Near-infrared (NIR) spectroscopy was used to investigate the dissolution and chemical interaction of water dissolved into supercritical carbon dioxide (scCO(2)) and the influence of CaCl2 in the co-existing aqueous phase at four temperatures: 40, 50, 75 and 100 degrees C at 90 atm. Consistent with the trend of the vapor pressure of water, the solubility of pure water in scCO(2) increased from 40 degrees C (0.32 mol%) to 100 degrees C (1.61 mol%). The presence of CaCl2 negatively affects the solubility of water in scCO(2). At a given temperature and pressure the solubility of water decreased as the concentration of CaCl2 in the aqueous phase increased, following the trend of the activity of water. At 40 degrees C, the water concentration in scCO(2) in contact with saturated CaCl2 aqueous solution was only 0.16 mol%, a drop of 50% whereas that at 100 degrees C was 1.12 mol%, a drop of over 30%, as compared to pure water under otherwise the same conditions. Analysis of the spectral profiles suggested that water dissolved into scCO(2) exists in the monomeric form under the evaluated temperature and pressure conditions, for both neat water and CaCl2 solutions. However, its rotational degrees of freedom decrease at lower temperatures due to higher fluid densities, leading to formation of weak H2O:CO2 Lewis acid-base complexes. Similarly, the nearly invariant spectral profiles of dissolved water in the presence and absence of saturated CaCl2 under the same experimental conditions was taken as evidence that CaCl2 dissolution in scCO(2) was limited as the dissolved Ca2+/CaCl2 would likely be highly hydrated and would alter the overall spectra of waters in the scCO(2) phase. (c) 2012 Elsevier B.V. All rights reserved.