Theoretical study on the [Si, C, P, S] potential energy surface

The structures, energetics, spectral parameters and stability of the doublet [Si, C, P. S] radical are explored at the density functional theory and ab initio levels. Sixteen isomers connected by 23 interconversion transition states are located on the PES. The structures of the stable isomers and their relevant transition states are further optimized at the QCISD/6-311G(d) level followed by CCSD(T)/6-311+G(2df) single-point energy calculations. At the QCISD/6-311G(d) level, the lowest-lying isomer is a bent SSiCP 1 (0.0 kcal/mol) with considerable isomerization barriers (the lowest barrier is 12.6 kcal/mol). In addition, the bent isomer SiCSP 5 (57.3 kcal/mol) and the cyclic species S-cCSiP 6 (2.7 kcal/mol) also possess considerable isomerization barriers (more than 10.0 kcal/mol). The valence bond structures of the three isomers 1, 5 and 6 are analyzed. The calculated results are compared with those of analogous molecules C2PS and [Si, C, N, O]. Implications in laboratory and interstellar space are also discussed. (c) 2008 Elsevier B.V. All rights reserved.