Unimolecular Decomposition of 5-Aminotetrazole and its Tautomer 5-Iminotetrazole: New Insight from Isopotential Searching

Authors

Kristian W. Paul, U.S. Army Research Laboratory, Aberdeen ProVing Ground, Maryland
Margaret M. Hurley
Karl K. Irikura

Date of this Version

2009

Comments

Published in J. Phys. Chem. A 2009, 113, 2483–2490.

Abstract

Aminotetrazole compounds have become attractive ingredients in gas generating compositions, solid rocket propellants, and green pyrotechnics. Therefore, a fundamental understanding of their thermal decomposition mechanisms and thermodynamics is of great interest. In this study, the specular reflection isopotential searching method was used to investigate the unimolecular decomposition mechanisms of 5-iminotetrazole (5-ITZ), 1H-5-aminotetrazole (1H-5-ATZ), and 2H-5-aminotetrazole (2H-5-ATZ). Subsequent thermochemical analysis of the unimolecular decomposition pathways was performed at the CCSD(T)/aug-cc-pVTZ//B3LYP/6- 311++G(3df,3pd) level of theory. Based upon the relative reaction barriers predicted in this study, the initial gaseous products of 5-ITZ unimolecular decomposition are HN₃ and NH₂CN (calculated activation barrier equal to 199.5 kJ/mol). On the other hand, the initial gaseous products of 1H-5-ATZ and 2H-5-ATZ unimolecular decomposition are predicted to be N₂ and metastable CH₃N₃ (calculated activation barriers equal to 169.2 and 153.7 kJ/mol, respectively). These predicted unimolecular decomposition products and activation barriers are in excellent agreement with thermal decomposition experiments performed by Lesnikovich et al. [Lesnikovich, A. I.; Ivashkevich, O. A.; Levchik, S. V.; Balabanovich, A. I.; Gaponik, P. N.; Kulak, A. A. Thermochim. Acta 2002, 388, 233], in which the apparent activation barriers were measured to be approximately 200 and 150 kJ/mol, respectively, for 5-ITZ and 1H-5-ATZ/2H-5-ATZ.