Theoretical study on the structures, isomerization, and stability of [Si, C, N, S] isomers

The structures, energies, spectral parameters, and stabilities of the doublet [Si, C, N, S] radical are explored at the density functional theory and ab initio levels. Eighteen isomers including chainlike, three-membered ring, four-membered ring and cagelike structures are located, connected by 25 interconversion transition states at the B3LYP/6-311G(d) level. The structures of the kinetically stable isomers and their relevant transition states are further optimized at the QCISD/6-311G(2d) level. At the CCSD(T)/6-311 + G(2d)//QCISD/6-311G(2d)+ZPVE level, the global lowest-lying isomer NCSiS1 is a bent structure. Additionally, the chainlike isomers CNSiS2, SiNCS3, SiSCN4, SiSNC5, and SiCNS6 also process considerable kinetic barriers (more than 10.0 kcal/mol). All the six isomers may be experimentally or astrophysically observable. The bonding natures of all the six isomers are analyzed seriously. The calculated results are compared with those of analogous molecules [Si, Si, N, S], [Si, C, P, S], and [Si, C, N, O]. Implications of the computational structures and spectroscopies are also discussed.