The singlet–triplet energy separation in silylene

Abstract
MCSCF calculations followed by large scale configuration interaction, comparable with the best done for isovalent methylene, give a singlet–triplet splitting in silylene of 21.0±1 kcal/mol. The singlet is the lower energy state. Structural parameters for the as yet unobserved triplet are re =1.48±0.005 Å and θe =118.5±1°.