Ionic dissociation of methanesulfonic acid in small water clusters

Ionic dissociation of methanesulfonic acid (MSA) in the aqueous environment is studied by density functional theory and ab initio calculations of the water clusters MSA–(H2O)n, n = 1–5. Molecular structures and stabilities are discussed based on the calculated stable conformers and relative energies. The clusters with up to three water molecules (n = 1–3) are dominated by strong hydrogen bond interactions. With a minimum of n = 4, MSA is dissociated as a result of proton transfer from MSA to H2O. All of the clusters are shown thermodynamically stable in the gas phase with respect to separate monomers.