THEORETICAL ANALYSES OF O(2) H(2)O SYSTEMS UNDER NORMAL AND SUPERCRITICAL CONDITIONS/

We show that a solution of O2 in supercritical water at 850 K and 250 bar is a 'weakly attractive' system, in terms of the classification sc heme of Debenedetti et al. This means that some solvent enrichment aro und the solute does occur but the partial molar volume of the latter i s positive. We have investigated the interaction of individual O2 and H2O molecules by both ab initio and non-local density functional metho ds, and confirmed that the O2-H2O complex is weak (binding energy less -than-or-equal-to 1.3 kcal/mol) and loose. The molecular electrostatic potentials of O2 and H2O show the former to have extremely weak negat ive regions. Molecular dynamics simulations for water and for O2/H2O s olutions under both normal (300 K, 1 bar) and supercritical (850 K, 25 0 bar) conditions show that O2. expands the volume of the supercritica l water and decreases the extent of clustering of the water molecules.