A Potential Surface Map of the H^-/N₂O System. The Gas Phase Ion Chemistry of HN₂O^-

Abstract

Dunkin, Fehsenfeld and Ferguson have reported that the gas phase reaction between H- and N₂O in a flowing afterglow instrument forms HO^- and N₂ with medium efficiency. The potential surface (UMP2-FC/6-311++G**//RHF/6-311++G**) for the H-/N₂O system confirms this to be the predominant reaction following initial approach of H- towards the central nitrogen of N₂O to form unstable intermediate [H-(N₂O)]. The intermediate then decomposes to HO^- and N₂ via a deep channel. The potential surface also shows the direct formation of adducts ^-O-⁺N(H)=N- and cis HN=NO^-. However, these are formed with excess energy: the former converts principally into reactants, while the latter decomposes to HO^- and N₂.

Ions having the formula 'HN₂O^-' may be formed in the gas phase by the reactions ( i ) HNO^-+N₂O → HN₂O^-+NO, and (ii) NH₂^-+Me₃CCH₂ONO → HN₂O^-+Me₃CCH₂OH. The product anion is stabilized by removal of some of its excess energy by the eliminated neutral. Evidence is presented which indicates that the product is either cis or trans HN=NO-, or a mixture of both. The characteristic ion molecule reaction of HN=NO^- involves oxidative oxygen transfer to suitable neutral substrates. For example: HN₂O^-+CS₂ → HS^-+N₂+COS.