ATR-FTIR study of the isosbestic point in water solution of electrolytes

Abstract

Here we report an ATR-FTIR study on aqueous electrolytic solutions aimed to investigate the nature of the isosbestic point observed in the stretching mode broad band. This feature reveals that the properties of the system are described by the superposition of two components at equilibrium whose relative abundance depends on the running parameter. Here we show that the OH intramolecular bond length changes differently in the two components. It has been observed that, surprisingly, the OH bond length of highly correlated water molecules decreases with the concentration of the solute. On the opposite, it expands in molecules belonging to small cluster. As the shortening of the OH bond shows that the water-water interaction prevails on water-ion interaction, we make the hypothesis that the decrease of the bond length is due to a collective behaviour of the water molecules replacing the classic concept of H-bond in water.