Effect of cations on the hydrated proton

Area of Science:

• Physical Chemistry
• Solution Chemistry
• Spectroscopy

Background:

• Protons (H+) significantly alter liquid water structure, decreasing dielectric response.
• The influence of co-ions on proton's effect on water structure is not well understood.

Purpose of the Study:

• To investigate the nonadditive effects of protons and other cations on water's structural dynamics.
• To quantify the influence of co-ions on proton-induced water structuring.

Main Methods:

• Dielectric relaxation spectroscopy (1-50 GHz).
• Analysis of aqueous solutions with varying concentrations of protons and salts (e.g., Mg2+, Ca2+).

Main Results:

• A strong nonadditive effect was observed for co-solvated protons and cations.
• The structuring effect of protons on water is reduced when co-solvated with salts.
• An empirical model was developed to describe this nonadditive behavior.

Conclusions:

• The nonadditive effect arises from the unique nature of the proton in water.
• Coulomb fields from other cations, especially divalent ones, localize proton hydration structures.
• This finding provides insights into ion-water interactions in electrolyte solutions.