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^-