A photodetachment photoelectron spectroscopy study of a doubly charged anion (S2O82-) in the gas phase is reported at three photon energies: 193, 266, 355 nm. Adiabatic and vertical electron binding energies of S2O82- were measured to be 1.7+/-0.2 and 2.2+/-0.1 eV, respectively. Several excited states were observed for the S2O8- singly charged anion at 193 nm. The repulsive Coulomb barrier that binds multiply charged anions was clearly shown in the detachment spectra of S2O82-. The effects of the Coulomb barrier to the detachment spectra and electron tunneling through the barrier are presented. The barrier height, which is equivalent to the magnitude of the Coulomb repulsion between the two excess charges in S2O82- was estimated to be similar to 3 eV.