ESR study of atomic hydrogen and tritium in solid T₂ and T₂:H₂ matrices below 1 K

Area of Science:

• Low-temperature physics
• Quantum chemistry
• Materials science

Background:

• Atomic hydrogen and tritium stabilization in solid matrices is crucial for fundamental research.
• Understanding their behavior at millikelvin temperatures presents unique challenges.

Purpose of the Study:

• To investigate the stabilization and behavior of atomic hydrogen and tritium in solid T2 and T2:H2 matrices.
• To determine the maximum achievable concentrations and study recombination mechanisms.

Main Methods:

• Electron Spin Resonance (ESR) spectroscopy was employed.
• Experiments were conducted on solid T2 and T2:H2 matrices at temperatures as low as 70 mK.

Main Results:

• Record concentrations of tritium (T) atoms (∼2 × 10^20 cm^-3) and hydrogen (H) atoms (∼1 × 10^20 cm^-3) were achieved.
• Atomic diffusion, enhanced by vacancies and phonons from beta-particles, limited maximum concentrations and promoted recombination.
• Explosive recombination was observed, stimulated and spontaneous, particularly in thick films with insufficient cooling.

Conclusions:

• The primary mechanism for H and T migration in these matrices is physical diffusion (tunneling or hopping to vacant sites).
• This contrasts with tunneling chemical exchange reactions observed for H and D in other matrices.
• The findings provide insights into the fundamental properties and interactions of light atoms in solid hydrogen isotopes.