Protonated nitrogen (N₂H⁺) was first reported as an unidentified triplet line at 93.174 MHz by Turner in 1974, though various traits pointed to a nitrogen species. On the basis of quantum chemical calculations, Green et al. proposed that the line was likely due to protonated N₂. Confirmation of the species was report in 1975 by Thaddeus and Turner. The deuterated form, N₂D⁺, was observed in 1977 by Snyder et al. The species has also been in a number of extragalactic sources by Mauersberger and Henkel and is used for probing traits of interstellar clouds.

Protonated N₂ (also known as diazenylium) is a linear molecule. Neutral molecules such as N₂ attract cations such as protons. The energy gained when a proton attaches to a neutral molecules is called the proton affinity. For N₂, it is 493.8 kJ/mol.