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Abstract
Relative diffusion coefficients were determined in water for the D, H, and Mu isotopes of atomic hydrogen by measuring their diffusion-limited spin-exchange rate constants with Ni(2+) as a function of temperature. H and D atoms were generated by pulse radiolysis of water and measured by time-resolved pulsed EPR. Mu atoms are detected by muonium spin resonance. To isolate the atomic mass effect from solvent isotope effect, we measured all three spin-exchange rates in 90% D2O. The diffusion depends on the atomic mass, demonstrating breakdown of Stokes-Einstein behavior. The diffusion can be understood using a combination of water "cavity diffusion" and "hopping" mechanisms, as has been proposed in the literature. The H/D isotope effect agrees with previous modeling using ring polymer molecular dynamics. The "quantum swelling" effect on muonium due to its larger de Broglie wavelength does not seem to slow its "hopping" diffusion as much as predicted in previous work. Quantum effects of both the atom mass and the water librations have been modeled using RPMD and a qTIP4P/f quantized flexible water model. These results suggest that the muonium diffusion is very sensitive to the Mu versus water potential used.
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Affiliation(s)
- J A Walker
- Radiation Laboratory and Department of Chemistry & Biochemistry, Notre Dame University , Notre Dame, Indiana 46556, United States
| | - S P Mezyk
- Department of Chemistry & Biochemistry, California State University , 1250 Bellflower Boulevard, Long Beach, California 90840, United States
| | - E Roduner
- Institute of Physical Chemistry, University of Stuttgart , Pfaffenwaldring 55, D-70569 Stuttgart, Germany.,Department of Chemistry, University of Pretoria , Pretoria 0002, South Africa
| | - D M Bartels
- Radiation Laboratory and Department of Chemistry & Biochemistry, Notre Dame University , Notre Dame, Indiana 46556, United States.,Chemistry Division, Argonne National Laboratory , 9700 South Cass Avenue, Argonne, Illinois 60439, United States
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Keppeler M, Bräuning G, Radhakrishnan SG, Liu X, Jensen C, Roduner E. Reactivity of diatomics and of ethylene on zeolite-supported 13-atom platinum nanoclusters. Catal Sci Technol 2016. [DOI: 10.1039/c6cy00182c] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
CO and NO react on hydrogen-covered 13-atom Pt clusters, O2 does not, and the hydrogenation of ethene shows structure sensitivity.
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Affiliation(s)
- M. Keppeler
- Institut für Physikalische Chemie
- Universität Stuttgart
- Pfaffenwaldring 55
- Stuttgart
- Germany
| | - G. Bräuning
- Institut für Physikalische Chemie
- Universität Stuttgart
- Pfaffenwaldring 55
- Stuttgart
- Germany
| | - S. G. Radhakrishnan
- Department of Chemistry
- University of Pretoria
- Pretoria 0002
- Republic of South Africa
| | - X. Liu
- Institut für Physikalische Chemie
- Universität Stuttgart
- Pfaffenwaldring 55
- Stuttgart
- Germany
| | - C. Jensen
- Institut für Physikalische Chemie
- Universität Stuttgart
- Pfaffenwaldring 55
- Stuttgart
- Germany
| | - E. Roduner
- Institut für Physikalische Chemie
- Universität Stuttgart
- Pfaffenwaldring 55
- Stuttgart
- Germany
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Roduner E, Louwrier PWF, Brinkman GA, Garner DM, Reid ID, Arseneau DJ, Senba M, Fleming DG. Quantum Phenomena and Solvent Effects on Addition of Hydrogen Isotopes to Benzene and to Dimethylbutadiene. ACTA ACUST UNITED AC 2014. [DOI: 10.1002/bbpc.199000008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Kromer A, Wedig U, Roduner E, Jansen M, Amsharov KY. Counterintuitive Anisotropy of Electron Transport Properties in KC60(THF)5⋅2 THF Fulleride. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201305808] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Kromer A, Wedig U, Roduner E, Jansen M, Amsharov KY. Counterintuitive Anisotropy of Electron Transport Properties in KC60(THF)5⋅2 THF Fulleride. Angew Chem Int Ed Engl 2013; 52:12610-4. [DOI: 10.1002/anie.201305808] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Revised: 08/20/2013] [Indexed: 11/11/2022]
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Aleksandrova E, Hink S, Hiesgen R, Roduner E. Spatial distribution and dynamics of proton conductivity in fuel cell membranes: potential and limitations of electrochemical atomic force microscopy measurements. J Phys Condens Matter 2011; 23:234109. [PMID: 21613704 DOI: 10.1088/0953-8984/23/23/234109] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The proton conductivity of a Nafion 112 membrane is measured with a high spatial resolution using electrochemical atomic force microscopy. Image analysis reveals an inhomogeneous conductivity distribution which is attributed to the limited connectivity of hydrophilic domains. This information relates to the micro-morphology which is due to phase separation of the hydrophobic polymer backbone and the hydrophilic pendant groups. The direct images relate to a different length scale and are complementary to the x-ray diffraction investigations which provide only average information. Furthermore, the measured current values reveal an interesting correlation with the size of the conductive areas. A bimodal conductivity distribution suggests that there are different mechanisms which contribute to the proton current in Nafion. Additionally, time dependence in local conductivity is found and interpreted in terms of redistribution of water in the membrane. A statistical analysis of the current distribution is performed and compared with theoretical simulations. Evidence is found for the existence of a critical current density. On a timescale of seconds the response of the conductive network is probed by applying voltage steps to the atomic force microscope tip.
