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 SO 4 - and HSO 4 - and their corresponding neutral species in the gas phase. We measured very high electron affinities for SO 4 and HSO 4, 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 SO 4 - and SO 4 have C 2 v symmetry, whereas both HSO 4 - and HSO 4 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.