g Factor and hyperfine coupling anisotropy in the electron spin resonance spectra of methyl-, ethyl-, and allyl- type radicals adsorbed on silica gel

Shiga, Tetsuo; Lund, Anders

doi:10.1021/j100623a007

Cited by 45 publications

(36 citation statements)

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“…Small discrepancies in the reproduction of the spectrum can be understood considering that couplings due to H(5) and H(6) are not compatible with an alkyl radical and indicate that even though these radicals are largely dominant, other radicals are formed in the irradiated polymer. Comparison of H(5) and H(6) couplings with literature values indicates that these are consistent with allyl radicals, which are assumed to be formed as a minor fraction during the irradiation process . Even though ENDOR and HYSCORE signal intensities cannot in general be used for quantization of the number of species, the relative intensities of the allyl proton with respect to the alkyl proton signals indicate at least an order of magnitude difference in the number of the two species.…”

Section: Resultsmentioning

confidence: 99%

HYSCORE and Davies ENDOR study of irradiated ultra high molecular weight polyethylene

Paganini¹,

Brunella²,

Chiesa³

2012

Magnetic Reson in Chemistry

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Ultra high molecular weight polyethylene (UHMWPE) has been studied with different magnetic resonance techniques to elicit information on the nature and the location of radicals generated during high energy irradiation. Field swept electron paramagnetic resonance, pulsed Davies electron nuclear double resonance and hyperfine sublevel correlation spectroscopic measurements allowed extracting for the first time the full 1H hyperfine coupling tensors of the most abundant radical, i.e. a secondary alkyl radical and to ascertain the formation of allyl radicals in the first stages of the irradiation process. The 1H hyperfine coupling tensors are analogous to those reported for single crystal irradiated polyethylene, suggesting that radicals generated in UHMWPE are located in the crystalline region of the polymer. Copyright © 2012 John Wiley & Sons, Ltd.

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Section: Resultsmentioning

confidence: 99%

HYSCORE and Davies ENDOR study of irradiated ultra high molecular weight polyethylene

Paganini¹,

Brunella²,

Chiesa³

2012

Magnetic Reson in Chemistry

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“…24͒ usually discuss END contributions to spin relaxation and linewidths in terms of anisotropies, both ␦A and ␦g. While anisotropy in the g tensor can be important in high-field ESR, g anisotropy is small for alkyl radicals 63 ͑for ethyl, ␦gՇ0.0004 [64][65][66] ͒ so that e ␦g/gӶ␦A for the conditions of our experiments, and can be ignored. The isotropic part of the hyperfine interaction can also contribute to spin relaxation if it is modulated at an appropriate frequency.…”

Section: Interpretation Of the Parametersmentioning

confidence: 99%

Spin relaxation of muonium-substituted ethyl radicals (MuCH2ĊH2) in the gas phase

