Large Intermediates in Hydrazine Decomposition: A Theoretical Study of the N 3 H 5 and N 4 H 6 Potential Energy Surfaces

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2019-06, Vol.123 (22), p.4679-4692
• Main Authors: Grinberg Dana, Alon, Moore, 3rd, Kevin B, Jasper, Ahren W, Green, William H
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.9b02217

Large complex formation involved in the thermal decomposition of hydrazine (N H ) is studied using transition state theory-based theoretical kinetics. A comprehensive analysis of the N H and N H potential energy surfaces was performed at the CCSD(T)-F12a/aug-cc-pVTZ//ωB97x-D3/6-311++G(3df,3pd) level of theory, and pressure-dependent rate coefficients were determined. There are no low-barrier unimolecular decomposition pathways for triazane (n-N H ), and its formation becomes more significant as the pressure increases; it is the primary product of N H + NH below 550, 800, 1150, and 1600 K at 0.1, 1, 10, and 100 bar, respectively. The N H surface has two important entry channels, N H + H NN and N H + N H , each with different primary products. Interestingly, N H + H NN primarily forms N H + N H , while disproportionation of N H + N H predominantly leads to the other N H isomer, HNNH. Stabilized tetrazane (n-N H ) formation from N H + N H becomes significant only at relatively high pressures and low temperatures because of fall-off back into N H + N H . Pressure-dependent rate coefficients for all considered reactions as well as thermodynamic properties of triazane and tetrazane, which should be considered for kinetic modeling of chemical processes involving nitrogen- and hydrogen-containing species, are reported.