Probing ion-specific effects on aqueous acetate solutions: Ion pairing versus water structure modifications.

The effect of monovalent cations (Li(+), K(+), NH4 (+), Na(+)) on the water structure in aqueous chloride and acetate solutions was characterized by oxygen K-edge X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy, and resonant inelastic X-ray scattering (RIXS) of a liquid microjet. We show ion- and counterion dependent effects on the emission spectra of the oxygen K-edge, which we attribute to modifications of the hydrogen bond network of water. For acetates, ion pairing with carboxylates was also probed selectively by XAS and RIXS. We correlate our experimental results to speciation data and to the salting-out properties of the cations.

Local electronic structure of aqueous zinc acetate: oxygen K-edge X-ray absorption and emission spectroscopy on micro-jets.

Oxygen K-edge X-ray absorption, emission, and resonant inelastic X-ray scattering spectra were measured to site selectively gain insights into the electronic structure of aqueous zinc acetate solution. The character of the acetate ion and the influence of zinc and water on its local electronic structure are discussed.

Shared solvation of sodium ions in alcohol-water solutions explains the non-ideality of free energy of solvation.

In order to explain the discrepancies between theories and experiments regarding the non-ideality in the free energy of solvation, here we present a microscopic picture of sodium ions dissolved in water-alcohol mixed solvents. We used X-ray absorption spectroscopy to probe the K-edge of sodium ions in mixed solvents of water and alcohols (methanol, ethanol) and in the respective pure solvents. In the mixed solvents a shared solvation of the sodium ions is observed. We find that specifically the water component plays a key role in stabilizing the solvation shell in mixed solvents, which was revealed by a selective photochemical process occurring only in the pure alcohol solvents.

Nature of the hydrogen bond of water in solvents of different polarities.

The hydrogen bonding of water molecules in different solvents is studied systematically using X-ray absorption and Fourier transform infrared spectroscopy. We show that (i) at the lowest water concentration measured in benzene and acetonitrile the water molecules are mainly symmetrically bonded. The electronic structure of these water molecules differs from the one of gas or liquid water and is rather icelike. (ii) The clustering of water molecules upon increasing concentration is solvent-specific. Upon comparing the results for nonpolar benzene and polar chloroform, a preferential orientation of the water molecules around the benzene is observed. In polar acetonitrile, a shared solvation of water and acetonitrile molecules would lead to the formation of a water structure of rings and chains.