Near-zero-energy dissociative electron attachment of the dimers N ₂ O ₃ and N ₂ O ₄

We report the formation of NO2− anions in a molecular beam containing NO and NO2 following two-colour laser excitation of the nf(N+=2) Rydberg series of NO. We attribute the formation of NO2− anions to the dissociative electron attachment (DEA) of the dimers N2O3 and N2O4 induced by direct electron transfer from laser-excited NO Rydberg states. No parent anions are observed in the mass spectrum, indicating complete fragmentation upon near-zero-energy electron attachment. Velocity map imaging of the NO2− anions reveals that they are formed with a distribution of kinetic energies from 0.2 to 0.7 eV, which is consistent with the formation of NO2− anions and the neutral co-fragments exclusively in the electronic ground state, with up to 1.1 eV of total internal energy. Theoretical calculations of the electron attachment of N2O3 and N2O4 reveal preferential energy partitioning into the N-N bond wagging and stretching motions as well as the localised NO2 bending and stretching modes. The combined experimental and theoretical work demonstrates that near-zero-energy DEA of N2O3 and N2O4 yield highly vibrationally and rotationally excited NO2−, NO, and NO2 fragments, which could impact the chemical outcome of NOx containing plasma applications.