High-level ab initio calculations are performed to determine the lowest singlet-triplet (S-T) gap in CCl 2 , CBr 2 and CI 2 . For CCl 2 all-electron basis sets are used. For CBr 2 all-electron and effective core potential (ECP) basis sets are used, whilst for CI 2 only ECP basis sets are used. Methods up to CCSD(T) are employed, as well as the B3LYP method. The conclusions are that for CCl 2 the S-T gap is 20+/-1 kcal mol - 1 and that the gaps for CBr 2 and CI 2 are 17+/-2 kcal mol - 1 and 9+/-2 kcal mol - 1 , respectively. Some comments are made regarding the disagreement with recent photodetachment studies.