  The recent synthesis of a four-fold silylated sila-adamantane molecule
(C$_{24}$H$_{72}$Si$_{14}$, T$_d$), [J. Fischer, J. Baumgartner, and C.
Marschner, {\it Science} {\bf 310,} (2005) 825] is the first attempt of making
the silicon analogue of adamantane. It has adamantane-like Si$_{10}$ core,
capped by methyl and sily-methyl ligands. We report its electronic structure,
vibrational spectrum, and the infra-red and Raman spectra calculated within the
density functional formalism using large polarized Gaussian basis sets. The
properties of sila-adamantane are compared with exact silicon analogue Si10H16
of adamantane. Results show that replacing hydrogens in Si10H16, by methyl and
silymethyl ligands results in expansion of the Si10 core and results in large
number of peaks in the Raman spectrum. The Si-C stretch at 664 1/cm and methyl
deformations frequencies compare well with recent measurements of vibrational
frequencies of methylated silicon surface.
