Formation of molecular cluster anions by laser ablation of a metal target near a supersonic jet

By laser ablation of a metal target (Zn, Mg or Gd) near the stream of a supersonic expansion, molecular oxygen cluster anions (O-2)(n)(-) were efficiently produced with n in the range of 1-20 or more. The cluster anions were analysed by a time-of-flight mass spectrometer. Molecular cluster anion formation is attributed to low-energy electron attachment and high-Rydberg-state electron transfer. In the case of Gd, the addition products Gd(O-2)(n)(-) and Gd-2(O-2)(n)(-) were also observed. These products are thought to originate from ion-molecule association reactions.