"Electron spin resonance study of atomic hydrogen and free electrons stabilized in solid hydrogen and neon films at temperatures below 1K", Sergei Sheludiakov, University of Pittsburgh, Department of Physics and Astronomy. Host: Dafei Jin

I shall present our results on electron-spin resonance (ESR) studies of atomic hydrogen and free electrons trapped in thin films of solid molecular hydrogen and hydrogen-neon mixtures at temperatures below 1K. We created H atoms and free electrons in the Ne/H₂ films by exposing them to a flux of 5.7keV electrons released during tritium decay or by running a rf discharge in the sample cell.

In our Ne/H₂ studies, we found that quench-condensed Ne films were highly porous and small H₂ clusters were formed in the film pores. We also observed melting of these H₂ cluster at temperatures 0.3-0.6K, well below the bulk H₂ melting temperature of 13.6K. Along with the H atom ESR lines, we observed the lines of free electrons trapped in pure-neon and pure-H₂ environments of Ne/H₂ mixture films. These ESR lines could be influenced by condensing a superfluid helium film into the sample cell and adjusting the film porosity by annealing.

I shall also briefly describe our recent experiments with H in H₂ where we carried out the first measurement of a pure spatial diffusion rate for H atoms in solid H₂, the only solid-state system besides ³He−⁴He mixtures, where atomic diffusion does not vanish even at temperatures below 1 K.