The molecular structure and the analytical potential energy function of S2- and S3-

In this paper, the equilibrium geometry, harmonic frequency and dissociation energy of S-2(-) and S-3(-) have been calculated at QCISD/6-311++G(3d2f) and B3P86/6-311++G(3d2f) level. The S-2(-) ground state is of (2)Pi(g), the S-3(-) ground state is of B-2(1) and S-3(-) has a bent (C-2V) structure with an angle of 115.65 degrees The results are in good agreement with these reported in other literature. For S-3(-) ion, the vibration frequencies and the force constants have also been calculated. Base on the general principles of microscopic reversibility, the dissociation limits has been deduced. The Murrell-Sorbie potential energy function for S-2(-) has been derived according to the ab initio data through the least-squares fitting. The force constant and spectroscopic data for S-2(-) have been calculated, then compared with other theoretical data. The analytical potential energy function of S-3(-) have been obtained based on the many-body expansion theory. The structure and energy can correctly reappear on the potential surface.