Negative ion formation from N₂O clusters by impact of highly excited Rydberg krypton atoms and electrons

Neutral clusters of nitrous oxide, (N₂O)_m, formed in a supersonic nozzle expansion were ionized by impact of high-Rydberg krypton atoms, Kr**, and slow electrons having kinetic energies of 1-10 eV. Negative cluster ions, (N₂O)_nO^- (n ≥ 3) and (N₂O)_n^- (n ≥ 5), were produced by Kr** impact, while (N₂O)_nO^- (n ≥ 0) and trace amounts of (N₂O)_nNO^- (n ≥ 0) and (N₂O)_n^- (n ≥ 1) were observed by electron impact. The intensity ratio, (N₂O)_n^-/(N₂O)_nO ^-, produced by Kr** impact was 2 orders of magnitude larger than that by electron impact. These observations are interpreted as follows: The (N₂O)_nO^- ions observed in both cases are produced via the N₂O^-(²Σ⁺)(N₂O) _m-1 resonance state, where the N₂O^-(²Σ⁺) unit is solvated by the rest of the molecules. In the Kr** impact ionization, several N₂O molecules are evaporated after dissociation of N₂O^-(²Σ⁺)(N₂O) _m-1 into (N₂O)_m-1O^- + N₂. Formation of (N₂O)_n^- by Kr** impact proceeds via the N₂O^-(²Π)(N₂O)_m-1 resonance state followed by substantial evaporation of N₂O. In contrast, intracluster ion-molecule reactions in (N₂O)_m-1O^- originating from N₂O^-(²Σ⁺)(N₂O) _m-1 give rise to (N₂O)_nNO^- and (N₂O)_n^- observed by EI.