Electron spin resonance measurement of organic radicals in petroleum source rock containing transition metal ions

The Electron Spin Resonance (ESR) spectrum with the width ΔH = 0.5 ± 0.02mT at g-factor of 2.0028 ± 0.0005 of kerogen collected at the shallow part of a petroleum deposit has a broader peak than that collected in its deeper part (ΔH = 0.4 ± 0.02mT). Two groups of samples were prepared. One was heated at several temperatures to liberate hydrocarbons and another was treated with pyridine, so that the generated hydrocarbons due to heating were removed. Narrowing of the linewidth was not caused by heating, but by treatment with pyridine. Molecular orbital calculation was performed to explain the septet-quartet ESR spectrum of organic radicals with g = 2.0023 ± 0.0005, A1 = 0.625 ± 0.003 mT (septet) and A2 = 0.187 ± 0.003 mT (quartet) in petroleum source rock and in heated carbonate: the presence of tert-butyl radical can be suitable to explain the septet-quartet spectrum.