Unimolecular decomposition of antimony and bismuth cluster ions studied by surface collision induced dissociation mass spectrometry

Abstract

Fragment ion distributions of antimony clusters Sb_n⁺ (n = 3–12) and bismuth clusters Bi_n⁺ (n = 3–8) after collision with different solid target surfaces at hyperthermal energies are reported. The measured fragmentation patterns for antimony and bismuth clusters of the same size are similar. Main fragmentation channels identified in our study at impact energies up to 150 eV correspond to the sequential unimolecular dissociation of the colliding clusters with a preferred loss of stable neutral tetrameric and dimeric cluster units. The efficiency of the energy transfer from kinetic energy into internal cluster energy during surface collision was found to be up to 10%. The fragmentation patterns are independent of the employed target surface. In contrast, the integral scattered ion yield strongly depends on the surface type. High scattered ion yields are observed for a silicon oxide surface with high work function, whereas graphite or metallic gold target surfaces result in considerably lower scattered ion yields. For a given surface the integral ion yield also shows strong variations as function of the size of the colliding clusters.