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Affiliation(s)
- E Aleksandrova
- Institut für Physikalische Chemie, Universität Stuttgart, 70569 Stuttgart, Germany
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Martyniak A, Dilger H, McKenzie I, Scheuermann R, Lagerwall J, Roduner E. Partitioning and reorientational dynamics of phenylalcohols in SDS lyotropic liquid crystalline mesophases: An ALC-μSR study. Colloids Surf A Physicochem Eng Asp 2007. [DOI: 10.1016/j.colsurfa.2006.10.068] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Martyniak A, Dilger H, Scheuermann R, Tucker IM, McKenzie I, Vujosevic D, Roduner E. Using spin polarised positive muons for studying guest molecule partitioning in soft matter structures. Phys Chem Chem Phys 2006; 8:4723-40. [PMID: 17043715 DOI: 10.1039/b610414b] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Fully polarised positive muons substituted for protons in organic free radicals can be used as spin labels which reveal information about the structure, dynamics and environment of these radicals. In applications via the technique of avoided-level-crossing muon spin resonance (ALC-microSR), the positive muon has been used to study the partitioning of phenyl alcohols in lamellar phase colloidal dispersions of a cationic dichain surfactant. Here we describe the experimental technique which permits highly sensitive spectroscopy as previously demonstrated for surfactant mixtures. We also demonstrate its capability in the study of partitioning of cosurfactant molecules in surfactant bilayers in order to elucidate the main factors which contribute to cosurfactant ordering at interfaces. The technique takes advantage of the positive muon combining with an electron to a hydrogen-like atom that is called muonium. This atom attaches to a phenyl group, forming a cyclohexadienyl-type radical that contains the muon as a polarised spin label, providing an excellent probe even for very low phenyl alcohol concentrations. The position of one type of resonance, which on the basis of spectroscopic selection rules is denoted as Delta(0), is related to the solvent polarity of the radicals' environment. The results derived from Delta(0) measurements reveal a systematic trend where the increasing chain length of the phenyl alcohol results in a deeper immersion of the phenyl ring of the alcohol into the surfactant bilayer with the OH group anchored at the interface. In addition, the data suggest partial penetration of water molecules into the bilayer. Furthermore, data ensuing from a second resonance (called Delta(1), which is dependent upon the degree of confinement of the radical within the surfactant aggregate structure) indicates not only that the phenyl alcohol resides in an anisotropic environment, (i.e. that the host molecule is unable to undergo full 3-D reorientation on a timescale of 50 ns), but the resonance line widths indicate that the radicals are undergoing fast rotation about a particular axis, in this instance about the first C-C substituent bond at the phenyl ring. Detailed analysis of these Delta(1) line shapes suggests that other types of motion involving reorientation of the above rotation axis are also present. At room temperature, the hydrocarbon chains of the double layers form an aggregate state commonly referred to as the L(beta) phase, where the motions of surfactant alkyl chains are effectively frozen out. These chains melt on heating over a temperature range which is solution composition dependent (ca. 51 to 67 degrees C), but in all cases leading to a liquid-like disordered hydrocarbon regime whilst retaining the overall lamellar structure (and in this state is termed L(alpha)). Above the L(alpha)/L(beta) chain ordering phase transition the tracer molecules reside within the bilayer, but below this transition (and depending on their water-oil solubility) they are completely or partly expelled. This interpretation is further supported by Heisenberg spin exchange experiments. The water-bilayer partitioning reflects both typical classical and nonclassical hydrophobic solvation depending on temperature and chain length of phenyl alcohols.
