Line-width Alternation Research Articles

Linewidth alternation in the e.s.r. spectrum of the 1,4-benzosemiquinone free radical anion in ether solution

The e.s.r. spectra of potassium, rubidium and caesium 1,4-benzosemiquinone in D.M.E. have been recorded from –80°C to room temperature. In all cases, marked line width alternation has been found and, from the behaviour of the caesium hyperfine splittings, the process responsible for the line broadening is one in which the spin state of the alkali metal is preserved. The observations suggest two-site cation oscillation as the line broadening process and all the features expected from the theory for this have been found for the three alkali metal semiquinone ion-pairs. As the temperature is lowered the degree of ionization of all the three ion-pairs increases. In the temperature range from –60 to –80°C the spectrum of an additional species has been found for each of the alkali metal semiquinones. Possible explanations of this have been discussed.

Solvation spectra. Part 18.—Solvent dependency of14N hyperfine coupling constants of the anions of p-dinitrobenzene and p-nitroanisole

The isotropic hyperfine coupling constants to 14N in the radical anions of p-dinitrobenzene and p-nitroanisole in mixed solvents have been measured as a function of solvent composition. The results are interpreted in terms of a simplified model of solvation involving strong specific solvation by one or two solvent molecules and market, unspecific solvation by the remainder. The onset of marked line-width alternation is interpreted in terms of the formation of solvent-separated ion-pairs and some details of their structure are inferred.

Line-Width Alternation in the Electron Spin Resonance Spectra of the Anion Radicals of Hydropyrenes

Line-Width Alternation in the Electron Spin Resonance Spectra of the Anion Radicals of Hydropyrenes

Line-width Alternation in the Electron Spin Resonance Spectra of Para-dinitrobenzene Anions in Various Mixed Solvents

As part of a general investigation of ion-solvent and ion-ion interactions by spectrometric methods we have monitored the changes in the electron spin resonance spectrum of the anion of para-dinitrobenzene in methanol on addition of a variety of solvents. The isotropic hyper-fine coupling to 14N in the two nitro-groups (aNAV), which is particularly sensitive to changes in solvent, is plotted against the mole-fraction of added solvent in Fig. 1. It was observed, however, that of the five components associated with 14N, those having mN = ± 1 (mN being the Z component of the nitrogen nuclear spin angular momentum), namely the second and fourth sets of lines, were often much broader than the remaining lines. Results are given in Fig. 2 and a typical spectrum is shown in Fig. 3a.

Alkali metal hyperfine splitting and oscillation of the alkali ion in the alkali‐radical ion complex of pyracene

AbstractThe ESR spectra of the ion pairs consisting of the anion of pyracene and the potassium or sodium cation, in 2‐methyltetrahydrofuran, at low temperatures exhibit a line width alternation which is caused by the oscillation of the cation in the potential well. The behaviour of the metal hyperfine interaction in rubidium‐and cesium‐pyracene complexes in relation to temperature has led us to the conclusion that the spin density at the alkali nucleus is composed of negative and positive contributions. The difference in temperature dependence between the two results in a reversal of the sign of the spin density at the alkali nucleus at a very specific temperature, depending on the solvent used.

The electron spin resonance spectra of paradinitrobenzene anions

Electron spin resonance spectra of paradinitrobenzene anions in methanoldioxane mixtures exhibit a very marked line-width alternation. It is shown that such alternation, stemming from a relatively small difference between the isotropic hyperfine coupling constants of the two nitrogen atoms can account for the apparently anomalous spectra in solvents of low dielectric constant.

Line Width Alternation in the Electron Spin Resonance Spectrum of the Alkali Radical-Ion Complex of Pyracene

Line Width Alternation in the Electron Spin Resonance Spectrum of the Alkali Radical-Ion Complex of Pyracene

Theory of line width alternation in certain electron resonance spectra

Line width alternation has been observed in the electron resonance spectrum of the durosemiquinone cation and is attributed to rotational isomerism. In this paper the situation is investigated theoretically and a method based on the Bloch equations is used to derive the shape of the spectrum for different rates of isomerization. Line width alternation arises because the total hyperfine splitting of each isomer is the same.

Line width alternation in the electron spin resonance spectrum of the durosemiquinone cation

The e.s.r. spectrum of the durosemiquinone cation exhibits a marked line width alternation effect which is dependent on the temperature and the solvent. The effect is ascribed to cis-trans isomerism, the lifetime of each isomer being comparable with the inverse frequency separation between the proton hyperfine components.