Theoretical Study of the First Acid Dissociation of H₂SO₄ at a Model Aqueous Surface^†

Electronic structure calculations on the H2SO4·(H2O)4,6 model system embedded at the surface of an aqueous layer have been performed to examine the feasibility of the first acid dissociation of H2SO4 to an ·H3O+ contact ion pair over a wide temperature range, with a special focus on the 190−250 K range relevant for atmospheric sulfate aerosols. The results indicate that the acid dissociation can be either thermodynamically favored or disfavored depending on the degree of solvation of the acid and the produced ions, as well as on the temperature.