Theoretical Study of [Si,O,C,O] Species: Prediction of New Species on Triplet Potential Energy Surface

The intermediates [Si,O,C,O] of the Si + CO2 reaction have been studied in detail using high level ab iniitio methods. Both singlet and triplet [Si,O,C,O] species are characterized structurally and energetically. On the singlet potential energy surface (PES), the vdw-OSi-CO isomer and in the triplet PES, the bent-SiOCO isomer is found to be thermodynamically as well as kinetically most stable species. All possible isomerization transition states (TS) are located on both singlet and triplet potential surfaces. On the triplet surface, the stability of the trans-OSiCO isomer is comparable with that of the bent-SiOCO isomer. A non-planar cis-SiOCO isomer is located on the triplet PES, which is predicted for the first time. Heats of formation at 0 K (Delta H-f degrees, 0 K) for all singlet and triplet species are computed using G3B3, G3MP2, and CBS-Q theories. The discrepancy between G3B3 and the other two methods for the heat of formation value for triplet trans-OSiCO is discussed. The PESs for singlet as well as triplet species with their dissociation asymptotes are explored at the CCSD(T)/6-311G(d, p)//MP2/6-311G(d, p) level of theory. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 111: 606-615, 2011