Dissociation and microsolvation of bisulfate anion

Bisulfate anion has vast applications in industrial and environmental chemistry. Its dissociation to sulfate anion has been studied computationally and by size-selected clusters. In this study, Micro-Raman spectroscopy is applied at different relative humidity (RH)% on small droplets of aqueous solutions of NaHSO₄, NH₄HSO₄, and H₂SO₄ to explore the dissociation of HSO₄ ^- experimentally in bulk and supersaturated state. Our cumulative experimental results support the conclusion obtained from gas-phase cluster study that HSO₄ ^- starts dissociating at very low number of water molecules (H₂O ~ 1). However, dissociation of HSO₄ ^- is found dependent on the cation attached with this weak acid. The magnitude of dissociation is found as NH₄HSO₄ ≈ H₂SO₄ > NaHSO₄. In addition, studying the hydration process of HSO₄ ⁻ in the presence of three different cations enabled us to observe various species in three systems. Theoretical values obtained from extended aerosol inorganic model supports the experimental results.