Abstract
The energy levels and electronic structure of the X2Σ+, B2Σ+ and 32Σ+ 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+ X2Σ+ state are predicted for the 32Σ+ state. Based on the calculated CI wavefunctions, avoided crossings of the potential energy curve for the 32Σ+ 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 2Σ+ 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 2Σ+ state in the neighbourhood of its R e is discussed.