GEOMETRICAL STRUCTURES AND VIBRATIONAL FREQUENCIES OF THE ENERGETICALLY LOW-LYING ISOMERS OF SIC3

The ground state of the SiC3 molecule is found to be a closed-shell cyclic C2v symmetry structure which can be described as a four-membered ring with a transannular (cross ring) carbon-carbon bond, r (C-C) = 1.469 Å. Theoretical studies with a triple-zeta plus double-polarization function (TZ2P) basis set in conjunction with the configuration-interaction technique at the TZ2P self-consistent-field optimized geometries predict this rhomboidal structure to be 4.1 kcal/mol more stable than the linear triplet Si-C-C-C isomer. A second closed-shell rhomboidal C 2v symmetry structure with carbon-silicon transannular bonding, r(Si-C) = 1.880 Å, was located and characterized as a local minimum lying 4.3 kcal/mol above the ground-state rhomboidal structure at this level of theory. Higher-level theoretical methods, including contributions from triple excitations, with larger basis sets will be required to obtain a more definitive set of relative energies. © 1990 American Institute of Physics.