Theoretical calculations have been performed and applied to determine the most likely geometry for the pyrosulfate ion. The main question was to determine as to whether the system has C-2 or C-2, conformation. The present study favors C-2 symmetry. Bond lengths and angles have been calculated for the isolated ion, and the results compare well with experimental results for the ion in solid-state salts. Also, the vibrational spectrum of the S2O72- ion has been calculated and compared with experimental results, obtained by extrapolation from Raman spectra of salt melts of M2S2O7, M = Na, K, Rb, and Cs.