Auto-ionised products from the reaction of sodium clusters with dioxygen: Theory and experiment

The reactive collision between sodium clusters and dioxygen is investigated by crossed beam experiment and density functional calculations. Specific c ations, particularly Na5O2+, are detected in the auto-ionisation mass spect rum, which contrasts with the less selective range of neutral products dete cted in the photoionisation mass spectrum. This is rationalised with the ai d of ab initio molecular dynamics and the computed energies of fragmentatio n of dioxides NanO2(+) (n less than or equal to 9) to clusters of monoxides NanO(+) and pure sodium Na-n((+)). A redox sequence is observed in simulat ion from superoxide to peroxide to bis-monoxide (O-2)(-)-->(O-2)(2-)--> 2O( 2-), which releases enough energy to allow fragmentation and auto-ionisatio n. Exoelectron emission may therefore be ultimately connected with the redu ctive dissociation of the O-O bond. Some confidence in the underlying hyper surface is obtained from comparison with experimental and higher-level theo retical data, including structures and energetic properties (previously pub lished), and the topology of the Na2O2 superoxide-peroxide electron transfe r curve.