Reorientational dynamics of water in aqueous ionic solutions at supercritical conditions:: A computer simulation study

We present results of a computer simulation study on the reorientational dynamics of water molecules in aqueous ionic solutions at supercritical conditions. We carried out molecular dynamics simulations along the isotherm T = 650 K and densities ranging from rho = 0.7 g cm(-3) down to rho = 0.05 g cm(-3). We adopted the SPC/E water model. The ionic species included Na+ and Cl- ions. Our attention has been focused on the reorientational dynamics of the solvation shell molecules. Reorientational correlation times are reported and compared with those corresponding to pure water at the same thermodynamic conditions. We find that the influence of the ions goes beyond the first solvation shell and significantly affects the motion of the molecules lying in the second solvation shell. This differs with earlier studies of aqueous ionic solutions at room temperature. (c) 2005 Elsevier B.V All rights reserved.