Trinitrogen

Names Other names Identifiers ChEBI ChemSpider 770 Properties N₃ Molar mass 42.021 g·mol⁻¹

Trinitrogen also known as the azide radical is an unstable molecule composed of three nitrogen atoms. Two arrangements are known: a linear form with double bonds and charge transfer, and a cyclic form. Both forms are highly unstable, though the linear form is the more stable of the two.^[1] More-stable derivatives exist, such as when it acts as a ligand, and it may participate in azido nitration, which is a reaction between sodium azide and ammonium cerium nitrate.^{[2] [3]}

The linear form of N₃ was discovered in 1956 by B. A. Thrush ^[4] by photolysis of hydrogen azide.^[5] As a linear and symmetric molecule, it has D_∞h symmetry, with a nitrogen–nitrogen bond length averaging 1.8115 Å. The first excited electronic state, A²Σ_u, is 4.56 eV above the ground state.^[1]

The cyclic form was identified in 2003 by N. Hansen and A. M. Wodtke using ultraviolet photolysis of chlorine azide. Although the reaction yielded mostly the linear form, about 20% of the molecules were cyclic.^{[4] [1]} The ring has C_2v symmetry^[1] —an isosceles triangle—in contrast to the linear form that has equal N–N bond-lengths.

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