Suppression and enhancement of tunneling ion recombination of electron bubbles in solid para-hydrogen–ortho-hydrogen mixtures at 4.2 K: controlling factors of tunneling reaction

The decay of electron bubbles due to a tunneling ion recombination was studied by ESR in γ-ray irradiated solid para-hydrogen (p-H2)–ortho-hydrogen (o-H2) mixtures at 4.2 K. In the range of 10–75% o-H2 (region I), the decay rates of the electron bubbles increase with decreasing o-H2 concentration. The decay rate constant shows the maximum around 10% o-H2. Then, the decay rates decrease with decreasing o-H2 concentration below 10% o-H2 (region II). The results were interpreted by two different rate-determining steps: a tunneling process in region I and an energy-dissipation process in region II.