Ab initio study of the lowest (3)Sigma(-), (3)Pi and (1)Sigma(+) states ofthe SiN+ cation

The equilibrium bond lengths, harmonic frequencies, first-order anharmonici ty constants, rotational constants, centrifugal distortion constants, and r otation-vibrational constants, as well as the dipole moments, excitation an d dissociation energies for the lowest (3)Sigma(-), (II)-I-3 and (1)Sigma() states of SiN+ have been calculated using CASSCF, CMRCI, CCSD(T) and dens ity functional (B3LYP and B3PW91) theories combined with Dunning's correlat ion-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 (3)Sigma(-) as the ground state; the (I I)-I-3 state lies only 460 cm(-1) above the (3)Sigma(-) state, while the (1 )Sigma(+) state lies 6865 cm(-1) above the ground state. Our DFT calculatio ns on the triplet surface of SiN+ converge to the (II)-I-3 state which is c learly not the ground state. (C) 1999 Elsevier Science B.V. All rights rese rved.