Formation of lead/sulfur binary cluster ions by laser ablation

Abstract

Lead/sulfur binary cluster ions were produced by laser single ablation and laser double ablation, respectively, photolyzed by a UV laser and detected with a tandem time-of-flight (TOF) mass spectrometer. The distribution of cluster ions produced by laser single ablation is different from that produced by laser double ablation. By laser single ablation on a mixed Pb + S target, Pb n S n−1 + and Pb n S n − are formed as stable compositions that serve as structural skeletons of the binary clusters. All other cluster ions can be indicated as Pb n S m + with m ≥ n − 1 or Pb n S m − with m ≥ n, produced by the attachment of excess S atoms to Pb n S n−1 + or Pb n S n −. The stable compositions shown above are also found in the fragments from the main photodissociation channels of cluster cations, confirming their special stability. The structural models of the cluster ions with stable compositions are proposed. On the other hand, by laser double ablation on a separated Pb target and S target, the Pb clusters and S clusters are formed independently and then react with each other to generate binary cluster ions Pb n S m + and Pb n S m − with n = 1–7 and m ≥ 0. These two different formation pathways, by laser single ablation and laser double ablation, respectively, can lead to distinct differences in the compositions and distributions of the cluster ions. The different properties, such as internal energies or structural isomers, for a single stoichiometry from the different formation pathways are also discussed.