H atom, e−, and H6+ ions produced in irradiated solid hydrogens: An electron spin resonance study

We carried out electron spin resonance (ESR) study of irradiated solid H2 and para-H2. H-atom, e−, and H6+ lines were observed. The H-atom radicals diffuse in solid H2 by the tunneling chemical reaction H+H2→H2+H below 4 K, and by the thermally activated process above 5 K. These decay via H-H recombination. Yield of trapped electrons e− produced by the radiolysis of solid para-H2 increases with increase in the concentration of added isotopic hydrogen, HD or D2. These decay via geminate recombination with positive ions with a half-life of 8 h at 4 K. H6+ ion is an ionic hydrogen radical whose spectrum has firstly been observed in irradiated solid para-H2. H6+ ions diffuse in solid H2 by sequence of H6++H2→H2+H6+ reactions, and terminate by the isotope-exchange reaction H6++HD→H5D++H2 or H6++D2→H4D2++H2. Unlike H6+, isotopically substituted H5D+ and H4D2+ cannot diffuse in solid para-H2. Rate-determining step of their decay is charge recombination with e−.