H3O2- ions with a strong quasi-symmetrical H-bond and their hydration in aqueous solutions of NaOH and KOH

Abstract

Ion-molecular interactions in aqueous solutions of NaOH (0–47.8%) and KOH (0–51.95%) are studied by multiple frustrated total internal reflection IR spectroscopy. Interpretation of the spectra and analysis of the spectral data are performed based on the results of DFT calculations (B3LYP/6-31++G(d, p)) of the characteristics of the free and double hydrated H₃O₂^- ion. It is established that the changes in the IR spectra of NaOH and KOH aqueous solutions caused by increasing alkali concentration are due to the formation of H₃O₂^- ions with a strong quasi-symmetrical hydrogen bond and their subsequent hydration by one or two water molecules. The influence of the cation nature on the degree of hydration of H₃O₂^- ions is demonstrated. The equilibrium concentrations of monohydrate (H₃O₂^- ∙ H₂O) and dihydrate (H₃O₂^- ∙ 2H₂O) are calculated and their IR continuous absorption spectra are isolated.