GAS-PHASE ANTIMONY MAGNESIUM OXYGEN CLUSTERS

Antimony/magnesium/oxygen clusters are produced by a gas aggregation s ource, in which a mixture of antimony and magnesium is vaporized and r eacted with N2O introduced in helium carrier gas. The resulting produc t distribution is detected by a time-of-flight mass spectrometer follo wing ionization with a KrF excimer laser. Four types of cluster produc ts are observed: Sb-x(+), SbxMgyOz+, SbxMgy+, and MgyOz+. The mass spe ctral intensity distributions display enhanced abundances for Mg2O+, S b2-4Mg3O+, Sb1-4Mg2O+, Sb4Mg+, Sb5Mg2+, and Sb6Mg2+. The experimental observation of Mg2O+ and Mg3O+ shows that the suboxides of group 2 are stable species, consistent with theoretical predictions. The binding abilities of antimony clusters to magnesium and magnesium oxides are f ound to be dependent on cluster size. When the number of antimony atom s in the clusters is smaller than 6, SbxMgyOz+ are the main products d ominating the mass distribution. On the other hand, when the cluster s ize of Sb-x is larger than 6, only Sb/Mg alloy clusters are observed. The unusual stabilities of Sb2-4Mg3O+ and Sb1-4Mg2O+ clusters are evid ently due to the formation of covalent bonds between Sb and Mg atoms. In Sb4Mg+, Sb5Mg2+, and Sb6Mg2+ alloy clusters, however, the Mg atom d onates two electrons to the skeleton of the Sb clusters in order to sa tisfy Wade's rules. The structures of these stable clusters can be pre dicted by the polyhedral skeletal electronic pair theory.