The vacuum ultraviolet photoelectron spectrum of the S₂(³Σ^–_g) molecule has been investigated Eleven ionic states of the disulphur molecule have been identified and good correlation has been found between the position of these states and those observed previously for O⁺₂ and SO⁺. Five of the observed eleven bands show well-resolved vibrational fine structure which has been analysed in order to assist with identification of the ionic state formed. The first band corresponding to the process S⁺₂(X²II_g)â†� S₂(X³Σ^–_g) also shows structure due to spin-orbit coupling. Relative intensities of the vibrational components within a band have been compared with calculated Franck–Condon factors in order to estimate the bond length of the ion in its various states. These bond lengths and the measured vibrational level separations have been used with the known ionization potentials of atomic sulphur to construct a potential energy diagram of S⁺₂.