AN AB-INITIO MOLECULAR-ORBITAL STUDY OF SIH2+F2-]SIH2F2

The insertion of SiH2 into F2 has been studied with MP2, CCD, CISD and QCISD. For fluorine approaching syn to the silicon lone pair, the complex is 2.5 kcal/mol below reactants and the insertion barrier is 0.5 kcal/mol above reactants at QCISD/6-31G*; for the anti approach, there is no barrier (only a broad plateau) and insertion proceeds with inversion at silicon. With RQCISD, both pathways go directly to SiH2F2, but with RMP2 and RCCD, there are several structures in the SiH2F-F region of the surface that are artifacts of the level of theory.