Paper SS-ThA2
Photoelectron Spectroscopy of Sulfuric Acid Aqueous Solutions

Thursday, November 1, 2012, 2:20 pm, Room 22

The air-liquid interface of aerosols is an important site for heterogeneous chemistry in the atmosphere, associated, for instance, with the formation of reaction products relevant for ozone depletion. Concentrated (5-14 M) super-cooled aqueous solutions of sulfuric acid are known as sulfate aerosols and are one of the most abundant types of atmospheric aerosols. Fully understanding the dissociation of sulfuric acid, on the molecular level, is important because heterogeneous chemistry occurring on the surface of sulfate aerosols depends on the availability, speciation, location, and solvation structure of the species in solution. Aqueous solutions of sulfuric acid and the subsequent acid dissociation are useful models for sulfate aerosols. As a strong acid, the bulk of an aqueous solution of sulfuric acid will have H₃O⁺, HSO₄^- and SO₄^2-, and at high concentrations when the water concentration is very low, un-dissociated H₂SO₄ may be present. The bulk species composition is a function of the initial solution concentration, as well as temperature, and this composition as been well characterized by a variety of methods, such as sum frequency generation and Raman spectroscopy. Here, the chemistry of sulfuric acid aqueous solutions is explored by photoelectron spectroscopy on a liquid micro-jet. Experiments were performed at Beamline U41-PGM at the BESSY II synchrotron facility. A series of sulfuric acid aqueous solutions is measured at a low temperature of 6˚C. Deconvolution of the photoelectron spectra yields electronic information on the ionization species of sulfuric acid.