Trihydrogen cation solvated by rare gas atoms: Rg_nH₃⁺

The triatomic hydrogen cation solvated by rare gases, Rg_nH₃⁺, n=1-5, Rg=He, Ne, Ar, Kr, Xe, is investigated by density functional theory. The results indicate that while the first solvent atom distorts and destabilizes the H₃⁺ center, the ion is restabilized by additional solvation. For the n=3 species, the symmetric D_3h structure is the global minimum for all rare gases except Xe; the n=4,5 solvent atoms are placed on the C₃ axis of the molecule. The computed potential energy surface of the isomerization reaction Rg_nH₃⁺→H₂Rg₂H ⁺Rg_n-2, n=2-4, provides insight into the possible H₃⁺ formation and destruction mechanisms in rare gas matrices. As expected, solid neon is the most suitable medium for H₃⁺ studies, with its stabilization becoming progressively more difficult in the heavier rare gas solids.