Ab initio study of the [formula omitted] and [formula omitted] states of the SiO + cation including the effect of core correlation

Abstract

The equilibrium bond lengths ( r e), harmonic frequencies ( ω e), first- and second-order anharmonicity constants ( ω e x e, ω e y e ), rotational constants ( B e), centrifugal distortion constants ( D e), rotation–vibrational and centrifugal coupling constants ( α e and β e, respectively) for the X 2 Σ + and A 2 Π 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 Dunning's correlation-consistent basis sets. The excitation energy ( T e) of the A 2 Π state has also been computed at these theoretical levels. Dipole moments ( μ 0) of SiO + in the X 2 Σ + and A 2 Π 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 2 Σ + state of SiO +.