Chemical compounds dissolve in solvents when there is a favourable interaction between the solute and solvent molecules. However, extracting precise information on these interactions from studies of bulk solutions is difficult at best and usually impossible.
Kinetic energy released into Li(NH3)3 by electronic excitation of Li(NH3)4
We therefore use a different approach in which the solute is combined with a finite number of solvent molecules. These solute-solvent complexes are formed in the gas phase and cooled to low temperatures in a supersonic gas expansion while avoiding excessive condensation. We then use spectroscopic techniques, such as mass-selective infrared spectroscopy, to record the spectra of these complexes as a function of size.
With this approach we are able to extract detailed information about what happens in the immediate vicinity of the solute, such as the number of molecules in the first solvation shell and the onset of solvent-induced charge transfer (ionic dissociation) within the solute. We have been trialing these techniques on a number of metal-solvent complexes, particularly when the solute is an alkali and the solvent is ammonia, since in this case solvated electrons can form.
This work is currently being extended to other metal-solvent complexes and in the long term the aim is to explore systems such as salt-water complexes.
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