Bond-forming and electron-transfer reactivity between Ar2+ and N2

Abstract

Collisions between Ar²⁺ and N₂ have been studied using a coincidence technique at a centre-of-mass (CM) collision energy of 5.1 eV. Four reaction channels generating pairs of monocations are observed: Ar⁺ + N₂⁺, Ar⁺ + N⁺, ArN⁺ + N⁺ and N⁺ + N⁺. The formation of Ar⁺ + N₂⁺ is the most intense channel, displaying forward scattering but with a marked tail to higher scattering angles. This scattering, and other dynamics data, is indicative of direct electron transfer competing with a ‘sticky’ collision between the Ar²⁺ and N₂ reactants. Here Ar⁺ is generated in its ground (²P) state and N₂⁺ is primarily in the low vibrational levels of the C²Σ_u⁺ state. A minor channel involving the initial population of higher energy N₂⁺ states, lying above the dissociation asymptote to N⁺ + N, which fluoresce to stable states of N₂⁺ is also identified. The formation of Ar⁺ + N⁺ by dissociative single electron transfer again reveals the involvement of two different pathways for the initial electron transfer (direct or complexation). This reaction pathway predominantly involves excited states of Ar²⁺ (¹D and ¹S) populating N₂⁺* in its dissociative C²Σ_u⁺, 2²Π_g and D²Π_g states. Formation of ArN⁺ + N⁺ proceeds via a direct mechanism. The ArN⁺ is formed, with significant vibrational excitation, in its ground (X³Σ⁻) state. Formation of N⁺ + N⁺ is also observed as a consequence of double electron transfer forming N₂²⁺. The exoergicity of the subsequent N₂²⁺ dissociation reveals the population of the A¹Π_u and D³Π_g dication states.