| Autor: |
Prabhananda, B. S., Hyde, James S. |
| Předmět: |
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| Zdroj: |
Journal of Chemical Physics; 12/1/1986, Vol. 85 Issue 11, p6705, 8p |
| Abstrakt: |
The p-benzosemiquinone radical anion has served as a model system in numerous electron spin resonance liquid-phase relaxation studies. An inconsistency exists of more than an order of magnitude between measured spin-lattice relaxation times T1e and calculated values based on the spin-rotational mechanism if the rotational correlation time τθ that is required in the calculation is obtained from linewidth measurements. This paper presents a number of experiments designed to contribute to the solution of this problem. The rigid-limit g values of tetrahalogenated benzosemiquinone anions have recently become available, permitting the study of the effect of Zeeman anisotropy in a relatively homologous series of compounds. 13C labeled tetrachlorobenzosemiquinone anion (TSCQ-) has additionally been prepared in order to determine the dependence of linewidth on the 13C nuclear quantum number. Linewidth and continuous wave (cw) saturation measurements have been made from 1.0 to 35 GHz. Saturation-recovery pulse measurements of T1e have been made at 9 GHz. Solvent viscosity and temperature have been varied. It is established that an expression of the form [T-11e=AT/η+B exp(-ΔE/RT)] is required to fit the data in hydrogen-bonding solvents with both terms arising from spin-rotation. Values of τθ were determined in five different ways for TCSQ-. The variation is fivefold in ethanol and tenfold in n-butanol. The discrepancy that motivated the research has not been fully resolved, but the data suggests the existence of an additional line broadening mechanism arising from the superposition of signals from radicals in a distribution of relatively long-lived local environments. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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