Correlatability of Thermodynamic and Spectroscopic Ideal and Real Behavior: Excess Gibbs Energy vs Raman Spectra

We analyze whether Raman spectra of various binary mixtures are related to their thermodynamic properties, specifically the molar excess Gibbs energy gE and the activity coefficients γi. Our analysis focuses on the intensity of excess molar Raman spectra, excess partial molar Raman spectra, and the shifts in peak positions. The results show that the summed absolute intensities of the excess molar Raman spectra and the excess partial molar Raman spectra do not correlate with the excess Gibbs energy gE or the activity coefficients γi. In addition, we find that peak shifts in Raman spectra do not necessarily reflect thermodynamic deviations from ideal behavior. Significant peak shifts can occur even in mixtures that thermodynamically are close to ideal. These results are relevant for the development of predictive models that aim to infer thermodynamic properties from Raman spectra.