Supercooled water, the hydrated proton and electron

4 problems

• Origin of the thermodynamic anomalies of supercooled water

  Contested

  As water is cooled below 0 C without freezing, its response functions grow as if heading toward a singularity. Several competing explanations exist and experiments have not yet chosen among them.

• Does the hydrated electron occupy a cavity in liquid water

  Contested

  An extra electron dissolved in water forms the hydrated electron, a key species in radiation chemistry. Whether it is held in a small empty pocket among water molecules or overlaps a region where water molecules crowd in is disputed.

• Solvation structure and infrared signature of the excess proton

  Contested

  An extra hydrogen ion in water is shared among several water molecules, and two textbook shapes for this group compete. Which shapes actually occur, and which features of the broad infrared absorption belong to each, is still argued over.

• Rate-limiting step of proton transport in liquid water

  Contested

  Extra hydrogen ions move through water several times faster than other ions by hopping between water molecules. Which molecular step sets the speed of this hopping is not agreed.