Reactions of Sc2O4− and La2O4− Clusters with CO: A comparative study

Scandium and lanthanum oxide cluster anions Sc2O4− and La2O4− are prepared by laser ablation and reacted with CO in a fast flow reactor. A time of flight mass spectrometer is used to detect the cluster distribution before and after the reactions. In the reaction of Sc2O4− with CO, Sc2O3− anion is observed as a product. In sharp contrast, no product anion is observed for La2O4− + CO although the CO reactant gas causes a fast depletion of La2O4−. The experiment thus provides evidence of electron auto-detachment in the reaction of La2O4− with CO. Density functional theory calculations are performed to study the mechanisms for the above two reactions and the results well interpret the experimental observations. This study is among the first to report electron auto-detachment in the oxidation of CO by metal oxide cluster anions.

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► Oxygen atom transfer reaction is observed in the reaction of Sc2O4− with CO.
► Electron auto-detachment rather than the oxygen atom transfer occurs in the reaction of La2O4− with CO.
► Oxidation of CO by atomic oxygen radical anions provides enough energy to evaporate electrons from the studied reaction systems.
► Formation of high-symmetry intermediate or product anions in which all metal atoms have high-coordination number is important for electron auto-detachment.