Effect of High Hydrostatic Pressure and Additiveson the Dynamics of Water: a Raman SpectroscopyStudy

In this work we study the dynamics of pure water and alkaline halogenide solutions under hydrostatic pressure (0.1–650 MPa) by means of Raman spectroscopy. This technique allows us to follow modifications in intramolecular and hydrogen bonds present in water at atmospheric pressure and ambient temperature. Studying pure water, we recorded the particular behaviour of this liquid in the pressure range 0.1–650 MPa and evidenced a singular point near 200 MPa. Below 200 MPa an increase in pressure as in temperature leads to a weakening of the hydrogen bonds, whereas above 200 MPa, pressure strengthens these intermolecular bonds. Upon adding salts such as chlorides and bromides of sodium and potassium at atmospheric pressure, water loses its organized structure and the hydration shells of ions are the pertinent dynamical entities giving specific signatures in the isotropic part of the Raman spectra. The modifications of water structure due to salt addition are enhanced in hyperbaric conditions. Moreover, water organization at atmospheric pressure as at 300 MPa is strongly dependent on salt concentration.