Ab initio study of the X2Σ+ and A 2Π states of the SiN radical

The equilibrium bond length, harmonic frequency, first and second order anharmonicity constants, rotational and centrifugal distortion constants, as well as the rotation-vibrational and centrifugal coupling constants for the ground X2Σ+ and first excited A 2Π states of the SiN radical have been calculated at the complete active space SCF (CASSCF), multireference CI (MRCI) and coupled cluster (CCSD(T)) levels using Dunningʹs correlation-consistent basis sets. The excitation energy of the A2Π state has also been computed at these theoretical levels. Dipole moments of SiN in the X2Σ+ and A2Π states are given. Our study shows that core correlation must be considered in order to obtain satisfactory accuracy for the spectroscopic constants.