The interactions of cations and liquid water studied by resonantly excited soft-x-ray emission spectroscopy

Full text: Metal-ion transport in both aqueous- and polymer-solvent media involves continual solvent-ligand exchange. Metal-ion coordination chemistry is therefore fundamental to these phenomena where a dramatic exchange of ligand occurs. Resonantly excited soft-x-ray emission spectroscopy is unique technique to study molecular structure in liquid condition. Alternatively the effects of solvated cations could be monitored via examining the spectra of solvent. The great advantage of this approach is that the restriction to cations no longer applies. For example, it can be used in studying what happens when salts of the alkali and alkaline earth metals are added to aqueous solvent. This study made it possible to establish a relative order cation-solvent (water) interaction. We report the soft-x-ray absorption and emission study of cations (Na+, Mg2+, and Al3+) in water solutions. The influences of cations on the water molecular structure can be seen as the threshold shifted towards high energy in the x-ray absorption spectra; the mixing of molecular orbital in 3a1 symmetry is reinforced as its intensity is further reduced; and the 1b1-emission peak is shifted differently for Na+, Mg2+, and Al3+, which indicates that the charge difference of the cations may not be the only playing role being responsible to the interactions between the cations and water molecules. The relative order of cation-solvent interaction due to the effects of charge and radius of the cations have been established