Spectra of excess molar absorptivity of aqueous solutions of ionic liquids: Universal chromophores for aqueous electrolytes?

Abstract

We devised a new data analysis methodology for Near Infrared spectroscopic data of aqueous solutions. We first isolate the non-ideal (i.e. real) part of the results as the excess molar absorptivity, εΕ, then define and calculate the excess partial molar absorptivity of solute, εSE, the effect of solute (S) on the excess molar absorptivity, εΕ. By using these, we learned that there are three universal chromophores in the ν2+ν3 combination band of H2O in the εΕ spectra of aqueous solutions of the total nine electrolytes. Furthermore, we learned from the excess partial molar absorptivity, εSE, we identified a specific chromophore out of three that distinguish the specific characteristics of a given solute on H2O. Here we add an evidence for the universality of three bands in εΕ to include two examples of ionic liquids. In addition, using the literature data, we show that the ν1 overtone of H2O in NaCl – H2O and CaCl2 – H2O also have a limited number of universal chromophores at the same wave numbers in their εΕ spectra.