Ab initio study of the X 2Σ+ and A 2Π states of the SiO+ cation including the effect of core correlation Original Research Article

The equilibrium bond lengths (re), harmonic frequencies (ωe), first- and second-order anharmonicity constants (ωexe, ωeye), rotational constants (Be), centrifugal distortion constants (De), rotation–vibrational and centrifugal coupling constants (αe and βe, respectively) for the X 2Σ+ and A 2Π states of the SiO+ cation have been calculated at the complete active space self-consistent field (CASSCF), internally contracted multireference configuration interaction (CMRCI), coupled cluster (CCSD(T)) and hybrid density functional (B3LYP and B3PW91) methods with Dunningʹs correlation-consistent basis sets. The excitation energy (Te) of the A 2Π state has also been computed at these theoretical levels. Dipole moments (μ0) of SiO+ in the X 2Σ+ and A 2Π states are also given. Our calculations show that core correlation must be considered in order to obtain a satisfactory accuracy for the spectroscopic constants, and that the B3PW91 method can predict very well the geometry and harmonic frequency of the X 2Σ+ state of SiO+.