Comparison of the energy dependences and branching ratios of the reactions of Ar⁺ and N₂⁺ with SO₂

The reactions of Ar⁺ and N₂⁺ with SO ₂, which have similar energetics due to the nearly equal ionization potentials of Ar and N₂, have been studied in a flow-drift tube from 0.04 to 3 eV relative kinetic energy. The energy dependences and product branching ratios of the two reactions are found to be almost identical. With increasing relative kinetic energy, the rate constants show a rather steep initial decline, followed by an equally steep increase. At the lower energies, both reactions yield only the charge-transfer product SO₂ ⁺, and at the higher energies, both reactions yield predominately the dissociative charge-transfer product SO⁺.