Velocity imaging study of charge exchange reactions between He+ and N2

Molecular nitrogen (N2) is a major constituent of the earth's atmosphere. Its charge exchange collisions with helium ion (He+) from the solar wind lead to N2+, N, and N+ yields, and these ionic yields, together with their neutral co-products, will participate into subsequent atmospheric reactions. Here, we investigate charge exchange (CE) only and dissociative charge exchange (DCE) reactions, He+(2S) + N2 (X1Σg+) → N2+ + He/N+ + N + He, by detecting the N2+ and N+ yields with a crossed-beam ion velocity map image technique. In the collision energy range of 1.25-3.96 eV, the angular and kinetic energy distributions of the CE-yield N2+ indicate collision-energy dependences while a persistent dominance of the resonant process; three channels of the DCE reaction are successively accessed with the enhancement of collision energy, producing N(4S) + N+(3P), N(4S) + N+(1D), and N(2D) + N+(3P). The N+ velocity images are further analyzed with the Doppler kinematics model, indicating two different pathways of each channel, namely, prompt and slow processes. Branching ratios of these channels and pathways are estimated, indicating the predominance of the channel leading to the ground-state yields N(4S) + N+(3P).