxygen and nitric oxide on radiation-induced free radicals in trypsin was studied by ESR spectroscopy. Evacuated samples were irradiated with X-rays at room temperature and kept at this temperature for 20 hours before the ESR measurements started. The samples were then opened to an atmosphere of oxygen or nitric oxide, and the reactions between the paramagnetic gases and the protein radicals were followed by qualitative and quantitative ESR observations. The reaction with oxygen resulted in a transient ESR signal consisting of a single line with a g value of 2.007, and a width of approximately 13 gauss. This line is presumably due to a peroxide radical. In the case of nitric oxide nonradical products were directly formed. In experiments with nitric oxide and protein particles, with different physical dimensions, it was found that the decay of radicals can be adequately described by diffusion theory. It was found that the sulfur radicals as well as the doublet-type radicals react with the par...

Electrons in Organic Glasses during Photoionization. ESR Observations of a Photodynamic Equilibrium

Electrons in Organic Glasses during Photoionization. ESR Observations of a Photodynamic Equilibrium

Ground state ESR measurements of ruby during laser action

The use of electron spin resonance for measurement of the ground state population (GSP) of Cr3+in a ruby rod during optical pumping is described. For a 7.7 cm long rod at 90°K and a mirror reflectance product R_{1}R_{2} > 0.08 , the GSP at laser threshold was found to be 55 ± 5 percent in good agreement with theory and previous optical measurements. At room temperature, a limiting value of approximately 30 percent for the GSP was approached at high pump energies. Observations of the relative R_{1}(3/2), R_{1}(1/2) thresholds at 90°K as a function of mirror reflectivity indicated that the2E excited state absorption cross section at the laser wavelength is less than 5 \times 10^{-21} cm2. Detection of total internal reflection oscillations in cooled ruby lasers from ESR observations is also described.

Paramagnetic Relaxation in Liquid-Crystal Solvents

The influence of a liquid-crystal solvent on paramagnetic relaxation processes involving Zeeman and hyperfine anisotropies is examined. Secular and pseudosecular relaxation mechanisms are reduced by molecular ordering. Secular contributions are most effectively quenched, and, for high degrees of order in viscous media, pseudosecular processes are most important. ESR studies were made of solutions of vanadyl complexes with six β-diketones in p-azoxyanisole. The linewidths in the spectra depend upon the 51V nuclear spin quantum number M, and vary as A+BM+CM2. As the degree of molecular ordering increases, one predicts and observes that first C and then B change in sign. It was also found that almost perfect ordering of a solute in an imperfectly ordered liquid crystal can be achieved, provided the solute molecule is sufficiently large and rigidly planar. Implications of ESR observations concerning the structure of liquid-crystal phases are discussed.

ESR Observation of Δm=1 Transitions of Triplet States in Glasses

First Page