Gas Phase Antimony/Magnesium/Oxygen Clusterst

Antimony/magnesium/oxygen clusters a re produced by a gas aggregation source, in which a mixture of antimony and magnesium is vaporized and reacted with N2O introduced in helium carrier gas. The resulting product distribution is detected by a time-of-flight mass spectrometer following ionization with a KrF excimer laser. Four types of cluster products are observed: Sb,+, SbxMgyOZ+, Sb,Mgy+, and MgyO,+. The mass spectral intensity distributions display enhanced abundances for MgzO+, S b 2 ~ M g 3 0 + , Sbl4Mg20+, Sb4Mg+, SbsMg2+, and SbsMg2+. The experimental observation of Mg20+ and Mg30+ shows that the suboxides of group 2 are stable species, consistent with theoretical predictions. The binding abilities of antimony clusters tomagnesium and magnesium oxides a re found to be dependent on cluster size. When the number of antimony atoms in the clusters is smaller than 6, SbxMgyO:+ are the main products dominating the mass distribution. On the other hand, when the cluster size of Sb, is larger than 6, only S b / M g alloy clusters are observed. The unusual stabilities of Sbz+Mg30+ and Sbl+MgzO+ clusters a re evidently due to the formation of covalent bonds between S b and M g atoms. In Sb4Mg+, SbsMg2+, and SbaMgz+ alloy clusters, however, the M g atom donates two electrons to the skeleton of the S b clusters in order to satisfy Wade’s rules. The structures of these stable clusters can be predicted by the polyhedral skeletal electronic pair theory.