High-resolution incoherent neutron spectroscopy has, for the first time, been applied to aqueous solutions and has demonstrated unambiguously the existence of a second zone of weakly interacting water molecules around two divalent cations ${\mathrm{Ni}}^{2+}$ and ${\mathrm{Mg}}^{2+}$.

• Received 24 August 1981

DOI:https://doi.org/10.1103/PhysRevLett.48.756