Structures and energetics of planar and tetrahedral dilithiomethane. A near degeneracy of singlet and triplet electronic states

Self-consistent field theory was used to provide state-of-the-art theoretical predictions, including the effects of electronic correlation, of the relative energies of planar and tetrahedral dilithiomethane in its lowest singlet and triplet electronic states. The basis set used in the approach was of double zeta plus polarization (DZ+P) quality and may be precisely designated C(9s 5p 1d/4s 2p 1d), Li(9s 4p/4s 2p), H(4s 1p/2s 1p). The predicted structures are in qualitative agreement with previous work. The C-Li distances are all longer, from 0.058 to 0.100 A, and the LiCLi bond angles are from 0.2 to 4.7/sup 0/ (planar triplet) larger. There is tentative agreement that the singlet LiCLi bond angles are much greater than the comparable triplet angles.