Geometrical structure and vibrational frequencies of several electronic states of Si2C

The ground state of the Si2C molecule is found to be a closed-shell C2v symmetry structure with unusually short Si–C bonds. In these theoretical studies a double zeta plus polarization (DZ+P) basis set was used initially. At the self-consistent-field (SCF) level of theory the DZ+P C2v symmetry structure collapses to the linear 1Σ+g state. Extension of the basis set to include a second set of d functions (DZ+2P) on each atom, however, shows the SCF linear state to be a transition state and the C2v structure to be the minimum. Optimization of the linear and C2v symmetry states using configuration interaction (CI) wave functions in conjunction with the DZ+2P basis gives a final prediction that the C2v structure lies 2.1 kcal/mol below linear Si–C–Si.