Fleming

Pan

Senba

et al. 1996

The Journal of Chemical Physics

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Articles you may be interested inAn electron spin resonance investigation of vanadium dioxide (51V16O2 and 51V17O2) and 51V17O in neon matrices with preliminary assignments for VO3 and V+ 2: Comparison with ab initio theoretical calculations Electron spin resonance matrix isolation and ab initio theoretical investigations of 69,71GaH2,69,71GaD2, H69,71GaCH3, and D69,71GaCD3 Conductive Cu(2,5dimethyldicyanoquinonediimine)2 radical ion salts: Systems with none, one, or two phase transitions Interaction of gasphase atomic deuterium with the Ru(001)-p(1×2)-O surface: Kinetics of hydroxyl and water formationThe spin relaxation of the muonium-substituted ethyl radical ͑MuCH 2 Ċ H 2 ͒ and its deuterated analog ͑MuCD 2 Ċ D 2 ͒ has been studied in the gas phase in both transverse and longitudinal magnetic fields spanning the range ϳ0.5-35 kG, over a pressure range from ϳ1-16 atm at ambient temperature. The Mu 13 CH 2 13 Ċ H 2 radical has also been investigated, at 2.7 atm. For comparison, some data is also reported for the MuCH 2 Ċ ͑CH 3 ͒ 2 ͑Mu-t-butyl͒ radical at a pressure of 2.6 atm. This experiment establishes the importance of the SR technique in studying spin relaxation phenomena of polyatomic radicals in the gas phase, where equivalent ESR data is sparse or nonexistent. Both T 1 ͑longitudinal͒ and T 2 ͑transverse͒ SR relaxation rates are reported and interpreted with a phenomenological model. Relaxation results from fluctuating terms in the spin Hamiltonian, inducing transitions between the eigenstates assumed from an isotropic hyperfine interaction. Low-field relaxation is primarily due to the electron, via both the nuclear hyperfine ͑S-A-I͒ and the spin rotation interactions ͑S-J͒, communicated to the muon via the isotropic muon-electron hyperfine interaction. At the highest fields, direct spin flips of the muon become important, due to fluctuations in the anisotropic part of the muon-electron hyperfine interaction. In the intermediate field region a muon-electron ''flip-flop'' relaxation mechanism dominates, due partly to the anisotropic hyperfine interaction and partly to modulation of the isotropic muon-electron hyperfine coupling. In the case of the T 2 rates, electron relaxation mechanisms dominate over a much wider field range than for the T 1 rates, and inhomogeneous line broadening also contributes. The fluctuations that induce both the T 1 and T 2 relaxation rates are described by a single correlation time, c , inversely proportional to the pressure. An effective spin-reorientation cross section is deduced from this pressure dependence, J ϳ100Ϯ20 Å 2 , for all isotopically substituted ethyl radicals. This is similar to the geometrical cross section, but about a factor of 4 larger than values of J found for similar-sized diamagnetic molecules by gas phase NMR, primarily reflecting the longer range of the electron-induced intermolecular potential.

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“…zeolites, alumina, aluminosilicalites or higher-order oxides are attractive materials in numerous applications in catalysis. Previous research has shown that those materials play a significant role in the separation and stabilization of various reactive intermediates as atoms, radicals, radical ions, and clusters [1][2][3][4][5][6][7]. Studies of such intermediates are very important for a better understanding of the mechanisms of chemical reactions in polymerization, heterogeneous catalysis, photochemistry, and radiation chemistry and biology.…”

Section: Introductionmentioning

confidence: 99%

“…Amorphous silica is one of the most common supports in catalysis and was the subject of several experimental studies during the past decades [4,5,24]. Silica gel support systems are widely used in studies of transition metal ions or complexes [25] and are successfully applied in controlled polymerization [26] and in studies of ionic radicals [27,28].…”

Section: Introductionmentioning

confidence: 99%

Monomer- and polymer radicals of vinyl compounds: EPR and DFT studies of geometric and electronic structures in the adsorbed state

Lund

Danilczuk

2012

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

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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 -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 coupling 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 coupling constants for all radicals confirmed the assignment of the experimental spectra.3

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g Factor and hyperfine coupling anisotropy in the electron spin resonance spectra of methyl-, ethyl-, and allyl- type radicals adsorbed on silica gel

Abstract: These data suggest that at 77 K the methyl radicals rotate about an axis perpendicular to the planes of the radical, whereas the ethyl radical rotates about the C-C bond axis. The analysis of spectra from allyl and methallyl radicals is less conclusive.

Cited by 45 publications

References 1 publication

HYSCORE and Davies ENDOR study of irradiated ultra high molecular weight polyethylene

HYSCORE and Davies ENDOR study of irradiated ultra high molecular weight polyethylene

Spin relaxation of muonium-substituted ethyl radicals (MuCH2ĊH2) in the gas phase

Monomer- and polymer radicals of vinyl compounds: EPR and DFT studies of geometric and electronic structures in the adsorbed state

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