Atmospherically Relevant Hydrogen-Bonded Interactions between Methanesulfonic Acid and H2SO4 Clusters: A Computational Study.

A detailed and systematic quantum-chemical calculation has been performed with high-level density functional theory (DFT) to analyze the electrostatic interaction of methanesulfonic acid (CH3SO3H), also known as MSA, with pre-formed clusters of sulfuric acid (H2SO4) molecules in ambient conditions. Both MSA and H2SO4 are considered as atmospheric molecules that might play active roles in aerosol formation. The interactions between MSA and H2SO4 clusters lead to the formation of MSA···(H2SO4)n (n = 2, 3) complexes stabilized by the formation of different types of intermolecular hydrogen bond networks. Analyses of cluster binding energies and free energy changes associated with their formation indicate that MSA could bring additional stability into the atmospheric molecular clusters responsible for aerosol formation. Variations of Gibbs free energy with temperature and pressure have been analyzed. The lower temperatures and pressures at the higher altitudes of the troposphere are found to play in favor of higher stability of the MSA···(H2SO4)n clusters. Effects of hydrogen bond formation on dipole moment, mean polarizability, and anisotropy of polarizability of the clusters have been analyzed. Rayleigh scattering intensities are found to increase many-fold when light interacts with the MSA···(H2SO4)n clusters.