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Affiliation(s)
- A Martyniak
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569, Stuttgart, Germany
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Liu X, Dilger H, Eichel RA, Kunstmann J, Roduner E. A Small Paramagnetic Platinum Cluster in an NaY Zeolite: Characterization and Hydrogen Adsorption and Desorption. J Phys Chem B 2006; 110:2013-23. [PMID: 16471777 DOI: 10.1021/jp0561874] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A well-defined cluster containing 12 equivalent platinum atoms was prepared by ion exchange of an NaY zeolite, followed by hydrogen reduction. It was characterized by electron paramagnetic resonance (EPR) spectroscopy, hyperfine sublevel correlation (HYSCORE), and theoretical calculations. Combing the results of the experiments with density functional calculations, the likely structure of this cluster is icosahedral Pt13Hm, possibly with a low positive charge. The adsorbed H/D on the Pt cluster surface can be exchanged reversibly at room temperature. From H/D desorption experiments, an H2 binding energy of 1.36 eV is derived, in reasonable agreement with the calculated value but clearly larger than that for a (111) Pt single-crystal surface, revealing a finite size effect. While the hydrogen-covered cluster should clearly be regarded as a molecule, it is conceivable that the cluster adopts metallic character upon hydrogen desorption. It is likely that up to m=30 H atoms bind to this cluster with 12 surface atoms, which has important implications for the determination of the dispersion of small Pt catalyst particles by hydrogen chemisorption. Calculations as well as experiments give evidence of an interesting magnetic behavior with high-spin states playing a prominent role. There are strong indications that a reservoir of EPR silent but structurally similar clusters exists which can partly be converted to EPR visible species by H/D exchange or by gas adsorption.
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Affiliation(s)
- X Liu
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
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Frantz S, Hübner GA, Wendland O, Roduner E, Mariani C, Ottaviani MF, Batchelor SN. Effect of Humidity on the Supramolecular Structure of Cotton, Studied by Quantitative Spin Probing. J Phys Chem B 2005; 109:11572-9. [PMID: 16852420 DOI: 10.1021/jp050791x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The effect of water content on the physicochemical properties of the amorphous regions in cotton were investigated by measuring the electron paramagnetic resonance (EPR) of TEMPOL nitroxide radicals, deposited in cotton at different loadings, as a function of the relative humidity (RH) and temperature. Three different components contribute differently to the experimental EPR spectra, corresponding to (a) mobile radicals absorbed in the bulk amorphous region, (b) slow moving radicals adsorbed on the crystallite surfaces in cotton, and (c) aggregated radicals. These components were analyzed by means of computer-aided simulations of the line shapes and simplified line width methods. Polarity and mobility parameters were extracted from the analysis of the spectra. For all loadings and temperatures, the polarity suddenly dropped when the water content fell below approximately 3 wt %, i.e., when water was removed from the bulk amorphous regions. At the lowest loading (2 x 10(-5) mol kg(-1)), the spectra were independent of the RH, and only mobile radicals were observed. At intermediate loading (10(-4)-10(-3) mol kg(-1)) both mobile (fast) and adsorbed (slow) moving radicals were present, the fraction of which depended on the RH. The mobility of the adsorbed and mobile radical signals was smaller at higher loadings, indicating microdomains of different character. The temperature dependence of the rotational correlation times provided the activation energies, which were much lower than in liquids. An equilibrium exists between the mobile and the adsorbed radicals. The temperature dependence of the equilibrium constant, K, gave the enthalpy and the entropy of the adsorption process. At low RH, the enthalpy and the entropy values indicated a simple adsorption process. At 10(-3) mol kg(-1), the values were independent of the RH, but at low loadings the values increased with the increase in the RH, which suggested a displacement of adsorbed water by the radicals at high water content. At loadings above 10(-3) mol kg(-1), signals from radicals strongly interacting via spin exchange were observed, which are assigned to aggregated radicals; simulation of the spectra gave an activation energy of 13 kJ mol(-1) for the spin exchange process. These effects are rationalized on the basis of microdomains of different character within cotton, reflecting the variation in pore sizes (0.5-8 nm) and the relaxation behavior of the cellulose chains.
