Ab initio configuration interaction study on the electronic structure of the X 2Σ+, B 2Σ+ and 3 2Σ+ states of SiO+

The energy levels and electronic structure of the X(2)Sigma(+), B(2)Sigma(+) and 3(2)Sigma(+) states of SiO+ are studied using ab initio configuration interaction (CI) calculations at and around their equilibrium internuclear distances R-e. Spectroscopic constants and the vertical excitation energy from the SiO+ X(2)Sigma(+) state are predicted for the 3(2)Sigma(+) state. Based on the calculated CI wavefunctions, avoided crossings of the potential energy curve for the 3(2)Sigma(+) state and a near-degeneracy effect in the avoided crossing region are examined. The effects of the mixing of excited configuration state functions in the total electronic wavefunctions for the 1-3 (2)Sigma(+) states are investigated by analysing correlation energies in terms of the contributions from classes of excited configurations. The importance of both the near-degeneracy effect and the correlation energy effect in describing correctly the electronic structure of the 3(2)Sigma(+) state in the neighbourhood of its R-e is discussed.