Spectroscopic Properties

Abstract

Application of spectrophotometric techniques to the study of water—water and water—solute interactions in aqueous solutions has followed the development of recording spectrophotometers. In principle, spectroscopic studies of aqueous solutions can be divided into three closely related classes. In the first class absorption spectra of water in aqueous solutions are compared to those of pure water at the same temperature and pressure. The majority of investigations in this class have used aqueous salt solutions and the differences observed are often dramatic. In the second class absorption spectra of solutes (cosolvents) in water are compared with the spectra of solutes in either the gas phase or in a nonpolar, nonaqueous solvent. In the third class changes in absorption spectra of one solute in water are monitored as another solute (cosolvent) is added. The first solute is present at very low concentration and acts as a probe because its characteristic (and usually intense) absorption spectra are very sensitive to environmental change. Ideally, detailed knowledge of the spectra of such a probe is necessary but it often happens that the absorption spectra of the probe in aqueous solution aid in the understanding of the spectroscopic characteristics of such species.