Singlet-triplet energy gap in halogen-substituted carbenes and silylenes: a difference-dedicated configuration interaction calculation

Abstract

Ab initio calculations including correlation energy are reported on a series of halogen-substituted carbenes and silylenes: CH2, CHF, CF2, CHCl, CCl2, CHBr, CBr2, SiH2, SiHF, SiF2, using the difference-dedicated configuration interaction method. All these compounds with the exception of CH2 have singlet ground states. The singlet-triplet energy differences are in very good agreement with experiment when available, as well as with other high level calculations. The singlet-triplet separation is also determined in trifluoromethyl carbenes, CHCF3, CFCF3, CClCF3 and CBrCF3. The CF3 substituent has little influence on the energy gap since CHCF3 like CH2 has a triplet ground state, with a gap of 11·1 kcal mol-1, and CFCF3, CClCF3 and CBrCF3 have singlet ground states, like CHF, CHCl and CHBr, with gaps of -17·6, -5·4, and -3·5 kcal mol-1.