Theoretical Study on Potential Energy Surface of the Interstellar Molecule SiC_2N

摘要

The potential energy surface of the interstellar molecule SiC_2N is explored at the B3LYP/6-311(d), QCISD/6-311G(d), and CCSD(T)/6-31G(2d) (single-point) levels. Eleven species including the chainlike, three-membered ring and four-membered ring structures are located as energy minima connected by twenty interconversion transition states. At the CCSD(T)/6-311G(2d) level, the lowest-lying isomer is linear SiCCN 1 with ~2∏ state followed by linear SiCNC 2 with ~2∏ state at 23.2 kcal/mol two close-energy isomers, i.e., cyclic SiCCN with SiC cross-bonding 9 with ~2A" state at 28.0 kcal/mol and bent SiNCC 5 with ~2A' state at 29.5 kcal/mol. The potential energy surface of SiC_2N indicates that only the three chainlike isomers 1, 2, and 5 are kinetically stable, whereas the low-lying cyclic isomer 9 and other isomers are kinetically unstable toward conversion to more stable isomers. The results are compared with those of the well-known analogous interstellar C_3N radical. The calculated bond lengths, harmonic vibrational frequencies, dipole moments, rotational constants, and the first excitation energies may assist future laboratory and interstellar identification of the three SiC_2N isomers 1, 2, and 5.