ABINITIO STUDY OF THE SI2O AND SI3O MOLECULES

The structures and vibrational frequencies of various structures and electronic states Of Si2O and Si3O have been studied at the MP2(full)/6-311+G* level, with geometries also calculated at the MP4SDTQ/6-311+G-(2df) and QCISD(T)/6-311+G(2df) levels. Triangular Si2O (C2v, 1A1) and planar-rhombus Si3O (C2v, 1A1) structures are found to be the most stable, but several other low-lying local minima are also found. The calculated dissociation energies for the lowest energy decompositions Of Si2O into SiO + Si and Of Si3O into Si2 + SiO are 50.1 and 59.8 kcal/mol, respectively. The energies for Si(n)O --> Si(n) + O are much larger. Even the lowest decomposition energies are larger than those found for Li2O, Li3O; Mg2O, Mg3O; and Al2O, Al3O. In both Si2O and Si3O, the O atom does not insert into coordination sites of highest symmetry; rather, the most stable structures involve coordination of the O atom to two Si atoms without destroying the Si-Si bonding. Again, this is different than in Li2O, Li3O, Mg2O, Mg3O, Al2O, and Al3O, where the O atom inserts into the site of highest coordination and highest symmetry.