The spectra and equilibria of nitrosonium ion, nitroacidium ion, and nitrous acid in solutions of sulphuric, hydrochloric, and phosporic acids

The ultraviolet spectrum of sodium nitrite in aqueous sulphuric acid is essentially that of nitrous acid below 40 per cent, acid, and that of nitrosonium ion above 70 per cant. acid. In the intermediate range there is evidence that the nitroacidium ion (H2NO2+) is an important constituent of the solution. Equilibria involving the three species have been calculated using activity data for water and sulphuric acid. Similar results are obtained in aqueous phosphoric acid as a solvent. In hydrochloric acid of low water activity the high chloride activity causes what appears to be almost total conversion to nitrosyl chloride. The ultraviolet spectrum of the nitrosonium ion is a structureless transition with εmax.=3850 at about 46 kK (2200 Ǻ). The nitroacidium ion does not absorb appreciably within the accessible range.