Hydrated ions binding energies

Fig. 2. Plots testing simple ionic model equations for diatomic molecules in the gas phase, ionic crystals and the hydration of ions. The slopes of the lines coincide with those of the simple theory, see Phillips and Williams. U is the binding energy from free gas ions.

Quantum chemical methods are valuable tools for studying atmospheric nucle-ation phenomena. Molecular geometries and binding energies computed using electronic structure methods can be used to determine potential parameters for classical molecular dynamic simulations, which in turn provide information on the dynamics and qualitative energetics of nucleation processes. Quantum chemistry calculations can also be used to obtain accurate and reliable information on the fundamental chemical and physical properties of molecular systems relevant to nucleation. Successful atmospheric applications include investigations on the hydration of sulfuric acid and the role of ammonia, sulfur trioxide and/or ions... 

In concentrated salt solutions, the vapor pressure is lower than that of pure water, and hence it exhibits reduced water activity. This phenomenon is explained by the fact that a considerable fraction of the water molecules are associated with the hydration of the salt ions. The binding energy of these water molecules (which forms the first and the second hydration shells) to the center ion is larger than 10 kcal/mol therefore, they are less likely to participate in the hydration of the newly formed proton. To observe successful proton dissociation, the thermodynamic stable complex must be formed within the ion-pair lifetime. The depletion of the solution from water molecules available for this reaction will lower the probability of the successful dissociation. As demonstrated in Figure 9, this function decreases with the activity of the water in the solution. 

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