Ab initio and pseudopotential calculations on the singlet and triplet states of the disilyne isomers

Ab initio SCF as well as pseudopotential calculations were performed for determining equilibrium structures and relative stabilities of several disilyne isomers. For the singlet state there are only two structures, the bridged and the silavinylidene carbene, which correspond to minima on the energy hypersurface. The most stable of the six isomeric structures investigated is the bridged conformer in the ¹A₁ electronic state, followed by the silavinylidene carbene in the ¹A₁ and ³A₂ electronic states. Inclusion of electron correlation by MRD-CI calculations has no qualitative influence on the relative stabilities found in the SCF calculations.