Theoretical Investigations On Spectroscopic Properties Of Low-lying Electronic States Of Several Diatomic Molecules(Cation And Radical)

In the present paper, silicon-carbon radical. Boron-nitride molecule and sulfur-oxygen cation were chosen as our research objects because of their great significance in theory and potential applications. Using the internally contracted multireference configuration interaction (MRCI) approach and the internally contracted multireference configuration interaction approach with the Davidson correction (MRCI+Q) in combination with the Dunning’s correlation consistent basis sets, the low-lying valence electronic states of the molecule (radical and cation) are calculated in high precision. Such calculations are performed in MOLPRO2008.1program package. The potential energy curves (PECs), spectroscopic parameters and vibrational manifolds are determined. The main results are summarized as follows:(1) In this paper, the PECs of the twenty-five electronic states of the SiC radical and the PECs of seventeen electronic states of the BN molecule have been studied using the MRCI approach in combination with the Dunning’s correlation consistent basis sets. The effects on the PECs and spectroscopic parameters by the core-valence correlation and relativistic corrections are evaluated. For the SiC radical, core-valence correlation corrections are included for the first time. And for the BN radical, relativistic corrections are also included for the first time. The PECs obtained by the MRCI calculations are corrected for size-extensivity errors by means of the Davidson modification. Synchronously, the PECs are extrapolated to the complete basis set (CBS) limit by the total-energy extrapolation scheme. Using the full Breit-Pauli operator, the spin-orbit (SO) coupling effect on the spectroscopic parameters is included in the X3∏nd D3∏electronic states of the BN molecule. Using these PECs, the spectroscopic parameters are evaluated with the aid of module VIBROT in the Molcas program package. The spectroscopic parameters are compared with those reported in the literature. Excellent agreement is found between the present spectroscopic results and the experimental ones. For the SiC radical, with the PECs obtained by the MRCI+Q/CV+DK+56calculations, the vibrational manifolds of the first30vibrational states of each electronic state are calculated for the non-rotation radical. For the BN molecule, with the PECs obtained by the MRCI+Q/DK+CV+Q5calculations, the vibrational manifolds are calculated for each vibrational state of each electronic state. And those of the first20vibrational states of each electronic state are reported for the non-rotation molecule.(2) The PEC of the b4∑-electronic state of the SO+cation is calculated using the internally contracted MRCI+Q. The basis set used is a correlation-consistent aug-cc-pV5Z basis set. The SO coupling effect on the spectroscopic parameters is included by the state interaction approach with the full Breit-Pauli operator with all-electron basis set, aug-cc-pCVTZ. To improve the quality of the PEC and SO coupling constant (A0), core-valence correlation and relativistic corrections are included for the first time. Core-valence correlation corrections are calculated using a cc-pCVTZ basis set. Relativistic corrections are included by the second-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. At the MRCI+Q/aug-cc-pV5Z+CV+DK level. The spectroscopic parameters are obtained and compared with those reported in the literature. Excellent agreement has been found between the present spectroscopic parameters and the experimental ones. The vibrational level G(υ), inertial rotation constant Bv and centrifugal distortion constant Dv are predicted for each vibrational state of the b4∑-electronic state by solving the ro-vibrational Schrodinger equation of nuclear motion using Numerov’s method, and those of the first30vibrational states are reported for the non-rotation32S16O+cation.Overall, comparison with the measurements demonstrates that the present vibrational manifolds are both reliable and accurate. The vibrational manifolds of a number of electronic states are reported for the first time. They should be good references for future experimental or theoretical research.