1. Could you explain the significance of your article to the non-specialist? 

It is our everyday experience to see the dissolution of table salt or sugar in water. However, the detailed molecular processes and the initial steps of dissolution are not well understood. There have been significant recent experimental and theoretical efforts aimed at achieving a molecular-level understanding of dissolution. Sulfate is also a common salt, albeit slightly more complicated than the table salt. In this communication, we generated isolated clusters of the form, NaSO₄^-(H₂O)_n, as model systems to study the first dissolution steps of a complex salt. We combined experimental work using photoelectron spectroscopy and ab initio theoretical calculations and obtained a vivid picture of the initial processes of how water molecules start to "desolve" a sodium sulfate molecular ion. 

2. What has motivated you to conduct this work? 

Most of experimental investigations have so far been focused on the dissolution processes of monovalent salts or acids like NaCl or HBr, but little work has been done concerning a more complex salt. Here we examine the microdissolution of a complex salt, Na₂SO₄. Sulfate is ubiquitous in solids, solutions, and atmospheric aerosols. Molecular level information about the dissolution of sulfate should prove valuable in understanding its behavior and chemistry in the bulk phases and in complex environments. The sulfate ion is divalent, which allows us to study NaSO₄^-. It is still a charged particle, which is very convenient and important for our gas phase study. 

3. Where do you see this work developing in the future? 

So far we have only been able to produce NaSO₄^-(H₂O)_n (n = 0 - 4) with up to four water molecules. We found that the first three waters already begin to "pry" apart the Na⁺ and SO₄^2- ions, forming a structure analogous to a contact ion pair also present in concentrated sulfate solution. It would be interesting to add more water molecules to see how many water molecules are needed to completely separate the two ions, achieving a so-called solvent-separated ion pair, which is more commonly observed in solution. 

4. Are there any particular challenges facing future research in this area? 

Yes, so far we are only able to make clusters with up to four water molecules. It is challenging to find the right conditions to make large solvated clusters containing both a positive Na⁺ ion and a doubly charged SO₄^2- ion. A second challenge is to control the temperatures of the clusters. We know that dissolution is a temperature dependent process. So far, we have been only able to do experiment with clusters at room temperature. It would be interesting to perform temperature-dependent studies.