Infrared spectra of cesium chloride aqueous solutions

The aqueous solutions of CsCl were studied at room temperature by infrared (IR) spectroscopy in the entire solubility range, 0-1200 g/L, using attenua ted total reflection (ATR) sampling. The influence of anomalous dispersion on the IR-ATR spectra was evaluated by calculating the imaginary refractive index, k(nu), of each sample. Factor analysis (FA) was used to determine t he number and abundance of species in the solutions. FA applied to both k(n u) spectra and IR-ATR spectra produced two principal spectra with a similar abundance of species. This result indicates that, even at high salt concen tration, the optical effects do not influence the chemical analysis of IR-A TR spectra. The spectral modifications related to the salt concentrations a re mainly first order. Second order effects were observed, but being weak, were not investigated. The two principal spectra are related to the two spe cies present in the solution: pure water and CsCl-solvated water. From the latter, 2.8 +/-0.4 water molecules were calculated to be associated with ea ch close-bound Cs+/Cl- ion pair. In the case of KCl and NaCl aqueous soluti ons, both of which showed the same number of species, the number of water m olecules associated to an ion pair was 5.0 +/-0.4. That the latter number i s different from that of CsCl indicates that the interaction between water molecules and ion pairs is different when cation Na or K in the chloride sa lt is replaced by Cs. (C) 2000 American Institute of Physics. [S0021-9606(0 0)51837-6].