Photoelectron spectroscopy and theoretical calculations of SO4- and HSO4-:: Confirmation of high electron affinities of SO4 and HSO4

We present a combined photoelectron spectroscopic and theoretical study of SO4- and HSO4- and their corresponding neutral species in the gas phase. We measured very high electron affinities for SO4 and HSO4, which are 5.10(0.10) and 4.75(0.10) eV, respectively. Theoretical calculations of the neutral and anionic species using both density functional and ab initio molecular orbital theory confirm the high electron affinities of the two species. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. We find that both SO4- and SO4 have C-2v symmetry, whereas both HSO4- and HSO4 have C-s symmetry. We predict significant geometry changes between the equilibrium geometries of the anion species and the neutral species for both systems that are consistent with the broad nature of the measured photoelectron spectra.