Proton solvation and proton mobility

Experimental evidence for proton solvation and proton mobility is analyzed and the results are compared with recent simulations. Three factors contribute to differences in proton solvation energies: hydrogen-bond cleavage, changes in hydrogen-bond lengths, and proton delocalization. These factors are estimated from experimental attributes. In dilute acidic aqueous solutions H₃O⁺ is more stable than H₅O₂⁺ by about 0.6 kcal/mol. This estimate, together with the activation energy for proton mobility, supports the 121 mechanism for proton mobility in which a protonated water monomer is transformed, by second-shell hydrogen-bond cleavage, to a protonated dimer and back to another protonated monomer.