Structure, spectroscopy and dynamics of halogen molecules interacting with water

Immediately on the discovery of the halogen molecules, their chemistry was closely linked with that of water. For some time, it was thought that water was a constituent of chlorine. The brightly coloured halogens have played an important role in spectroscopy almost from the beginning of its use as a quantitative tool for understanding molecular structure. Already in the 19th century, the remarkable colour change upon dissolving iodine in aqueous solution was noted and studied. However, a complete, microscopic explanation for this phenomenon is yet to be achieved. We review this field and propose that the time is right to achieve this fundamental goal of chemical physics for the halogen-water system. In addition, we review recent work on the UV-vis, Raman and ultrafast dynamics studies of halogen molecules in clathrate hydrate cages, spectroscopy of water-halogen dimer molecules and theory of small water-halogen clusters. Based on recent findings, we propose a variety of 'next steps' for the complete understanding of this fascinating model system.