Luminescence cross sections in the low-energy collisions of H⁺, H₂⁺, and H₃⁺ ions with H₂

Luminescence cross sections for the optical emission of molecular hydrogen in the 200–600 nm spectral range and for the atomic Balmer-β line were measured for low-energy ( ≤1 keV) H⁺, H₂⁺, and H₃⁺ ions colliding with H₂ gas targets. Molecular hydrogen transitions between singlet states were observed for all the systems studied, while the emission continuum H₂(a-b) and discrete spectra associated with other transitions between triplet states appeared only in the H₂⁺ + H₂ collisions, where the spin conservation rule is fulfilled. Isotopic substitutions in the H₂⁺/D₂⁺ + H₂, D₂ system show that at E_lab = 1 keV, a dominant molecular luminescence mechanism is the collision-induced excitation (CIE) of the target. Graphical abstract:

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