Raman spectroscopic study of nitronium ion formation in mixtures of nitric acid, sulfuric acid and water

Abstract

Quantitative Raman spectroscopic measurements of the intensity of the ν(NO) symmetric stretching band of NO₂⁺ in aqueous solutions of nitric and sulfuric acid mixtures have been carried out over the temperature range 293–313 K. From the spectroscopic data it was found that the NO₂⁺ species concentration decreased with an increase in temperature. Equilibrium constants for the reaction HNO₃+ 2H₂SO₄⇌ NO₂⁺+ H₃O⁺+ 2HSO₄^– were determined at 293 and 313 K and the average enthalpy of NO₂⁺ formation was found to be ΔH=–25 ± 5 kJ mol^–1.