  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.
