Ab Initio Investigation on the Lowest Singlet and Triplet State of Si₂H₂

Ab initio SCF and electron correlation calculations are reported for the Si₂H₂ system. In the case of the singlet ground state the global minimum is a nonplanar bridged structure (IV) followed by H₂SiSi (II) and trans-bent HSiSiH (I). Both H₂SiSi and trans-bent HSiSiH are predicted to be local minima. Stability differences (Δ°_298.16) obtained from our most extensive calculations are II/IV 11.8 kcal/mol and I/IV 14.3 kal/mol. In the triplet case H₂SiSi (II) is the global minimum. Trans bent HSiSiH (I) and a planar bridged structure (III) are local minima. The following stability differences were obtained: I/II 1.7 kcal/mol, III/II 19.7 kcal/mol.