The electronic and geometrical structures of the ground stated and low-lying isomers of MnO4 and MnO4- have been calculated as a function of spin-multiplicities by using the molecular orbital theory based on generalized gradient approximation to the density functional formalism. Total energies of isomers are used for evaluating the energetics of the MnO4- decay through various fragmentation channels. Two primary channels were found depending on the energy of photons. The preferred photofragmentation channel, accessible with approximate to 2 eV photons, is found to involve an initial excitation of the ground-state MnO4- anion into its peroxo isomer followed by subsequent excitations into a superoxo form. Photodetachment of an extra electron from this superoxo isomer anion leads to the formation of a neutral superoxo isomer of MnO4, which, in turn, dissociates to MnO2 + O-2. Excitations of the anion peroxo isomer into biperoxo isomer are also possible with 3.7 eV, photons and the latter could dissociate spontaneously to MnO2-+ O-2. A number of other decay channels are accessible with low-energy photons, but their intensities are expected to be Low because these require flipping the spin of one or more electrons.