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Affiliation(s)
- S Frantz
- Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
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Janz GJ, Roduner E, Coutts JW, Downey JR. Raman studies of sulfur-containing anions in inorganic polysulfides. Barium trisulfide. Inorg Chem 2002. [DOI: 10.1021/ic50162a002] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Janz GJ, Downey JR, Roduner E, Wasilczyk GJ, Coutts JW, Eluard A. Raman studies of sulfur-containing anions in inorganic polysulfides. Sodium polysulfides. Inorg Chem 2002. [DOI: 10.1021/ic50162a004] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Prassides K, Dennis TJS, Christides C, Roduner E, Kroto HW, Taylor R, Walton DRM. Mu@C70: monitoring the dynamics of fullerenes from inside the cage. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100205a007] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Janz GJ, Coutts JW, Downey JR, Roduner E. Raman studies of sulfur-containing anions in inorganic polysulfides. Potassium polysulfides. Inorg Chem 2002. [DOI: 10.1021/ic50162a003] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Scheuermann R, Roduner E, Batchelor SN. Quantitative Electron Paramagnetic Resonance Study of the Motion, Adsorption, and Aggregation of TEMPOL Radicals in the Nanopores of Dry Cotton. J Phys Chem B 2001. [DOI: 10.1021/jp011995q] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- R. Scheuermann
- Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
| | - E. Roduner
- Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
| | - S. N. Batchelor
- Unilever Research Port Sunlight, Quarry Road East, Bebington, Wirral CH63 3JW, Great Britain
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Affiliation(s)
- E Roduner
- Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
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Lossack AM, Bartels DM, Roduner E. Rate constants and kinetic isotope effects in hydrogen abstractions by H from formic acid. Res Chem Intermed 2001. [DOI: 10.1163/156856701104202129] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Zheng J, Schmauke T, Roduner E, Dong J, Xu Q. The influence of Fe on the dispersion, electronic state, sulfur-resistance and catalysis of platinum supported on KL zeolite. ACTA ACUST UNITED AC 2001. [DOI: 10.1016/s1381-1169(01)00096-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Glöckle M, Kaim W, Klein A, Roduner E, Hübner G, Zalis S, van Slageren J, Renz F, Gütlich P. The stable diiron(2.5) complex ion [(NC)(5)Fe(mu-tz)Fe(CN)5](5-), tz = 1,2,4,5-tetrazine, and its neighboring oxidation states. Inorg Chem 2001; 40:2256-62. [PMID: 11327899 DOI: 10.1021/ic001229i] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The conceptually simple mixed-valent diiron compound (NEt(4))(5)[(NC)(5)Fe(mu-tz)Fe(CN)(5)] with the 1,2,4,5-tetrazine (tz) bridging ligand was obtained as a thermally and air-stable material that displays large and highly variable electrochemical comproportionation constants between about 10(8) (in water) and 10(19.0) (in acetonitrile). Strong metal-metal interaction is also evident from spectroscopic results obtained for the solid and for the dissolved species. The rather intense intervalence charge-transfer band occurs around 2400 nm; infrared and Mössbauer spectra reveal the high spectroscopic symmetry of the system according to an (Fe(2.5))(2) formulation. DFT calculations on the [(NC)(5)Fe(mu-tz)Fe(CN)(5)](6-) ion confirm the presence of very low-lying pi(tz) and high-lying d(Fe) orbitals.
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Affiliation(s)
- M Glöckle
- Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany
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Dilger H, Schwager M, Tregenna-Piggott PLW, Roduner E, Reid ID, Arseneau DJ, Pan JJ, Senba M, Shelley M, Fleming DG. Addition Kinetics and Spin Exchange in the Gas Phase Reaction of the Ethyl Radical with Oxygen. ACTA ACUST UNITED AC 1996. [DOI: 10.1021/jp963480i] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Shelley M, Arseneau D, Senba M, Pan J, Snooks R, Kreitzman S, Fleming D, Roduner E. Muon Spin Relaxation Studies of Cyclohexadienyl Radicals in Nausy. ACTA ACUST UNITED AC 1994. [DOI: 10.1016/s0167-2991(08)64147-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/13/2023]
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Niedermayer C, Reid ID, Roduner E, Ansaldo EJ, Bernhard C, Binninger U, Glückler H, Recknagel E, Budnick JI, Weidinger A. Simultaneous observation of muonium and multiple free radicals in muon-implanted C70. Phys Rev B Condens Matter 1993; 47:10923-10926. [PMID: 10005219 DOI: 10.1103/physrevb.47.10923] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Jent F, Paul H, Roduner E, Heming M, Fischer H. Rates of addition oftert-butyl and pivaloyl radicals to acrylonitrile measured by modulated ESR and ?SR spectroscopy. INT J CHEM KINET 1986. [DOI: 10.1002/kin.550181002] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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