Raman spectroscopic study of the effects of dissolved NaCl on water structure

Raman spectroscopy was utilized to investigate the effects of dissolved NaCl on water structure. For aqueous NaCl solutions, the difference spectra indicate a clear isosbestic point at 3345 cm−1 and a weak isosbestic point around 3625 cm−1. According to our explanation on Raman OH stretching band of water, it can be inferred that the addition of NaCl primarily breaks the tetrahedral hydrogen bonding and promotes formation of the donor hydrogen bonding in water, and slightly lowers the amount of free OH bonds. This is different from the effects of pressure and temperature on water structure. For liquid water, a water molecule interacts with neighboring water molecules through various local hydrogen bonded networks. Additionally, the enthalpy change of hydrogen bonding in water can be determined to be 11.35 kJ/mol.