The results of first principles calculations on H-silsesquioxanes (i.e., (HSiO 3/2 ) n with n ) 4, 6, 8, 10, 12, 14, and 16) are reported here. Double numeric basis sets and local and nonlocal density approximations to density functional theory are employed for calculations. It is shown that use of the nonlocal density approximation is required for the reliable prediction of the most stable isomer for silsesquioxanes. Furthermore, a progression of the preferred building unit with the increase in size of the T cage is revealed. The smaller T cages prefer four-and five-member rings while the larger cages are found to prefer four-and six-member rings. Analysis of the energy of the hydrolysis reaction, binding energy, and fragmentation paths finds the relative stability of the silsesquioxane cages containing four-, five-, and six-member rings in agreement with experimental observations. For the (HSiO 3/2 ) 16 cage, the calculated results predict the stability of the D 2d -6 4 5 0 4 6 configuration over the D 4d -6 0 5 8 4 2 configuration in contradiction to suggestions based on 29 Si NMR measurements. We find a consistent picture for the highest occupied molecular orbitals (HOMOs) of all silsesquioxanes considered showing them to be composed of (lone-pair) oxygen p-type atomic orbitals. On the other hand, the lowest unoccupied molecular orbitals (LUMOs) show size dependence in their composition which appears to cause the presence of a state in the HOMO-LUMO gap for higher silsesquioxane cages. Density of states plots and analysis of molecular orbitals reveal this state to be due to the terminal hydrogens bonded to silicon atoms.

Calculations based on density functional theory (DFT) were performed on various structural isomers of methyl silsesquioxanes, [MeSiO 3/2 ] n where n ) 4, 6, 8, 10, 12, 14, and 16, to study their structural and electronic properties. The calculated results find the stability of methyl silsesquioxanes, except [MeSiO 3/2 ] 4 , against fragmentation and hydrolysis, and of one isomer of [MeSiO 3/2 ] 14 against hydrolysis. The deformation density plots show that chemical bonding in methyl silsesquioxanes is mainly determined by the building block unit, (MeSiO 3/2 ) as also seen in hydridosilsesquioxanes (HSQ). However, unlike HSQ, the large cages of methyl silsesquioxanes do not develop a localized electronic state in the HOMO-LUMO gap.

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Single and multicomponent mixed layers of silsesquioxane clusters on freshly evaporated gold surfaces have been investigated by X-ray photoelectron spectroscopy and reflection-absorption infrared spectroscopy. Approximately 5-10% of the cluster layers (e.g., H8Si8O12 and H10Si10O15) on gold desorb upon evacuation of the adsorbate from the reaction chamber. These open adsorption sites are an avenue for cluster displacement reactions that yield mixed monolayers (e.g., H8Si8O12/D8Si8O12 and H8Si8O12/C6H13-H7Si8O12) of several compositions on gold. This dynamic behavior is not observed for the C6H13-H7Si8O12 cluster layer on gold. Rather, this molecule acts as a poison to these reported displacement processes at the gold surface.