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We report on electron spin resonance studies of H atoms stabilized in solid H2 films at temperature 0.7 K and in a magnetic field of 4.6 T. The H atoms were produced by bombarding H2 films with 100 eV electrons from a radiofrequency discharge run in the sample cell. We observed a one order of magnitude faster H atom accumulation in the films made of para-H2 gas with a small ortho-H2 concentration (0.2% ortho-H2 ) as compared with those made from normal H2 gas content (75% ortho-H2 ). We also studied the influence of ortho-H2 molecules on spatial diffusion of H atoms in solid H2 films. The spatial diffusion of H atoms in both normal and para-H2 films is faster than the diffusion obtained from the measurement of H atom recombination. The rate of spatial diffusion of H atoms in para-H2 films was slower in comparison with that in the normal H2 films. We discuss possible explanations of these observations. 

We studied the electron spin resonance (ESR) spectra of nitrogen atoms stabilized in nitrogen-neon nanoclusters immersed in superfluid 4He. The nanoclusters were formed during the condensation of the products of the discharge in N2–Ne–He gas mixtures into bulk superfluid 4He at temperature 1.5 K. We studied nanoclusters formed by injection of gas mixtures with different ratios of heavy impurities in the helium N2/(Ne + N2 ) ranging from 2% to 90%. Analysis of the ESR spectra of nitrogen atoms stabilized in nitrogen-neon nanoclusters provides important information about the environment of the stabilized atoms and a shell structure of the nanoclusters was revealed. For all samples studied, preferential stabilization of N atoms on the surfaces of the nanoclusters was observed. Annealing of the collection of the nanoclusters in the temperature range 1.1–10 K resulted in substantial changes in the structure of the nanoclusters.