Electron spin resonance hyperfine structure

Quadrupole coupling constants for molecules are usually determined from the hyperfine structure of pure rotational spectra or from electric-beam and magnetic-beam resonance spectroscopies. Nuclear magnetic resonance, electron spin resonance and Mossbauer spectroscopies are also routes to the property. There is a large amount of experimental data for and halogen-substituted molecules. Less data is available for deuterium because the nuclear quadrupole is small. 

Knight, L. B., Kaup, J. G., Petzold, B., Ayyad, R., Ghanty, T. K., Davidson, E. R., 1999, Electron Spin Resonance Studies of 45Sc170, 89Y170, and 139La170 in Rare Gas Matrices Comparison With Ab Initio Electronic Structure and Nuclear Hyperfine Calculations , J. Chem. Phys., 110, 5658. 

In order to identify organic free - radicals present at quantifiable concentrations during the sonication of PCBs, we employed Electron Spin Resonance (ESR) with a spin trap, N-t-butyl-a-phenyl-nitrone (PBN). PBN reacts with the reactive free - radicals to form more stable spin-adducts, which are then detected by ESR. The ESR spectrum of a PBN spin adduct exhibits hyperfine coupling of the unpaired election with the 14N and the (3-H nuclei which leads to a triplet of doublets. The combination of the spin-adduct peak position and peak interval uniquely identifies the structure of a free-radical. 

Electron-spin resonance (e.s.r.) spectra with characteristic hyperfine structure have been recorded during the initial stages of the Maillard reaction between various sugar and amino compounds. The products responsible for the spectra appear to be IV, Af -disubstituted pyrazine radical cations. The pyrazine derivatives are assumed to be formed by the bimolecular condensation of two- and three-carbon enaminol compo-... 

In the case of those complexes which are paramagnetic, additional information can be obtained from (a) the fine structure and occasionally (b) hyperfine structure of the observed electron-spin-resonance (ESR) spectra. 

The effect of temperature on the association of vanadium compounds in asphaltenes was investigated by Tynan and Yen (1969). Using electron spin resonance (ESR), they observed both anisotropic and isotropic hyperfine structures of vanadium, interpreted as bound or associated and free vanadium, from asphaltenes precipitated for a Venezuelan petroleum and reintroduced to various solvents. Higher temperatures and more polar solvents resulted in a transition from bound to free vanadium, as shown in Fig. 12. At 282°C, only 1% of the anisotropic spectrum was observed. An activation energy of 14.3 kcal/mole was observed for the transition. 

Electron spin resonance spectra of coals usually consist of a single line with no resolvable fine structure however, the electron nuclear double resonance (ENDOR) technique can show hyperfine interactions not easily observable in conventional electron spin resonance spectra. Recently, this technique has been applied to coal, and it is claimed that the very observation of an ENDOR signal shows interaction between the electron and nearby protons and that the results indicate that the interacting protons are twice removed from the aromatic rings on which, it is assumed, the unpaired electron is stabilized. 

We report an electron spin resonance (ESR) study on a C60 anion and a metal (M) encapsulated in fullerene (C ) (a metallofullerene M C ). The anisotropy components of the g-factor of Cg0 were determined accurately from the analysis of angular-dependent ESR spectra of single crystal Cg0 salt. The evaluation of the g-factor was performed according to the classification of symmetry of the C60 geometry. It was found out from the evaluation that the molecular structure of Cg0 should he distorted to lower symmetry, C2h or C,. The variety of ESR spectra of metallofullerenes of La C s was obtained in terms of a g-factor, a hyperfine coupling constant, and a line width. In the case of the isomer I of La C80 and the isomer II of La C84, an abnormally large line width was measured. The molecular structure with high symmetry would reflect on the specific spin dynamics. 

Historically, the triphenylmethyl radical (1), studied by Gomberg in 1987, is the first organic free radical. The triphenylmethyl radical can be obtained by the reaction of triphenylmethyl halide with metal Ag as shown in eq. 1.1. This radical (1) and the dimerized compound (2) are in a state of equilibrium. Free radical (1) is observed by electron spin resonance (ESR) and its spectrum shows beautiful hyperfine spin couplings. The spin density in each carbon atom can be obtained by the analysis of these hyperfine spin coupling constants as well as information on the structure of the free radical. 

The hyperfine-structure from nuclear magnetic moments on the electron spin resonance curve was first interpreted by Owen and Stevens in the case of IrClg-. There is no doubt that this gives a perfect qualitative proof for the delocalization of the partly filled shell. However, it is less clear whether there is a simple equivalence between the ligand nuclear influence and b in eq. (19). The point is that the partly filled shell has to be orthogonal, in a very complicated way, on all the previously filled shells such as Is and 2s of the X atoms. 

A large number of paramagnetic transition metal nitrosyl complexes have been studied using electron spin resonance (ESR) spectroscopy. Information on the electronic ground state can be derived from the g-value and the hyperfine coupling constants, and many [MLslNO)]" (see Table IV) and nitrosyl porphyrin complexes (99) have been studied in this way with a view to understanding their electronic structures. 

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