Hyperfine structure line broadening

The ESR spectra of a large variety of sulfonyl radicals have been obtained photolytically in liquid phase over a wide range of temperature. Some selected data are summarized in Table 2. The magnitudes of hyperfine splittings and the observations of line broadening resulting from restricted rotation about the C—S bond have been used successfully in conjunction with INDO SCF MO calculations to elucidate both structure and conformational properties. Thus the spin distribution in these species is typical of (T-radicals with a pyramidal center at sulfur and in accord with the solid-state ESR data. 

It is interesting to note than an 11-line hyperfine structure with aiso = 10 G was observed at gjm = 2.007 when the Al-exchanged HY zeolite was irradiated in vacuo. This hyperfine structure was reported to be reversibly broadened by oxygen (103). Although the hyperfine structure appears to be similar to that observed by Vedrine et al. (266) for the V center associated with two aluminum atoms, it does not lead to the formation of OJ on adsorption of oxygen. 

If no collision interferes with the emission process, the line is very sharp. In the presence of collisions, on the other hand, the line will be broadened. The intensity at the line center may rise by several orders of magnitude, depending on various factors, such as the presence of unresolved hyperfine structure components, etc. [119]. The core of the line still remains sharp the collisional broadening is most striking in the wings, especially the far wings where the intensities have fallen off by orders of magnitude. 

The disadvantages of these methods is that radicals have random orientations, and hence hyperfine and (7-value anisotropies give rise to considerable line-broadening. However, if oriented radicals can be used, these anisotropies can be measured, and often the resulting information is of considerable help in elucidating structural details. 

Three membrane-bound adenosine triphosphatase enzymes have been characterized using Mn(II) and Gd(III) electron paramagnetic resonance (EPR) and a variety of NMR techniques. Mn(II) EPR studies of both native and partially delipidated (Na+ + K+)-ATPase from sheep kidney indicate that the enzyme binds Mn2+ at a single, catalytic site with Kq = 0.21 x 10- M. The X-band EPR spectrum of the binary Mn(II)-ATPase complex exhibits a powder line shape consisting of a broad transition with partial resolution of the 55 n nuclear hyperfine structure, as well as a broad component to the low field side of the spectrum. ATP, ADP, AMP-PNP and Pj all broaden the spectrum, whereas AMP induces a substantial narrowing of the hyperfine lines of the spectrum. 

Samples of the ceramic polycrystalline Ti02 (rutile) doped electrodes of the VxTi . x02 composition were studied at different vanadium content (0.001 < x < 0,05) in [128, 129]. It was shown that at x < 0,003 the EPR spectra perform a well resolved hyperfine structure (hfs) typical of V4+-doped rutile (Fig. 8.10), in which V4+ ions substituted Ti4+ ions in the crystal lattice. At 0.003 < x < 0.01, the dipolar broadening of the individual lines 8H occurred. At x > 0.01, in parallel with continuing broadening of the hfs lines, a broad single line appears (Fig. 8.11). Its part in the spectrum increased with the increase of vanadium content. 

The negative ion of naphthalene can be made in a suitable solvent, such as di-methoxyethane (dme), by treatment with an alkali metal in the absence of oxygen. This stable free radical-ion has an esr spectrum with hyperfine structure. If more naphthalene is added, a broadening of the spectral lines occurs which is attributed to the reaction... 

Furthermore, isotopic structure and hyperfine structure, and also resonance broadening, resulting from the interaction between radiating and non-radiating atoms of the same species, and Stark broadening, resulting from interaction with electrical fields, contribute to the physical widths of the spectral lines. 

Isolated Mi ions in dilute solution exhibit six. hyperfine lines due to coupling of the e ctron and nuclear spin (21). In more concentrated solutions the Mi ions interact more frequently, which results in a broadening of the ESR spectrum. In sufficiently concentrated solutions the hyperfine structure may no longer be resolved and the spectrum becomes a single broad line. 

For a toluene/methanol solution, figure 6, the hyperfine structure is well resolved, but the spectrum is broadened as a result of dipole-dipole interactions. As with the THF solution, both isolated and associated ions are present, but in toluene/-methanol the isolated species is predominant. Figure 6 compares the solution spectra of a 1.15 mole % Mh-SPS in toluene with various concentrations of methanol co-solvent. These materials are insoluble in toluene and some methanol is needed in order to dissolve them. At the lowest methanol concentration studied, 2% (v/v), a single broad line spectrum was observed. At higher concentrations of methanol, the six hyperfine structure became evident. These results indicate that the methanol is effective at solvating the cations, which is consistent with the conclusion made... 

As discussed in the Introduction to this paper, different viscosity versus concentration behavior is observed for SFS solutions in toluene/methanol and in DMF. Folyelectrolyte behavior is observed only in the latter solvent. The ESR spectrum of a 2.65 mole % Mn-SPS in these two solvents was studied at various concentrations. For both lvents, the hyperfine structure characteristic of isolated Mn ions was observed in very dilute solutions and at concentrations for which Lundberg and Phillips(10) observed strong intermolecular interactions. The ESR data indlcat that in dilute solution in both DMF and toluene/methanol, the Mn exists mainly as Isolated cations. In addition, the IR spectra indicated that the cation is removed from the anion to a similar degree in both solvents. Yet, a polyelectrolyte effect is observed experimentally only in DMF solutions. Although there was some dipole-dipole broadening of the toluene/methanol spectrum, the line width and the g-factor (g 2,000) in both cases were ldent fal. The g-factor of 2.000 is characteristic of an isolated Mn in solution ). 

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