Electron spin resonance study of atomic hydrogen stabilized in solid neon below 1K

TL;DR

This study uses electron spin resonance to investigate atomic hydrogen trapped in solid neon at sub-1K temperatures, revealing high mobility, rapid recombination, and enhanced dissociation due to secondary electron emission.

Contribution

It provides new insights into hydrogen behavior in solid neon, including trapping sites, recombination rates, and the effects of secondary electrons on dissociation efficiency.

Findings

Hydrogen atoms are trapped in substitutional sites and within H₂ clusters in neon.

Recombination rate constant at 0.6 K is at least 5×10⁻²⁰ cm³s⁻¹, much higher than in pure H₂ films.

Dissociation of H₂ in neon is two orders of magnitude more efficient than in pure H₂ due to secondary electron emission.

Abstract

We report on an electron spin resonance study of atomic hydrogen stabilized in a solid Ne matrices carried out at a high field of 4.6 T and temperatures below 1 K. The films of Ne, slowly deposited on the substrate at the temperature $\sim$1 K, exhibited a high degree of porosity. We found that H atoms may be trapped in two different substitutional positions in the Ne lattice as well as inside clusters of pure molecular H$_{2}$ in the pores of the Ne film. The latter type of atoms was very unstable against recombination at temperatures 0.3-0.6$\,$K. Based on the observed nearly instant decays after rapid small increase of temperature, we evaluate the lower limit of the recombination rate constant $k_{r}\geq5\cdot10^{-20}\,$cm$^{3}$s$^{-1}$ at 0.6$\,$K, five orders of magnitude larger than that previously found in the thin films of pure H$_{2}$ at the same temperature. Such behavior assumes a very high mobility of atoms and may indicate a solid-to-liquid transition for H$_{2}$ clusters of certain sizes, similar to that observed in experiments with H$_{2}$ clusters inside helium droplets (Phys. Rev. Lett 101, 205301 (2008)). We found that the efficiency of dissociation of H$_{2}$ in neon films is enhanced by 2 orders of magnitude compared to that in pure H$_{2}$, which is instigated by a strong emission of secondary electrons.