Using large Gaussian basis sets ab initio calculations on the molecules SN+, SN, and S2N2 have been performed at the SCF level. Additionally, electron correlation effects were studied for SN + and S2N2 by the PNO-CI and CEPA-PNO methods. The following equilibrium geometries were obtained: SN+, r SNe =2.64 (SCF), 2.72 a.u. (CEPA); SN, rSN e=2.78 a.u. (SCF); S2N2, D2h symmetry, rSNe=3.07 (SCF), 3.16 a.u. (CEPA), ≮ NSN=90.2° (SCF), 90.5° (CEPA). Complete harmonic force fields of S 2N2 and the corresponding vibrational frequencies were computed. The assignments of the experimental ir and Raman spectra for S 2N2 are discussed critically on the basis of the theoretical results.