Abstract:

The adiabatic potential energy curves of the ground state of S² molecule and those of low\|lying excited state of S⁺₂ molecular ion were calculated by means of  ab initio method with multi\|configurational quasi-degenerate perturbative theory, and spectroscopic parameters were fitted. The adiabatic and vertical ionization energies of 3p valent electron  in S2 molecule in a range of 9—16 eV were obtained. The first adiabatic ionization energy was determined as 9.34 eV according to present calculations, which agrees with  experimental value (9.356±0.002)eV. The theoretical values for vertical and adiabatic  ionization energies of other bands were compared  with  experimental values, and the reasons of   error were analyzed, and the photoelectronic spectra of S⁺₂(A²Π_u) and S⁺₂(B²Σ^-_g) bands were assigned by means of  calculated results. 

Key words: S⁺₂ molecular ion; , multireference method; , potential energy curve; , ionization energy