Triplet H−C−SiHCl₂:  Combined Matrix-IR and CCSD(T) Identification, and the Role of the Open-Shell Singlet State

Triplet carbene H−C−SiHCl₂ (1), prepared by a photochemical [1,2]H-shift from 1,1-dichlorosilaethylene, was identified by matching experimental and [CCSD(T)/cc-pVTZ] infrared absorptions. Parts of the potential energy surface were explored utilizing CCSD(T)/cc-pVTZ and B3LYP/6-311+G** computations. DFT reproduces the experimental features and CCSD(T) computations for the triplet surface but fails in the description of the open-shell singlet state of 1. We emphasize the notion of electropositive heterosubstitution for the generation of persistent ground-state triplet carbenes.