Weak and dynamic hydrogen bonding interactions are responsible for the structure and function of a whole host of systems ranging from water clusters and atmospheric aerosols to proteins and DNA. We use a combination of classical molecular dynamics sampling and high-level quantum mechanical methods to identify and calculate free energies for stable gas phase clusters of atmospheric interest. Using MP2 energies extrapolated to the complete basis set limit and including finite temperature corrections within the anharmonicity corrected rigid-rotor-harmonic-oscillator framework, we calculated Gibbs free energies for (H2O)n=1-10, (H2SO4)m=1-2(H2O)n=1-6 and H2SO4*NH3/CH3NH2(H2O)n=1-6. From the Boltzmann averaged free energies of water clusters, we predicted their abundances in low temperature pulsed supersonic expansions. Similarly, our investigation of the thermodynamics of the binary (H2SO4-H2O) and ternary (H2SO4-NH3/CH3NH2-H2O) cluster formation yielded insights into acid dissociation in small clusters, the stability of neutral and ionic species and the abundance of small hydrates under atmospheric conditions.

Accurate modeling of noncovalent clusters of atmospheric interest

245th National Meeting (2013)

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