Our present understanding of solvation is largely based on thermodynamic measurements, for instance, of the solvation free energy or enthalpy associated with the rearrangement of the water molecules around the solute ion. It is an interesting fact that isolated molecular anions, especially multiply charged anions, are often intrinsically electronically unstable; i.e., the Coulomb repulsion between the extra electrons leads to a spontaneous electron detachment in the gas phase. Many common multivalent inorganic anions such as sulfate, SO42−, phosphate, PO43-, or carbonate, CO32−, thus cannot be isolated in the gas phase. Typically, the relative anion stabilization in solution is achieved by means of intermolecular interactions, either with solvent molecules in a solution, or in the solid state that is facilitated by the counterions in a crystal. In recent years, the development of the liquid microjet technique coupled with photoelectron spectroscopy has enabled the direct measurement of orbital energies of solvated (an)ions and has linked the existing thermodynamic data with electronic structure information on an absolute energy scale. I will present the most recent experimental results including vertical detachment energies, adiabatic energies, and reorganization energies of many textbook inorganic anions in aqueous solution, namely halides, pseudohalides, oxychlorides, nitrates, nitrites, oxalates, sulfates, sulfites, carbonates, and phosphates. We have identified (chemical) trends with respect to solute molecular structure, hydration configuration, chemical reactivity, ionic strength (concentration), protonation and charge state and compared these with their gas phase counter parts. Additionally, I will present for the sodium sulfate, Na2SO4, for sodium hydrogensulfate, NaHSO4, and for sulfuric acid, H2SO4, concentration and (in-solution) depth-dependent dissociation constants, purely derived from spectroscopic measures, which could not have been done before.

Aqueous inorganic textbook ions revisited: Photoelectron spectroscopy study

2019 Fall National Meeting

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