Electron-spin resonance experiment

The electron densities for a spin electrons and for spin electrons are always equal in a singlet spin state, but in non-singlet spin states the densities may be different, giving a resultant spin density. If we evaluate the spin density function at the position of certain nuclei, it gives a value proportional to the isotropic hyperfine coupling constant that can be measured from electron spin resonance experiments. 

The effectiveness of a crude oil demulsifier is correlated with the lowering of the shear viscosity and the dynamic tension gradient of the oil-water interface. The interfacial tension relaxation occurs faster with an effective demulsifier [1714]. Short relaxation times imply that interfacial tension gradients at slow film thinning are suppressed. Electron spin resonance experiments with labeled demulsifiers indicate that the demulsifiers form reverse micellelike clusters in the bulk oil [1275]. The slow unclustering of the demulsifier at the interface appears to be the rate-determining step in the tension relaxation process. 

The assumption of membrane softness is supported by a theoretical argument of Nelson et al., who showed that a flexible membrane cannot have crystalline order in thermal equilibrium at nonzero temperature, because thermal fluctuations induce dislocations, which destroy this order on long length scales.188 189 The assumption is also supported by two types of experimental evidence for diacetylenic lipid tubules. First, Treanor and Pace found a distinct fluid character in NMR and electron spin resonance experiments on lipid tubules.190 Second, Brandow et al. found that tubule membranes can flow to seal up cuts from an atomic force microscope tip, suggesting that the membrane has no shear modulus on experimental time scales.191 However, conflicting evidence comes from X-ray and electron diffraction experiments on diacetylenic lipid tubules. These experiments found sharp diffraction peaks, which indicate crystalline order in tubule membranes, at least over the length scales probed by the diffraction techniques.123,192 193... 

EPR measurements were first performed on wurtzite GaN in 1993 by Carlos and co-workers [2-4] and on cubic GaN by Fanciulli and co-workers at about the same time [5], The primary resonance in the wurtzite films is slightly anisotropic (gy = 1.9510 and gi = 1.9483) with a width 0.5 mT at 4.2 K and generally acknowledged to be due to a band of delocalised effective mass (EM) donor electrons. The average g value is consistent with the expectations of a 5-band k.p analysis and is also similar to that obtained by Fanciulli [5] for a much broader line (—10 mT) in their conduction electron spin resonance experiments on zincblende films. With this exception all of the work discussed in this Datareview is on the wurtzite phase. 

The fundamentals and analysis of electron spin echo modulation have been described in some detail (9). Here the essential details will be sumnarized to aid in understanding the structural data to be presented. Electron spin echoes are generated in pulsed electron spin resonance experiments. The most comnon type... 

Electron spin resonance experiments in ion-beam irradiated samples... 

When, thermolysis of an aryl azide leads to an arylnitrene, the latter is generated in the singlet (182) state, which can be in equilibrium with the triplet (183). Electron spin resonance experiments have... 

The catalysts were prepared by contacting alumina with aqueous solutions of chloroplatinic acid and ammonium perrhenate. The consumption of hydrogen during reduction corresponded to complete reduction of platinum from the +4 oxidation state to the metal and of rhenium from the +7 to the +4 state. The X-ray diffraction data on the metal residue from the leached catalysts showed no evidence for the presence of rhenium metal or a platinum-rhenium alloy. Most of the rhenium was found in the leaching solution. Finally, the authors stated that data from an electron spin resonance experiment on one of the reduced platinum-rhenium catalysts were consistent with their conclusion that the rhenium was present in the +4 state. 

The existence of alternancy symmetry leads to very strong predictions concerning the electronic properties of the system. For instance, it imposes that the lowest energy excitation is dipole allowed. However, in long polyenes, there is unambiguous experimental evidence for states below the lowest dipole-allowed excited state [17]. The alternancy symmetry also predicts that in polyene radicals (with an odd number of carbon atoms), the spin density should reside on only one sublattice and that the spin density on the other sublattice be strictly zero. However, electron spin resonance experiments indicate the presence of spin density on both sublattices, with the spin projections on the sites of one sublattice being opposite in direction to those of the sites belonging to the other sublattice [18]. 

The side chain can also affect electronic events of the tricyclic ring system. Electron spin resonance experiments allowed Fenner S to suggest that the influence of the side chain of phenothiazine on the formation of free radicals showed a correlation between the redox activity of the phenothiazine nucleus and dynamic aspects of stereochemistry. For example, there was a difference in the formation of cationic free radicals between promazine and alimemazine. The latter has a branched side chain, and forms cationic free radicals only under irradiation. It differs from promazine in pharmacodynamic properties, reported s to result in considerably shifted ion exchange equilibria. A kinetic study of the oxidation of dopamine by dialkylaminoalkyl phenothiazine cationic free radicals showed that a strong correlation existed between side-chain structures and oxidation rates phenothiazine free radicals with two carbon side chains had faster rates than those with three carbon side diains, albeit both were very rapid at physiological pH. 

Goldberg, I. B. McKinney, T. M. Principles and Techniques of Electrochemical-Electron Spin Resonance Experiments. In Laboratory Techniques in Electroanalytical Chemistry, Kissinger, P. T. Heineman, W. R., Eds. Marcel Dekker, New York, 1984, Chapter 24, pp 675-728. 

ESR (electron spin resonance) experiments of disappearance of OH-TEMPO in reactions of polymerization in which pure styrene or stjrene with small amounts of MA (1-2% wt.) are heated at 80 °C in the presence of a small amount of OH-TEMPO (4.5 X 10 M), are shown in Figure ID. These indicate that the nitroxide disappears faster when the concentration of MA increases. The disappearance of the nitroxide would be probably due to the formation of the corresponding alkoxya-mine. The possibility of reaction with a free... 

Electron-spin resonance experiments are concerned with the transition between the lowest-lying levels of the paramagnetic ions in an external magnetic field. The analyses of the absorption spectra can be carried through by the use of the spin-HamUtonian method developed by Pryce and his collaborators. This useful method is applied to describe the complicated behavior of the levels l3ung lower than the microwave frequency by an effective Hamiltonian written in a compact form. 

Buback M, Kowollik C, Kamachi M, Kajiwara A. Free-radical propagation rate coefficients of dodecyl methacrylate deduced from electron spin resonance experiments. Macromolecules 1998 31 7208-7212. 

Chen, J., and Heeger, A. J. (1988) "In Situ Electron Spin Resonance Experiments on Polyacetylene during Electrochemical Doping" Synth. Met. 24, 311-327. 

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