IR Spectroscopy of aqueous alkali halides. Factor analysis

The infrared spectra of ten salts in aqueous solutions were obtained in the ir solubility range using attenuated total reflection (ATR). The salts are: LiCl, NaCl, KCl, CsCl, MgCl2, NaBr, KBr, NaI, KI, and CsI. The salts, whic h are completely ionized in water, do not absorb in the IR. Only their inte ractions with water are observed and analyzed. Factor analysis (FA) applied to the spectra showed that two principal species are present in the soluti ons: pure water and salt-solvated water. The modifications of the water spe ctrum are dependent on the nature of the salts, their concentrations and ar e mainly of first-order. Second-order effects were observed but, being weak , were not investigated. The modifications of the IR-ATR spectrum from pure water to a salt solution are proportional to the modifications of the imag inary part of the refractive index spectrum (k(v)). This indicates that the anomalous dispersion effects do not interfere with the chemical analysis o f the IR-ATR spectra. In every salt studied, the two main species present i n the solutions remained stable throughout the salt solubility ranges. Comp arison between the IR spectra of the different salts solutions indicates th at both anions and cations are in strong interaction with water molecules a nd are solvated together in stable clusters.