The structure of liquid water in aqueous solutions: A proposed model from near and mid infrared spectroscopy

Mid infrared spectra acquired using a micro CIRCLE cell with a ZnSe crystal, and near IR spectra were used to study the structure of liquid water in aqueous salt solutions. HDO and H2O mid TR spectra from 5.0 to 55.0 degrees C, and near and mid IR spectra for aqueous solutions of alkaline and alkaline earth chlorides and copper and zinc chlorides and sulfates were obtained. Difference spectra were used to detect changes in the water spectrum. The references were the spectrum of water at 20 degrees C for the temperature effect study and the spectrum of pure water for the solutions study. The temperature effect on the water spectrum pointed to two water molecule populations: ''free'' water (detected at 3650 cm(-1)) and ''bonded'' water at (3125 cm(-1)). From the solution spectra, another population was detected: ''ion-bonded'' water, which is affected differently by the different ions, mainly the cations. High charge density cations make stronger interactions, detected from 3100 to 3000 cm(-1). Low charge density cations make weak interactions (3400 to 3350 cm(-1)). Anions do not affect this structure much because their interactions with water are weaker.7640341