Vanadyls from oil shale. Rotational motion studied by electron spin resonance spectroscopy

Abstract

Electron spin resonance studies of several vanadyl complexes from the Antrim oil-shale formation of the lower Michigan peninsula reveal a wide range of rotational correlation times. The hyperfine splittings and g factors are all consistent with porphyrin structures, but three vanadyls have very different rotational correlation times. At ambient temperature, one gives a motionally averaged spectrum, one gives a slow-tumbling spectrum and one has its spectrum broadened into unobservability. A temperature-dependence study was carried out for the species which is in the slow tumbling region at ambient temperature. A rotational correlation time of 4.0 × 10^–8 s rad^–1 is estimated for this species at 303 K and an activation energy of 6.9 kcal mol^–1 is estimated for the rotation.