Ab initio study of the X2Σ+ and A2Π states of the SiO+ cation including the effect of core correlation

The equilibrium bond lengths (r(e)), harmonic frequencies (omega(e)), first- and second-order anharmonicity constants (omega(e)x(e), omega(e)y(e)), rotational constants (B-e), centrifugal distortion constants (D-e), rotation-vibrational and centrifugal coupling constants (alpha(e) and beta(e), respectively) for the X(2)Sigma(+) and A (2)Pi 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)Pi state has also been computed at these theoretical levels. Dipole moments (mu(0)) of SiO+ in the X(2)Sigma(+) and A (2)Pi 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)Sigma(+) State of SiO+. (C) 1998 Elsevier Science B.V. All rights reserved.