  The triiodide ion is an example of a system where symmetry-breaking may be
induced by a solvent. The Landau free energy is expected to have a similar form
to that for the mean field Ising model, but with solvent strength rather than
temperature as the control parameter determining whether there is symmetry
breaking. In order to examine the possibility of critical phenomena we have
studied the properties of the ion in solvents based on a model for water with
charges scaled which causes a change from strong symmetry breaking to no
symmetry breaking. The behavior of the susceptibility and the Shannon entropy
near the critical point show no divergences. We examine the behavior of a
simple model and show that divergences would only be expected in the limit of
low temperatures, and the essential difference between the solvent-induced
symmetry breaking and the mean field Ising model is that in the latter the
observed quantity is an average over many spins, while in the former
observations are made on individual molecules.
