Electron spin resonance study on γγ-ray-induced radical species in ethylene hydrate

Electron spin resonance (ESR) study on γγ-irradiated synthetic ethylene hydrate was performed to investigate induced radicals and their thermal stability. ESR spectra of induced 3-butenyl radical (⋅CH2C2H3=CH2,g=2.0039±0.0005,Aα=2.2±0.1mTandAβ=3.0±0.1mT) and induced ethyl radical (⋅C2H5(⋅C2H5, g=2.0044±0.0005g=2.0044±0.0005, Aα=2.2±0.1mT and Aβ=2.7±0.1mT) were observed in irradiated ethylene hydrate. The decay of the 3-butenyl radicals was observed above 200 K with the activation energy of 51.9±4.4kJ/mol. The obvious decay of ethyl radicals starts above 240 K that is close to the dissociation temperature of ethylene hydrate at atmospheric pressure. The activation energy of the ethyl radical decay is estimated as 63.4±8.2kJ/mol and nearly equal to the enthalpy change of ethylene hydrate into liquid water and gaseous ethylene. It is suggested that the decay of ethyl radicals would be caused by the hydrate dissociation and that ethylene hydrate dissociates into water (supercooled) and ethylene at 240–265 K.