Thermal stability of methyl radical in γ-ray irradiated methane hydrate under different pressure from 0.003 to 1 MPa

Synthetic methane hydrate irradiated by γ-rays at 77 K was measured by electron spin resonance (ESR) to investigate the thermal stability of the methyl radical under different pressures from 0.003 to 1 MPa. The decay of the radical was composed of at least two decay processes. The first decay process was observed within an annealing time of 150 min and the second one on a longer time scale. The decay constant for the second process was estimated using a second order decay model. An Arrhenius plot gave almost the same activation energy at lower temperature under each pressure, and it was estimated to be 20.0±2.7kJ/mol.