Assignment of the vibrational spectra of the parent polysilsesquioxane (POSS): Octahydridosilasequioxane, H8Si8O12.

Polysilsesquioxanes (POSS) are molecules with the empirical formula (RSiO 1.5 ) n where R is a hydrogen atom or hydroxyl or an organic moiety such as an alkyl, alkene, acrylate or epoxide. The silicon atoms occupy the corners of a cube and oxygen atoms are located on the edges, the versatility of silsesquioxanes arises from the vacant fourth position of silicon. The choice of substituent enables a wide variety of properties to be engineered in a straightforward manner. The parent POSS is octasilsesquioxane, H 8 Si 8 O 12 , with R = H and n = 8. The present work employs periodic density functional theory calculations in conjunction with all the available vibrational (infrared, Raman and inelastic neutron scattering) spectra to generate a complete assignment of all the modes of the parent POSS octasilsesquioxane and some of its isotopomers for both the free, ( O h ), molecule and the solid state material ( C 3i site symmetry) including the forbidden and very weak modes. The latter are of interest because in less symmetrical silsesquioxanes, these modes will be activated. [ABSTRACT FROM AUTHOR]