Ab initio study of the lowest 3Σ−, 3Π and 1Σ+ states of the SiN+ cation

The equilibrium bond lengths, harmonic frequencies, first-order anharmonicity constants, rotational constants, centrifugal distortion constants, and rotation–vibrational constants, as well as the dipole moments, excitation and dissociation energies for the lowest 3Σ−, 3Π and 1Σ+ states of SiN+ have been calculated using CASSCF, CMRCI, CCSD(T) and density functional (B3LYP and B3PW91) theories combined with Dunningʹs correlation-consistent basis sets. Core-correlation effects have also been included in order to obtain a satisfactory accuracy for the spectroscopic constants. Our calculations strongly support 3Σ− as the ground state; the 3Π state lies only 460 cm−1 above the 3Σ− state, while the 1Σ+ state lies 6865 cm−1 above the ground state. Our DFT calculations on the triplet surface of SiN+ converge to the 3Π state which is clearly not the ground state.