Superposition-state N₂ ⁺ produced in the intermolecular charge transfer from low-energy Ar⁺ to N₂

Molecular electronic or vibrational states can be superimposed temporarily in an extremely short laser pulse, and the superposition-state transients formed therein receive much attention, owing to the extensive interest in molecular fundamentals and the potential applications in quantum information processing. Using the crossed-beam ion velocity map imaging technique, we disentangle two distinctly different pathways leading to the forward-scattered N₂ ⁺ yields in the large impact-parameter charge transfer from low-energy Ar⁺ to N₂. Besides the ground-state (X²Σ_g ⁺) N₂ ⁺ produced in the energy-resonant charge transfer, a few slower N₂ ⁺ ions are proposed to be in the superpositions of the X²Σ_g ⁺-A²Π_u and A²Π_u-B²Σ_u ⁺ states on the basis of the accidental degeneracy or energetic closeness of the vibrational states around the X²Σ_g ⁺-A²Π_u and A²Π_u-B²Σ_u ⁺ crossings in the non-Franck-Condon region. This finding potentially shows a brand-new way to prepare the superposition-state molecular ion.