Theoretical study of spectroscopic and molecular properties of several low-lying electronic states of CO molecule

摘要

The potential energy curves (PECs) of eight low-lying electronic states (X~1Σ+, a~3Π, a′ ~3Σ~+, d~3Δ, e~3Σ ~-, A~1Π, I~1Σ-, and D ~1Δ) of the carbon monoxide molecule have been studied by an ab initio quantum chemical method. The calculations have been performed using the complete active space self-consistent field method, which is followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with the correlation-consistent aug-cc-pV5Z basis set. The effects on the PECs by the core-valence correlation and relativistic corrections are included. The way to consider the relativistic corrections is to use the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. Core-valence correlation corrections are performed using the cc-pCVQZ 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 (MRCI+Q). The spectroscopic parameters (D_e, T_e, R_e, ω_e, ω_ex _e, ω_ey_e, B_e, α_e, and γ_e) of these electronic states are calculated using these PECs. The spectroscopic parameters are compared with those reported in the literature. Using the Breit-Pauli operator, the spin-orbit coupling effect on the spectroscopic parameters is discussed for the a ~3Π electronic state. With the PECs obtained by the MRCI+Q/aug-cc-pV5Z+CV+DK calculations, the complete vibrational states of each electronic state have been determined. The vibrational manifolds have been calculated for each vibrational state of each electronic state. The vibrational level G(ν), inertial rotation constant B_ν, and centrifugal distortion constant D_ν of the first 20 vibrational states when the rotational quantum number J equals zero are reported and compared with the experimental data. Comparison with the measurements demonstrates that the present spectroscopic parameters and molecular constants determined by the MRCI+Q/aug-cc-pV5Z+CV+DK calculations are both reliable and accurate.