An energetically low-lying silacyclopropyne isomer of SiC2

We have discovered a low-lying cyclic isomer of Si–C–C which is best described as a three-membered ring with a weak carbon–carbon triple bond. In these theoretical studies a double zeta plus polarization basis set was used initially. At the self-consistent-field (SCF) and two-configuration (TC) SCF levels of theory the ring structure is a transition state leading to linear Si–C–C. A configuration interaction (CI) treatment at the SCF optimized cyclic geometry, however, show it to lie 1.1 kcal/mol below the linear structure. Extension of the basis set to include a second set of d functions on each atom gives a final prediction that the ring structure lies ∼5 kcal below linear SiCC.