Abstract: 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 1K.

Bio: Sergei Sheludiakov is Research Assistant Professor and Cryogenics director at the University of Pittsburgh. He received his MSc and PhD from the University of Turku (Finland),