Chloride-ion hydration in supercritical water by neutron diffraction

Pulsed neutron diffraction measurements by using chlorine-isotopic substitution have been made on 3.0 molar aqueous lithium chloride solutions in supercritical D2O at T = 648 K and P = 169 MPa as well as under ambient condition (Tc = 643.9 K and Pc = 21.7 MPa for D2O). The first-order difference data have revealed that the hydrogen bonding between the chloride ion and water is substantially weakened, accompanied by a much less correlated orientation between the water molecules and the chloride ion. The number of nearest water D atoms around Cl− decreases from 5.8 at 298 K to 2.5 at 648 K, suggesting that dehydration of the chloride ion proceeds at 648 K. The present findings are compared with the results obtained from computer simulations.