Trinitrogen Explained

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. 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.^{[1] [2]}

The linear form of N₃ was discovered in 1956 by B. A. Thrush^[3] by photolysis of hydrogen azide.^[4] 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.

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.^{[3] [5]} The ring has C_2v symmetry^[5] —an isosceles triangle—in contrast to the linear form that has equal N–N bond-lengths.

Notes and References

1. Schlegel . H. Bernhard . Skancke . Anne . Thermochemistry, energy comparisons, and conformational analysis of hydrazine, triazane, and triaminoammonia . Journal of the American Chemical Society . August 1993 . 115 . 16 . 7465–7471 . 10.1021/ja00069a053.
2. Book: 10.1007/b59072. Inorganic Molecules. 25A. Landolt-Börnstein - Group II Molecules and Radicals. 1998. 3-540-61713-2. Kuchitsu. K.
3. Jin . Lin . Yu . Xue-fang . Pang . Jing-lin . Zhang . Shao-wen . Ding . Yi-hong . Theoretical Study on the Reactions of the Cyclic Trinitrogen Radical toward Oxygen and Water . The Journal of Physical Chemistry A . 30 July 2009 . 113 . 30 . 8500–8505 . 10.1021/jp810741v. 19719307 . 2009JPCA..113.8500J .
4. Thrush . B. A. . The Detection of Free Radicals in the High Intensity Photolysis of Hydrogen Azide . Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences . 10 April 1956 . 235 . 1200 . 143–147 . 10.1098/rspa.1956.0071. 1956RSPSA.235..143T . 95714517 .
5. Hansen . N. . Wodtke . A. M. . Velocity Map Ion Imaging of Chlorine Azide Photolysis: Evidence for Photolytic Production of Cyclic-N₃ . The Journal of Physical Chemistry A . December 2003 . 107 . 49 . 10608–10614 . 10.1021/jp0303319. 2003JPCA..10710608H .