Singlet-triplet energy gaps in chlorine-substituted methylenes and silylenes

The singlet-triplet splittings of chlorine-substituted methylenes and silylenes have been studied by using the ab initio generalized valence bond (GVB) dissociation-consistent configuration interaction (DCCI) method. All chlorine-substituted methylenes and silylenes have singlet ground states, with calculated singlet-triplet splittings of 6.0, 20.5 35.8, and 55.2 kcal/mol for CHCl, CCl₂, SiHCl, and SiCl₂, respectively. We expect these results to be within 1 kcal/mol of experiment. The DCCl result strongly suggests that the correct experimental singlet-triplet splitting of CHCl is 6.4 ± 0.7 kcal/mol. [Photoelectron studies of CHCl^- lead to either 11.4, 8.9, 6.4, 3.9, or 1.4 kcal/mol, depending on assignment.]