The electronic structures of triplet S2 ground and excited states are studied by ab initio molecular orbital and configuration interaction calculation. Potential energy curves correlated with S(3P)+S(3P) and S(3P)+S(1D) at the dissociation limit are evaluated, and electronic terms for a total of 11 states are assigned. Transition dipole moments, as a function of internuclear distance, are determined for two allowed transitions to B″3Πu and B3Σu- excited states. The total absorption cross-sections are computed to estimate isotope-fractionation constants, ε, for four most common isotopologues: 32S32S, 32S33S, 32S34S, and 32S36S by quantum close-coupling (R-matrix) expansion approach and they are found to lie in a mostly opaque to competing absorbers spectral window. We suggest that the photochemistry and isotopic effects of S2 are of significant importance and provide data showing high sensitivity of mass-independent fractionation to excitation wavelength. Zero-point energy based constants εZPE are estimated as well to compare with the obtained isotope effects and two modes for MIF are present in three-isotope plots; large isotopic effects were observed for both 36S and 33S with an excitation wavelength-dependent fluctuation.