Theoretical study on structures and stability of SiC3S isomers.

Various levels of calculations are carried out to explore the potential energy surfaces (PES) of singlet and triplet SiC3S, a molecule of potential interest in interstellar chemistry. At the DFT/B3LYP/6-311G(d) level, a total of 57 minimum isomers and 92 interconversion transition states are located. The structures of the most relevant isomers and 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 level, the lowest-lying isomer is the chain-like SiCCCS 31 (0.0 kcal/mol) with a great kinetic stability of 54.1 kcal/mol. In addition, ring isomers CC-cCSSi 19 (19.8 kcal/mol), S-cCCCSi 112 (30.4 kcal/mol), S-cCCSiC 118 (9.4 kcal/mol), S-cSiCCC 121 (34.4 kcal/mol) and cage-like isomer cage-SiSCCC 123 (51.8 kcal/mol) also possess considerable kinetic stability (more than 10.0 kcal/mol). As a result, these six isomers are predicted to be possible candidates for future experimental and astrophysical detection. The bond natures and possible formation pathways in interstellar space of the SiCCCS are discussed. The predicted structure and spectroscopic properties for it are expected to be informative for the identification of SiC3S and even larger SiCnS species either in laboratory or in space. [ABSTRACT FROM AUTHOR]