H₂ and N₂ ionization and dissociative ionization by C⁻ and O⁻ ions at intermediate velocities: Direct and electron loss channels

Cross sections for single ionization and dissociative ionization of molecular targets under the impact of atomic anions were measured. Three systems were investigated, a H₂ target with C⁻ and O⁻ projectiles, and a N₂ target with O⁻ projectiles. The velocity range was 1.07–2.14 a.u. Recoil ions originated from the target (H₂⁺,H⁺,N₂⁺,N⁺, and N²⁺) were measured in coincidence with projectiles in several final charge states (q=−1, 0, +1, and +2). These states, negative, neutral, and positive, respectively, correspond to direct, single, and multiple electron loss channels. Target ionization is mostly due to the projectile single electron loss and direct processes, while target fragmentation is dominated by the projectile double electron loss. These results point to both target ionization and projectile direct or single electron loss processes being dominated by large impact parameters, while fragmentation and multiple electron loss are associated to small impact parameters.