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 S₂^- and S₃^- have been calculated at QCISD/6-311++G(3d2f) and B3P86/6-311++G(3d2f) level. The S₂^- ground state is of ^-Pi_g, the S₃^- ground state is of ^-B₁ and S₃^- has a bent (C_2V) structure with an angle of 115.65°. The results are in good agreement with these reported in other literature. For S₃^- 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 S₂^- has been derived according to the ab initio data through the least-squares fitting. The force constants and spectroscopic data for S₂^- have been calculated, then compared with other theoretical data. The analytical potential energy function of S₃^- have been obtained based on the many-body expansion theory. The structure and energy can correctly reappear on the potential surface.