Theoretical studies on the SiC radical: electronic structure, spectroscopy and spin-orbit couplings

The potential energy curves (PECs) of twenty-five Λ-S states and twenty Ω states generated from eight Λ-S states of the SiC radical are calculated by using an ab initio quantum chemical method. The PEC calculations are performed for internuclear separations from 0.10 to 1.00 nm using the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction (MRCI) approach in combination with a correlation-consistent aug-cc-pV6Z basis set. To improve the quality of the PECs, core-valence correlation and relativistic corrections are included. Core-valence correlations are included using a cc-pCVTZ basis set. Relativistic corrections are calculated using the third-order Douglas-Kroll Hamiltonian approximation at the level of cc-pV5Z basis set. The spin-orbit coupling effect is accounted for by the Breit-Pauli Hamiltonian in combination with the aug-cc-pVTZ basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are corrected for size-extensivity errors by means of the Davidson modification. The PECs are extrapolated to the complete basis set (CBS) limit by the total-energy extrapolation scheme. The spectroscopic parameters are obtained by fitting the vibrational levels, which are calculated by solving the ro-vibrational Schrödinger equation using the Numerov’s method. The spectroscopic results are compared with those reported in the literature. Excellent agreement has been found between the present results and the measurements. The vibrational manifolds of the first 30 vibrational states are calculated for each electronic state of the non-rotating radical. Comparison with the measurements demonstrates that the present results are accurate. The spectroscopic parameters and the molecular constants reported here are expected to be reliable predicted results.