CHLORIDE-ION HYDRATION IN SUPERCRITICAL WATER BY NEUTRON-DIFFRACTION

Pulsed neutron diffraction measurements by using chlorine-isotopic sub stitution have been made on 3.0 molar aqueous lithium chloride solutio ns in supercritical D2O at T = 648 K and P = 169 MPa as well as under ambient condition (T-c = 643.9 K and P-c = 21.7 MPa for D2O). The firs t-order difference data have revealed that the hydrogen bonding betwee n the chloride ion and water is substantially weakened, accompanied by a much less correlated orientation between the water molecules and th e chloride ion. The number of nearest water D atoms around Cl- decreas es from 5.8 at 298 K to 2.5 at 648 K, suggesting that dehydration of t he chloride ion proceeds at 648 K. The present findings are compared w ith the results obtained from computer simulations.