The Investigations On The Spectroscopic Parameters Coand Molcular Nstants For SiO And SiO~+Molecules

Molecular spectroscopy is an important tool to investigate the molecular structure andproperties. By the understanding of the molecular spectroscopy, we can obtain the molecularvibraitonal energy levels, rotational energy levels, et al. In addition, using the molecularspectroscopy, various molecules which exists in the fixed star, planet, comets andstar-forming regions can be detected. Then, the physical environment in the interstellar spacecan be investigated.Molecular potential energy curve is one of the important branches in atomic andmolecular physics. It gives one absolute description of molecular and electronic energy withBorn-Oppenheimer approximation, namely molecular energy, geometry, force constants andspectrum properties.In the present work, the spectroscopic parameters and molecular constants for2diatomicmolecules (SiO and SiO~+) are calculated. The effects on the spectroscopic parameters andmolecular constants by the Davidson modification, core-valence correlation and relativisticcorrections are considered. And the extrapolation is also investgated.First, the potential energy curves (PECs) of SiO (X~1Σ~+, a~3Σ~+, C~1Σ-and A~1Ⅱ) and SiO~+(X~2Σ~+, A~2Ⅱ, B~2Σ~+, a~4Σ~+,1~4Ⅱ,1~4Δ,1~4Σ~-and2~2Ⅱ) are calculated using the multi-referenceconfiguration interaction method (MRCI) with Dunning’s correlation consistent basis sets inMOLPRO2008.1program package. The basis set used for Si， O and O~+atoms isaug-cc-pV6Z. With the aid of module VIBROT in Molcas program package, the PECs arefitted and the spectroscopic parameters (D_e, R_e, ω_e, ω_ex_e, α_eand B_e) for each electronic stateare determined. The complete vibrational states are also obtained by fitting the PECs. Foreach vibrational state, the vibrational level G(ν), inertial rotation constant Bνand centrifugaldistortion constant D_νare calculated when J=0. The results are compared with the othertheoretical and experimental values available, and the comparison shows that excellent agreement exists between the present results and the available experiments.Then, the effects on the spectroscopic parameters and molecular constants by theDavidson, core-valence correlation and relativistic corrections are also considered in thepresent work. The same MRCI method and the correlation consistent basis sets are adopted toinvestigate all the electronic states of SiO and SiO~+molecules. To obtain more accurate results,the Davidson modification and core-valence correlation and relativistic corrections areincluded. For the SiO and SiO~+molecules, the core-valence correlation correction is carriedout with the cc-pCVQZ basis set. And the relativistic correction is done at the level ofcc-pVQZ basis set. The way to consider the relativistic correction is to use the second-orderDouglas-Kroll Hamiltonian approximation. Fitting the PECs including the Davidsonmodification and core-valence correlation and relativistic corrections, the spectroscopicparameters and molecular constants are determined.Finally, using the two-point energy extrapolation formula, the totle energies calculatedare extrapolated to the CBS limit. In detail, for the SiO and SiO~+molecule, the extrapolationsare all based on the aug-cc-pV5Z and aug-cc-pV6Z basis sets. Then using the PECs obtainedby the extrapolation, the corresponding parameters and molecular constants are calculated.On the whole, by comparing the present results with the experiments, the Davidson,core-valence correlation, relativistic corrections and the extrapolation obviously improve thespectroscopic parameters quality.