COLLISION-INDUCED DISSOCIATION OF MASS-SELECTED PHOSPHORUS CLUSTER CATIONS

Phosphorus cluster cations of various sizes have been generated by laser ablation of red phosphorus powders. The magic numbers of these cluster ions appearing in the recorded spectrum were 4, 7, 11, 14, 18, 21 and 25. On a home-made tandem time-of-flight mass spectrometer, P-n(+) (n = 4-25) were studied via collision-induced dissociation (CID) by crossing the mass-selected phosphorus cluster ion beam with a supersonic nitrogen beam. After collision, P-n(+) has the tendency to lose P-4 units and the number of tetramer fragments ejected upon dissociation increases with the parent phosphorus cluster size. The CID results show that the tetramer is the structural unit of the phosphorus clusters and larger cluster ions are generally less stable. Among the daughter ions surviving from the collisions, P-4(+) is most stable, and P-7(+) and P-8(+) come next.