Knowledge Bank

Structures, vertical excitation energies to the first electronic states and spectroscopic parameters for the ground electronic state are determined for several small $Cn$, $Cn$H and $Cn$Si astrophysically important molecular species } \underline{\textbf{124}}, 234304 (2006); M.L.~Senent H.~Masso and M.~Hochlaf, \textit{ApJ}, \underline{\textbf{670}}, 1510 (2007); H.~Masso, V.~Veryazov, P.A.~Malmqvist, B.O.~Roos and M.L.~Senent, \textit{J.Chem.Phys.} \underline{\textbf{127}}, 154318 (2007); M.~Hochlaf, C.~Nicolas and L.~Poisson, \textit{J.Chem.Phys.} \underline{\textbf{127}}, 014310 (2007) N.~Inostroza, M.~Hochlaf, M.L.~Senent and J.R.~Letelier (submitted 2008)}. The main aim of these investigations is to help the interpretation of several previous astrophysical observations } \underline{\textbf{609}}, 225 (2004); J.~Cernicharo, J.R.~Goicochea and Y.~Benilan, \textit{ApJ} \underline{\textbf{580}}, L157, 2002.} State-of-the art ab initio calculations are performed for this purpose. All species display isomerism although the inter-transformation processes, that involve various electronic states, are not well known. Anharmonic spectroscopic parameters are computed from full-dimensional Potential Energy Surfaces which are mapped close to their respective local minima. In light of these calculated properties (band positions, spectroscopic parameters, predictions of ro-vibronic effects, spin-spin constants,..) assignments for FIR astrophysical observed bands, are discussed. vspace{1em} \noindent